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Page 1: Dcs course

www

Control Network

wwwwww

Control Network

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Distributed Control System and Programmable Logic Control

1

Course Aim

The aim of this training course is to build up the procedural and

declarative knowledge required to be recognized by projects engineer that

don not have past background of DCS or PLC. This will help them to

supervise projects dealing with control systems with a strong background.

In this course, the training cycle is divided in five steps that necessitate

the cooperation between the instructor and the trainees. These steps are

shown in figure below, they are summarized as follows:

1. Define the knowledge and skills required to be developed.

2. Define the elements of each knowledge or skill.

3. Formulate a verbal phrase for the learning objective of each

element.

4. Choose an adequate instructional activity to present each element.

5. Set up an indicator to measure the outcomes of the course and

modify the training skills to adapt the vocational needs.

Determine

Elements

Learning

Objectives

Define

Knowledge

& Skills

Instruction

Activity

Measure

& Correction

Determine

Elements

Learning

Objectives

Define

Knowledge

& Skills

Instruction

Activity

Measure

& Correction

Training Cycle.

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Knowledge and Elements

Illustrate DCS & PLC Benefits, Usage and History.

Overview of control system history.

Control system benefits and usage.

Types of control

Develop Knowledge of DCS Components (Hardware & Software).

Infrastructure [Communication Bus, Interfaces, Controllers,

Gateways, RTU, Others].

Hardware and technologies.

Software [Configuration, Graphics, Alarming, Trending, System

Management, Others].

Extend Knowledge of DCS installation and Maintenance.

Site Installation, Commissioning and Startup.

Diagnostics, Spares, Tools and Power Distribution.

Maintenance [Backup, Replacements and System Installation].

Develop Knowledge of PLC Components.

PLC fundamentals.

PLC Logic.

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Table of Contents

Section I

Chapter 1 Introduction

Chapter 2 Regulatory Control

Section II

Chapter 3 DCS Infrastructure

Chapter 4 DCS Hardware

Chapter 5 DCS Software

Section III

Chapter 6 Installation

Chapter 7 Maintenance

Chapter 8 Power Distribution

Section IV

Chapter 9 PLC Fundamentals.

Chapter 10 Ladder Logic And SFC

Appendices

A Electrical Relay Diagram And P&ID Symbols

B Serial Communication

C Networking

D Software Engineering

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Chapter 1

Control Systems

1.1 Automation System Structure

Although applications differ widely, there is little difference in the

overall architecture of their control systems. Why the control system of a

power plant is not sold also for automating a brewery depends largely on

small differences (e.g. explosion-proof), on regulations (e.g. Food and

Drug Administration) and also tradition, customer relationship.

The ANSI/ISA standard 95 defines terminology and good practices

1.1.1 Large Control System Hierarchy

Administration: Production goals, planning

Enterprise: Manages resources, workflow, coordinates activities of

different sites, quality supervision, maintenance, distribution and

planning.

Enterprise Resource Planning

Manufacturing Execution System

Control & Command System

Business Planning & Logistics Plant Production Scheduling

Operational Management, etc.

Manufacturing Operations & Control

Dispatching Production, Detailed Product Scheduling, Reliability Assurance,...

Level 4

Level 3

Level 2,1,0

Batch Control

Continuous Control

Discrete Control

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Supervision: Supervision of the site, optimization, on-line

operations. Control room, Process Data Base, logging (open loop)

Group (Area): Control of a well-defined part of the plant. closed

loop, except for intervention of an operator)

o Coordinates individual subgroups

o Adjusting set-points and parameters

o Commands several units as a whole

Unit (Cell): Control (regulation, monitoring and protection) of a

small part of a group (closed loop except for maintenance).

o Measure: Sampling, scaling, processing, calibration.

o Control: regulation, set-points and parameters

o Command: sequencing, protection and interlocking

Field: Sensors & Actors, data acquisition, digitalization, data

transmission, no processing except measurement correction and

built-in protection.

Figure 1.1 Large control system hierarchy

enterprise

Group Control

Unit Control

Field

Sensors & Actors A V

Supervisory

Primary technology

Workflow, Resources, Interactions

SCADA = Supervisory

Control And Data Acquisition

T

administration Planning, Statistics, Finances

supervision

1

2

3

4

0

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1.1.2 Response Time and Hierarchical Level

Figure 1.2 Response Time And Hierarchical Level

1.2 What is DCS?

A DCS is an integrated set of modules with distributed functions.

– Multi-loop controllers (10’s-100’s) that connect to field

devices

– Supervisory coordinating controllers

– Multi-loop operator stations and engineering stations

– Servers for system data management

– Control network for intercommunication

– External connections

Planning Level

Execution Level

Control Level

Supervisory Level

ms seconds hours days weeks month years

ERP (Enterprise Resource

Planning)

DCS

MES (Manufacturing

Execution System)

PLC (Programmable Logic Controller)

(Distributed Control System)

(Supervisory Control and Data Acquisition)

SCADA

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Figure 1.3 DCS Hierarchy

A DCS, throughout the whole system, must provide:

– Performance: control must be faster than the process.

– Determinism: control must always take the same time.

– Fault tolerance: redundancy; must fail to a known state.

– Security: must have access restrictions/controls.

Even though performance, ease of use, and interoperability are key

evaluation criteria for any control system software package, the following

is intended to provide the manufacturing engineer with a concise list of

control system software evaluation criteria.

1. INTEROPERABILITY.

This refers to the interaction of all control system hardware and

software components at all levels.

2. INTERCONNECTIVITY.

This criterion is concerned with the transmission medium, which is

constrained by the network topology and how efficiently the

system’s components communicate with each other.

Remote Server

Remote Users System Server

Operator Stations

Supervisory Controller

Engineering

Station

www

Multi-loop

Controller

Direct I/O Module

Other Industrial Devices

Control Network

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3. DISASTER PROCESSING.

This component is defined by the efficiency with which the

software provides the operator with system failure information and

the ease at which the operator is permitted to bring the system back

to maximum operation after system failure.

4. DATABASE.

This refers to the software’s ability to maintain the system’s

database.

5. PROCESSES/DATA.

This criterion is concerned with the variety of processes and data

that can be controlled by the SCADA package.

6. DIAGNOSTICS.

The SCADA package’s ability to assist in the resolution of system

failures is evaluated by this diagnostic utility.

7. SECURITY.

This component is concerned with the levels of security provided

by the software.

8. MONITORING/CONTROL

Monitoring of a given process in real-time and control of that

process, within preset parameters, is evaluated by this criteria.

9. ALARM MANAGEMENT/LOGGING.

This is the category for detecting, annunciating, managing, and

storing alarm conditions.

10. STATISTICAL PROCESS CONTROL.

This is the portion of the SCADA package that evaluates the

process data. Production and quality is greatly effected by this data.

12. OPERATOR INTERFACE.

The graphical user interface (GUI) is evaluated using this criterion.

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13. TRENDING.

The software’s ability to display trending plots using historical and

current data is considered in this category.

14. REPORT GENERATION.

The production of logs and reports using current real-time data and

data retrieved from historical files is evaluated under this category.

Due to the advancements in computer technology and low cost, a

personal computer-based distributed control system can be installed for a

fraction of the cost required just a few years ago. However, prior to

selecting any piece of DCS equipment, first examine the existing

equipment, in particular the smart controllers, for network compatibility.

Then, examine and select the software to be employed.

1.3 What is PLC?

A programmable logic controller, also called a PLC or

programmable controller, is a computer-type device used to control

equipment in an industrial facility. The kinds of equipment that PLCs can

control are as varied as industrial facilities themselves. Conveyor

systems, food processing machinery, auto assembly lines…you name it

and there’s probably a PLC out there controlling it.

In a traditional industrial control system, all control devices are

wired directly to each other according to how the system is supposed to

operate. In a PLC system, however, the PLC replaces the wiring between

the devices. Thus, instead of being wired directly to each other, all

equipment is wired to the PLC. Then, the control program inside the PLC

provides the “wiring” connection between the devices.

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The control program is the computer program stored in the PLC’s

memory that tells the PLC what’s supposed to be going on in the system.

The use of a PLC to provide the wiring connections between system

devices is called soft-wiring.

Let's say that a push button is supposed to control the operation of

a motor. In a traditional control system, the push button would be wired

directly to the motor. In a PLC system, however, both the push button and

the motor would be wired to the PLC instead. Then, the PLC's control

program would complete the electrical circuit between the two, allowing

the button to control the motor.

Figure 1.4 PLC development

A PLC basically consists of two elements:

The central processing unit

The input/output system

1.3.1 The Central Processing Unit

The central processing unit (CPU) is the part of a programmable

controller that retrieves, decodes, stores, and processes information. It

also executes the control program stored in the PLC’s memory. In

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essence, the CPU is the “brains” of a programmable controller. It

functions much the same way the CPU of a regular computer does, except

that it uses special instructions and coding to perform its functions. The

CPU has three parts:

The processor

The memory system

The power supply

The processor is the section of the CPU that codes, decodes, and

computes data. The memory system is the section of the CPU that stores

both the control program and data from the equipment connected to the

PLC. The power supply is the section that provides the PLC with the

voltage and current it needs to operate.

Figure 1.5 Microprocessor Hardware

1.3.2 The input/output (I/O) system

It is the section of a PLC to which all of the field devices are

connected. If the CPU can be thought of as the brains of a PLC, then the

I/O system can be thought of as the arms and legs. The I/O system is what

actually physically carries out the control commands from the program

stored in the PLC’s memory.

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The I/O system consists of two main parts:

The rack

The rack is an enclosure with slots in it that is connected to the CPU.

I/O modules

I/O modules are devices with connection terminals to which the field

devices are wired.

Together, the rack and the I/O modules form the interface between the

field devices and the PLC. When set up properly, each I/O module is both

securely wired to its corresponding field devices and securely installed in

a slot in the rack. This creates the physical connection between the field

equipment and the PLC. In some small PLCs, the rack and the I/O

modules come prepackaged as one unit.

Figure 1.6 I/O Racks

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1.4 How is a DCS different from a PLC system?

DCS PLC

Mfr sells a complete system of integrated

components.

Mfr sells some components; an SI

acquires others and engineers the system.

Mfr supports the system. Mfr supports the components.

On-line repair/ maintenance are the norm. Off-line repair/ maintenance are the norm.

System management built-in. System management designed per project.

Users expect to evolve/upgrade/expand a

system over 10/20/30 years.

System is a one-off project (like a house).

Upgrades / expansions are new projects.

1.5 Redundancy and Fault Tolerance

1.5.1 Redundancy

Hardware redundancy

– add extra hardware for detection or tolerating faults

Software redundancy

– add extra software for detection and possibly tolerating faults

1.5.2 Fault Tolerance

Error Detection

Damage Confinement

Error Recovery

Fault Treatment

1.5.2.1 Error Detection

Ideal check

– Check should be independent from system

– Check fails if system crashes

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Acceptable check

– Cost

– Reasonable check, e.g. monitor rate of change

diagnostics

– Performed “by system on system components”

– E.g. power-up diagnostics

1.5.2.2 Damage Confinement

Error might propagate and spread

Identify boundaries to state beyond which no information exchange

has occurred

1.5.2.3 Error Recovery

Backward recovery

– State is restored to an earlier state

– Requires checkpoints

– Most frequently used

– Recovery overhead

Forward recovery

– Try to make state error-free

– Need accurate assessment of damage

– Highly application-dependent

1.5.2.4 Fault Treatment

If transient fault: restart system, goto error-free state

System repair

– On-line, no manual intervention, (automatic)

– Dynamic system reconfiguration

– Spare (hot or cold)

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1.5.2.5 Fault Coverage

Measure of system’s ability to perform:

– Fault detection

– Fault location

– Fault containment

– (and/or fault recovery)

Note:

– Recovery implies that the system as a whole is operational

– This does not imply that a “repair” occurred

– E.g. duplex system with benign fault can recover to continue

operation on one non-faulty processor

1.5.2.6 Hardware Redundancy

Passive (static)

– Uses fault masking to hide occurrence of fault

– No action from the system is required

– E.g. voting

Active (dynamic)

– Uses comparison for detection and/or diagnoses

– Remove faulty hardware from system => reconfiguration

Hybrid

– Combine both approaches

– Masking until diagnostic complete

– Expensive, but better to achieve higher reliability

1.5.2.7 Passive Hardware Redundancy

N-Modular Redundancy (NMR)

– N independent modules replicate the same function

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Parallelism

– Results are voted on requirements: N >= 3

TMR (Triple Modular Redundancy)

1.5.2.8 Fault tolerant structures

Fault tolerance allows continuing operation in spite of a limited

number of independent failures. Fault tolerance relies on work

redundancy.

1.5.2.9 Static redundancy: 2 out of 3

Workby of 3 synchronised and identical units.

– All 3 units OK: Correct output.

– 2 units OK: Majority output correct.

– 2 or 3 units failure: Incorrect output.

– Otherwise: Error detection output.

Figure 1.7 (2 out of 3) Redundancy

1.5.2.10 Dynamic Redundancy

Redundancy only activated after an error is detected.

– Primary components (non-redundant)

– Reserve components (redundancy), standby (cold/hot standby)

sync

Voter

sync

Process input

Process output

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Figure 1.8 Dynamic Redundancy

1.5.2.11 Workby and Standby

Figure 1.9 Workby and Standby

1.5.2.12 Workby Fault-Tolerance for Integrity and Persistency

Figure 1.10 Workby Fault-Tolerance for Integrity and Persistency

Primary unit Standby unit

Switch

Output

Input

on-line workby sync

= ?

on-line standby sync

Hot standby Cold standby

Both computers are doing the same calculations at the same time

Comparison for easy error detection.

Comparator needed. Non-redundant continuation

in case of failure?

Standby is not computing Error detection needed. Easy switchover in case

of failure. Easy repair of reserve unit.

Standby is no operational Error detection needed. Long switchover period with loss of state info.

No aging of reserve unit.

Workby

disjunctor

comparator

INTEGER

Worker

synchronization

Matching

input

Co-

Worker

Output

output

Worker

commutator

synchronization

Matching

PERSISTENT

input

Co-

Worker

Output

output

E D

E D

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1.5.2.13 Hybrid Redundancy

Mixture of workby (static redundancy) and standby (dynamic redundancy).

Figure 1.11 Hybrid Redundancy

1.6 Microprocessor Control

For simple programming the relay model of the PLC is sufficient.

As more complex functions are used the more complex VonNeuman

model of the PLC must be used. A computer processes one instruction at

a time. Most computers operate this way, although they appear to be

doing many things at once. Consider the computer components shown in

Figure 1.12.

Figure 1.12 Simplified Personal Computer Architecture

voter

work- by

work- by

work- by

stand- by

stand- by

voter

work- by

failed work-

by work-

by stand-

by Reconfiguration (self-purging redundancy)

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Input is obtained from the keyboard and mouse, output is sent to the

screen, and the disk and memory are used for both input and output for

storage. (Note: the directions of these arrows are very important to

engineers, always pay attention to indicate where information is flowing.)

This figure can be redrawn as in Figure 1.13 to clarify the role of inputs

and outputs.

Figure 1.13 An Input-Output Oriented Architecture

In this figure the data enters the left side through the inputs. (Note:

most engineering diagrams have inputs on the left and outputs on the

right.) It travels through buffering circuits before it enters the CPU. The

CPU outputs data through other circuits. Memory and disks are used for

storage of data that is not destined for output. If we look at a personal

computer as a controller, it is controlling the user by outputting stimuli on

the screen, and inputting responses from the mouse and the keyboard.

A PLC is also a computer controlling a process. When fully

integrated into an application the analogies become;

Inputs - the keyboard is analogous to a proximity switch input

circuits - the serial input chip is like a 24Vdc input card

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Computer - the 686 CPU is like a PLC CPU unit

Output circuits - a graphics card is like a triac output card

Outputs - a monitor is like a light

Storage - memory in PLCs is similar to memories in personal

computers

It is also possible to implement a PLC using a normal Personal Computer,

although this is not advisable. In the case of a PLC the inputs and outputs

are designed to be more reliable and rugged for harsh production

environments.

1.7 Role Play

Each trainee should act a role play on the following:

1. Automation system structure.

2. What DCS and PLC and their differences?

3. Redundancy and fault tolerance.

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Chapter 2

Regulatory Control

2.1 Learning Objectives

Introduce Regulatory Control.

Understanding PID control.

Differentiate between various control loops.

2.2 Introduction

Most of the applications of industrial control process used simple

loops which regulated flows, temperatures, pressures and levels.

Occasionally ratio and cascade control loops could be found. There are

many benefits for using regulatory control. One of the most important is

simply closer control of the process. Process control is one part of an

overall control hierarchy that extends downwards to safety controls and

other directly connected process devices, and upward to encompass

process optimization and even higher business levels of control such as

scheduling, inventory management.

Most control engineers would recognize the form of response

shown in figure 2.1. Actually the response could be determined by

solving a differential equation. It is more important to have a good

understanding of the physical response than to be able to predict the

solution by solving the differential equation.

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Figure 2.1 Response of simple dynamic process to step input change

Instrumentation, control and process engineers abstract the pictorial

form of the process into an iconographic diagram called "Piping and

Instrumentation Diagram", i.e. P&ID. Figure 2.2 is an example of the

P&ID.

Figure 2.2 Control loop representation used on P&IDs.

For description and analysis of a control loop, without referring to

whether it is implemented with analog or digital hardware, a block

diagram as shown in figure 2.3 is beneficial.

Figure 2.3 Simplified block diagram representation of process control loop.

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2.3 PID Control

2.3.1 Feedback Control

The principle of feedback is one of the most intuitive concepts

known. An action is taken to correct a less satisfactory situation then the

results of the action are evaluated. If the situation is not corrected then

further action takes place. Feedback control can be classified by the form

of the controller output. One of the simplest forms of output is discrete

form, also called on-off or two position control. An example of this is the

household thermostat, which activates heating unit if the temperature is

below the setting, or deactivates the unit if the temperature is above the

setting.

Figure 2.4 On-Off Control.

The idea of two position control can be extended to multi-position

control; an example is commercial air-conditioning refrigeration

equipment which is operated by loading and unloading compressor

cylinders. The ultimate extension is infinite number of positions which is

called modulating control; an example is the process controller output

that can drive a valve to any position between 0 and 100 percent, as

shown in figure 2.5.

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Figure 2.5 Flow versus position, infinite position Control.

2.3.2 Modes of Control

Feedback controllers use one, two, or three methods to determine

the controller output. These methods, called the modes of control,

including the following:

Proportional (P)

Integral (I)

Derivative (D)

In general these modes can be used singly or in combination.

2.3.2.1 Proportional Mode

With a controller containing only the proportional mode, the

controller output is proportional to the measurement value only. Neither

history of the measurement value nor consideration to the rate of change

is utilized. Adjustment, i.e. tuning, of the controller is simple because

there is only one adjustment as shown in figure 2.6.

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Figure 2.6 Relationship between input and output for proportional control.

Figure 2.7 illustrates a proportional control system. The rate of

fluid flow into the tank represents the load. To be in equilibrium, the

outflow must be the same as the inflow. The outflow is achieved by a

particular valve position where the fixed mechanism between the float,

pivot and link attain.

Figure 2.7 Proportional control.

2.3.2.2 Integral Mode

An integrator is the ideal device for automating the procedure for

adjusting the controller output bias. It is called the automatic reset.

2.3.2.3 Derivative Mode

The derivative is used to anticipate the effect of load changes by

adding a component to the controller output that is proportional to the rate

of change of the measurement. See figure 2.8.

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Figure 2.8 PID control.

2.3.3 Control Loop Structure

For microprocessor control system, control strategy is configured

by a series of software function blocks. Just like a set of hardware

modules require interconnections to form a complete control system, a set

of software function blocks also acquire interconnections, i.e. soft-wiring.

Figure 2.9 shows a simple feedback loop with the software portion

consists of three function blocks:

An analog input block that causes the analog to digital converter to

convert the incoming 4-20mA signal to an analogous value. The value

is deposited in a memory register.

A PID control block which obtains the measurement value from the

analog input block and compares it with the setpoint then it executes a

PID algorithm to calculate the output.

An analog output block that obtains from the PID block the required

valve position value. The value is converted by a digital to analog

converter to 4-20mA signal.

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Figure 2.9 Control loop hardware/software structure.

2.3.4 Control Loop Tuning

The power of PID control is that by good choice of control

parameters the controller can be adjusted to provide the desired behavior

on a wide variety of process applications. Determining acceptable values

of these parameters is called tuning the controller. A good criterion for

acceptable performance is the "quarter cycle decay" shown in figure 2.10.

Figure 2.10 quarter cycle decay criterion

Most loops are tuned by experimental techniques, i.e. trial and error.

Figures 2.11 and 2.12 give a tuning map for adjusting control parameters.

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Figure 2.11 Gain and Reset effects.

Figure 2.12 Derivative effects.

2.4 Control Loop Types

2.4.1 Ratio Control

Figure 2.13 shows the P&ID of a process heater in which the fuel

flow is measured and multiplied by the required air-to-fuel ratio; this

results in the required air flow rate, which is introduced as a setpoint of

the feedback controller. The required air-to-fuel ratio is automatically

adjusted as the output of the stack O2 controller.

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Figure 2.13 ratio Control..

2.4.2 Cascade Control

In figure 2.14 the temperature controller cascades a steam flow

controller. The temperature controller would react to outlet temperature

drop by increasing the setpoint of the steam flow controller, which in turn

would increase the signal to the valve. The flow will quickly respond to

increased demand from the temperature controller and thus reaching the

desired setpoint of the outlet temperature stream.

Figure 2.13 Cascade Control.

2.4.3 Feedforward Control

With feedforward control, the objective is to drive the controlling

device from a measurement of the disturbance that is affecting the

process, rather than from the process variable itself. In figure 2.14, the

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application was analyzed the variation in process inlet temperature was

the principle of disturbance. Hence, a feedforward controller is used to

drive the fuel flow controller by sensing the inlet temperature.

Figure 2.14 Feedforward Control.

2.4.4 Selector (Override) Control

There are several ways of using selector switches in control

strategies. One way is to select the higher (or lower) of several

measurement signals to pass the process variable to a feedback controller.

For example, the highest of several process temperatures may be selected

automatically to become the controlling temperature as shown in figure

2.15.

Figure 2.15 Override Control.

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2.4.5 Split Range Control

Split range control when one process variable such as plant inlet

pressure is used to manage two different output devices such as plant

bypass control valve and flow control loop for fractionation area. The 4-

12 mA signal is used to control the flow control loop. If the plant cannot

handle all incoming feed, the 12-20 mA signal control the plant bypass

valve to direct extra feed to the outside of the plant.

2.5 Role Play

The trainees are required to play roles about:

1. Introducing regulatory control.

2. Introducing modes of control.

3. Intruding control loop types.

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Chapter 3

DCS Infrastructure

3.1 Learning Objectives

Introduce system infrastructure interoperability and interconnectivity.

Illustrate system components of level 2 control.

3.2 Communication Bus

Figure 3.1: Communication Bus

The communication bus, i.e. the Nodebus, interconnects stations

(Control Processors, Application Processors, Application Workstations,

and so forth) in the system to form a process management and control

node. Depending on application requirements, the node can serve as a

single, stand-alone entity, or it can be configured to be part of a more

extensive communications network.

Operating in conjunction with the Nodebus interface electronics in

each station, the Nodebus provides high-speed, redundant, peer-to-peer

communications between the stations.

The high speed, coupled with the redundancy and peer-to-peer

characteristics, provide performance and security superior to that

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provided by communication media used in conventional computer-based

systems. Station interfaces to the Nodebus are also redundant, further

ensuring secure communications between the stations. The Nodebus can

be implemented in a basic, non-extended configuration or it can be

extended through the use of Nodebus Extenders and Dual Nodebus

Interface Extenders.

3.2.1 Nodebus Interface

The Nodebus Interface is a module which allows direct connection

of a personal workstation (PW), with appropriate Nodebus connector card

and software, to the Nodebus figure 3.2. In this configuration, the PW

functions as a station on the node. The Nodebus Interface allows

connection of a station application workstation hosting an Ethernet

configuration to Nodebus. See figure 3.2.

Figure 3.2 Nodebus Interface Implementation (Typical)

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An Attachment Unit Interface (AUI) cable, connects the PW or an

Ethernet hub configuration to the Nodebus via a Nodebus Interface. A

coaxial cable (ThinNet) connects an Ethernet daisy chain configuration to

the Nodebus via a Nodebus Extender. The Nodebus Interface is non-

redundant, and can be used in any of the Nodebus configurations

described.

3.2.2 Dual Nodebus Interface

The Dual Nodebus Interface (DNBI) is a module which allows

direct connection of stations to the appropriate Nodebus. Connection

between the DNBI and station is made via an AUI cable.

For data transmission security, a separate (RS-423) control cable

connects between the station and the DNBI to allow switching between

the two redundant Nodebus cables. Switching of the Nodebus cables is

controlled by the station, which transmits commands to the DNBI via the

control cable. Figure 3.3 shows connection of a station to the Nodebus

using a DNBI.

Figure 3.3 Local Connection of Station

3.2.3 Dual Nodebus Interface Extender

The Dual Nodebus Interface Extender (DNBX) is functionally

similar to the DNBI, but provides a greater cabling distance. The

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principal transmission medium used is a coaxial Ethernet cable directly

connected to the station end by a standard Ethernet transceiver. Figure 3.4

remote connection of a station to the Nodebus using a DNBX.

Figure 3.4 Remote Connection of Station

3.3 Control Processor

The Control Processor performs regulatory, logic, timing, and

sequential control together with connected:

Fieldbus Modules (FBMs)

Fieldbus Cluster I/O Cards (FBCs)

It also performs data acquisition (via the Fieldbus Modules), alarm

detection and notification, and may optionally serve as an interface for

one or more Panel Display Stations.

The non-fault-tolerant version of the Control Processor is a single-width

processor module. The fault-tolerant version consists of two single-width

processor modules.

3.3.1 Enhanced Reliability

The Control Processor offers optional fault- tolerance for enhanced

reliability. The fault-tolerant control processor configuration consists of

two parallel-operating modules with two separate connections to the

Nodebus and to the Fieldbus.

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The two control processor modules, married together as a fault-

tolerant pair, are designed to provide continued operation of the unit in

the event of virtually any hardware failure occurring within one module

of the pair. Both modules receive and process information

simultaneously, and the modules themselves detect faults. One of the

significant methods of fault detection is comparison of communication

messages at the module external interfaces. Upon detection of a fault,

self-diagnostics are run by both modules to determine which module is

defective. The non-defective module then assumes control without

affecting normal system operations.

To further ensure reliable communications, the fault-tolerant

control processor performs error detection and address verification tests

in its Nodebus and Fieldbus interfaces. For enhanced reliability during

maintenance operations, the Control Processor is equipped with a

recessed reset button. This feature provides for manually forcing a

module power off and on (reboot) without removing the module from the

enclosure.

3.3.2 Diagnostics

The Control Processor uses three types of diagnostic tests to detect

and/or isolate faults:

Power-up self-checks

Run-time and watchdog timer checks

Off-line diagnostics

Power-up self-checks are self-initiated when power is applied to

the control processor. These checks perform sequential tests on the

various control processor functional elements. Red and green indicators at

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the front of the control processor module reflect the successful (or non-

successful) completion of the various phases of the control processor

startup sequence.

The run-time and watchdog timer checks provide continuous

monitoring of control processor functions during normal system

operations. The operator is informed of a malfunction by means of

printed or displayed system messages.

Off-line diagnostics are temporarily loaded into the system for the

purpose of performing comprehensive tests and checks on various system

stations and devices. Using the off-line diagnostics, a suspected fault in

the control processor can be isolated and/or confirmed.

3.4 Engineering Interface

The engineering interface, i.e. Application Processor, is

microprocessor-based application processor/file server stations. They

perform two basic functions:

As application processor (computer) stations, they perform

computation intensive functions.

As file server stations, they process file requests from tasks within

themselves or from other stations. Bulk storage devices used with

the Application Processors include floppy disk drives, hard disk

drives, streaming tape drives, and CD-ROMs.

The Application Processors operate in concert with other system

stations (such as communication processors, workstation processors, and

control processors), which provide the necessary means for data

input/output and operator interfacing. A smaller system can utilize a

single Application Processor, while a larger system can incorporate

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several Application Processors, each configured to perform specific

functions. Some functions can be performed by individual Application

Processors, while others can be shared by two or more Application

Processors in the same network.

For all models of the Application Processor, applications range

from minimal functions, such as the storage of memory images, alarm

events, and historical data, to larger-scale applications such as database

management and program development.

3.4.1 Application Processor Functions

The following sections describe the major functions performed by

the Application Processors.

3.4.1.1 System and Network Management Functions

The Application Processors perform system management

functions, which include collecting system performance statistics, data

reconciliation, performing station reloads, providing message

broadcasting, handling all station alarms and messages, and maintaining

consistent time and date in all system stations. The Application Processor

also performs network management functions, which comprise that

portion of system management functions which deal with the network.

3.4.1.2 Database Management

Database management involves the storage, manipulation, and

retrieval of files containing data received and/or produced by the system.

The Application Processors utilize the industry-standard Relational Data

Base Management System.

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3.4.1.3 File Requests

Each Application Processor contains a file manager, which

manages all file requests associated with bulk memory attached to the

Application Processor. Each Application Processor also supports a

remote file system that allows tasks in one station to share files in

another.

3.4.1.4 Historical Data

The Application Processors can be configured to contain the

Historian function, which maintains a history of application messages and

continuous and discrete I/O values. These values may represent any

parameters such as measurements, setpoints, outputs, and status switches

from stations that have been configured to collect data and send it to a

Historian. In addition, the Historian computes and stores a history of

averages, maximums, minimums, and other derived values. This

information is maintained for display, reporting, and access by

application programs. An archiving facility saves the data on removable

media, where applicable.

The Application Processors can be configured to maintain a history

of errors, alarm conditions, and selected operator actions. The occurrence

of errors, alarms, and events in other stations can be stored (for later

review and analysis) by sending a message defining the event to the

Historian in one or more Application Processors.

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3.4.1.5 Graphic Display Support

The Application Processor supports graphic displays by storing and

retrieving display formats, by providing access to objects stored on the

Application Processor, and by storing tasks which execute in a

workstation processor. Application Processors not only provide storage of

information and file management for displays, but also execute programs

that perform display and trend service.

3.4.1.6 Production Control Software

Production control software represents a large range of packages

that require varied Application Processor resources. The following is a

list of packages provided:

DBMS

Historian

Spreadsheet

Physical Properties Library

Mathematics Library

BATCH

The operation and performance of the production control software are

determined by the particular Application Processor configuration.

3.4.1.7 Configuration

Configuration refers to the process of entering or selecting

parameters to define what a software package does, or to define the

environment for a software package. The Application Processors support

configuration functions by providing bulk storage for configuration

parameters and by executing some of the configuration processes.

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3.4.1.8 Application Development Facilities

Application development tools are provided to build programs for

all system stations. These include tools to document, enter, translate, link,

test, and maintain programs written in several programming languages.

The Application Processor supports program development for all stations

(workstation processors, control processors, and so forth).

Assembly language, FORTRAN, and C programs can be written on

the Application Processor using standard operating system tools. An

optional package is available including text editors, debuggers, linkers,

revision control, and compilers, plus execution statistics functions.

3.4.1.9 User Application Program Execution

The Application Processors also execute user application programs.

These may be application packages such as special optimizations, test

data collections, special data reductions, or other packages that you may

have already developed. The allocation of resources reserved for user

application varies with each Application Processor.

3.4.2 Diagnostics

The Application Processors utilize three types of diagnostic tests to

detect and/or isolate faults:

Power-up self-checks

Run-time and watchdog timer checks

Off-line diagnostics

Power-up self-checks are initiated when power is applied to the

Application Processor. These checks perform sequential tests on the

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various Application Processor functional elements. Any malfunction

detected during the power-up self-checks is reported by means of

messages printed or displayed on a directly connected printer or terminal.

The run-time and watchdog timer checks provide continuous

monitoring of Application Processor functions during normal system

operations. For any processor model, you are informed of a malfunction

by means of printed or displayed system messages. Off-line diagnostics

are temporarily loaded into the system for the purpose of performing

comprehensive tests and checks on various system stations and devices.

Using the off-line diagnostics, a suspected fault in the Application

Processor can be isolated and/or confirmed.

3.4.3 Workstation Components

The workstation components provide user interface to all System

CRT display functions. A selection of workstation components is

available for command and data entry, along with CRT pointer

manipulation and control. These components interact with software

resident in versions of the system Workstation Processors (WPs) and

Application Workstation Processors (AWs). Many of these components

(displays and keyboards) are "common" and allow interchangeability and

simplicity in mixed technology configurations.

Workstation components include:

Alphanumeric Keyboard

Annunciator and Annunciator/Numeric Keyboards

Workstation Display (with/without Touchscreen)

Mouse

Trackball

Industrial Pointing Device

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Workstation Processor or Application Workstation Processor

Personal Workstation

Modular Industrial Console

Selection of the touch screen, mouse, trackball or industrial

pointing device is required for picking display objects on the CRT. The

touch screen has sufficient resolution for all functions normally

associated with a process operator. Only the mouse or trackball provides

the picking resolution necessary for engineer-related functions (for

example, building graphic displays). The touch screen associated with

Workstation Display and the annunciator type keyboards connects to a

Graphics Controller Input Output (GCIO) interface unit located beneath

the workstation display. The GCIO interfaces to the Workstation

Processor and/or Application Workstation that provide secure, high-

speed, bidirectional data flow. The alphanumeric keyboard and trackball

connect together in a functional grouping via a serial communications

link to the processors. Personal Workstations (PW) utilize separate serial

communication links for alphanumeric keyboard and mouse/trackball.

These buses allow a variety of component connections.

Figure 3.5 Table- Workstation Components.

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3.4.3.1 Alphanumeric Keyboard

The alphanumeric keyboard is used any time text is entered into the

system. It consists of the full set of alphanumeric keys plus punctuation

and special symbol keys laid out in the standard format, and a numeric

data entry pad (with cursor control).

Figure 3.6 Alphanumeric Keyboard

3.4.3.2 Annunciator Keyboard

The Annunciator Keyboard Figure 3.7 is an array of LED/switch

pairs. It also contains a horn silence switch and a lamp-test switch. Each

LED, under control of the processor software, may be ON, OFF, or

FLASHING as determined by the process conditions. The LEDs, when

used in conjunction with the unit's audible annunciator, form an effective

means of calling a user's attention to specific areas of the system. The

switch associated with each LED can be used to invoke any pre-

configured displays or operator responses..

Figure 3.7 Annunciator Keyboard

3.4.3.3 Workstation Display with/without Touchscreen

The workstation display is an analog cathode ray tube (CRT) color

monitor supporting ultra-high resolution applications. The monitor is

suitable for mounting onto a Modular Industrial Workstation or on a

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desktop. The monitor can include a touchscreen optional feature. Figure

3.8 shows the monitor with a tilt and swivel base mounted on the GCIO

interface unit. The GCIO interface supports the touchscreen, annunciator

and annunciator/ numeric keyboard, and audible horn options.

Figure 3.8 Table-Top Workstation Display

The optional touch screen is bonded to the front surface of the CRT

monitor. The user selects display objects by touching them on the screen.

The touch screen senses the action and sends a data signal to the

workstation processor's software indicating the position of the selection.

3.4.3.4 Trackball

The trackball is a stationary component that contains a rotatable

sphere. The trackball can be located on a table top. Rotation of the sphere

causes CRT pointer movement analogous to the mouse action. Buttons

are also provided for user selections/manipulations. See Figure 3.9

Figure 3.9 Trackball

3.4.3.5 Modular Industrial Console

Modular Industrial Consoles provide flexible mounting

arrangements of components. They allow users to configure centralized

or distributed control centers tailored to the functional requirements of

each interaction point in the plant. The modular console furniture

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described herein may incorporate a mix of equipment - console displays,

input devices, processors, Fieldbus Modules, data storage devices, and so

on. Alternately, only display-specific equipment can be incorporated.

Modular Industrial Consoles (MICs) are ideal for supporting powerful

multiple-screen, real-time display software interactions. This combination

allows console resources to be optimally allocated to meet changing day-

to-day needs.

3.5 Operator Interface

Operating in conjunction with human interface input/output

components, the workstation processors serve as a link between the

operator and other distributed processor modules. They receive graphic

and textual information both stored internally or from application

processors and generate signals to display the information on a

workstation display. Display formats and data files are available from

bulk storage. Live display information (distributed data objects) is

available from any control -processor, or from shared system global data.

The video information displayed can include free form combinations of

text, graphic illustrations, charts, and control displays.

The workstation processors display textual information as 80 text

characters per line, with four fonts. The processors provide resizable and

restackable windows. Displays for all of the workstation processors may

also be developed using the system software running in a compatible

personal computer.

A workstation processor, together with its workstation monitor and input

components, can be configured with combinations of peripherals to suit

functions and user preferences.

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3.6 Gateways

The architecture of the DCS permits it to be connected to other

foreign systems using a gateway module for adapting different

communication protocols. See figure 3.10.

Figure 3.10 Field Automation Subsystem

3.7 Role Play

Each trainee should introduce one of the main components:

1. Communication Bus

2. Control Processor.

3. Application Processor

4. Operator Interfaces and Gateways

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Chapter 4

DCS Hardware

4.1 Learning Objectives

Define fieldbus communication.

Illustrate system components of level 1 control.

Demonstrate interconnection between different components.

Develop knowledge base of foundation fieldbus technology.

4.2 Fieldbus Modules

Fieldbus Modules provide connection of digital I/O, analog I/O,

and Intelligent Transmitters to control processors. There are two types of

Fieldbus Modules: Main and Expansion. Some main modules can be

expanded using an expansion module.

A wide range of Fieldbus Modules is available to perform the

signal conversion necessary to interface the control processor with field

sensors and actuators.

4.3 Fieldbus Interconnection

The Control Processor is used in three different configurations, which

provide broad flexibility in Fieldbus implementation:

Local Fieldbus (Figure 4.1) - Used only within the enclosure.

Fieldbus Modules attach directly to the redundant local bus.

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Figure 4.1 Local Fieldbus

Twinaxial (Dual-Conductor Coaxial) Fieldbus Extension (Figure

4.2) - Using twinaxial cable, the Fieldbus can optionally extend

outside of the enclosure. Fieldbus Modules attach to the extended

bus through Fieldbus isolators. The twinaxial Fieldbus extension

may be redundant.

Figure 4.2 Twinaxial Fieldbus Extension

Fiber Optic Fieldbus Extension (Figure 4.3) - The fiber optic

Fieldbus can optionally extend the distance as well as add

application versatility and security.

Figure 4.3 Fiber Optic Fieldbus Extension

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All three Fieldbus configurations use serial data communication

complying with Electronic Industrial Association (EIA) Standard RS-485.

4.4 Cluster I/O Subsystem Interfacing

The Control Processor interfaces with the Fieldbus Cluster

Input/Output Subsystem that consists of the Fieldbus, a multi-slot chassis

configuration of a Fieldbus Processor, analog/digital Fieldbus Cards

(FBCs), and power supply and power monitor card. These Cluster I/O

subsystems meet the needs of applications where a high number of

channels per card are required. Figure 4.4 shows a typical twinaxial

Fieldbus configuration.

Figure 4.4 Twinaxial Fieldbus Cluster I/O Subsystem Interface Configuration

4.5 Fieldbus Cluster I/O Subsystem

The Fieldbus Cluster Input/Output Subsystem provides full support

for analog measurement, digital sensing, and analog or discrete control

capabilities. The Subsystem integrates with the Control Processor or

Personal Workstation via the Fieldbus, and includes a multi-slot chassis

configuration made up of a Fieldbus Processor, Analog/Digital Fieldbus

Cards (FBC), subsystem main power supply, and power monitor card.

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The Fieldbus Cluster I/O Subsystem is configurable, gathering

analog measurements, while simultaneously handling analog and digital

input and output channels. The Fieldbus Cluster I/O Subsystem is offered

in both non-redundant and redundant configurations. Each in a redundant

pair is individually addressable on the Fieldbus with a unique logical

address. In a redundant configuration, the FBPs provide switchover from

the primary FBP to the redundant FBP and back again automatically. The

FBCs are suitable in applications where a high number of channels per

card are required. They are ideal for non-isolated and isolated input signal

gathering and data acquisition systems where high quantities of "points

per cluster" areas are desired. The FBCs may be optionally connected as

redundant pairs. Various input cards are available with one of the

following three levels of isolation:

Non-isolated - Each channel is referenced to ground and the card

itself is referenced to ground.

Group-isolated - Electrically separate card-to-card but not channel-

to-channel on the same card.

Isolated - Each channel is electrically separated from any other

channel, card, group, building, site, etc.

4.6 Fieldbus Processor

The Fieldbus Processor (FBP) module provides communication

between the Fieldbus Cards (FBCs) and the Control Processor. Optionally

available is redundancy for the FBP module. Each FBP module is

individually addressable via the Fieldbus. If the primary FBP fails or is

taken off-line, the secondary FBP automatically assumes control. It

remains in control until the primary FBP returns on-line (figure 4.5).

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Figure 4.5 FBP Overview

4.7 Fieldbus Cards

The Fieldbus Cards support a variety of analog and digital I/O

signals. The FBCs convert electrical I/O signals used by field devices to

permit communication with these devices via the Fieldbus.

The FBCs can be connected in a redundant configuration via the

hardware. The redundant FBCs must be in adjacent slots and they are

connected via a hardware adapter at the interface to the field devices. In

an FBC redundant configuration, the FBP determines which FBC of the

redundant pair is to supply the data to the Control Processor. This is done

in the software by a predetermined set of conditions.

4.7.1 Analog FBCS

The analog FBCs support analog signal types and control functions

equipped with accurate signal conditioning circuitry, the analog cards

interface between process sensors and actuators.

To input an analog voltage (into DCS) the continuous voltage value

must be sampled and then converted to a numerical value by an A/D

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converter. Figure 4.6 shows a continuous voltage changing over time.

There are three samples shown on the figure. The process of sampling the

data is not instantaneous, so each sample has a start and stop time. The

time required to acquire the sample is called the sampling time. A/D

converters can only acquire a limited number of samples per second. The

time between samples is called the sampling period T, and the inverse of

the sampling period is the sampling frequency (also called sampling rate).

The sampling time is often much smaller than the sampling period.

Figure 4.6 Sampling an analog voltage

Analog outputs are much simpler than analog inputs. To set an

analog output an integer is converted to a voltage. This process is very

fast, and does not experience the timing problems with analog inputs.

But, analog outputs are subject to quantization errors. Figure 4.7 gives a

summary of the important relationships. These relationships are almost

identical to those of the A/D converter. Assume we are using an 8 bit D/A

converter that outputs values between 0V and 10V. We have a resolution

of 256, where 0 results in an output of 0V and 255 results in 10V. The

quantization error will be 20mV. If we want to output a voltage of

6.234V, we would specify an output integer of 159, this would result in

an output voltage of 6.235V. The quantization error would be 6.235V-

6.234V=0.001V. The current output from a D/A converter is normally

limited to a small value, typically less than 20mA.

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Figure 4.7 D/A converter

4.7.2 Digital FBCS

The digital FBCs consist of 32- and 64-channel types. Inputs can

be either voltage monitoring or contact sensing.

Contact inputs must convert a variety of logic levels to the 5Vdc

logic levels used on the data bus. This can be done with circuits similar to

figure 4.8. Basically the circuits condition the input to drive an

optocoupler. This electrically isolates the external electrical circuitry from

the internal circuitry. Other circuit components are used to guard against

excess or reversed voltage polarity.

Figure 4.8 Contact input circuitry.

Contact outputs must convert the 5Vdc logic levels on the DCS

data bus to external voltage levels. This can be done with circuits similar

to figure 4.9. Basically the circuits use an optocoupler to switch external

circuitry. This electrically isolates the external electrical circuitry from

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the internal circuitry. Other circuit components are used to guard against

excess or reversed voltage polarity.

Figure 4.9 Contact output circuitry.

4.8 Other Modules

0 to 20 mA Input/Output Interface

Pulse Input, 0 to 20 mA Output Interface

Thermocouple/ Millivolt Input Interface

RTD Input Interface

High Power Contact/dc Input/Output Interface

4.9 Foundation Fieldbus Technology

FOUNDATION fieldbus is an all-digital, serial, two-way

communications system that serves as the base-level network in a plant or

factory automation environment.

Figure 4.10 Foundation Fieldbus Network

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Figure 4.11 Historical development of field devices technology.

It's ideal for applications using basic and advanced regulatory

control, and for much of the discrete control associated with those

functions. Two related implementations of FOUNDATION fieldbus have

been introduced to meet different needs within the process automation

environment. These two implementations use different physical media

and communication speeds.

H1 works at 31.25 Kbit/sec and generally connects to field devices.

It provides communication and power over standard twisted-pair

wiring. H1 is currently the most common implementation and is

therefore the focus of these courses.

HSE (High-speed Ethernet) works at 100 Mbit/sec and generally

connects input/output subsystems, host systems, linking devices,

gateways, and field devices using standard Ethernet cabling. It

doesn't currently provide power over the cable, although work is

under way to address this.

Figure 4.12 Field Device Capacity.

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Conventional analog and discrete field instruments use point-to-

point wiring: one wire pair per device. They're also limited to carrying

only one piece of information -- usually a process variable or control

output -- over those wires. As a digital bus, FOUNDATION fieldbus

doesn't have those limitations.

Multidrop wiring. FOUNDATION fieldbus will support up to 32

devices on a single pair of wires (called a segment) -- more if

repeaters are used. In actual practice, considerations such as power,

process modularity, and loop execution speed make 4 to 16 devices

per H1 segment more typical.

That means if you have 1000 devices -- which would require 1000 wire

pairs with traditional technology -- you only need 60 to 250 wire pairs

with FOUNDATION fieldbus. That's a lot of savings in wiring (and

wiring installation).

Figure 4.12 Fieldbus wiring diagram.

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Multivariable instruments. That same wire pair can handle

multiple variables from one field device. For example, one

temperature transmitter might communicate inputs from as many as

eight sensors -- reducing both wiring and instrument costs.

Other benefits of reducing several devices to one can include fewer pipe

penetrations and lower engineering costs.

Two-way communication. In addition, the information flow can

now be two-way. A valve controller can accept a control output

from a host system or other source and send back the actual valve

position for more precise control. In an analog world, that would

take another pair of wires.

New types of information. Traditional analog and discrete devices

have no way to tell you if they're operating correctly, or if the

process information they're sending is valid.

But FOUNDATION fieldbus devices can tell you if they're operating

correctly, and if the information they're sending is good, bad, or

uncertain. This eliminates the need for most routine checks -- and helps

you detect failure conditions before they cause a major process problem.

Control in the field. FOUNDATION fieldbus also offers the

option of executing some or all control algorithms in field devices

rather than a central host system. Depending on the application,

control in the field may provide lower costs and better performance

-- while enabling automatic control to continue even if there's a

host-related failure.

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FOUNDATION fieldbus is covered by standards from three major

organizations:

ANSI/ISA 50.02

IEC 61158

CENELEC EN50170:1996/A1

The technology is managed by the independent, not-for-profit

Fieldbus Foundation, whose 150+ member companies include users as

well as all major process automation suppliers around the globe.

Some suppliers have even donated fieldbus-related patents to the Fieldbus

Foundation to encourage wider use of the technology by all Foundation

members.

Interoperability simply means that FOUNDATION fieldbus

devices and host systems can work together while giving you the full

functionality of each component.

4.10 Role Play

Each trainee should introduce one of the main components:

5. Fieldbus Module and Interconnection

6. Fieldbus Processor and Clusters.

7. Foundation Fieldbus technology

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Chapter 5

DCS Software

5.1 Learning objectives

To be familiar with main software components of DCS.

Understand main tasks for each application.

5.2 Standard Application Packages

5.2.1 System Management

Features include:

Display of equipment information for the station and its associated

input/output devices, buses, and printers.

Capability for change actions directed to the associated equipment.

Processing of station alarm conditions and messages.

5.2.2 Database Management

Features include:

Storage, retrieval, and manipulation of system data files.

A run-time license for the embedded use of the Relational Database

Management System.

A spreadsheet package.

5.2.3 Historian

Features include:

Maintenance of a history of values for process-related

measurements that have been configured for retention by the

Historian.

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Maintenance of a history of application messages that have been

sent to the Historian.

Maintenance of a history of alarms and error conditions which

generate messages for the Historian.

Access to all Historian data by display and report application

programs.

5.2.4 View Display Manager

Features include:

Presentation of the operating environment.

Setting of the overall operating environment according to the type

of user. Process engineers, process operators, and software

engineers have access to specialized functions and databases suited

to their specific requirements and authorizations.

Dynamic and interactive process graphics.

Display and processing of current process alarms.

Group and default displays for control blocks.

Execution of embedded trending within displays.

5.2.5 Draw Display Builder

Features include:

Graphical display configuration for viewing and control of process

operation.

Access to graphical object palettes allowing easy inclusion of

pumps, tanks, valves, ISA symbols, and similar complex objects.

Ready modification of existing displays using a mouse pointer,

menu items, and quick-access toolbars.

Association of process variables with objects in the displays.

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Dynamic variation of object attributes such as fill level, color,

position, size and visibility with changes in the associated process

variable.

Inclusion of operator control elements such as pushbuttons and

sliders into displays.

A library of faceplates which may be configured by simply

specifying the compound and block name of the block to which the

faceplate is to be connected.

5.3 Alarm System

Figure 5.1 Alarm manger

Alarm Manager provides an easy-to-use graphical interface of

preconfigured alarm displays for viewing and quickly responding to

process alarm conditions. The alarm display windows present alarm

messages initiated by the control blocks and related to digital input, state

change, absolute analog, deviation, rate of change, device status

mismatch, and other alarm conditions.

Accessible from any environment, the Alarm Manager Display windows

provide:

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Quick, easy access to the most recent alarm messages via the Most

Recent Alarm display or Current Alarm display

Alarm status and value information dynamically updated from the

control station

Color-coded priority and status indicators that allow you to quickly

focus in on critical alarms

Summary displays for different views of the alarm database based

on alarm status

An historical list of alarms

The capability to view subsets of alarms based on specific user-

defined criteria

The capability to silence or temporarily mute workstation and

annunciator horns.

Secured access to alarming functions dependent on user or system

responsibility

This set of resizable alarm displays providing a variety of current and

historic views of the process alarm database includes:

A multi-page list of all the current alarms

A single page of the most recent, active, unacknowledged alarms

with dynamically updating value and status fields

Three summary displays specific to alarm status also with updating

values and statuses:

o all active, unacknowledged alarms

o all unacknowledged alarms that have returned to normal

o all active, acknowledged alarms

A list of historized alarms related to the selected historian database

An operations display for silencing horns, temporarily muting

horns, changing environments

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These displays allow you to respond to alarm conditions, filter and

analyze specific alarm data, and maintain alarm message files for

reporting purposes.

The Process or Alarm button in the Display Manager (DM) window

indicates the presence of alarms (both acknowledged and

unacknowledged) and provides access to Alarm Manager Displays.

Initially, the Current Alarm Display (CAD) appears and the other

displays are easily accessible from the CAD via its default Displays

menu:

Most Recent Alarm display (MRA)

New Alarm display (NEWALM)

Unacknowledged Alarms display (UNACK)

Acknowledged Alarms display (ACKALM)

Alarm History display (AHD)

Operations display (OPR)

These easy-to-use displays support the following features:

A pre-configured number of alarms per screen or page

Pre-configured alarm message information and formatting per

alarm type

A status area for indication of current Alarm Manager and display

status, such as horns muted, match active, display paused, initial

call-up time

Buttons for responding to alarm conditions, such as acknowledging

or clearing alarms, and for accessing additional alarm information

and process displays

Pull-down menus for editing, viewing, and filing functions

A pull-down menu for accessing other displays

Pop-up menus for quick access to commonly used functions

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A scroll bar and Go To Page option for moving easily through the

alarm list

Although a preconfigured set of alarm displays is provided, many aspects

of the displays and alarm message content are user configurable to

accommodate different process control applications and operational

needs. See the section on Alarm/Display Manager Configurator.

5.4 Historian

The Historian collects, stores, processes, and archives process data

from the control system to provide data for trends, Statistical Process

Control (SPC) charts, logs, reports, spreadsheets, and application

programs. The Historian software is an easy-to-use data collection tool

that allows the user to organize and enforce a plant data collection

philosophy. The Historian provides extensive data collection and

management functions, and data display functions for use by process

engineers or operators.

Typical historical data are process analog and/or digital variables

(points). The Historian can also collect and display application generated

messages. You can use the Historian to collect data in support of the

following production control functions:

Cost accounting

Equipment performance analysis

Historical trending

Information retrieval

Inventory management

Legal record maintenance

Lost time analysis

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Maintenance reporting

Material accounting

Process analysis

Production reporting

Quality control

The Historian can:

Retrieve variables from process databases or accept data from

production control databases maintained by user application

programs.

Perform built-in calculations on the collected data.

Store calculated (reduced) data in a real time, relational database.

Application software in a plant-wide control system can access the

Historian database to obtain historical data for process control, production

control, and management information reporting.

You can use SPC chart displays of Historian data to monitor process

variables on-line via the Statistical Process Control Package (SPCP).

You can build displays for trending historical data via the Display Builder

and Display Configurator with Trending software.

Using the Report Writer, you can generate detailed reports of historical

data for management information.

Examples of Industrial Software that interface with the Historian are:

Batch Plant Management

Data Validator

Display Manager

Display Configurator with Trending

Object Manager (for process data histories)

Operator Action Journal

Operator Message Interface

Real-Time Data Base Manager

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Spreadsheet

Statistical Process Control Package

System Monitor

Report Writer

5.5 Draw

Figure 5.2 Draw

Draw is a display builder and configurator that allow you to create

and maintain dynamically updating process displays. Displays can

represent the plant, a process area or a detailed portion of the process.

You can draw basic objects using Draw's toolbars, menu items and

shortcut keys. You assign graphic attributes such as color and line style to

the objects, and then configure them to reflect process variable changes or

operator actions. Draw includes numerous palettes of objects such as

operator buttons, pumps, tanks, pipes, motors, valves and ISA symbols.

You can also create your own palettes for storing complex objects and

company-standard symbols. Displays can include faceplates, trends and

bitmapped images. You can easily edit your displays to reflect changes in

the process control scheme or to maximize operating efficiency and

security.

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5.5.1 Configuration

There are two ways of configuring a display object. You can:

1. Choose the Dynamic Update tab to connect one of the object's

attributes, such as visibility or fill level, to a process variable or a

file. With this type of configuration, changes in an attribute are

triggered dynamically by changes in the process variable. No

operator intervention is necessary.

2. Choose the Operator Action tab to connect the entire object to an

action, such as opening a display or executing a command. An

operator triggers the action by selecting the object.

An individual object can have both types of connections, although it can

have only one operator action.

5.5.2 Operator Actions

In a display configured for operator action, an operator can trigger

events by selecting an object (typically a button), moving a slider, or

typing text or a numeric value. In response to an operator action,

variables can be modified, a new display can open or an overlay can

appear.

While you can configure only one operator action for each display

object, you can trigger two or more events with a single operator action

by configuring an object with a View display command script.

Operator Actions include:

Open Display

Open Overlay

Close Display/Overlay

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Display Command

Relative Pick

Momentary Contact

Ramp

Connect Variable

Move Horizontal or Vertical

Numeric/Text Entry

5.5.3 Faceplates

A faceplate is a dynamic representation of control block

parameters. Draw provides a complete library of faceplates, ready to be

connected to any control block in the control database. In addition, you

can build your own faceplates using the standard Draw drawing tools.

To configure a faceplate, you need only define the Compound:block to

which the faceplate is connected. Draw automatically determines the

proper configuration attributes for the associated Compound:block.

5.5.4 Trends

Trend areas represent changing data values from the real-time

database and historian database. A data is displayed as a series of plotted

points connected by straight lines and scaled according to the high and

low limits configured for each trend line.

5.5.5 Group Displays

Group displays allow you to group faceplates and trends into

unique layouts to meet changing operational needs.

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5.6 View

Figure 5.3 View

View is a window into the system software, providing a user-

friendly interface to the total process. You can interact with any or all of

the real-time plant, field, and process data available in the system.

View provides:

Direct access to dynamic process displays.

Entry into user-configurable operating environments specific to

each user - the process engineer, process operator, and software

engineer.

Execution of embedded real-time and historical trending.

Service and display of process alarms via the Alarm Manager.

An overview of the compounds and blocks in the control database

and access to block default detail displays via Select.

Access to other applications, such as:

o Draw software for building and configuring dynamic user

graphics.

o System Management Displays for monitoring system

equipment health.

o Integrated Control Configurator for configuring the control

database.

o Historian for configuring the historization of data and system

messages.

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o Access to the four most recently used displays.

Additionally, with View you have:

Flexibility in customizing environments to conform to your site

requirements.

Rapid access to View while in other applications.

Screen print utility.

Window sizing options.

The multi-window capability of Solaris and Windows NT operating

systems allows you to monitor the information on a process control

display as well as access other applications without closing any window.

5.6.1 View Window

View Window contains the following features:

A top menu bar for accessing displays, configurators, and other

applications as specified by the environment.

A display bar of named display buttons or eight "thumbnail" mini-

display buttons for directly accessing process displays.

A system bar with System and Process alarm buttons indicating

system and process health; a message bar with a dropdown list of

the latest messages; display of the current date and time.

A status bar indicating the current display name, current operating

environment, Operator Action Journal logging name, printer

logging name, Historian name.

Using the control window menu, you can:

Resize the View window automatically or manually.

Move the window.

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5.6.2 Operating Environments

A collection of programs, utilities, and displays related to user

tasks is provided for each of the following: process operator, process

engineer, and software engineer. These environments, including menu

bars, menu content, and Display Bar content, can be modified to conform

to your site requirements. You can easily switch from one configured

environment to another. To secure environments against unauthorized

use, environment passwords can be configured and menu entries disabled

based on the environment.

5.7 Operator Action Journal

The Operator Action Journal is a record of specific operator actions

taken during process control operations. These actions generally consist

of manipulating certain Control Processor, and gateway parameters as

well as Application Processor, Application Workstation, and Workstation

Processor shared variables. Actions of this type are the ramping or direct

data entry of point values, toggling points, changing block statuses,

acknowledging block alarms, and horn muting. Operator action reporting

is limited to operator actions from the Display Manager, View, and

Alarm Manager. Also logged are environment change actions, scripts,

applics, and invoking other applications such as configuration.

When the Operator Action Journal feature is enabled, all operator

actions within the Display Manager, View, and the Alarm Manager that

change parameters in the process database are logged to a printer and/or

to the specified Historian database. These operator actions include

toggling points, ramping or direct data entry of new point values,

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changing block statuses, acknowledging block alarms, and other actions

such as horn muting.

Information logged as a result of each database change includes:

Name of the Display Manager, FoxView, or Alarm Manager that

requested the database change.

Compound:Block.Point for which the change was made.

The "old value" TO "new value" text for non-packed Boolean.

Current mask and data value for packed Boolean/long.

Following is an example of an Operator Action Journal Report.

Operator Action Journal Report

Tue Aug 1 1997 17:04:05 Page 1

08-02-97 07:57:08 GC3E31 SCRIPT /usr/fox/hi/init.cmds 08-02-97 07:57:15 GC3E31 ChgEnv Init_Env ->Init_env

08-02-97 07:58:19 GC3E31 ChgEnv Init+Env ->Proc_Eng_Env

08-02-97 08:00:34 CG3E31 UC01_LEAD :SINE .OUT 16.18 to 46.18

08-02-97 08:00:54 GC3E31 UC01_LEAD :SINE .MA Manual to Auto

08-02-97 08:00:57 GC3E31 UC01_LEAD :SINE .LR Remote to Local

08-02-97 08:01:01 GC3E31 UC01_LEAD :SINE .MA Auto to Manual

5.8 Control Configuration

Process control for DCS is based on the concepts of compounds

and blocks. A compound is a logical collection of blocks that performs a

control strategy. A block is a member of a set of algorithms that performs

a certain control task within the compound structure. Figure 7.4 shows

the compound/block relationship.

The compound provides the basis for the integration of:

Continuous control

Ladder logic

Sequential control.

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Within this structure, any block in any compound can be connected to

any other block in any other compound in the system. The entire

compound structure can be viewed through the workstation display.

The block contains parameters that have values of the types: Real,

Boolean, Packed Boolean, Boolean Long, Integer, or String.

Figure 5.4 Compound/Blocks relationship

5.8.1 Compound Functions

The compound supports the following functions for the related blocks:

Process alarm priority, alarm inhibiting, and alarm grouping

Sequence status notification (see Sequential Control section)

Phasing for execution load leveling at execution time.

5.8.2 Compound/Block Process Alarming

Alarms and status messages are generated by specific alarm blocks

and by alarm options in selected blocks. Alarms have five levels of

priority, 1-5, (where 1 = highest priority) that enable you to quickly focus

on the most important plant alarm conditions. An alarm priority of 0

indicates the absence of any alarm. These are summarized in a single

alarm summary parameter for each compound. This parameter contains

the priority of the highest current alarm in that compound. To reduce

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nuisance alarms, alarms can be inhibited at the compound level on a

priority level basis. Alarms can also be inhibited at the block level, on

either an alarm type basis, or an overall basis.

Alarms are initiated by the blocks within the compound. Alarm

messages are then sent to groups of stations or applications (for example,

Workstations, Historians, Printers) according to configured alarm groups.

The UNACK alarm acknowledge output parameter allows the user to

propagate alarm acknowledge actions to all blocks in a compound.

Stations, applications, and devices corresponding to various alarm

destination groups are configured at the compound level or at the station

level in the case of station compounds.

Group numbers for individual block alarm types are configured at the

block level.

5.8.3 Compound/Block Phasing

A user-defined phase number can be assigned to each compound

using a range of integer values that varies with assigned period. Phasing

allows the starting time of one compound/block to lead or lag the starting

time of another compound/block, thereby leveling the block processor

load.

5.8.4 Compound Attributes

The compound has the following attributes:

Name: User-defined name that must be system-unique and no more

than 12 characters in length. The name can be any mix of numeric

(0 to 9), upper case alphabetic (A to Z), and the underscore (_).

Descriptor: 32-character field for user-defined identification.

On/Off: Parameter that enables or disables the execution of all

blocks within the compound, where: 1 = on; 0 = off.

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5.8.5 Compound/Block Parameters

Compound and block parameters contain values that are of one of

the types Real, String, Integer, Short Integer, Long Integer, Boolean,

Packed Boolean, Packed Long, or Character. Additionally, parameters are

defined as being configurable, and either connectable/settable, not

connectable/not settable, or a combination that is dependent upon the

compound, block, and state.

5.8.5.1 Configurable Parameters

Configurable parameters are those parameters that can be defined

through the Integrated Control Configurator. They can be displayable

only, or displayable and editable.

5.8.5.2 Connectable Parameters

Connectable parameters are those parameters of the user interface

in which secured, change-driven connections may be made between

network stations, or as local direct connections within the same station.

Each connection consists of a connectable source and a connectable sink.

Output parameters (all outputs are connectable) are sources, while a

connectable input may be a sink or a source, or both.

Certain parameters that may be considered functional inputs (such as SPT

in the PID blocks, and RATIO in the RATIO block) are settable but not

connectable. A connectable parameter has a value record that contains the

parameter's value, its status, and its designated value type (Real, Boolean,

or Integer).

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5.8.5.3 Input Parameters

Input parameters are connectable types that are the receivers of

data from other connectable parameters via a path connection.

If no source path is specified during configuration, then the resident data

of the value record is the actual "source" of data. It can be either the

initial default or configured value, or a new value through a SET call to

the input parameter.

If a source path is specified, then the data value is an output parameter of

the same or another block, or a shared variable, thereby securing the

input. By linking a shared variable to a block input during configuration,

the user can establish a long-term secured connection between a remote

application program and the block input.

5.8.5.4 Output Parameters

All output parameters are connectable data sources that have value

records. There are two types: settable and nonsettable. The settability of a

settable output is controlled by the secured status of the value record. The

secured status is dependent on whether the block's operational mode is in

Auto or in Manual. In either Auto or Manual, nonsettable output

parameters cannot be written by any other source under any conditions.

Settable outputs may be conditionally released by the block

algorithm in the Manual mode. In Manual, the block unsecures settable

output parameters. They can then be written by other tasks via SET calls.

When the block switches to Auto, the block secures and updates its

output parameter(s).

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5.8.5.5 Nonconnectable Parameters

Nonconnectable parameters have no value records and are not

linkable. They mainly consist of string-type variables like NAME, or

nonsettable parameters that are used in the configurator only, for

example, block options. Local algorithm variables are also

nonconnectable. Nonconnectable parameters are generally accessible

through GET calls.

There is also a class of nonconnectable input parameters that comprise the

block user interface which can be manipulated through SET calls. An

example is an alarm deadband.

5.9 Role Play

Each trainee should introduce one of the main applications:

8. System Management.

9. Historian

10. Graphics Applications.

11. Control Configurator.

12. Operator Journal

13. Alarm System.

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Chapter 6

Installation

6.1 Learning objectives

To be able to define installation procedure for each component.

6.2 Modular Industrial Console

The Modular Industrial Console (MIC) provides flexible mounting

arrangements for components. The MIC can incorporate a mixture of

equipment: console displays, input devices, processors, Fieldbus

modules, data storage devices, and so on.

Modular Industrial Consoles support powerful multiple-screen, real-time

display software interactions. This hardware/software combination allows

console resources to be allocated with the flexibility to meet changing

day-to-day needs. Multi-screen consoles enable comprehensive handling

of more plant information in a coordinated fashion.

The MIC product line (Figure 6.1) allows a highly flexible

packaging configuration of console equipment. Individual MIC modules

are joined on-site to provide a customized configuration using standard

components.

This modular approach offers you combinations of single-screen and

multi-screen real-time display software interactions as required at a given

console. There are, however, specific allocations for mounting equipment

within configurations.

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Figure 6.1 MIC Arrangement

The MIC is built up from four basic pieces of equipment, each of which

is individually configurable:

MIC bay - basic full bay unit, full height, 27-inches wide, with bay

module

Spacer module - storage space between MIC full bay units

Desktop/printer bay - a rear bay similar to the full bay unit's with a

flat tabletop

Free standing table - a basic multipurpose table.

6.3 System Equipment

6.3.1 Unloading

The system units must be designed to withstand vibration and

shock normally encountered during shipping and installation; however,

extreme shocks and vibration should be avoided. The system units may

be moved from the transportation vehicle to their intended locations by

forklift or manual jack truck. If practical, all major movements of the

units should be accomplished before the units are unpacked.

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6.3.2 Unpacking Procedure

The following unpacking procedure applies, in general, to all system

units:

Inspect the exterior of the shipping carton for obvious damage. (Any

noticeable damage should be indicated in the shipper's bill of lading.)

Verify that the equipment received is that described in the bill of

lading.

Remove shipping straps, shipping shroud, and other packing materials,

such as polyethylene bags and Styrofoam cushioning materials.

If the unit is attached to a skid, remove all shipping hardware and

hold-down bolts used to fasten the unit to the skid. Separate the skid

from the unit.

Ensure that the appropriate interconnecting cables are present, by

comparing the cable part numbers and quantities with those listed in

the bill of lading.

6.3.3 System Power Checks

Perform the following checks before you install the equipment:

Check that all the required ac or dc power distribution network lines

are installed.

Check that the appropriate number of ac power outlets are installed

and spaced appropriately.

Switch on main system power.

Using a multimeter, check that the appropriate operating voltage exists

at each ac outlet or connection point.

Switch off main system power.

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6.3.4 Industrial Enclosures Mounting Procedures

Figure 6.2 shows a single dual-height modular mounting structure

area for containing processors and modules in an Industrial Enclosure.

Figure 6.2 Industrial Enclosure Mounting Structure Area

Enclosures are designed for floor mounting, and accept processor

modules, Fieldbus modules, and data storage devices. Wires, cables, and

conduits can enter either the bottom or the top of the enclosure. Side

doors provide access to the wiring areas. Additionally, the doors can be

mounted to open from left-to-right or right-to-left.

Industrial Enclosures are available in two configurations, vented

and sealed. The vented configuration has openings at the top and bottom

to provide ventilation, and has a metal plate, with gasket, at the bottom

for electrical protection purposes. A sealed enclosure has metal plates,

with gaskets, at the top and bottom to provide a watertight seal.

1. Check that mounting holes have been drilled in floor. If they have

not, proceed as follows. (If below-floor cabling is to be employed,

refer to the Site Planning document for information on the

recommended size and placement of the floor cutout.)

a. Place enclosure in desired location.

b. Mark hole locations.

c. Move the enclosure away from the markings.

d. Drill holes in floor.

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2. If the enclosure is the vented type and conduit entry is to be from

the bottom:

a. Drill or punch the bottom conduit enclosure plate, and

provide appropriate conduit fittings.

b. Place the conduit enclosure plate on the floor, in the precise

location that the enclosure is to be mounted.

c. Go to Step 6.

3. If the enclosure is the vented type, and conduit entry is to be from

the top:

a. Remove the vent cap and top conduit enclosure plate(s).

b. Drill or punch the conduit enclosure plate(s).

c. Replace the vent cap and conduit enclosure plate(s).

d. Place the enclosure plate on the floor, in the precise location

that the enclosure is to be mounted.

e. Go to Step 6.

4. If the enclosure is the sealed type and conduit entry is to be from

the bottom:

a. Drill or punch the bottom conduit enclosure plate, and

provide appropriate conduit fittings for a watertight seal.

b. Place the conduit enclosure plate on the floor, in the precise

location that the enclosure will be mounted.

c. Go to Step 6.

5. If the enclosure is the sealed type and conduit entry is to be from

the top:

a. Remove the top conduit enclosure plate.

b. Drill or punch the conduit enclosure plate, and provide

appropriate conduit fittings for a watertight seal.

c. Replace the conduit enclosure plate.

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6. Position the enclosure, with mounting gasket and enclosure plate,

so that the holes in the enclosure base, gasket, and enclosure plate

are aligned with the mounting holes in the floor.

7. Install two bolts, with flat washers and lockwashers, in diagonally

opposite mounting holes. (Do not tighten.)

8. Install two more bolts, with flat washers and lockwashers, in the

other two diagonally opposite mounting holes. (Do not tighten.)

9. Install the remaining bolts, with flat washers and lockwashers, in

the center mounting holes.

10. Tighten all bolts evenly and equally, working from center to

outside bolts, being careful not to overtighten. Maximum torque

should be applied carefully.

6.4 Software Installation

The Installation Phase performs the installation of software

packages. Installation of software packages is performed by vendor

representative on target stations.

6.5 Discussion

Initiate a dialogue between trainees to discuss their own

experiences and notes about different installation phases related to the

text in this chapter.

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Chapter 7

Maintenance

7.1 Learning objectives

Understand maintenance philosophy and procedures.

7.2 Maintenance Philosophy

The maintenance approach is oriented toward module replacement.

The use of diagnostics, fault location tables, and troubleshooting guides

described in system document, as well as the presence of status lamps

(LEDs) on each module, enables isolation of problems to the module

level. In addition, any module can be replaced without affecting the

operation of any other module, including the module of a fault-tolerant

pair.

7.3 Preventive Maintenance

The design of DCS equipment and associated peripheral devices is

such that scheduled preventive maintenance on the equipment is limited

to visual inspections, periodic cleaning procedures, and adjustment of

system modules if necessary. While performing these routines, you

should check for damaged cables, loose connections, inoperative fans and

indicator lamps, wear or binding of drives and fan motors, and take

appropriate corrective action.

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7.3.1 Enclosures

Perform a general visual inspection and exterior cleaning of each

enclosure after the first six months of service. Approximately every

12 months thereafter perform the same, depending on local environmental

conditions. Preventive maintenance procedures for enclosures include the

following:

1. Wipe down the exterior of the enclosure with a soft cloth. A damp

cloth and/or a nonabrasive cleaner can be used for hard-to-remove

spots.

2. Clean any dust buildup from module heat fins. Use a soft cloth. If

heat fins are accessible from rear of enclosure, they can be cleaned

during normal operation. Otherwise, modules can be removed and

cleaned from front of enclosure during routine equipment

shutdowns.

3. Check fans (if installed) for proper operation.

4. Check module status indicators for proper operation.

Green light indicates normal operation.

Red light indicates faulty operation.

7.3.2 Enclosures Air Filters

The vented configurations of all metal enclosures have an air filter

located inside the door, behind the vents. Periodically check the condition

of the filter for dust/dirt accumulation. Perform the following steps to

check the condition of the filter:

1. Locate the plastic assembly that retains the filter that is on the

inside of the door behind the vents.

2. Unsnap the plastic assembly from the vents and remove the filter.

3. Wash and replace the filter, or if desired, install a new filter, and

snap the filter retainer assembly back onto the vent assembly.

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7.3.3 Modular Industrial Workstations

Perform a general visual inspection and exterior cleaning of each

workstation as often as necessary to ensure proper operation of the

equipment. Preventive maintenance procedures for the workstations

should include the following:

1. Wipe down the exterior of the enclosure with a soft cloth. A damp

cloth and/or a nonabrasive cleaner can be used for hard-to-remove

spots.

2. Clean any dust buildup on disk drives (especially the signal

connection areas), keyboards, control panels, and monitors. Use a

soft cloth.

3. Check fans (if installed) for proper operation.

4. Check module status indicators for proper operation.

Green light indicates normal operation.

Red light indicates faulty operation.

7.3.4 Monitor-Based Peripheral Devices

As a rule, preventive maintenance on these devices should be

limited to cleaning only and should be performed as often as necessary, or

at least every twelve months.

Wipe down the exterior of the device (excluding the monitor) with a soft

cloth. A damp cloth and/or nonabrasive cleaner can be used for hard-to-

remove spots.

To clean the monitor, proceed as follows:

1. Select a screen that does not have direct access to the process, for

example, the Initial display.

2. Remove power from the GCIO unit (annunciators are also

deactivated).

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3. Turn the monitor's power off. Do not move the mouse or depress

any keys while the monitor is off.

4. Dampen - do not saturate - a clean, lint-free cloth with liquid

glass cleaner.

5. Clean the screen by wiping with damp cloth, using circular wiping

motion to avoid streaks.

6. Carefully dry the screen by wiping with a second clean, lint-free

cloth.

7. Restore power to the monitor and GCIO.

7.3.5 Printers

All printers should be serviced every six months (or after 300 hours

of operation), whichever occurs first. Refer to the associated printer user's

guide (packed with the printer) and perform the following:

1. Perform a general visual inspection and cleaning of the printer.

2. Remove printer cover and inspect internal moving parts for signs of

wear, broken or loose parts, frayed cables, and so on.

3. Take a clean, dry, soft cloth and dust the area around carriage shaft

and platen. Remove any loose particles of paper and dust.

4. Lubricate printer as described in associated service instructions.

5. Restore printer power.

7.3.6 Keyboard

A keyboard should be cleaned at a frequency determined by the

environment in which it is used.

1. Use a soft, lint-free cloth dampened with a mild detergent solution

to clean the keys and large surfaces.

2. Clean confined areas between the keys with a vacuum cleaner

equipped with a fine brush attachment.

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7.3.7 Mouse

The following care and cleaning procedure applies to both the inner

and outer area of the mouse:

1. The mouse is a very precise mechanical device, so handle it with

care. Do not drop, hit, or otherwise subject it to shock.

2. Do not pull on the cable. It may cause damage to both the cable

and connector.

3. Do not carry the mouse by holding onto the cable.

4. Be sure to place a clean sheet of paper or use a mouse pad between

the mouse and the flat surface. Dirt and grit could collect on the

ball. Try not to touch the ball on the bottom.

5. Do not use the mouse in extreme temperatures or in direct sunlight.

6. Do not allow the mouse to come in contact with liquid spills

(water, solutions, and so forth).

7. The mouse housing should be cleaned with a lint-free cloth using a

mild detergent. Use an unsoiled lint-free cloth to dry housing.

8. Do not disassemble the mouse. If the ball in the unit needs to be

cleaned, remove it from the lower case by detaching the cover to

the housing. Do not remove all the screws to remove the ball.

9. Use a lint-free cloth with mild detergent to clean the ball, and an

unsoiled cloth to dry it.

7.3.8 Data Storage Devices

1. Blow away any lint or dust accumulation on or near the face of the

floppy disk and streaming tape drive casings.

2. Clean the outer plastic surface of the drive with a lint-free cloth or

a sponge slightly dampened with water. Wipe off residue and dry

with soft, lint-free cloth. Do not use abrasive cleaners, solvents, or

strong detergents.

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3. Blow away any lint or dust accumulation on the signal and power

connectors at the rear of the drive.

4. For the streaming tape drive, clean the head using only Freon TF

and polyurethane swabs, commonly available with VCR head

cleaning kits. Wet the swab with the Freon TF solution, and wipe

the head using an up and down motion. Use a dry swab to clean

any remaining residue from the head.

7.4 Fault Analysis

Through the System Management facility, you can monitor the

health of the system and perform diagnostic tests on all the system

stations and associated peripheral devices.

7.4.1 Startup Diagnostics

Startup diagnostics are invoked automatically as a result of a

power-on reset, an error, or an off-line diagnostic command. The

diagnostics exist in each station at all times and are of two basic types:

Reportable diagnostic - Tests a station function which, if faulty,

does not prevent the error from being reported over the network.

Nonreportable diagnostic - Tests a station function which, if faulty,

inhibits the station from communicating over the network.

7.4.2 On-line Diagnostics

On-line diagnostics consist of Carrierband LAN LI (LAN

Interface) Cable Tests and Nodebus Cable Tests. These tests are either

operator-initiated or automatically invoked to isolate faults and to check

the integrity of the communication path.

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7.4.3 Off-line Diagnostics

Off-line diagnostics are used to check for, or verify the proper

"independent" operation of a station's internal components. These tests do

not verify any external reason for failure, thus they can be individually

bench tested without regard to the station's subsystem configuration.

7.5 Corrective Maintenance

7.5.1 Module Status Indicators

All power modules, Processor modules, LAN modules, and

Fieldbus Modules have red and green status indicators that operate in

accordance with the maintenance manual codes.

7.5.2 I/A Series Module Replacement

The maintenance approach is oriented toward module replacement.

Fault analysis provides assistance with isolating station and peripheral

faults. The presence of status lamps (LEDs) on each module enables an

initial detection of problems that can exist on the module level. In

addition, any module can be replaced without affecting the operation of

any other module, including the other module of a fault-tolerant pair.

Replacement of modules is similar to installation, which is described in

the System Equipment Installation.

7.6 Discussion

Exchange of ideas with trainees to talk about their own experiences

and comments about maintenance related to the text in this chapter.

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Chapter 8

Power Distribution

8.1 Learning objectives

Understand power distribution of control systems.

8.2 Power Connections

Main power consists of primary and secondary power. Note the

voltage and main power distribution requirements for each enclosure

before you connect main power. The power should be connected through

an uninterruptible power supply.

8.3 Connection Procedure

To connect the power lines proceed as follows:

1. Switch off main system power.

2. Open the right side door of the enclosure to access the junction

boxes. (Two junction boxes are located in the field termination

area.)

3. Place the junction box power switches in the OFF position.

4. Remove the bottom cover from each junction box.

5. Route the power lines to the junction boxes.

6. Connect the power lines.

7. Replace the junction box covers.

8. Switch ON the main system power.

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8.4 Earth Connections

To make earth connections to the metal enclosures, locate one of

the tapped holes along the bottom interior of the enclosure (see Figure

8.1). Use a ring type solderless crimp connector appropriate for the size

of wire used, and use a star-type lock washer between the connector and

the enclosure chassis.

Figure 8.1 Metal Enclosures, Earth Connection

8.5 Discussion

Discuss power distribution schemes.

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Chapter 9

PLC Fundamentals

9.1 Learning objectives

• Know general PLC issues

• Understand the operation of a PLC

• Understand the different types of inputs and outputs.

9.2 Introduction

Control engineering has evolved over time. In the past humans

were the main methods for controlling a system. More recently electricity

has been used for control and early electrical control was based on relays.

These relays allow power to be switched on and off without a mechanical

switch. It is common to use relays to make simple logical control

decisions. The development of low cost computer has brought the most

recent revolution, the Programmable Logic Controller (PLC). The advent

of the PLC began in the 1970s, and has become the most common choice

for manufacturing controls. PLCs have been gaining popularity on the

factory floor and will probably remain predominant for some time to

come. Most of this is because of the advantages they offer.

• Cost effective for controlling complex systems.

• Flexible and can be reapplied to control other systems quickly

and easily.

• Computational abilities allow more sophisticated control.

• Trouble shooting aids make programming easier and reduce

downtime.

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• Reliable components make these likely to operate for years before

failure.

9.3 Hardware

Many PLC configurations are available, even from a single vendor.

But, in each of these there are common components and concepts. The

most essential components are:

Power Supply - This can be built into the PLC or be an external

unit. Common voltage levels required by the PLC (with and

without the power supply) are 24Vdc, 120Vac, 220Vac.

CPU (Central Processing Unit) - This is a computer where ladder

logic is stored and processed.

I/O (Input/Output) - A number of input/output terminals must be

provided so that the PLC can monitor the process and initiate

actions.

Indicator lights - These indicate the status of the PLC including

power on, program running, and a fault. These are essential when

diagnosing problems.

The configuration of the PLC refers to the packaging of the components.

Typical configurations are listed below from largest to smallest as shown

in Figure 9.1.

Rack - A rack is often large (up to 18” by 30” by 10”) and can hold

multiple cards. When necessary, multiple racks can be connected

together. These tend to be the highest cost, but also the most

flexible and easy to maintain.

Mini - These are similar in function to PLC racks, but about half

the size.

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Shoebox - A compact, all-in-one unit (about the size of a shoebox)

that has limited expansion capabilities. Lower cost, and

compactness make these ideal for small applications.

Micro - These units can be as small as a deck of cards. They tend to

have fixed quantities of I/O and limited abilities, but costs will be

the lowest.

Software - A software based PLC requires a computer with an

interface card, but allows the PLC to be connected to sensors and

other PLCs across a network.

Figure 9.1 Typical configuration of PLC

9.4 Inputs And Outputs

Inputs to, and outputs from, a PLC are necessary to monitor and

control a process. Both inputs and outputs can be categorized into two

basic types: logical or continuous. Consider the example of a light bulb. If

it can only be turned on or off, it is logical control. If the light can be

dimmed to different levels, it is continuous. Continuous values seem

more intuitive, but logical values are preferred because they allow more

certainty, and simplify control. As a result most controls applications (and

PLCs) use logical inputs and outputs for most applications. Hence, we

will discuss logical I/O and leave continuous I/O for later.

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Outputs to actuators allow a PLC to cause something to happen in a

process. A short list of popular actuators is given below in order of

relative popularity.

Solenoid Valves - logical outputs that can switch a hydraulic or

pneumatic flow.

Lights - logical outputs that can often be powered directly from

PLC output boards.

Motor Starters - motors often draw a large amount of current when

started, so they require motor starters, which are basically large

relays.

Servo Motors - a continuous output from the PLC can command a

variable speed or position.

Outputs from PLCs are often relays, but they can also be solid state

electronics such as transistors for DC outputs or Triacs for AC outputs.

Continuous outputs require special output cards with digital to analog

converters.

Inputs come from sensors that translate physical phenomena into

electrical signals. Typical examples of sensors are listed below in relative

order of popularity.

Proximity Switches - use inductance, capacitance or light to detect

an object logically.

Switches - mechanical mechanisms will open or close electrical

contacts for a logical signal.

Potentiometer - measures angular positions continuously, using

resistance.

LVDT (linear variable differential transformer) - measures linear

displacement continuously using magnetic coupling.

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Inputs for a PLC come in a few basic varieties, the simplest are AC

and DC inputs. Sourcing and sinking inputs are also popular. This output

method dictates that a device does not supply any power. Instead, the

device only switches current on or off, like a simple switch.

Sinking - When active the output allows current to flow to a

common ground. This is best selected when different voltages are

supplied.

Sourcing - When active, current flows from a supply, through the

output device and to ground. This method is best used when all

devices use a single supply voltage.

This is also referred to as NPN (sinking) and PNP (sourcing). PNP is

more popular.

9.5 Operation Sequence

All PLCs have four basic stages of operations that are repeated

many times per second. Initially when turned on the first time it will

check its own hardware and software for faults. If there are no problems it

will copy all the input and copy their values into memory, this is called

the input scan. Using only the memory copy of the inputs the ladder logic

program will be solved once, this is called the logic scan. While solving

the ladder logic the output values are only changed in temporary memory.

When the ladder scan is done the outputs will updated using the

temporary values in memory, this is called the output scan. The PLC now

restarts the process by starting a self check for faults. This process

typically repeats 10 to 100 times per second as is shown in Figure 9.2.

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Figure 9.2 PLC Scan

Self test - Checks to see if all cards error free, reset watch-dog

timer, etc. (A watchdog timer will cause an error, and shut down

the PLC if not reset within a short period of time - this would

indicate that the ladder logic is not being scanned normally).

Input scan - Reads input values from the chips in the input cards,

and copies their values to memory. This makes the PLC operation

faster, and avoids cases where an input changes from the start to

the end of the program (e.g., an emergency stop). There are special

PLC functions that read the inputs directly, and avoid the input

tables.

Logic solve/scan - Based on the input table in memory, the

program is executed 1 step at a time, and outputs are updated. This

is the focus of the later sections.

Output scan - The output table is copied from memory to the

output chips. These chips then drive the output devices.

The input and output scans often confuse the beginner, but they are

important. The input scan takes a snapshot of the inputs, and solves the

logic. This prevents potential problems that might occur if an input that is

used in multiple places in the ladder logic program changed while half

ways through a ladder scan and thus changing the behaviors of half of the

ladder logic program. This problem could have severe effects on complex

programs. One side effect of the input scan is that if a change in input is

too short in duration, it might fall between input scans and be missed.

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When the PLC is initially turned on the normal outputs will be turned off.

This does not affect the values of the inputs.

9.5.1 The Input and Output Scans

When the inputs to the PLC are scanned the physical input values

are copied into memory. When the outputs to a PLC are scanned they are

copied from memory to the physical outputs. When the ladder logic is

scanned it uses the values in memory, not the actual input or output

values. The primary reason for doing this is so that if a program uses an

input value in multiple places, a change in the input value will not

invalidate the logic. Also, if output bits were changed as each bit was

changed, instead of all at once at the end of the scan the PLC would

operate much slower

9.5.2 The Logic Scan

Ladder logic programs are modeled after relay logic. In relay logic

each element in the ladder will switch as quickly as possible. But in a

program elements can only be examines one at a time in a fixed sequence.

The ladder logic will be interpreted left-to-right, top-to-bottom. The

ladder logic scan begins at the top rung. At the end of the rung it

interprets the top output first, and then the output branched below it. On

the second rung it solves branches, before moving along the ladder logic

rung.

9.5.3 PLC Status

The lack of keyboard and other input-output devices is very

noticeable on a PLC. On the front of the PLC there are normally limited

status lights. Common lights indicate;

Power on - this will be on whenever the PLC has power.

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Program running - this will often indicate if a program is running,

or if no program is running.

Fault - this will indicate when the PLC has experienced a major

hardware or software problem.

These lights are normally used for debugging. Limited buttons will also

be provided for PLC hardware. The most common will be a run/program

switch that will be switched to program when maintenance is being

conducted, and back to run when in production. This switch normally

requires a key to keep unauthorized personnel from altering the PLC

program or stopping execution. A PLC will almost never have an on-off

switch or reset button on the front. This needs to be designed into the

remainder of the system.

9.6 Role Play

Conduct role plays for:

1. Introduce PLC and benefits.

2. Describe PLC hardware.

3. Introduce various inputs and outputs.

4. Describe PLC scan sequence.

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Chapter 10

Ladder Logic and SFC

10.1 Learning objectives

• To be able to write simple ladder logic programs

• Understand basic functions for calculations and comparisons.

• Be able to develop SFCs, sequential flow charts, for a process.

10.2 Ladder Logic

Ladder logic is the main programming method used for PLCs. As

mentioned before, ladder logic has been developed to mimic relay logic.

Relays are used to let one power source close a switch for another (often

high current) power source, while keeping them isolated. An example of a

relay in a simple control application is shown in Figure 12.1. In this

system the first relay on the left is used as normally closed, and will allow

current to flow until a voltage is applied to the input A. The second relay

is normally open and will not allow current to flow until a voltage is

applied to the input B. If current is flowing through the first two relays

then current will flow through the coil in the third relay, and close the

switch for output C. This circuit would normally be drawn in the ladder

logic form. This can be read logically as C will be on if A is off and B is

on.

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Figure 10.1 Simple Relay Control.

The example in Figure 10.1 does not show the entire control

system, but only the logic. When we consider a PLC there are inputs,

outputs, and the logic. Figure 10.2 shows a more complete representation

of the PLC. Here there are two inputs from push buttons. We can imagine

the inputs as activating 24V DC relay coils in the PLC. This in turn drives

an output relay that switches 115V AC, which will turn on a light. Note,

in actual PLCs inputs are never relays, but outputs are often relays. The

ladder logic in the PLC is actually a computer program that the user can

enter and change. Notice that both of the input push buttons are normally

open, but the ladder logic inside the PLC has one normally open contact,

and one normally closed contact. Do not think that the ladder logic in the

PLC needs to match the inputs or outputs. Many beginners will get

caught trying to make the ladder logic match the input types.

Figure 10.2 PLC with Relays.

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Many relays also have multiple outputs (throws) and this allows an

output relay to also be an input simultaneously. The circuit shown in

Figure 10.3 is an example of this; it is called a seal in circuit or latch

circuit. In this circuit the current can flow through either branch of the

circuit, through the contacts labeled A or B. The input B will only be on

when the output B is on. If B is off, and A is energized, then B will turn

on. If B turns on then the input B will turn on and keep output B on even

if input A goes off. After B is turned on the output B will not turn off.

Figure 10.3 Latch circuit

10.2.1 Ladder Logic Inputs

PLC inputs are easily represented in ladder logic. Below there are

two types of inputs shown, normally open and normally closed inputs.

10.2.2 Ladder Logic Outputs

In ladder logic there are multiple types of outputs, but these are not

consistently available on all PLCs. Some of the outputs will be externally

connected to devices outside the PLC, but it is also possible to use

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internal memory locations in the PLC. Five types of outputs are shown

below. The first is a normal output, when energized the output will turn

on, and energize an output. The circle with a diagonal line through is a

normally on output, when energized the output will turn off. This type of

output is not available on all PLC types. When initially energized the

OSR (One Shot Relay) instruction will turn on for one scan, but then be

off for all scans after, until it is turned off. The L (latch) and U (unlatch)

instructions can be used to lock outputs on. When an L output is

energized the output will turn on indefinitely, even when the output coil

is deenergized. The output can only be turned off using a U output.

10.2.3 Programming

The first PLCs were programmed with a technique that was based

on relay logic wiring schematics. This eliminated the need to teach the

electricians, technicians and engineers how to program a computer - but,

this method has stuck and it is the most common technique for

programming PLCs today. An example of ladder logic can be seen in

Figure 10.4. To interpret this diagram, imagine that the power is on the

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vertical line on the left hand side, we call this the hot rail. On the right

hand side is the neutral rail. In the figure there are two rungs, and on each

rung there are combinations of inputs (two vertical lines) and outputs

(circles). If the inputs are opened or closed in the right combination the

power can flow from the hot rail, through the inputs, to power the

outputs, and finally to the neutral rail. An input can come from a sensor,

switch, or any other type of sensor. An output will be some device

outside the PLC that is switched on or off, such as lights or motors. In the

top rung the contacts are normally open and normally closed. This means

if input A is on and input B is off, then power will flow through the

output and activate it. Any other combination of input values will result

in the output X being off.

Figure 10.4 Simple Ladder Logic Diagram

The second rung of Figure 10.4 is more complex, there are actually

multiple combinations of inputs that will result in the output Y turning on.

On the left most part of the rung, power could flow through the top if C is

off and D is on. Power could also (and simultaneously) flow through the

bottom if both E and F are true. This would get power half way across the

rung, and then if G or H is true the power will be delivered to output Y.

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10.2.4 Move Functions

The simple MOV will take a value from one location in memory

and place it in another memory location. Examples of the basic MOV are

given in Figure 10.5. When A is true the MOV function moves a floating

point number from the source to the destination address.

Figure 10.5 MOV function

10.2.5 Mathematical Functions

Mathematical functions will retrieve one or more values, perform

an operation and store the result in memory. Figure 10.6 shows an ADD

function that will retrieve values from N7:4 and F8:35, convert them both

to the type of the destination address, add the floating point numbers, and

store the result in F8:36. The function has two sources labelled source A

and source B.

Figure 10.6 Mathematical Functions

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10.2.6 Block Operations

A basic block function is shown in Figure 10.7. This COP (copy)

function will copy an array of 10 values starting at N7:50 to N7:40.

Figure 10.7 Copy Function

10.2.7 Comparison of Values

Comparison functions are shown in Figure 10.8. Previous function

blocks were outputs, these replace input contacts. The example shows an

EQU (equal) function that compares two floating point numbers. If the

numbers are equal, the output bit B3:5/1 is true, otherwise it is false.

Figure 10.8 Comparison Functions

10.2.8 Boolean Functions

Figure 10.9 shows Boolean algebra functions. The function shown

will obtain data words from bit memory, perform an AND operation, and

store the results in a new location in bit memory. These functions are all

oriented to word level operations. The ability to perform Boolean

operations allows logical operations on more than a single bit.

Figure 10.9 Boolean Functions

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10.3 Sequential Flow Charts

Sequential Function Charts (SFCs) have been developed to

accommodate the programming of more advanced systems. These are

similar to flowcharts, but much more powerful. The example seen in

Figure 10.10 is doing two different things.

To read the chart, start at the top where is says start. Below this

there is the double horizontal line that says follow both paths. As a result

the PLC will start to follow the branch on the left and right hand sides

separately and simultaneously. On the left there are two functions the first

one is the power up function. This function will run until it decides it is

done, and the power down function will come after. On the right hand

side is the flash function; this will run until it is done.

These functions look unexplained, but each function, such as

power up will be a small ladder logic program. This method is much

different from flowcharts because it does not have to follow a single path

through the flowchart.

Figure 10.10 SFC Simple example

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The basic elements of an SFC diagram are shown in Figure 10.11.

Figure 10.11 Basic Elements of SFC

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A simple SFC for controlling a stamping press is shown in Figure

10.12. (Note: this controller only has a single thread of execution, so it

could also be implemented with state diagrams, flowcharts, or other

methods.) In the diagram the press starts in an idle state. When an

automatic button is pushed the press will turn on the press power and

lights. When a part is detected the press ram will advance down to the

bottom limit switch. The press will then retract the ram until the top limit

switch is contacted, and the ram will be stopped. A stop button can stop

the press only when it is advancing. (Note: normal designs require that

stops work all the time.) When the press is stopped a reset button must be

pushed before the automatic button can be pushed again. After step 6 the

press will wait until the part is not present before waiting for the next

part. Without this logic the press would cycle continuously.

Figure 10.12 SFC for Controlling a Stamping Press

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10.4 Case Study

Each Trainee should try to develop the following:

1. Ladder Logic for pump operation connected to the suction of a tank

where two level switches are available for automatic operation and

two push buttons are for start and stop.

2. SFC for loading three tanks through different valve. Tank 1 is load

first, and then tanks 2 and three are loaded simultaneously. If the

pressure switch on pump discharge line is alarming then tank 2

stops loading from pump and tank 1 would transfer to tank through

different line. Tank 3 continues to load from pump.

.

PSL

T1 T2 T3

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Appendix A

Electrical Relay Diagram

And

P&ID Symbols

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Appendix B

Serial Communication

B.1 Introduction

Multiple control systems will be used for complex processes. These

control systems may be PLCs, but other controllers include robots, data

terminals and computers. For these controllers to work together, they

must communicate. This chapter will discuss communication techniques

between computers, and how these apply to PLCs. The simplest form of

communication is a direct connection between two computers. A network

will simultaneously connect a large number of computers on a network.

Data can be transmitted one bit at a time in series, this is called serial

communication. Data bits can also be sent in parallel. The transmission

rate will often be limited to some maximum value, from a few bits per

second, to billions of bits per second. The communications often have

limited distances, from a few feet to thousands of miles/kilometers.

Data communications have evolved from the 1800’s when

telegraph machines were used to transmit simple messages using Morse

code. This process was automated with teletype machines that allowed a

user to type a message at one terminal, and the results would be printed

on a remote terminal. Meanwhile, the telephone system began to emerge

as a large network for interconnecting users. In the late 1950s Bell

Telephone introduced data communication networks, and Texaco began

to use remote monitoring and control to automate a polymerization plant.

By the 1960s data communications and the phone system were being

used together. In the late 1960s and 1970s modern data communications

techniques were developed. This included the early version of the

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Internet, called ARPAnet. Before the 1980s the most common computer

configuration was a centralized mainframe computer with remote data

terminals, connected with serial data line.

In the 1980s the personal computer began to displace the central

computer. As a result, high speed networks are now displacing the

dedicated serial connections. Serial communications and networks are

both very important in modern control applications. An example of a

networked control system is shown in Figure B.1. The computer and PLC

are connected with an RS-232 (serial data) connection. This connection

can only connect two devices. Devicenet is used by the Computer to

communicate with various actuators and sensors. Devicenet can support

up to 63 actuators and sensors. The PLC inputs and outputs are connected

as normal to the process.

Figure B.1 Communication example

B.2 Serial Communication

Serial communications send a single bit at a time between

computers. This only requires a single communication channel, as

opposed to 8 channels to send a byte. With only one channel the costs are

lower, but the communication rates are slower. The communication

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channels are often wire based, but they may also be can be optical and

radio. Figure B.2 shows some of the standard electrical connections. RS-

232c is the most common standard that is based on a voltage change

levels. At the sending computer an input will either be true or false. The

line driver will convert a false value in to a Txd voltage between +3V to

+15V, true will be between -3V to -15V. A cable connects the Txd and

com on the sending computer to the Rxd and com inputs on the receiving

computer. The receiver converts the positive and negative voltages back

to logic voltage levels in the receiving computer. The cable length is

limited to 50 feet to reduce the effects of electrical noise. When RS-232 is

used on the factory floor, care is required to reduce the effects of

electrical noise - careful grounding and shielded cables are often used.

Figure B.2 Serial data standard

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The RS-422a cable uses a 20 mA current loop instead of voltage

levels. This makes the systems more immune to electrical noise, so the

cable can be up to 3000 feet long. The RS-423a standard uses a

differential voltage level across two lines, also making the system more

immune to electrical noise, thus allowing longer cables. To provide serial

communication in two directions these circuits must be connected in both

directions.

To transmit data, the sequence of bits follows a pattern, like that

shown in Figure B.3. The transmission starts at the left hand side. Each

bit will be true or false for a fixed period of time, determined by the

transmission speed.

A typical data byte looks like the one below. The voltage/current

on the line is made true or false. The width of the bits determines the

possible bits per second (bps). The value shown before is used to transmit

a single byte. Between bytes, and when the line is idle, the Txd is kept

true, this helps the receiver detect when a sender is present. A single start

bit is sent by making the Txd false. In this example the next eight bits are

the transmitted data, a byte with the value 17. The data is followed by a

parity bit that can be used to check the byte. In this example there are two

data bits set, and even parity is being used, so the parity bit is set. The

parity bit is followed by two stop bits to help separate this byte from the

next one.

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Figure B.3 a serial data byte

Some of the byte settings are optional, such as the number of data

bits (7 or 8), the parity bit (none, even or odd) and the number of stop bits

(1 or 2). The sending and receiving computers must know what these

settings are to properly receive and decode the data. Most computers send

the data asynchronously, meaning that the data could be sent at any time,

without warning. This makes the bit settings more important.

Another method used to detect data errors is half-duplex and full-

duplex transmission. In half-duplex transmission the data is only sent in

one direction. But, in full-dup transmission a copy of any byte received is

sent back to the sender to verify that it was sent and received correctly.

(Note: if you type and nothing shows up on a screen or characters show

up twice you may have to change the half/full duplex setting.)

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The transmission speed is the maximum number of bits that can be

sent per second. The units for this are baud. The baud rate includes the

start, parity and stop bits. For example a 9600 baud transmission of the

data in Figure B.3 would transfer up to 800 bytes each second. Lower

baud rates are 120, 300, 1.2K, 2.4K and 9.6K. Higher speeds are 19.2K,

28.8K and 33.3K. (Note: When this is set improperly you will get many

transmission errors, or garbage on your screen.)

Serial lines have become one of the most common methods for

transmitting data to instruments: most personal computers have two serial

ports. The previous discussion of serial communications techniques also

applies to devices such as modems.

B.3 RS-232

The RS-232c standard is based on a low/false voltage between +3

to +15V, and an high/true voltage between -3 to -15V (+/-12V is

commonly used). Figure B.4 shows some of the common connection

schemes. In all methods the txd and rxd lines are crossed so that the

sending txd outputs are into the listening rxd inputs when communicating

between computers. When communicating with a communication device

(modem), these lines are not crossed. In the modem connection the dsr

and dtr lines are used to control the flow of data. In the computer the cts

and rts lines are connected. These lines are all used for handshaking, to

control the flow of data from sender to receiver. The null-modem

configuration simplifies the handshaking between computers. The three

wire configuration is a crude way to connect to devices, and data can be

lost.

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Figure B.4 Common RS-232 Connection Schemes

Common connectors for serial communications are shown in

Figure B.5. These connectors are either male (with pins) or female (with

holes), and often use the assigned pins shown. The DB-9 connector is

more common now, but the DB-25 connector is still in use. In any

connection the RXD and TXD pins must be used to transmit and receive

data. The COM must be connected to give a common voltage reference.

All of the remaining pins are used for handshaking.

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Figure B.5 Typical RS-232 Pin Assignments and Names

The handshaking lines are to be used to detect the status of the

sender and receiver, and to regulate the flow of data. It would be unusual

for most of these pins to be connected in any one application. The most

common pins are provided on the DB-9 connector, and are also described

below.

TXD/RXD - (transmit data, receive data) - data lines

DCD - (data carrier detect) - this indicates when a remote device is

present

RI - (ring indicator) - this is used by modems to indicate when a

connection is about to be made.

CTS/RTS - (clear to send, ready to send)

DSR/DTR - (data set ready, data terminal ready) these handshaking lines

indicate when the remote machine is ready to receive data.

COM - a common ground to provide a common reference voltage for the

TXD and RXD.

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Appendix C

Networking

C.1 Introduction

A computer with a single network interface can communicate with

many other computers. This economy and flexibility has made networks

the interface of choice, eclipsing point-to-point methods such as RS-232.

Typical advantages of networks include resource sharing and ease of

communication. But, networks do require more knowledge and

understanding.

Small networks are often called Local Area Networks (LANs).

These may connect a few hundred computers within a distance of

hundreds of meters. These networks are inexpensive, often costing $100

or less per network node. Data can be transmitted at rates of millions of

bits per second. Many controls system are using networks to

communicate with other controllers and computers. Typical applications

include;

Taking quality readings with a PLC and sending the data to a

database computer.

Distributing recipes or special orders to batch processing

equipment.

Remote monitoring of equipment.

Larger Wide Area Networks (WANs) are used for communicating

over long distances between LANs. These are not common in controls

applications, but might be needed for a very large scale process. An

example might be an oil pipeline control system that is spread over

thousands of miles.

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C.2 Topology

The structure of a network is called the topology. Figure C.1 shows

the basic network topologies. The Bus and Ring topologies both share the

same network wire. In the Star configuration each computer has a single

wire that connects it to a central hub.

Figure C.1 Network Topologies

In the Ring and Bus topologies the network control is distributed

between all of the computers on the network. The wiring only uses a

single loop or run of wire. But, because there is only one wire, the

network will slow down significantly as traffic increases. This also

requires more sophisticated network interfaces that can determine when a

computer is allowed to transmit messages. It is also possible for a

problem on the network wires to halt the entire network.

The Star topology requires more wire overall to connect each

computer to an intelligent hub. But, the network interfaces in the

computer become simpler, and the network becomes more reliable.

Another term commonly used is that it is deterministic; this means that

performance can be predicted. This can be important in critical

applications.

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For a factory environment the bus topology is popular. The large

number of wires required for a star configuration can be expensive and

confusing. The loop of wire required for a ring topology is also difficult

to connect, and it can lead to ground loop problems. Figure C.2 shows a

tree topology that is constructed out of smaller bus networks. Repeaters

are used to boost the signal strength and allow the network to be larger.

Figure C.2 The Tree Topology

C.3 OSI Network Model

The Open System Interconnection (OSI) model in Figure C.3 was

developed as a tool to describe the various hardware and software parts

found in a network system. It is most useful for educational purposes, and

explaining the things that should happen for a successful network

application. The model contains seven layers, with the hardware at the

bottom, and the software at the top. The darkened arrow shows that a

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message originating in an application program in computer #1 must travel

through all of the layers in both computers to arrive at the application in

computer #2. This could be part of the process of reading email.

Figure C.3 The OSI Network Model

Application - This is high level software on the computer.

Presentation - Translates application requests into network operations.

Session - This deals with multiple interactions between computers.

Transport - Breaks up and recombines data to small packets.

Network - Network addresses and routing added to make frame.

Data Link - The encryption for many bits, including error correction

added to a frame.

Physical - The voltage and timing for a single bit in a frame.

Interconnecting Medium - (not part of the standard) The wires or

transmission medium of the network.

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The Physical layer describes items such as voltage levels and

timing for the transmission of single bits. The Data Link layer deals with

sending a small amount of data, such as a byte, and error correction.

Together, these two layers would describe the serial byte shown in the

previous chapter. The Network layer determines how to move the

message through the network. If this were for an internet connection this

layer would be responsible for adding the correct network address. The

Transport layer will divide small amounts of data into smaller packets, or

recombine them into one larger piece. This layer also checks for data

integrity, often with a checksum. The Session layer will deal with issues

that go beyond a single block of data. In particular it will deal with

resuming transmission if it is interrupted or corrupted. The Session layer

will often make long term connections to the remote machine. The

Presentation layer acts as an application interface so that syntax, formats

and codes are consistent between the two networked machines. For

example this might convert ’\’ to ’/’ in HTML files. This layer also

provides subroutines that the user may call to access network functions,

and perform functions such as encryption and compression. The

Application layer is where the user program resides. On a computer this

might be a web browser, or a ladder logic program on a PLC.

Most products can be described with only a couple of layers. Some

networking products may omit layers in the model.

C.4 Networking Hardware

The following is a description of most of the hardware that will be

needed in the design of networks.

Computer - (or network enabled equipment)

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Network Interface Hardware - The network interface may already

be built into the computer/PLC/sensor/etc. These may cost $15 to

over $1000.

The Media - The physical network connection between network

nodes.

10baseT (twisted pair) is the most popular. It is a pair of

twisted copper wires terminated with an RJ-45 connector.

10base2 (thin wire) is thin shielded coaxial cable with BNC

connectors.

10baseF (fiber optic) is costly, but signal transmission and

noise properties are very good.

Repeaters (Physical Layer) - These accept signals and retransmit

them so that longer networks can be built.

Hub/Concentrator - A central connection point that network wires

will be connected to. It will pass network packets to local

computers or to remote networks if they are available.

Router (Network Layer) - Will isolate different networks, but

redirect traffic to other LANs.

Bridges (Data link layer) - These are intelligent devices that can

convert data on one type of network, to data on another type of

network. These can also be used to isolate two networks.

Gateway (Application Layer) - A Gateway is a full computer that

will direct traffic to different networks, and possibly screen

packets. These are often used to create firewalls for security.

Figure C.4 and C.5 shows the basic OSI model equivalents for some of

the networking hardware described before.

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Figure C.4 Network devices and the OSI model

Figure C.5 The OSI network model with a router

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Appendix D

Software Engineering

D.1 Introduction

A careful, structured approach to designing software will cut the

total development time, and result in a more reliable system.

D.2 Fail Safe Design

It is necessary to predict how systems will fail. Some of the

common problems that will occur are listed below.

Component jams - An actuator or part becomes jammed. This can be

detected by adding sensors for actuator positions and part presence.

Operator detected failure - Some unexpected failures will be detected by

the operator. In those cases the operator must be able to shut down the

machine easily.

Erroneous input - An input could be triggered unintentionally. This

could include something falling against a start button.

Unsafe modes - Some systems need to be entered by the operators

or maintenance crew. People detectors can be used to prevent

operation while people are present.

Programming errors - A large program that is poorly written can

behave erratically when an unanticipated input is encountered. This

is also a problem with assumed startup conditions.

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Sabotage - For various reasons, some individuals may try to

damage a system. These problems can be minimized preventing

access.

Random failure - Each component is prone to random failure. It is

worth considering what would happen if any of these components

were to fail.

Some design rules that will help improve the safety of a system are

listed below.

Programs

A fail-safe design - Programs should be designed so that they

check for problems, and shut down in safe ways. Most PLC’s also

have imminent power failure sensors; use these whenever danger is

present to shut down the system safely.

Proper programming techniques and modular programming will

help detect possible problems on paper instead of in operation.

Modular well designed programs.

Use predictable, non-configured programs.

Make the program inaccessible to unauthorized persons.

Check for system OK at start-up.

Use PLC built in functions for error and failure detection.

People

Provide clear and current documentation for maintenance and

operators.

Provide training for new users and engineers to reduce careless and

uninformed mistakes.

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D.3 Debugging

Most engineers have taken a programming course where they

learned to write a program and then debug it. Debugging involves

running the program, testing it for errors, and then fixing them. Even for

an experienced programmer it is common to spend more time debugging

than writing software. For PLCs this is not acceptable! If you are running

the program and it is operating irrationally it will often damage hardware.

Also, if the error is not obvious, you should go back and reexamine the

program design. When a program is debugged by trial and error, there are

probably errors remaining in the logic, and the program is very hard to

trust. Remember, a bug in a PLC program might kill somebody.

D.4 Troubleshooting

After a system is in operation it will eventually fail. When a failure

occurs it is important to be able to identify and solve problems quickly.

The following list of steps will help track down errors in a PLC system.

Look at the process and see if it is in a normal state. i.e. no jammed

actuators, broken parts, etc. If there are visible problems, fix them and

restart the process.

1. Look at the PLC to see which error lights are on. Each PLC vendor

will provide documents that indicate which problems correspond to

the error lights. Common error lights are given below. If any off

the warning lights are on, look for electrical supply problems to the

PLC.

a. HALT - something has stopped the CPU

b. RUN - the PLC thinks it is OK (and probably is)

c. ERROR - a physical problem has occurred with the PLC

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2. Check indicator lights on I/O cards, see if they match the system.

i.e., look at sensors that are on/off, and actuators on/off, check to

see that the lights on the PLC I/O cards agree. If any of the light

disagrees with the physical reality, then interface

electronics/mechanics need inspection.

3. Consult the manuals, or use software if available. If no obvious

problems exist the problem is not simple, and requires a technically

skilled approach.

4. If all else fails call the vendor (or the contractor) for help.

D.5 Forcing

Most PLCs will allow a user to force inputs and outputs. This

means that they can be turned on, regardless of the physical inputs and

program results. This can be convenient for debugging programs, and, it

makes it easy to break and destroy things! When forces are used they can

make the program perform erratically. They can also make outputs occur

out of sequence. If there is a logic problem, then these don’t help a

programmer identify these problems.

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References

1. I/A series Foxboro documentation.

2. HoneyWell Experion process knowledge system, "Honeywell

Training.ppt"

3. "Automation Hierarchy", By: Prof. Dr. H. Kirrmann, ABB

Research Center, Baden, Switzerland, " AI_14_Hierarchy.ppt"

4. http://newton.ex.ac.uk , By: C.D.H. Williams

5. "Electrical Relay Diagram And P&ID Symbols", From Industrial

Text and Video Co. The Leader in Electrical, Motor Control and

PLCs Video Training Programs (www.industrialtext.com).

6. "A PLC Primer", " www.industrialtext.com".

7. "Automating Manufacturing Systems with PLCs", By:" Hugh

Jack" ([email protected]).

8. "Regulatory and Advanced regulatory control system

development", By: Harold L. Wade, Instrumentation society of

America.

9. Rosemount Measurement Catalog.