Evolution of Computer Application in the Industry

Evolution of computer application in the industry

ByV.S.Krushnasamy

Evolution of computer application in the industry

• Data logging• SCADA• DDC• PLC• DCS

Data logging

Data logger

Data logging

• With the development of high speed digital computers with mass storage,it became possible to record such data continuously and automatically,display the data on command,and perform calculations on the data to reduce it to a form suitable for evalution by appropriate technical individuals.

• The efficient operation of a manufacturing process may involve the interplay of many factors such as production rates,materials cost,efficiences of control.

Data logging

• When the process requires implementation of many process-control loops,then the interaction of one stage of the system with another often can be analyzed interms of the controlled variables of the loops.

• Data logging divided in to two typesFixed data loggersPortable data loggers

Data logging

Fixed data loggers• The process is under the control of many analog

process –control loops and there is provision for analog process variable measurements to be available as a commonly scaled voltage.

• Thus some signal conditioning coverts all measurements in to a given range,often a specified voltage range as required by data acquisition system.

Data logging

• Computer This is the central element of the system.Through programming, the computer accepts

input data or state and perform the process or evaluates the program through arithmetic and logic operations.

It act as a discrete-state control or programmable controller.

Data logging• DAS/DAQ Data acquisition is the process of sampling signals that

measure real world physical conditions and converting the resulting samples into digital numeric values that can be manipulated by a computer. Data acquisition systems (abbreviated with the acronym DAS or DAQ) typically convert analog waveforms into digital values for processing. The components of data acquisition systems include:

Sensors that convert physical parameters to electrical signals. Signal conditioning circuitry to convert sensor signals into a

form that can be converted to digital values. Analog-to-digital converters, which convert conditioned

sensor signals to digital values.

Data logging• Peripheral units The PU are the support equipment to communicate

computer operations to outside world. This unit consists of operator console where the programs

are entered and through which commands can be given to initiate specfic actions, such as calculations and data outputs by computer.

The console usually has a CRT/key board and a typewriter unit for input and outputs mass storage system such as magnetic tape,is used to store data such as periodically sampled inputs from the process.

Data logging

• AlarmsAn important part of any data logging is an

alarm system.such an alarm system is usually a computers or for help in a situation beyond its direct control.

• Types of alarmsSimple alarmMultivariable alarms

Data logging

• Simple alarm• One of the simplest digital application to process

control is the implementation of simple alarm circuits.

• These are very elementary binary processes because we are only concerned about whether a variable is above or below an alarm level.

• Simple alarm constructed from a comparator ,where a voltage level indicates the alarm condition.

Data logging

• Multivariable alarms• If each of a variable expressed through two

states[logic1 and logic 0], then digital approaches are ideally suited for a multivariable alarm.

• The general procedure is to express the variables as boolean parameters and to find the boolean equation between the variables that gives an alarm(0/1)

• This equation then is implemented using logic circuit elements.

Data logging

• Portable data loggers There are many cases when data needs to be logged for

a period of time from a loop and no fixed logger is provided.

A portable logger can be temporarily connected to the measurement output of the loop for this purpose.

The basic elements are DAS,computer/opertaor console, alarm.

Some portable data loggers do not use a computer.They are merely strip chart/magnetic tape recorders.

Data logging• The computer based portable data loggers have some mechanism

for saving the logged for later analysis. Recording mediums are Printed output Digitized strip-chart recording Magnetic tape Magnetic floppy disks Networked data communications• In NDA the data logger may be connected to a LAN.• The data then can be transmitted over the network to another,

fixed computer installation.• The data can be stored on mass storage facilities that are part of

the network.

SCADA

SCADA

SCADA

• SCADA: Supervisory Control And Data Acquisition System

• A Supervisory System• Encompasses all control ,indicating and

associated telemetry equipments at the master station and all of the complimentary devices in the remote stations

SCADA

SCADA stands for Supervisory Control And Data Acquisition.

SCADA refers to a system that collects data from various sensors at a factory, plant or in other remote locations and then sends this data to a central computer which then manages and controls the data.

WHAT IS DATA ACQUISITION

• Data acquisition is the process of retrieving control information from the equipment which is out of order or may lead to some problem or when decisions are need to be taken according to the situation in the equipment. So this acquisition is done by continuous monitoring of the equipment to which it is employed. The data accessed are then forwarded onto a telemetry system ready for transfer to the different sites.

SCADA

SCADA

• PURPOSE To Provide the user with the capability to

exercise control over a specific device and confirm its performance in accordance with the directed action.

To process those data for use by operator Operator control of remote devices

SCADA

• FUNCTIONS OF SCADADATA ACQUISITIONINFORMATION DISPLAYSUPERVISORY CONTROLALARM PROCESSINGINFORMATION STORAGE AND REPORTSDATA CALCULATIONS

SCADA

DATA ACQUISITION Periodic acquisition of data from RTUs Data acquired on a polled basisTwo options available on how a RTU responds:1. Send the actual value of points2. Send only those points where change has occurred The latter option preferred and referred to as

“Reporting By Exception” It’s a collective process of several specialized and

highly related sub processes

SCADA

• INFORMATION DISPLAYThis process consists of:1. Retrieving both fixed and real time data from database2. Combining them3. Presenting them to the operator in the form of limited

graphics CRT color pagesThis section is organized in a hierarchical tree structureDisplay selection by dedicated function keys provides very rapid access to frequently used displays

SCADA

• SUPERVISORY CONTROL Process of actuating equipment operation at remote

locationsThis process includes:1. Selection of station2. Selection of the device to be controlled3. Execution of desired commands such as TRIP or close

“Check-before-operate” method is employed for security of personnel and electric system

SCADA

• ALARM PROCESSINGThis process includes:1. Alerting the operator to unscheduled events 2. Informing him the time of occurrence, the

station location, the device ID and the nature of event

• The most common output of the alarm are CRT alarm lists, hardcopy printouts and audible alarms

SCADA

• INFORMATION STORAGE AND REPORTSAccurate records are necessary to satisfy legal

and governmental requirements for accounting, for support and forecasting future system operations and for engineering planning purposes

Pre-selected data sets are captured at periodic intervals and saved in rotating file

Periodicity of storage frequently set at certain time intervals called file time span

SCADA

• DATA CALCULATIONS• Data calculations done with single variables are:1. Determination of averages2. Maximum or minimum values over given intervals3. Integration with respect to time• Calculations done with multiple variables include

sums, differences, products, exponents, squares, square roots, exponentiation and others

• A practical application of such calculation is load monitoring of large transformer banks

SCADA

• FUNDAMENTALS OF OPERATION• POLLING SCHEMES• DATA INPUTS• CONTROL OUTPUTS• DATABASE• MAN MACHINE INTERFACE

SCADA POLLING SCHEMES

SCADA

• In communications engineering this method is known as “time division multiple access (TDMA)”

• Master station controls and the RTUs respond to only polling requests.

Following points are discussed through the diagram given:1. Multiple 2 or 4 wire telephone grade circuits2. Polling command requests, and RTU responses are

time multiplexed3. Automatic generation control (AGC)

SCADA• DATABASE• The newer database updates the real time part of the user

programs which retrieves data from the database and save computed results back into the database

• They are not fixed in size but can easily be expanded provided the physical memory is available

• Information contained in SCADA database may be categorized into:

1. Real time2. Parametric3. Calculated4. Application

SCADA

• MAN MACHINE INTERFACE• One of the greatest challenges in SCADA is to provide

efficient and user-friendly man machine interface• It consists of the hardware as well as the program

function which makes it all work• Example of such a man machine interface : now in

SCADA systems the simple audible alarm has been supplanted with a voice synthesizer which actually verbalizes alarm messages

SCADA

• APPLICATIONS• Industrial control• Oil & gas transmission, production and

distribution• Waste water utilities• Electric utility for remote control of

substations• Power distribution automation

SCADA

SCADA ADVANTAGES

SCADA DISADVANTAGES

SCADA MANUFACTURER AND NAME OF THE SOFTWARE

WONDERWARE Intouch ALLEN BRADLEY R.S View

SIEMENS Wincc MODICON oriecon

G E FANUC implicity INTELLUSION I Fix KPIT Ashtra

BENEFITS OF SCADA

• Long distance monitoring• Long distance training• Protection against terrorism/vandalism-alarm• Data management (engineering and

operations)• Automated operations with real time control

CONCLUSION

SCADA is a control system with● More interfaces and efficient storage● More record or device oriented configuration● But system wide configuration tools are

needed● Are less expensive than DCS, but offer

different functionality than DCS● And finally various applications

DIRECT DIGITAL CONTROL (DDC)




BASIC DDC CONFIGURATION

OVERVIEW OF A DUAL COMPUTER SYSTEM FOR DDC

DDC BACK-UP CONCEPT

DIRECT DIGITAL CONTROL (DDC)• In early systems a single mainframe computer

accomplished DAS,control.reporting to the operator, and higher level computation.

• In one of the first systems, the computer directly controlled the process,without intervening controllers.

• This architecture became known as DDC.• Only one computer was used in the first system because

of the high cost per processor and because of the general absence of computer to computer communications.

• Later systems used an auxiliary computer.


• The DDC technique essentially consists in replacing number of analog controllers by single digital computer.A single loop is replaced by a digital computer.

• The process values measured by the sensors,are cyclically sampled,and after the necessary ADC conversion transferred to the control algorithm.

• The output value a(k) is then calculated ,based on the input deviation e(k) ,where e(k) is the difference between set point value and the measured process value


• Where T is the sampling period,Kp,Ii,TD the relevent controller parameters.This is the first digital algorithm ,practically applied in the process control.

• In the twin computer concept back-up computer monitors the proper functioning of the main computer and,in case of any failure,takes over its functions

DIRECT DIGITAL CONTROL (DDC)• Computer mode© also called DDC mode,in which the computer

performs control functions of the loop.• Automatic mode(A),or controller mode ,in which the analog back-up

controller controls the plant.• Manual mode (M),or open –loop control mode,in which the field

operator directly acts on actuators.• In C ,the value of process variable,measured by the sensor, is

simultaneously transferred to the computer and the back up computer.

• For the given set point value,the DDC computes the relevent output for actuator,which is latched for back-up purpose(incase of computer or power fails).

• For the same purpose, the computer also repeatedly outputs the stotred set-point value to be latched.


• In this way, the back-up controller,having both the measured process value and the given setpoint value can continuously compute the corresponding actual value.

• If computer fails• Sensor outpt to analog back –up controller-set

point value from keypoard compare and operates the actuator.

• Manual –s1- operates.

DIRECT DIGITAL CONTROL (DDC)• The DDC came into picture for thermal power plant

operation sidelining analog control system due to following advantages.

Easy configuration,re-configuration and parameterization of control loops.

Simple introduction of new control loops Possibility of realization of advanced control algorithms Model based optimization of optimal set point values Comprehensive data acquisition and presentation Easy self-tuning of controller parameters.


• Disadvantage of DDC• Low fail safety of the system:the failure of the

computer caused the failure of all digital control loops.

• Higher investment,maintenance,and personnel costs,including the programming costs.

• Overloads of CPU and difficulties in programming when process computer had to handle some process automation functions in addition to DDC

DIRECT DIGITAL CONTROL (DDC)• Disadvantage of DDC

Though DDC take care of many things required for power plant control,relization of logic and sequential control functions were missing.

In case of boilers operations like startup and shutdown traditionally done by relays which are separate from control systems.

These systems executed both logic and sequential control.hence overall system became expensive and the reliability suffered.

To overcome these problems,PLC are introduced. They took care in addition to logic and sequence control functions,the function of timers,counters,registers,etc,besides diagnostic features

PROGRAMMABLE LOGIC CONTROLLER(PLC)



Introduction PLCs are specialized industrial devices for interfacing to and

controlling analog and digital devices. They are designed with a small instruction set suitable for

industrial control applications. They are usually programmed with ladder logic,which is graphical

method of laying out the connectivity and logic between system inputs and outputs.

They are designed with industrial control and industrial environments specifically in mind.

Therefore ,in addition to being flexible and easy to program,they are robust and relatively immune to external interference.


A programmable logic controller is a digital electronic device that uses a programmable memory to store instructions and to implement functions such as logic sequencing, counting and arithmetic in order to control machines and processes.

It has been specifically designed to make programming easy.Uses of PLCs PLCs are widely used and extend from small –contained

units with perhaps 20 digital inputs/outputs to modular systems which can be used for large number of inputs/outputs handle digital or analog inputs/outputs,and also carry out PID control modes.


Selection of a PLC Types of inputs/outputs required such as – Isolation– Out-board power supply for inputs/outputs– Signal conditioning Input/output capacity required Size of the memory required. This is linked to the number of

inputs/outputs and the complexity of program used. Speed and power required for CPU-This is linked to the

number of types of instructions that can be handled by a PLC


Special featuresThe interfacing for inputs and outputs is inside

the controllerEasy programmable. They have an easily

understood programming language. Programming is mainly concerned with logic and switching operation.

Rugged and designed to withstand vibrations,temperatures,humidity and noise.


PLC consists of the following main componentsCPU[Central Processing Unit]MemoryInput / Output circuitry


• Main units of PLCPower supplyInput/output (I/O) systemReal-time central processing unitMemory unitProgrammer unitsPeripheral devices


CPU[Central Processing Unit] It controls and processes all the operations with in the

PLC. It is provided with a clock with a frequency of typically

between 1 and 8 MHz.This frequency determines the operating speed of PLC and provides the timing and synchronisation for all elements of the system.

A bus system carries information and data to and from the CPU,memory and input/output units.


• The various memory elements available in a PLC are A system ROM to give permanent storage for operating system and fixed

data. RAM for users program Temporary buffer stores for input/output channels The program in the RAM can be changed by the user.However to prevent

the loss of these programs when the supply is switched off a battery is likely to be used in the PLC to maintain the RAM contents for a period of time.

Specifications for small PLCs often specify the program memory size in terms of the number of program step(A program step is an instruction for some event to occur)that can be stored.

Typically the number of steps that can be handled by a small PLC is the order of 300 to 1000,which is generally more than adequate for most control situations.


Input/output(I/O) circuitry The I/O unit provides the interface between the system and the

outside world. Programs are entered in to the I/O unit from a panel which can

vary from small keyboards with LCDs to those using visual display unit with keyboard and screen display.

The programs,alternatively,can be enter in to the system by means of a link to a personal computer which is loaded with an appropriate software package.

The I/O channel provides signal conditioning and isolation functions so that sensors and actuators can be generally directly connected to them without the need for other circuitry.


The basic form of programming commonly used with the PLCs is ladder programming.

This involves each program task being specified as through a rung of a ladder.

Following methods can be used for I/O processing

Continuous updatingMass I/O copying


Timers• The timers are commonly regarded as relays with coils

which,when energized,result in the closing or opening of input contacts after some preset time.

• A timing circuit is specified by starting the interval to be timed and the conditions or events that are to start and /or stop the timer.

• PLCs are generally provided with only delay-on timers that is a timer which comes on after time delay.

Internal relays• These relays are often used when there are programs with

multiple input conditions.• The internal relays are also used for starting of multiple outputs.


Counters The use of counters is restored to when there is a need to count a

specified number of contact operations. Counter circuits are supplied as an internal feature of PLCs.Shift registers Several internal relays can be grouped together to form a register

which can provide a storage area for a series sequence of individual bits.

Thus a 4-bit and 8-bit registers would be formed by using four and eight internal registers respectively.

The term shift register is used because the bits can be shifted along by one bit when there is a suitable input to the register.


• Advantages Flexibility Implementing changes and correcting errors Large quantities of contacts Pilot running Visual observation Speed of operation Ladder programming method Reliability and maintainability Security Fail-safe operation

PROGRAMMABLE LOGIC CONTROLLER(PLC) Low cost Easy to install Ensures increased productivity Faster operation speed Provides high reliability and easier maintenance Can withstand harsh industrial environment/manufacturing environment Provides consistency in manufacturing Can input/output both analog and digital signals Reduced cost of scrap and rework(since the user/designer can change the

PLC program without changing any hardware or scraping the present hardware).

Small size PLC modules can be added, depending upon the input/output requirements Easier troubleshooting


• DisadvantagesLacks the flexibility for expansion and

reconfiguration.The operator interface in PLC systems is also

limited.Implementing advanced control algorithms is

also limited.

DCS

DCS

DCS

DCS

Documents

Evolution of Computer Application in the Industry