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Final Project Report of BE (IE) Year 2007
PR –15b- IIEE – 438 – 2007
MIDAS Multiplexed Industrial Data Acquisition System
Using NI LabVIEW
M. Ubaid Khan Kamali (1526)
Rizwan Ahmed Khan (1530)
Sikander Ali (1534)
Syed Wasif Ali Shah (1538)
Submitted to In-charge
Final Project Work
Ashab Mirza Associate Professor IIEE
I
SUPERVISORS OF THE PROJECT
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Multiplexed Industrial Data Acquisition System (MIDAS)
__________________________________________________________________ PCSIR - Institute of Industrial Electronics Engineering, IIEE ST-22/C, Block-6 Gulshan-e-Iqbal, Karachi – 75300
II
TEAM MEMBERS Enrollment No. Syed Wasif Ali Shah IIEE-615 (Group Leader) Cell: +92-321-2185029 Email: [email protected] Rizwan Ahmed Khan IIEE-607 Cell: +92-331-3143364 Email: [email protected] M. Ubaid Khan Kamali IIEE-603 Cell: +92-300-3087561 Email: [email protected] Sikander Ali IIEE-611 Cell: +92-0301-2880070 Email: [email protected]
.
House # A-368, Ward # 4, Majeed Shah Street, JHUDO, District Mirpurkhas-Sindh House # 314, Wapda Colony, T.P.S, Guddu, District Kashmore-Sindh House # 512, behind Police Station. District Tando Adam-Sindh Unit # 1, Near Meat Market, P.O Bhiria Road, District Naushehro Feroze-Sindh
III
Acknowledgment
During our project work Associate Professor IIEE Ashab Mirza helped us all the
possible ways. He guide us in getting the most suitable data acquisition card, the
application software for HMI and also gave technical information about DAQ card and
signal conditioning.
We are indebt of Dr. Syed Naimat Ali Rizvi; Principal IIEE allowed the purchase
of data acquisition card and solving our problems. Engr. Farhan Khan, Ex. Lecturer of
IIEE, who provide us technical help in designing digital scanner using microcontroller.
Engr. Farah Haroon, Assistant Professor of IIEE, provided us the strong basis of
electronic devices, circuits and systems.
We are also thankful to Engr. Azmat Sher, IIEE graduate and CEO Industronics
which provides industrial solutions to various control systems, helped us in developing
the mechanical hardware and indigenously designed DAQ card, which was used before
purchase of NI DAQ card. Engr. Tehseen Jabbar, BE Electronics, helped us in managing
project work that only with their help and untiring guidance; we are able to turn this
project into reality.
IV
PREFACE At this auspicious occasion when we are submitting the project report on “Multiplexed
Industrial data Acquisition System Using National Instrument’s LabVIEW”, we
ourselves highly indebted towards Allah Almighty Who enabled us to complete this
project in due time.
We choose Multiplexed Industrial Data Acquisition System as a final project
because it was the most important instrumentation project. It is a complete industrial
Virtual Instrumentation system, which is the future of industrial automation. For this
purpose the NI multifunction DAQ card was employed. This project contains the
three most important quantities of any process industry as demo which are level,
temperature and servo valve position. Besides data acquisition card this project also
contains the signal conditioning of different transducer and also hardware display for
input quantities. This project contains certain complexities and one can learn a lot
from this project.
The report consists of seven chapters in all. First chapter gives
introduction which includes the project need, problem description, block diagram and
schematics with description of each block and part, all possible solutions of problem
and description plus reason of that solution which we selected. Second chapter
contains analysis and simulation which includes the mathematical models of system
and sub-systems, theoretical solution and its performance analysis and computer
simulation of those subsystems for which simulation was possible on available
software. Third chapter describes mechanical model which includes industrial
prototype development for the selected parameters. Fourth chapter describes
sensor’s selection and signal conditioning which describes different sensors available
and advantages of selected sensors and their signal conditioning. Fifth chapter is on
digital scanner which includes its designing techniques and features and describes its
importance in industry. Sixth chapter describes the configuration of DAQ card.
Seventh chapter gives human machine interface developed on LabVIEW, its
graphical programming and describes its features and advantages. The conclusion
V
includes the points which we learned during the designing of this project and it also
includes the possible recommendation.
During designing of this project we faced many difficulties. Most
problems were related to unavailability of required electronic devices. So we had to
complete this project with available technology as well as employed the latest virtual
instrumentation techniques. As industrial transducers are very expensive so
transducer’s arrangement was also a problem but we designed transducers ourselves as
well. They were manufactured on industrial standard quality and were linear with
respect to physical quantity.
In the end we would like again to express our gratitude towards ALLAH
almighty, then our parents who are constant source of encouragement and our teachers
for their efforts to make us acquainted with the electronics and control and most of our
Institute the IIEE which provide us the platform to become the practically oriented
engineers.
Karachi January 3rd, 2008.
VI
LIST OF FIGURES Figure-1.1: Traditional instruments (left) and software based virtual instruments (right) largely share the same architectural components, but radically different philosophies [Courtesy NI website]. Page # 3 Figure-1.2: Virtual instrumentation combines productive software, modular I/O, and scalable platforms. [Courtesy NI website], Page# 5 Figure-1.3: LabVIEW is a leader in application software used in PC-based data acquisition and instrument control. [Survey of Design News and R&D Magazine, QI 2004], Page# 7 Figure-1.4: A PC based data acquisition [Courtesy National Instrument Website], Page#8 Figure-2.1: Thermal System Block Diagram, page # 13 Figure-2.2: See Back Effect, page # 14 Figure-2.3: A simple thermocouple, page # 16 Figure-2.4: Physical circuit for thermocouple, Page # 17 Figure-2.5: Conceptual T(x) plot of thermocouple, Page# 18 Figure-2.6: Cold junction compensation, Page# 20 Figure-2.7: A general block diagram for position control, page# 21 Figure-2.8: Graph between generated voltage and applied RPM, page# 23 Figure-2.9: Graph between generated and voltage, Page# 23 Figure-2.10: Graph for J-Type Thermocouple, page# 25 Figure-2.11: Open loop impulse response, page# 26 Figure-3.1: Mechanical model for liquid level system with inlet pump motor, page# 29 Figure-3.2: Electric furnace surrounded by wooden block for safety and protection attached with the temperature controller. The controller is based upon SCR pulse firing technique, page# 30 Figure-3.3: Servo controlled valve mechanism to control the outlet flow of liquid tank , page# 31
VII
Figure-3.4: Overall mechanical assembly, page# 32 Figure-4.1: Graph between transmitter output and height of level, page# 37 Figure-4.2: Block Diagram of Level Transmitter Signal Conditioning, page # 38 Figure-4.3: Circuit Diagram of Level Transmitter Signal Conditioner, page # 38 Figure 4.4: Graph between temperature and RTD Output, page # 39 Figure-4.5: Graph between AD594 output voltage with respect to temperature, page# 40 Figure-4.6: Block Diagram of Thermocouple Signal Conditioning Output, page # 41 Figure-4.7: Circuit Diagram of Thermocouple Signal Conditioner, page # 42 Figure-4.8: Block Diagram of PI Controller for Controlled Valve, page# 43 Figure-4.9: Graph of feedback signal from pot meter against valve position, page# 44 Figure-4.10: Circuit Diagram of proportional controller for the servo controlled valve position, page # 45 Figure-5.1: Block diagram of digital scanner, page# 51 Figure-5.2: Circuit schematic of digital scanner, page# 52 Figure-5.3: Controller Program flowchart, page# 55 Figure-6.1: The block diagram of indigenously developed DAQ card. The parameter to be processed and displayed will be selected by the controller from select logic, page# 60 Figure-6.2: Circuit schematic of indigenously developed data acquisition card, page # 62 Figure-6.3: : NI USB-6008 multifunction DAQ card, page # 64 Figure 6.4: The block diagram of NI SUB-6008 multifunction DAQ card, page # 65 Figure-6.5: Setting up hardware, page# 66 Figure-6.6: Device recognition tree in max, page # 67
VIII
Figure-6.7: : Device self test. A success message will be displayed if device pass the self test as shown, page # 68 Figure-6.8: Attaching sensors/signal lines with the device to the selected channels and setting up timing and triggering from software, page# 69 Figure-7.1: Screenshot of a simple LabVIEW program [Courtesy of NI website], page# 72 Figure-7.2: Data acquisition task in LabVIEW [courtesy NI website], page # 74 Figure-7.3: DAQ assistant express VI, page # 75 Figure-7.4: DAQ device physical channels configuration window, page# 76 Figure-7.5: The front panel of developed HMI on LabVIEW, page# 78 Figure-7.6: Block diagram programming of developed HMI using LabVIEW G-programming environment, page# 80
IX
LIST OF TABLES Table-2.1: Readings for generator action. Applied RPM and generated voltage, page# 22 Table-2.2: Readings for generator action. Applied and generated voltages, page# 22 Tabel-4.1: Level Transmitter output table during Calibration, page# 37 Table-4.2: RTD's measured values, page# 39 Table-4.3: AD594 output voltage with respect to temperature, page# 40 Table-4.4: Valve position and feedback signal, page# 43
CONTENTS
Title
Project Supervisors ……………………………………………………………… I
Group Members ………………………………………………………… II
Acknowledgment ……………………………………………………………… III
Preface ………………………………………………………… IV
List of Figures ………………………………………………………… VI
List of Tables ………………………………………………………… IX
1. INTRODUCTION [1-11]
1.1 Instrumentation ………………… 2
1.2 Traditional Versus Virtual Instrumentation ………………… 2
1.3 Virtual Instrumentation in the Engineering Process ………… 5
1.4 Data Acquisition ………………………………………… 7
1.5 Modern Instrumentation Techniques ………………………… 9
1.6 Project Description ………………………………………… 10
1.7 Summary ………………………………………… 11
2. PLANT AND PROCESS [12-26]
Introduction
2.1 Mathematical Modeling of Process Parameters ………………… 13
2.2 Mathematical Simulation and Analysis ………………… 25
3. MECHANICAL MODEL [27-32]
Introduction ………………………………………………… 28
3.1 Industrial Prototype ………………………………………… 28
3.2 Liquid Level System ………………………………………… 29
3.3 Thermal System ………………………………………… 30
3.4 Servo Controlled Valve Mechanism ……………………….. 31
3.5 Overall Assembly ……………………………………….. 32
3.6 Summary ……………………………………….. 32
4. SENSOR & SIGNAL CONDITIONING [33-46]
Introduction ……………………………………………… 34
4.1 Sensor’s Selection ……………………………………… 34
4.2 Signal Conditioning ……………………………………… 36
4.6 Summary ……………………………………………… 46
5. DIGITAL SCANNER [47-57]
Introduction ……………………………………………… 48
5.1 Scanner in Industry ……………………………………… 48
5.2 Required Features ……………………………………… 48
5.3 Available Designing Techniques ……………………… 49
5.4 Selected Design ……………………… 50
5.5 Programming Flowchart ……………………………………… 55
5.6 Possible Improvements ………………………………... 56
5.7 Summary ……………………………………………… 57
6. DAQ CARD CONFIGURATION [58-69]
Introduction ……………………………………………… 59
6.1 Project Requirements ……………………………………… 59
6.2 Indigenously Developed DAQ Card ……………………….. 60
6.3 NI USB-6008 Multifunction DAQ Card ……………….. 63
6.4 Getting Started Steps ……………………………………….. 66
6.5 Device Recognition ……………………………………….. 67
6.6 Summary ……………………………………………….. 69
7. HUMAN MACHINE INTERFACE [70-81]
Introduction ……………………………………………….. 71
7.1 LabVIEW ……………………………………………….. 71
7.2 Data Acquisition Task ……………………………………….. 74
7.3 Developed HMI ……………………………………………….. 77
7.4 Block Diagram Programming ……………………………….. 78
7.5 Summary ……………………………………………….. 80
8. CONCLUSION ………………………………………………. [81-84]
9. REFERENCES ………………………………………………. [85-87]
10. APPENDICES ………………………………………………. 88
10. A NI USB-6008 DAQ User Guide
10. B Controller Programming for Digital Scanner
10. C Datasheets and Tables
10. D Project Manual
Multiplexed Industrial Data Acquisition System (MIDAS)
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1.1 INSTRUMENTATION Instrumentation is about measurement and control. Instrumentation can refer
either to the field in which instrument technicians and engineers work, or to the
available methods of measurement and control and the instruments which facilitate
this ‘[24].
Instruments are devices which are used in measuring attributes of physical
systems. The variable measured can include practically any measurable variable
related to the physical sciences. These variables commonly include:
• Pressure • Flow • Temperature • Level • Density • Position • Radiation • Current • Voltage • Inductance • Capacitance • Frequency • Chemical composition • Chemical properties • Various physical properties Instruments can often be viewed in terms of a simple input-output device. For
example, if we "input" some temperature into a thermocouple, it "outputs" some sort
of signal. (This can later be translated into data) In the case of this thermocouple, it
will "output" a signal in mill volts.
1.2 TRADITIONAL VERSUS VIRTUAL INSTRUMENTATION
Stand-alone traditional instruments such as oscilloscopes and waveform
generators are very powerful, expensive, and designed to perform one or more specific
Multiplexed Industrial Data Acquisition System (MIDAS)
__________________________________________________________________ PCSIR - Institute of Industrial Electronics Engineering, IIEE ST-22/C, Block-6 Gulshan-e-Iqbal, Karachi – 75300
3
tasks defined by the vendor. However, the user generally cannot extend or customize
them. The knobs and buttons on the instrument, the built-in circuitry, and the functions
available to the user, are all specific to the nature of the instrument. In addition,
special technology and costly components must be developed to build these
instruments, making them very expensive and slow to adapt ‘[30].
The primary difference between 'natural' instrumentation and virtual
instrumentation is the software component of a virtual instrument. The software
enables complex and expensive equipment to be replaced by simpler and less
expensive hardware; for example analog to digital converter can act as a hardware
complement of a virtual oscilloscope, a potentiostat enables frequency response
acquisition and analysis.
Virtual instruments are defined by the user while traditional
instruments have fixed vendor-defined functionality.
Every virtual instrument consists of two parts – software and hardware. A
virtual instrument typically has a sticker price comparable to and many times less than
a similar traditional instrument for the current measurement task. However, the
savings compound over time, because virtual instruments are much more flexible
when changing measurement task.
Figure 1-1: Traditional instruments (left) and software based virtual instruments (right) largely share the same architectural components, but radically different philosophies [Courtesy NI website]
Multiplexed Industrial Data Acquisition System (MIDAS)
__________________________________________________________________ PCSIR - Institute of Industrial Electronics Engineering, IIEE ST-22/C, Block-6 Gulshan-e-Iqbal, Karachi – 75300
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By not using vendor-defined, prepackaged software and hardware, engineers
and scientists get maximum user-defined flexibility. A traditional instrument provides
them with all software and measurement circuitry packaged into a product with a finite
list of fixed-functionality using the instrument front panel. A virtual instrument
provides all the software and hardware needed to accomplish the measurement or
control task. In addition, with a virtual instrument, engineers and scientists can
customize the acquisition, analysis, storage, sharing, and presentation functionality
using productive, powerful software.
A virtual instrument consists of an industry-standard computer or workstation
equipped with powerful application software, cost-effective hardware such as plug-in
boards, and driver software, which together perform the functions of traditional
instruments. Virtual instruments represent a fundamental shift from traditional
hardware-centered instrumentation systems to software-centered systems that exploit
the computing power, productivity, display, and connectivity capabilities of popular
desktop computers and workstations.
Virtual instruments are compatible with traditional instruments almost without
exception. Virtual instrumentation software typically provides libraries for interfacing
with common ordinary instrument buses such as GPIB, serial, or Ethernet.
Engineers and scientists whose needs, applications, and requirements change
very quickly, need flexibility to create their own solutions. You can adapt a virtual
instrument to your particular needs without having to replace the entire device because
of the application software installed on the PC and the wide range of available plug-in
hardware.
Multiplexed Industrial Data Acquisition System (MIDAS)
__________________________________________________________________ PCSIR - Institute of Industrial Electronics Engineering, IIEE ST-22/C, Block-6 Gulshan-e-Iqbal, Karachi – 75300
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1.3 VIRTUAL INSTRUMENTATION IN THE ENGINEERING PROCESS
Virtual instruments provide significant advantages in every stage of the
engineering process, from research and design to manufacturing test. [4]
1.3.1 RESEARCH AND DESIGN In research and design, engineers and scientists demand rapid development and
prototyping capabilities. With virtual instruments, you can quickly develop a program,
take measurements from an instrument to test a prototype, and analyze results, all in a
fraction of the time required to build tests with traditional instruments. When you need
flexibility, a scalable open platform is essential, from the desktop, to embedded
systems, to distributed networks.
The demanding requirements of research and development (R&D) applications
require seamless software and hardware integration. Whether you need to interface
stand-alone instruments using GPIB or directly acquire signals into the computer with
a data acquisition board and signal conditioning hardware, VI makes integration
simple. With virtual instruments, you also can automate a testing procedure,
Figure 1-2: Virtual instrumentation combines productive software, modular I/O, and scalable platforms. [Courtesy NI website]
Virtual instrumentation
is necessary because it delivers
instrumentation with the rapid
adaptability required for today’s
concept, product, and process
design, development, and
delivery. Only with virtual
instrumentation can engineers
and scientists create the user-
defined instruments required to
keep up with the world’s
demands ‘[31].
Multiplexed Industrial Data Acquisition System (MIDAS)
__________________________________________________________________ PCSIR - Institute of Industrial Electronics Engineering, IIEE ST-22/C, Block-6 Gulshan-e-Iqbal, Karachi – 75300
6
eliminating the possibility of human error and ensuring the consistency of the results
by not introducing unknown or unexpected variables.
1.3.2 DEVELOPMENT TEST AND VALIDATION With the flexibility and power of virtual instruments, you can easily build
complex test procedures. For automated design verification testing, you can create test
routines in LabVIEW and integrate software such as National Instruments TestStand,
which offers powerful test management capabilities. One of the many advantages
these tools offer across the organization is code reuse. You develop code in the design
process, and then plug these same programs into functional tools for validation, test, or
manufacturing.
1.3.3 MANUFACTURING TEST Decreasing test time and simplifying development of test procedures are
primary goals in manufacturing test. Virtual instruments based on LabVIEW
combined with powerful test management software such as TestStand deliver high
performance to meet those needs. These tools meet rigorous throughput requirements
with a high-speed, multithreaded engine for running multiple test sequences in
parallel. TestStand easily manages test sequencing, execution, and reporting based on
routines written in LabVIEW.
TestStand integrates the creation of test code in LabVIEW. TestStand also can
reuse code created in R&D or design and validation. If you have manufacturing test
applications, you can take full advantage of the work already done in the product life
cycle.
1.3.4 MANUFACTURING Manufacturing applications require software to be reliable, high in
performance, and interoperable. Virtual instruments based on LabVIEW offer all these
advantages, by integrating features such as alarm management, historical data
trending, security, networking, industrial I/O, and enterprise connectivity. With this
Multiplexed Industrial Data Acquisition System (MIDAS)
__________________________________________________________________ PCSIR - Institute of Industrial Electronics Engineering, IIEE ST-22/C, Block-6 Gulshan-e-Iqbal, Karachi – 75300
7
functionality, you can easily connect to many types of industrial devices such as PLCs,
industrial networks, distributed I/O, and plug-in data acquisition boards. By sharing
code across the enterprise, manufacturing can use the same LabVIEW applications
developed in R&D or validation, and integrate seamlessly with manufacturing test
processes.
Figure 1-3 shows the increasing strength of NI LabVIEW based virtual
instrumentation in the engineering processes of R&D and industry over other available
software packages. The increasing advancement and functionality of NI LabVIEW
will soon replace the traditional and other software based virtual instrumentation.
1.4 DATA ACQUISITION
Data acquisition is the processing of multiple electrical or electronic inputs
from devices such as sensors, timers, relays, and solid-state circuits for the purpose of
monitoring, analyzing and/or controlling systems and processes. Instruments or
systems are fully packaged with input and output, user interface, communications
capability, etc. They may include integral sensors.
Input modules are devices (module or card) configured to accept input of
sensors, timers, switches, amplifiers, transistors, etc. for use in the data acquisition
Figure 1-3: LabVIEW is a leader in application software used in PC-based data acquisition and instrument control. [Survey of Design News and R&D Magazine, QI 2004].
Multiplexed Industrial Data Acquisition System (MIDAS)
__________________________________________________________________ PCSIR - Institute of Industrial Electronics Engineering, IIEE ST-22/C, Block-6 Gulshan-e-Iqbal, Karachi – 75300
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system. Output modules are devices with specific functionality for output of amplified,
conditioned, or digitized signal. I/O modules have both input and output functionality.
Digital or discrete I/O includes on-off signals used in communication, user interface,
or control. A general data PC based data acquisition system is shown in figure 1.4:
A typical data acquisition system consists of:
Transducers
Signal Conditioning
Plug-in DAQ device
Driver
Software
Acquired data is displayed, analyzed, and stored on a computer, either using
vendor supplied software, or custom displays and control can be developed using
various general purpose programming languages such as BASIC, C, Fortran, Java,
Lisp, Pascal. Specialized programming languages used for data acquisition include,
EPICS used to build large scale data acquisition systems, LabVIEW, which offers a
graphical programming environment optimized for data acquisition and MATLAB
provides a programming language but also built-in graphical tools and libraries for
data acquisition and analysis.
Figure 1.4: A PC based data acquisition [Courtesy National Instrument Website]
Multiplexed Industrial Data Acquisition System (MIDAS)
__________________________________________________________________ PCSIR - Institute of Industrial Electronics Engineering, IIEE ST-22/C, Block-6 Gulshan-e-Iqbal, Karachi – 75300
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1.5 MODERN INSTRUMENTATION TECHNIQUES The required task can be practically implemented by several
techniques depending upon complexity of the task. We studied three techniques given
below and choose the best one on the bases of available technology, degree level and
industrial requirement.
1.5.1 WIRELESS SOLUTION One method to achieve task was to use wireless communication
technique. By using this technique we have to make individual transmitter for each
transducer and one receiver for all transmitters if only monitoring is required. Signal
of each transducer is converted into electromagnetic wave and is transmitted through
radio antenna. Receiver is tuned over that particular quantity’s frequency. If we are
using only one receiver then we has to auto scan it for all quantities frequency because
receiver can catch only one signal at a time. The choice of receiver’s quantity depends
on the response of physical quantities. If response is very fast changing as in case of
mechanical vibration then we have to use single receiver for that particular quantity.
But in case of slow variant quantity we can use single receiver for more than one
quantity. We did not select this technique because this technique was using wireless
communication which is avoided in industry. One signal can interfere with other
signals in air at same frequencies which may be harmful.
1.5.2 DATA NETWORKING Second method to achieve this task was to use any one networking
topology. By using networking topology we can insert as many transducers as we
want and now a days it is standard which is being used in industry. In this technique
each transducer is server on the selected topology bus while our host computer is
client. Servers provide information whenever client request it. So we program the
client request so that it demands new server information after selected time and go
ahead to get information from next server. When all required servers information is
completed it again repeats cycle and updates all servers’ information and shows on the
Multiplexed Industrial Data Acquisition System (MIDAS)
__________________________________________________________________ PCSIR - Institute of Industrial Electronics Engineering, IIEE ST-22/C, Block-6 Gulshan-e-Iqbal, Karachi – 75300
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display panel. It is the cheapest way to achieve this task. But in this designing
technique we have to make all transducer as server so that they can work as servers on
topology bus. This technique was best but we still did not use this technique because
we have to make each transducer a server and have to log it on selected topology bus.
This technique required complex knowledge of networking communication while our
primary concern was to design data acquisition card but not to implement networking
topologies.
1.5.3 DIRECT CABLE SYSTEMS A third and last technique was to pick the signal directly from the
physical system through cables without networking and after suitable signal
conditioning these signals are fed to DAQ card. This method is mostly adopted by the
industry due to its safe and secure nature. It removes all the dangers of signal
interruption. It also provides the simple design to implement. We have selected this
one as it does not involve signal transmission complexities as was in above given
techniques and one can work upon his concern problem that is DAQ card and it’s
HMI. In all technique the received signals are provided to the DAQ card. We take our
signal’s quantity and direct insert into DAQ card. We employed here three analog
inputs of DAQ card which can be multiplexed up to eight inputs.
1.6 PROJECT DESCRIPTION Monitoring of physical parameters in different industrial fields
with accuracy always remains a problem. Different techniques were developed to
make monitoring as friendly as possible so that operators and engineers can control
parameters easily. HMI or GUI gives the user friendly controlling and monitoring
interface of actuators and transducer to operators.
These days all industries are going to revolutionizes with
advancement in technology especially in the field of instrumentation. In any process
industry control room is the mind of the industry which takes production related
decision and which also monitor all the physical parameters. These parameters are
Multiplexed Industrial Data Acquisition System (MIDAS)
__________________________________________________________________ PCSIR - Institute of Industrial Electronics Engineering, IIEE ST-22/C, Block-6 Gulshan-e-Iqbal, Karachi – 75300
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displayed on monitoring panels which shows the GUI for the DAQ cards working
behind the monitoring panel.
The proceeding project can be divided into two main parts which
are described as follows:
1.6.1 HARDWARE The hardware consists of DAQ card and transducer’s signal
conditioning cards. We have used USB-6008 national instrument DAQ card for our
instrumentation system. The signal conditioning is done to make transducer’s signals
compatible with DAQ card.
1.6.2 SOFTWARE We have used LABVIEW software for designing our graphical user
interface. All quantities are displayed on pc screen through knobs, dial and digital
indicator. Due to increasing popularity of LABVIEW in virtual instrumentation, we
decided to use this software.
1.7 SUMMARY We started this chapter with the introduction of instrumentation
system and then differentiated the traditional and virtual instrumentation. Virtual
instrumentation in process engineering and data acquisition is also discussed here in
detail. As we saw in this chapter that there is a number of different techniques to solve
the problem of industrial data acquisition. We discussed three most important
techniques here.
In the end we discussed project objectives dividing it into two
sections that are hardware and software.
Multiplexed Industrial Data Acquisition System (MIDAS)
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INTRODUCTION This chapter is concerned with the analysis and simulation of our system by
developing its mathematical model of level and thermal system and the speed of servo
mechanism. For level measurement a pot meter is implemented which will provide the
linear output voltage proportional to the level height. In process temperature, the
temperature is measured by thermocouple up to 750C.
2.1 MATHEMATICAL MODELLING OF PROCESS PARAMETERS
Mathematical modeling of different plants of our project is given one by one as follow.
2.1.2 THERMAL SYSTEM In this thermal system the temperature of the furnace is
monitored up to 600OC using thermocouples. The furnace is provided energy through
electrical supply as shown in figure 2.1:
Thermocouples are linear over long range and suitable in the rigged
environment also inexpensive and versatile devices for measuring temperature. Before
going into the mathematics of thermocouple one should understand see beck effect
[22].
“Electrically conductive materials exhibit three types of thermoelectric phenomena:
Figure-2.1: A thermal system block diagram
Multiplexed Industrial Data Acquisition System (MIDAS)
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The See beck effect, the Thompson effect, and the pettier effect. The See beck
Effect is manifest as a voltage potential that occurs when there is a temperature
Gradient along the length of a conductor. This temperature-induced electrical
Potential is called an electromotive force and abbreviated as EMF.”
Figure 2.1: represents a conceptual experiment that exhibits the See beck
effect. The two ends of a conducting wire are held at two different temperatures T1and
T2. For clarity, assume that T2 > T1, although with appropriate changes of sign, the
development that follows is also applicable to the case where T2 < T1.If the probes of
an ideal voltmeter could be connected to the two ends of the Wire without disturbing
the temperature or voltage potential of the wire, the Voltmeter would indicate a
voltage difference on the order of 10−5 volts per degree Celsius of temperature
difference. The relationship between the EMF and the temperature difference can be
represented as
12 1 2( )E T Tσ= − (2.1) Where σ is the average See beck coefficient for the wire material.
In general, the See beck coefficient is a function of temperature. To develop a
more precise and versatile relationship than Equation (2.1), consider an experiment
Where T1 is fixed, and T2 is varied. For practical thermocouple materials the
relationship between E and T is continuous. Hence, for sufficiently small Change
σ T2 in T2, the EMF indicated by the voltmeter will change by a corresponding Small
Figure-2.2 See Back Effect
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amount σ E12. Since σ T2 and σ E12 are small, it is reasonable to linearize the EMF
response as
112 12 2 2 1( ) ( )E E T T T Tσ σ+ ∆ = − + ∆ (2.2) Where ó (T2) is the value of the See beck coefficient at T2. The change in EMF only
depends on the value of the See beck coefficient at T2 because T1 is held fixed.
Subtract Equation (2.1) from Equation (2.2) to get
12 2 2( )E T Tσ=∆ ∆ (2.3) This can be rearranged as
122
2( ) ET
Tσ =
∆∆ (2.4)
If ó is an intrinsic property of the material, then the preceding equation must hold for
any temperature. Replacing all references to T2 with an arbitrary temperature T, and
taking the limit as the temperature perturbation goes to zero, gives
0lim( ) TdETdT
σ ∆= (2.5)
Using the Fundamental Theorem of Calculus, the limit becomes a derivative.
The result is the general definition of the Seebeck Coefficient
0lim( ) TdETdT
σ ∆= (2.6)
Equation (2.6) contains all the theoretical information necessary to analyze
thermocouple circuits.
Practical exploitation of the Seebeck effect to measure temperature requires a
combination of two wires with dissimilar Seebeck coefficients.
Figure 2.2: represents such a basic thermocouple. The two wires of the
thermocouple are joined at one end called the junction, which is represented by the
solid dot on the right side of Figure 2.2.The junction is in thermal equilibrium with a
local environment at temperature Tj . The other ends of the thermocouple wires are
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attached to the terminals of a voltmeter. The voltmeter terminals are both in thermal
equilibrium with a local environment at temperature Tt.
Equation (2.6) is applied to the thermocouple circuit in Figure 2 by writing
( )dE T dTσ= (2.7) Thus, the EMF generated in material A between the junction at Tt and the junction at Tj is
, ( )A
Tj
A tj
Tt
E T dTσ= ∫ (2.8)
Applying Equation (2.8) to consecutive segments of the circuit gives
A B
Tj Tt
AB
Tt Tj
E dT dTσ σ= +∫ ∫ (2.9)
Where óA is the absolute Seebeck coefficient of material A and óB is the absolute
Seebeck coefficient of material B. The order of integration is specified by moving
continuously around the loop: from the terminal to the junction, and back to the
terminal.
Notice that the value of ABE in Equation (2.9) is due to integrals along the length
of the thermocouple elements. This leads to the following essential and often
misunderstood fact of thermocouple thermometry:
The EMF generated by the See beck effect is due to the
Temperature gradient along the wire. The EMF is not generated
At the junction between two dissimilar wires.
Figure-2.3: A simple thermocouple
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The EMF of the thermocouple exists because there is a temperature difference
between the junction at Tj and the open circuit measuring terminals at Tt. Switching
the order of the limits for the second integral in Equation (2.9) allows the following
manipulation
)(A B A B
Tj Tj Tj
AB
Tt Tt Tt
E dT dT dTσ σ σ σ−= − =∫ ∫ ∫ (2.10)
Now define the Seebeck coefficient for the material pair AB as
( )AB A Bσ σ σ−= (2.11) Substituting the definition of óAB into Equation (10) gives
Tj
AB AB
Tt
E dTσ= ∫ (2.12)
Equation (2.12) is the fundamental equation for the analysis of thermocouple
circuits. It is not yet in the form of a computational formula for data reduction. Before
a data reduction formula can be developed, however, the role of the reference junction
needs to be clarified given bellow,
Equation (2.12) shows how the EMF generated by a thermocouple depends on
the temperature difference between the Tj and Tt. All thermocouple circuits measure
one temperature relative to another. The only way to obtain the absolute1 temperature
of a junction is to arrange the thermocouple circuit so that it measures Tj relative to an
independently known temperature. The known temperature is referred to as the
reference temperature Tr. A second thermocouple junction, called the reference
junction, is located in an environment at Tr.
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Figure 2.3 shows a thermocouple circuit with a reference junction at temperature
Tr. At the reference junction, copper extension wires connect the voltmeter to the legs
of the thermocouple. The thermocouple wires are labeled P for positive and N for
negative. Beginning with the terminal block at temperature Tt, there are five junctions
around the circuit. Using x as a position indicator, the five labeled junctions are
numbered in order of increasing x. To find the EMF produced by the thermocouple
circuit in Figure 2.4, apply Equation (2.8) to each segment of wire in the circuit
15
TjTr Tr Tt
C P N C
Tt Tr Tj Tr
E dT dT dT dTσ σ σ σ= + + +∫ ∫ ∫ ∫ (2.13)
Figure-2.4: Physical circuit for thermocouple
Figure-2.5: Conceptual T(x) plot of thermocouple
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Where óC is the absolute See beck coefficient of copper, óP is the absolute See
beck coefficient of the material in the positive leg, and óN is the absolute See beck
coefficient of the material in the negative leg. Reversing the limits of integration for
the first term in Equation (2.13) gives
Tr Tt
C C
Tt Tr
dT dTσ σ= −∫ ∫ (2.14)
Therefore, the first and last terms in Equation (2.13) cancel. Furthermore, reversing
the limits of integration in the third term in Equation (2.13) and simplifying yields
15
Tj
PN
Tr
E dTσ= ∫ (2.15)
Where
óPN = óP − óN
The result in Equation (2.15) can be interpreted graphically with the lower
half of Figure 2.4. The EMF across the copper segments 1-2 and 4-5 cancel because
the EMF on these segments is of equal magnitude and opposite sign. Think of going
down in potential from 1 to 2, and up in potential from 4 to 5. The EMF across
segments 2-3 and 3-4 does not cancel, however, because the absolute Seebeck
coefficients for these two segments are not equal. Indeed, a thermocouple is only
possible when two dissimilar wires are joined so that
óPN = óP − óN The circuit in Figure 2.4 provides a practical means for measuring temperature
Tj relative to temperature Tr. To use this circuit an independent method of measuring
Tr is required, along with the value of óPN. The calibration tables and equations use
Equation (2.15) with a reference temperature of 0 Cο , which is easily obtainable with a
mixture of ice and water. The integral in Equation (2.15) is a formal statement of the
relationship between EMF on temperature. To develop a calibration for a particular
thermocouple type, the EMF is measured as Tj is varied and Tr is held fixed at 0 Cο .
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The result of the calibration is a table of EMF versus T values. The integral is never
directly evaluated. Instead a polynomial curve fit to the calibration data gives
20 0 1 2( )j j j j jE F T b b T b T bnT= = + + + +… (2.16)
In terms of the formalism of the preceding sections,
0
Tj
oj PNE dTσ= ∫ (2.17)
From the same calibration data a curve fit of the form
0 1 0( ) mj oj oj m jT G E c c E c E= = + + +… (2.18)
is also obtained. The F(Tj) and G(E0j) symbols provide convenient
shorthand notation for the two calibration polynomials. Equation (2.18) is directly
useful for temperature measurements with thermocouples. For the circuit in Figure 2,
with Tr = 0, Equation (2.18) allows a measured EMF to be converted to a temperature.
Figure 2.4 depicts a useful thermocouple circuit. The most straightforward
implementation of this circuit is to place the reference junctions (block labeled Tr) in
an ice bath. The resulting circuit is sketched in Figure 2.5. The two junctions can share
the same ice bath if they are electrically insulated from each other
For the thermocouple circuit in Figure 2.5, the standard calibration equations are
used directly. Applying Equation (2.12) to each segment of wire in the circuit gives
Figure-2.6: Cold junction compensation
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16
TjTb Tr Tb Tt
C P N p C
Tt Tb Tj Tr Tb
E dT dT dT dT dTσ σ σ σ σ= + + + +∫ ∫ ∫ ∫ ∫ (2.19)
The first and last integrals cancel, (Cf. Equation (2.14).) Rearranging the remaining terms gives
16
16
16
TjTb Tr
P p N
Tr Tb Tj
Tj Tj
P N
Tr TrTj
PN
Tr
E dT dT dT
E dT dT
E dT
σ σ σ
σ σ
σ
= + + +
= −
=
∫ ∫ ∫
∫ ∫
∫ (2.20)
Since Tr = 0 Cο (the standard reference temperature), Equations (2.17) and (2.18) may
be used directly for the thermocouple circuit in Figure 2.5. The equation (2.16) is the
voltage produced by thermocouple when reference junction is at 0 Cο
Now neglecting the square and higher order terms in equation (2.16) gives direct
linear relationship between junction temperature & produced emf.
0 0 1( )j j jE F T b b T= = + (2.21) Note that the nonlinearity increase with increase in temperature due to variation in
material coefficient.
2.1.2 SERVO MOTOR
Figure-2.7: A general block diagram for position control
The general transfer function of the motor [18]
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(1 )( ) ( )Ks sG s τ+= (2.22)
Calculatingτ : First we coupled our motor without gears with another motor and applied
voltage on it and measured the output voltages (generator action) as well as the
RPMs of the external motor. The following readings were obtained
Table-2.1:Reading for generator action
Applied Voltages (v)
Generated Voltages (v)
7 2.7 8.5 3.6 10 4.8 12 5.15
The corresponding graphs are shown on the next page in figure 2.8 and 2.9. Calculating the values of the feedback gain from the graph is taken as
/ sec 20rad∆ = 0.7v v∆ =
Since / secradvKb ∆
∆= (2.23)
/ sec/28.57rad vKb =
The forward gain will be 1
KbK = (2.24)
/ / sec0.035v radK =
Table-2.2: Applied and generated voltages. rad/sec Generated voltage
70 2.7 90 3.6 100 4.8 115 5.15
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Figure-2.8: Graph between generated voltage and applied voltage.
Figure-2.9: Graph between generated voltage and applied RPM
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The τ is the sum of electrical ( eτ ) plus mechanical ( mτ )
e mτ τ τ+= (2.25) But
m eτ τ>> Therefore neglecting eτ
mτ τ= Where
2.
( )R JomKb
τ τ= = (2.26)
Now calculating motor’s parameters
FL NLKo I IJ −= (2.27)
0.035
210 170oJ = −
0.875 / / sec/o v rad mAJ =
2.
( )R JoKb
τ = (2.28)
Where 70R = Ω 0.075secτ =
So the transfer function of the motor became
0.035(1 0.075 )( ) ( )s sG s += (2.29)
-
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2.2 MATHEMATICAL SIMULATION & ANALYSIS The mathematical simulation results for level, temperature and position are
shown and analyzed.
2.2.1 THERMOCOUPLE
Taking data from the standard thermocouple reference table, following graph has
been drawn for our required range [10].
The graph shows that thermocouple offers very high mark of linearity over a
long temperature range which makes it very applicable in industrial measurement for
high temperatures and in the rugged environment as well.
0 100 200 300 400 500 600 700 800 900 10000
10
20
30
40
50
60
Temprature (C)
Ther
moe
lect
ric V
olta
ge (m
V)
Figure-2.10: Graph for J-Type Thermocouple
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2.2.2 SERVO MOTOR The transfer function of the motor was came out to be
0.035(1 0.075 )( ) ( )s sG s += (2.30)
Applying unit impulse, the open loop response came out as
The graph shows that system is unstable in open loop as it is not being get
settled by achieving settle down back. The system can be made stable in close loop
configuration or applying suitable compensator like P, PI, PD, PID controllers.
0 20 40 60 80 100 120 140 1600
0.005
0.01
0.015
0.02
0.025
0.03
0.035Impulse Response
Time (sec)
Ampl
itude
Figure-2.11: Open loop impulse response
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INTRODUCTION
This chapter concentrates on the description of whole mechanical
assembly of our project. As we know that it is always remained a problem to measure
the physical quantity accurately and to solve this problem different techniques are
used to develop the mechanical models as friendly as possible so that operators and
engineers can measure and control the required parameters. Since after the selection of
suitable sensors and mathematical modeling for their parameters it was necessary to
implement the design by developing the precise mechanical model for the
measurement of selected parameters with accuracy. In this project three individual
models are developed that is level system, thermal system and servo controlled valve
mechanism which then finally assembled.
3.1 INDUSTRIAL PROTOTYPE
A working model created to demonstrate fundamental aspects of
industrial measurements without creating a detailed program. Adding details and
content incrementally to advancing stages of prototypes is one process for creating
successful applications. In this project a sample prototype of industrial measurements
is fabricated in advance of production to allow monitoring, controlling, demonstration,
evaluation, or testing of the physical parameters, which is a full-scale working model
of an original industrial measurements or an updated version of existing industries.
The project mechanical model is developed as accurately as possible to meet
the industrial standard prototype. It is not only developed for the project purpose but
can also be exercised in institute practical work of students for instrumentation and
control subjects. It will help in understanding the proper placement of different sensors
for different plants.
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3.2 LIQUID LEVEL SYSTEM
As level of liquid was first parameter to measure in our project so in
order to implement the proposal we have made a tank with the width ,height and
length all equal to one foot. According to the requirement we have set two limits that
is upper and lower limit. Upper limit was marked up to 260mm height and lower limit
up to 5mm.Since we have used water column based current transmitter to measure the
level which gives the output current on basis of pressure difference, so we attached
two nozzles that is one at ground level of tank and other at upper limit. When current
transmitter is connected to these two nozzles through pipes, a pressure difference is
created which fulfils the transmitter’s requirement.
The inlet of the tank is through the motor pump from the reservoir while the
outlet is attached with servo controlled valve mechanism so that the outlet flow is
controlled at ground level of tank as shown in figure 3-1.
Figure 3-1: Mechanical model for liquid level system with inlet pump motor.
The tank is placed at a
certain height of about 10
inches from the base
board in order to fulfill the
proper functioning of
current transmitter so that
it can take the proper
pressure for its lower limit
(zero limits).
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3.3 THERMAL SYSTEM Since we are measuring a high temperature range up to 600 oC using J-
type thermocouple sensor, so it was really very difficult to develop such high
temperature in the lab. To serve the purpose we have taken a solder iron of 500 watts
which could generate highest temperature of 1200 oC which was fulfilling our
requirement and best suited for the model as it reserves a very narrow space and could
easily be isolated for safety purpose. This solder iron is used as furnace which is
heated by electric utility of 220 volts AC. A voltage regulator is also used to control
the temperature of the furnace. For protection from such high temperature we
surrounded the furnace with thick wooden block with thin metallic sheets at inner side
of wooden block so that maximum temperature may absorbed by the sheets and block
remain safe as shown in figure 3-2.
Figure 3-2: Electric furnace surrounded by wooden block for safety and protection attached with the temperature controller. The controller is based upon SCR pulse firing technique
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3.4 SERVO CONTROLLED VALVE MECHANISM
The third parameter to be measured in the project was position of servo
controlled valve to control the outlet flow of the liquid tank as in addition to
measurement we also have introduced its controlling option in the project. For position
measurement and control we have developed the mechanism of a valve and attached it
with the outlet to liquid tank. This valve is coupled both with the geared dc motor and
the feedback pot meter in such a way that opening and closing of valve changes the
resistance. The valve takes five turns of rotation to completely open or close; therefore
the ten turn pot meter is used as a sensor, so when the whole valve is fully opened or
closed it utilizes its five turns which falls in the midrange of feedback sensor. The
servo controlled valve mechanism is shown in figure 3-3.
Figure 3-3: Servo controlled valve mechanism to control the outlet flow of liquid tank
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3.5 OVERALL MECHANICAL ASSEMBLY
As the mechanical model for each of three parameters being measured is
developed, so it was necessary to assemble them together. In order to serve the
purpose we have taken a wooden block and all individual models have assembled on it
using solid screws. Pictorial view of the whole mechanical assembly of our project is
below:
3.6 SUMMARY In this chapter we discussed the importance of mechanical assembly
from the industrial point of view and introduced the industrial prototype development
which follows the fabrication of individual mechanical models for the accurate
measurement of the selected physical parameters which are level system, thermal
system and servo controlled valve mechanism. To satisfy the rules of simplicity
finally all these models are assembled on a single wooden block.
Figure-3.4: Overall mechanical assembly
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INTRODUCTION
In general for measuring the effect of any physical quantity
like temperature, pressure, level etc we require some kind of device called a sensor.
Sensors are used in everyday objects such as touch-sensitive elevator buttons and
lamps which dim or brighten by touching the base. There are also innumerable
applications for sensors of which most people are never aware. Applications include
automobiles, machines, aerospace, medicine, industry, and robotics.
Signal conditioning is to process the form or mode of a
signal, taken from sensor usually but not always, so as to make it intelligible to or
compatible with a given device, such as a data acquisition card, dial indicator,
recorders etc.In our project we signal conditioned all quantities to give 0 to 5V so as
they could be interfaced with DAQ card and digital scanner.
4.1 SENSOR’S SELECTION For measuring one type of physical quantity a lot of sensors
are available in market so selection of a proper sensor for a particular quantity
becoming a specialized field. As we are measuring three most important and common
industrial parameters (liquid level, temperature and position) we divide their selection
in proceeding sections.
4.1.1 SENSOR FOR LIQUID LEVEL SYSTEM During selection of liquid level sensor there were several
options we had. First of all we thought about potentiometer based liquid level sensor
which is most common method of measuring liquid level at this stage. As we have told
that we were going to make this project an industrial prototype so we required some
industrial sensor. We decided to make the potentiometer base method as stand by and
started to search some suitable Sensor from industries. Variety of sensors was
available in industry working on different principles.
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By definition all transmitter gives current output in
contrast to the transducers which give voltage output. The use of transmitter (current
output) is exponentially increasing by replacing the transducers (voltage output).
We got level transmitter which was actually a difference
pressure water column level transmitter. It holds the following main advantages:
• It could measure up to 600 millimeter level which falls within our required range.
• It could be used both in 2-wire and 3-wire configuration
• It could be calibrate both for 0 to 20mA and 4 to 20mA.
4.1.2 SENSOR FOR THERMAL SYSTEM To meet the needs of an industrial prototype we decided to
measure temperature above 500oC. LM35 is common sensor for measuring
temperature but it is used only for non-contact measurements like ambient
temperature. We rejected the LM35 due to the reason that first it is a non-contact and
low temperature purposes second it gives about 5oC error at room temperature. So
different sensors were available for temperature measurement but we selected the
thermocouple due to following reasons:
• Capable of being used to directly measure temperatures up to 2600oC.
• The thermocouple junction may be grounded and brought into direct contact with
the material being measured.
• Thermocouples allow measurement of temperatures higher than that possible with
resistance devices (RTDs) like the platinum resistance thermometer. Their
operating range is far wider: compare -200 to 650°C for platinum probes with -200
to more than 2000 °C with refractory thermocouples.
• Thermocouples are inexpensive, rigid and easy to construct as compare to any
other temperature sensor.
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4.1.3 SENSOR FOR CONTROLLED VALVE MECHANISM Besides measuring the position of valve we are controlling
the position of liquid flow control valve as an application of position control. So for
measuring the valve position we required a sensor which generate electrical signal in
response to the varying position of valve. For this purpose we decided to use
potentiometer as feedback sensor. The total number of turns involved in opening and
closing of valve were five so we arranged a ten turn potentiometer as feedback sensor. Encoder could also be used as feedback sensor but it does not
give continuous output and also an expensive option so we rejected this option.
4.2 SIGNAL CONDITIONING We configure DAQ card for 0V to 5V range and developed
soft display for this range similarly we also designed digital scanner for this range. So
we wanted to make signal compatible with this range. For this purpose we had to
signal conditioned our all quantities.
4.2.1 SIGNAL CONDITIONING FOR LEVEL TRANSMITTER As we have already discussed that for level measurement we
used industrial level transmitter. It was a current output transmitter and we had to
convert this current into voltage. We used level transmitter in 3-wire configuration
with 0 to 20mA output. Before converting current into voltage we had to calibrate it
first as follow so we divide signal conditioning of level transmitter into two parts first
calibration and second signal conditioning. The detailed about calibration of level
transmitter is given in project manual for user in Appendix 10.D. Different reading obtained during calibration are given in
Table- 4.1 and its corresponding graph is given in Figure-4.1
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Tabel-4.1: Level Transmitter output table during Calibration
S # Tank Height (mm)
Transmitter output (mA)
1 0 0.2 2 27 1.99 3 54 4.01 4 81 6.2 5 108 7.98 6 135 10.07 7 162 12.1 8 189 13.99 9 216 16.3 10 243 17.89 11 270 19.79
Figure-4.1: Graph between transmitter output and height of level
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When transmitter was calibrated for full range we converted
this current to voltage for further processing. We placed a 250ohms burden load at
transmitter’s output which as to get voltage and then used an operational amplifier in
current-to-voltage configuration as shown in Figure-4.2. The detailed circuit of this
block diagram is shown next in Figure-4.3.
Figure-4.2: Block Diagram of Level Transmitter Signal Conditioning
Figure-4.3: Circuit Diagram of Level Transmitter Signal Conditioner
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4.2.2 SIGNAL CONDITIONING FOR THERMOCOUPLE The toughest job in our sensor’s signal conditioning
portion was thermocouple’s signal conditioning. The main problem in thermocouple
signal conditioning is its cold junction compensation and its nonlinearity at higher
temperature. To overcome these problems we used Analog Device’s an expensive
industrial signal conditioner AD594AQ which have built-in cold junction
compensation and nonlinearity adjustment. However there were small non-linearties
still in AD594’s output so we used positive feedback to remove this non-linearity. The
detail of signal conditioner’s adjustment with thermocouple voltage is given below.
Before going into detail it is necessary to remember that
AD594AQ is factory calibrated at 10mV/ oC. For measuring the atmosphere
temperature and furnace temperature we used RTD (pt-100) as reference sensor.
RTD’s measured resistance at different temperature and its corresponding table is
shown in Table-4.2 and respective graph in Figure-4.4.
Table-4.2: RTD's measured values # Temperature
oC Resistance
(ohms) 1. 0 100 2. 32 113 3. 212 180 4. 410 250
Figure-4.4: Graph between temperature and RTD Output
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Now we took thermocouple wires and connected to IC’s
input and check IC’s output voltage. It was showing that voltages which were when
converted to temperature was giving room temperature at that time is 32 oC. Same
times we measured RTD resistance that was also showing the same room temperature.
Now this time we put thermocouple in furnace and adjust the temperature at 400 oC
with the help of RTD as reference temperature sensor. Again we measured output
voltage of IC it was showing the same temperature that is 400 oC. Different readings
obtained during AD594’s calibration and their corresponding graph is shown in Table-
4.3 and Figure-4.5.
Table-4.3: AD594 output voltage with respect to temperature. S.No Temperature
oC AD594 output voltage
V 1. 0 0
2. 32 0.32
3. 212 2.13
4. 410 4.12
Figure-4.5: Graph between AD594 output voltage with respect to temperature
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The detail of the used reference temperature sensor,
selected signal conditioner and thermocouple output with corresponding tables and
graphs was given in above discussion. Now we can draw a simple block diagram of
the thermocouple signal conditioning as shown in Figure-4.6. Corresponding detailed
circuit diagram of the block diagram is given in Figure-4.7.
The LED shown in Circuit diagram of thermocouple signal
conditioner is for fault indication. The only possible fault in thermocouple is its
opening from hot junction because of excessive heat. Whenever thermocouple
becomes open or input supply exceeds its limit, this LED will blink.
Figure-4.6: Block Diagram of Thermocouple Signal Conditioning Output
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Figure-4.7: Circuit Diagram of Thermocouple Signal Conditioner
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4.2.3 SIGNAL CONDITIONING FOR FEEDBACK MECHNUSM We have already discussed that we are not only
measuring but also controlling the servo valve using potentiometer as feedback sensor
for measurement and PI controller for position control. The block diagram of the
controlling and measuring system is given as follow in Figure-4.8.
We used voltage source for excitation of potentiometer which
was giving our required linearity. However we could use current source which was a
difficult option but current source is always used where a high degree of linearity is
required.
After excitation of potentiometer following different readings
were taken during calibration shown in Table-4.4:
Where as the graph taken from above readings are shown in figure-4.9. The
graph shows that sensor’s output is quite linear and does not require linear zing it
Figure-4.8: Block Diagram of PI Controller for Controlled Valve
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further. It just requires further to buffer the signal before giving it to the data
acquisition card in order to avoid loading effects.
As shown in Table-4.4: that the sensor’s minimum output was
0.36V and maximum output was 2.8V but we wanted minimum signal 0V and
maximum, when valve is fully closed, 5V. So to get our required limits we have to
signal conditioned this sensor by inserting an operational amplifiers based network
which in turn gave us our required limits.
We designed PI controller for servo valve for controlling the flow
of liquid. The detailed circuit diagram of PI controller is given in Figure-4.10.
Multiplexed Industrial Data Acquisition System (MIDAS)
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Multiplexed Industrial Data Acquisition System (MIDAS)
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4.3 SUMMARY This chapter was consisting of two main parts. One was the
selection of different sensors which were suitable for our required processes and
second was their signal conditioning in which we made sensors output compatible
with our required output.
In sensor’s selection we selected differential pressure level
transmitter for our liquid level system and we also discussed how this transmitter was
best suitable for our requirement. For temperature measurement we choose
thermocouple j-type and for feedback sensor in controlling the position of valve we
selected potentiometer.
In signal conditioning of all sensors we made all output signals
compatible with our required range that was 0V (for minimum) and 5V (for
maximum) using different techniques discussed in this chapter in detail.
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INTRODUCTION “A system that reports the value of a physical quantity in numerical
form one by one is called a digital scanner.”
When a measurement is made (such as in our project thermocouple,
level transmitter & a servo controlled valve) a numerical quantity is determined from a
physical quantity, at a specific time and location. It is important to define exactly what
is being measured: is it all three components of a vector, one component of a vector, a
magnitude, or a scalar? Also, are you measuring the instantaneous value (DC value),
or the range of variation (AC value) of the quantity? If AC is chosen, there are various
ways to measure this number (RMS, absolute average variation, peak-to-peak, peak
negative or peak positive). With AC, frequency range is also an important
consideration, as well as the averaging time. In our project we are measuring the
instantaneous value (DC value).
5.1 SCANNER IN INDUSTRY In industry, dependence on a single display is usually avoided. A
single quantity is displayed on 2 to 3 different displays. It is due to the reason that an
electronic error may occur in single display’s reading & if operator is dependent on a
single display it will be dangerous and even if process is full of hazards (like in
nuclear reactions or boiler’s temperature/pressure) then dependence on a single
display will be a fool.
So in our project we have used two displays. One is software based
(HMI) and second one is discussed here that is digital scanner. Digital scanner are also
getting importance due to the reason that a single display shows all the quantities and
need for multiple displays is vanished.
5.2 REQUIRED FEATURES
We wanted to design a digital scanner for displaying the three
industrial parameters (temperature, level & position) .A single display was to used to
show the three quantities which was to be done by using the time sharing /multiplexing
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technique. One quantity was to be displayed at a time and after set time next quantity
would appear and so on. After last quantity appearance cycle would be repeated. Set
time for appearance of quantities could be changed (increase or decrease) externally
by operator & scanning could be stopped by operator at appearance of any particular
quantity. Moreover operator could be jumped at any required parameter if he wanted.
5.3 AVAILABLE DESIGNING TECHNIQUES
There are different techniques available for designing digital scanner.
The adopted design depends on designer’s technical approach. But at system level
there were two possible solutions to achieve desired goal in our mind.
(I) Complete embedded system
(II) Partial embedded system
The detail of selected and rejected design is given following.
5.3.1 COMPLETE EMBEDDED SYSTEM An embedded system or complete embedded system is one in which
whole system is designed on a single chip which is usually a programmable chip like
microcontrollers and microprocessor based systems. Embedded systems are designed
for performing dedicated tasks and these systems work on the principles of digital
computers. All those functions, which are performed by different external components
in an un-embedded system, are performed on a single chip by using different
programming techniques.
For a complete embedded system based digital scanner beside other
basic requirements we required a programming device with following built-in
features:
• Require at least 10bit microcontroller system.
• Three analog input channels.
• Also 10bit ADCs built-in into the microcontroller
Still having all above features we had to perform scaling externally.
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5.3.2 PARTIAL EMBEDDED SYSTEM A partial embedded is one in which both embedded and un-embedded
features are merged. In this system designer divide his tasks into two groups, one
suitable for embedded system and other suitable for un-embedded system. It is not
necessary to perform all tasks on a single chip because some tasks can be performed
externally better and easier as compare to on a programmable chip. So if we design
scanner using partial embedded system we require following feature in programmable
chip.
• 8bit architecture like AT89s51 is enough.
• No analog input channel is required.
• No built-in ADC is required because analog-to-digital conversion is performed
outside controller.
5.4 SELECTED DESIGN Due to more flexibility in partial embedded system we choose this
one. Besides flexibility following are the main advantages of partial embedded
system.
• Awareness with technology. • All required components are available in market. • High accuracy/linearity in reading is easily achievable. • Trouble shooting is easy and economical.
The detail of implemented is given in following sub headings.
5.4.1 DESIGN IMPLEMENTATION As our required input channels were three so we implemented our
design using scaling, analog Mux, 7-segment decoder, millivolts measuring IC etc as
shown in block diagram of digital scanner.[ figure: 5.1].Circuit diagram of the same
system is given on next page in figure:5.2
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Figure -5.2: Circuit Diagram of Digital Scanner
Figure 5-1: Block diagram of digital scanner.
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Position
30pF
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Figure 5-2: Circuit schematic of digital scanner
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5.4.2 DESCRIPTION OF SYSTEM BLOCK DIAGRAM The detail of system block diagram shown in figure-5.1 is given as
follow:
(I) Scaling As shown in block diagram that three quantities after signal
conditioning comes at scaling card’s input. The designed scanner is a versatile scanner
which can be used for any three parameters whose upper limit lies within the range of
three digits that is 999.So here the purpose of scaling is to adjust the upper limit of all
quantities individually. We adjusted the first channel for 260, second channel for 600
and third channel for 100 respectively for level (in mm), temperature (in oC) and
position (in %).
(II) Analog Multiplexer After scaling, three signals are given to the input of analog
multiplexer. Analog multiplexer gives one signal at output at a time after selecting
from three input signals according to the selection code given at selection pins. The
two selection pins of the analog multiplexer are controlled here by microcontroller.
(III) Digit Selector and BCD Converter Actually it is an analog-to-digital converter for 3 digit display. It
accepts one analog input and converts it into digital BCD code. It provide multiplexed
BCD output with three bits reserved for digit selection that is to what digit(MSB,NSB
or LSB) present BCD code belongs. This digit selection bit is used for activating the
particular transistor which further activates the relevant 7-segment.
More deeply the actual display circuit is a voltmeter which measure
000mv to 999mv linearly. As our sensor/transducer output is greater than one volt so
we used scaling to decrease voltage level by decreasing the gain of amplifier and set
the Maximum range of all physical quantities at display by adjusting gain of all
quantities.
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(IV) Microcontroller and Selection Panel As we have already discussed that the selection bits of the analog
multiplexer is controlled by a microcontroller so the switching speed is control here by
using an eight bit microcontroller AT89C51. When user interacts with selection panel,
Microcontroller does the following task.
• Display reading can be stopped at particular appearance by pressing STOP button.
• Display reading can be start (continue) from that stopped particular appearance by
pressing START button.
• Display can be reset by pressing RESET button. After pressing reset button display
will start from very first quantity whatever at any quantity it is.
• Sequence time can be increased by pressing INCREASE button.
• Similarly sequence time can be decreased by pressing DECREASE button.
• Operator can jumped at any position by first pressing STOP button and then
required quantity number as P.1, P.2 or P.3.
•
(V) Position Segment We used three 7-segment displays to show 3-digits however there is
also another 7-segment. Before clearing the presence of this segment one question
arises in mind. When different quantities appear at display, how will operator / viewer
will recognize that to which physical quantity this reading belongs?
The answer to above question is that the single 7-segment shows arithmetic
digit with changing sequence of physical quantities at display. This arithmetic digit
shows particular quantity as defined by the installer of hardware display. Here we set
this display to show the following digits for particular quantities.
• Appearance of 1 shows the level.
• Appearance of 2 shows the temperature
• Appearance of 3 shows the position
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5.5 PROGRAM FLOWCHART N Y Y Y N
Y N N
Y N Y Y N N
Figure-5.3: Controller Program flowchart.
Start
A= 0
P1=A
Dly +
Inc A
Dly1500ms
A=01
Dly -
A=03A=02
A=04
Intrpt(STP)
P.1
T-
P.2 P.3
T+
Strt
Strt=1
T+=1
T-=1
P.2 =1
P.1 =1
P.3 = 1
Reti
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5.6 POSSIBLE IMPROVEMENTS
Whatever perfect is a thing, there is always a need for changing and
improvements and present day scientific world is the result of these changing and
improvements. Those possible improvements which are possible in our designed
scanner are given below in detail.
5.6.1 Addition of New Input Channels We have designed this scanner for three channels according our
requirement. However the number of input channels can be increased up to user
requirement using the same technique. In industry hundreds of different parameters
are to be measured at a time. Another reason of using partial embedded was that in
complete embedded system we can not have a microcontroller with hundreds of
analog inputs so in complete embedded system we have to use multiplexing
externally.
In our selected design new input channels can be increased by just
replacing the analog multiplexer, with one which has user desired number of input
channels, and some changing in controller’s program.
5.6.2 INCREASING UPPER RANGE The display in our designed scanner is limited to three digits. In our
project the maximum upper range was 600 for temperature which lies in three
digits so we designed scanner with maximum of 999 upper ranges. However upper
range can be increased up to 999…N as per user requirement by adding new 7-
segments.Designer have modify the basic circuit of display for achieving this task.
5.6.3 ADDITION OF NEW FEATURES Besides available features new features can be added if necessary
.Actually we have added almost all required features for digital scanner. However
other features, which make it more users friendly, can be added, like indication of
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buzzer when any quantity exceeds its limit and LCD display can be used instead of
seven segment display.
By adding new features designer can convert this scanner into a data logging system.
5.7 SUMMARY
In this chapter we introduce the reader with digital scanner and
its importance in industry. After that we discussed about all available techniques for
designing a digital scanner. Meanwhile we discussed in detail about the selected
design including block diagram description. The advantages and disadvantages of both
complete and partial embedded system are discussed. The detailed description of
block diagram was also given.
In the end we discussed about the available features and possible
improvements in the designed scanner. Some possible improvements examples were
also discussed here.
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INTRODUCTION This chapter describes the NI USB-6008 multifunction DAQ card hardware
and software configuration using its setting techniques and driver software
respectively according to the project requirement and developed human machine
interface as a part of soft display. In addition a brief description of our self
indigenously developed data acquisition card is also discussed since it has already
been discussed that before getting national instruments hardware package we were
developed our own DAQ card.
6.1 PROJECT REQUIREMENT
Since in the project we have three physical parameters as liquid level, furnace
temperature and servo controlled valve position. After signal conditioning of all these
parameters we have 0-5 volts which has to be fed up into the DAQ card. Therefore it
must have at least three analog inputs for all three parameters to be displayed. In
indigenously developed DAQ card we have three analog input channels as per project
requirement. But after getting the NI USB-6008 DAQ card we have added also the
control features in our project. Therefore to control the valve position we require at
least one analog output for the desired reference position and one digital output to
actuate the water pump in order to maintain the required liquid level in the tank. So it
can be summarized that DAQ card must have following minimum features as our
project requirements.
• Three Analog Inputs channels.
• One Digital Output Channel.
• One Analog Output Channel.
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6.2 INDEGENOUSLY DEVELOPED DAQ CARD
Data acquisition card is responsible for taking input signals, process it, and
make compatible for PC for analysis, database and display (user interface). Self
designed data acquisition card has three analog input channels and serially
communicated with the PC through com port at a rate of 9600 bps. This card has 8-bit
resolution ADC to convert data into digital signals. The card block diagram is shown
in figure 6-1.
6.2.1 MUXING Analog mux is used at the first stage for selecting a single quantity out of three
parameters at a time and switching them frequently. Since all of the parameters are
slowly varying so switching speed is not a problem. In the circuit design we have
used dual four channel analog mux so that this card can be extended up to four
channels with just a single connection and simple addition of command in the
controller program.
Level Temp: Position
Analog
Mux ADC
Micro Controller
Serial Interface To
Computer
Select Logic
Figure-6.1: The block diagram of indigenously developed DAQ card. The parameter to be processed and displayed will be selected by the controller from select logic.
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6.2.2 ANALOG TO DIGITAL CONVERSION The single output from mux is fed up to 8-bit ADC. The resolution is restricted
due to microcontroller. We used here a successive approximation fast ADC having
conversion rate of just 100 micro seconds which is high enough for the selected
parameters. All the control signals of ADC are controlled by the microcontroller.
6.2.3 MICROCONTROLLER The microcontroller is responsible for three matters. First selecting the desired
channel of the mux by giving logics to its select pins. Secondly to control the ADC
and receive data from it and third to transmit data serially to the computer by giving
the signal of selected channel as well.
6.2.4 SERIAL INTERFACING The controller transmits and receives signal through its UART, since we have
used RS-232 standard serial communication for which it requires a line driver in order
to make compatible the controller signals with RS-232 standard. The transmission is
configured at a baud rate of 9600 bits per second. The handshaking signals of com
port (DB-9) are not utilized because the selected microcontroller does not supports it.
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HI
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Figure 6-2: Circuit schematic of indigenously developed data acquisition card.
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6.3 NI USB-6008 MULTIFUNCTION DAQ CARD
The card was import so that a complete virtual instrumentation system can be
developed by using modular hardware and customizable application software. Before
selecting the DAQ card it was obligatory that it must fulfill the project requirement as
described earlier in detail but also it should be low cost, easy configurable and the
most of important that was in our mind that it must be capable to be used in different
labs of the institute like control, instrumentation, PLC and electronics lab so that
students may adequate of virtual instrumentation by using embedded multifunction
data acquisition card and can perform their course practical.
Therefore we have selected the NI USB-6008 multifunction data acquisition
card as it offers all the features that we required but also included the complete student
kit so that a virtual instrumentation system may be developed within minutes as it
includes a free LabVIEW student edition as well.
6.3.1 FEATURES • Small and portable
• 12 or 14-bit input resolution, at up to 48 kS/s
• Built-in, removable connectors for easier and more cost-effective
connectivity
• 2 true DAC analog outputs for accurate output signals
• 12 digital I/O lines (TTL/LVTTL/CMOS)
• 32-bit event counter
• Student kits available
• OEM versions available
ANALOG INPUTS
• Number of channels.......8 single-ended/4 differential
• Type of ADC... Successive approximation
• ADC and DAC resolution .......12 bits
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ANALOG OUTPUTS
• Number of channels........... 2
• Maximum update rate150 Hz, software-timed
DIGITAL I/O
• Number of channels..................12
• Direction control: Each channel individually programmable as input or
output
32 BIT COUNTER BUS TYPE: USB PLUG N PLAY CONNECTIVITY
This card is based upon the same techniques as we utilized in the self
developed DAQ card. It multiplexes all the input channels at a maximum sampling
rate of 10KS/s. The complete block diagram of the card is shown in figure 6-4.
Figure 6-3: NI USB-6008 multifunction DAQ card. The complete description can be taken from appendix 10-A.
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6.3.2 HARDWARE SETUP Install combicon screw terminal blocks by inserting them into the combicon
jacks. Then apply the signal labels to the screw terminal blocks for easy signal
identification and connect the wiring to the appropriate screw terminals. Now device is
ready just plugging USB cable with both the PC and device. All these steps cab simply
be followed as shown in figure 6-5.
Figure 6-4: The block diagram of NI SUB-6008 multifunction DAQ card
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6.4 GETTING STARTED STEPS
There are certain steps which have to be followed before using the device in
order for proper configuration and functioning. The followed steps describe how to
install and configure the NI-DAQmx (driver software for NI USB-6008) and USB
data acquisition device and how to verify the device is working properly.
Step 1. Install the Application Software Install you NI application software that is LabVIEW 8.2.1, shipped with the
kit. If you have an existing application written with an earlier version, make a backup
copy of the application. You then can upgrade your software and modify the
application.
Figure 6-5: Setting up hardware. Complete description can be taken from manual in appendix 10-A.
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Step 2. Install NI DAQmx Software This software must be installed before connecting the device with computer so
that the system can detect and install the device whenever it is plugged with the PC
Step 3. Set Up the Device Set up the device as described under the heading of hardware set up and follow
those steps. Treat the DAQ device as you would any static sensitive device. Always
properly ground yourself and the equipment when handling the DAQ device or
connecting to it.
6.5 DEVICE RECOGNITION
Before attaching the signal lines first we have
to check either the system has recognized the
device or not. For the purpose open
measurement and automation (max) software
and expand devices and interfaces and further
expand NI DAQ-devices. Check that your
device appears under devices and interfaces as
shown in figure 6-6.
Highlight your recognized device right
click it and select self test as shown in figure
6-7.
When the self test finishes a message
indicates successful verification or if an error
occurred.
Figure 6-6: Device recognition tree in max.
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6.5.1 ATTACH SENSORS/SIGNAL LINES
Attach sensors and signal lines to the terminal block as described in the figure
6-8. For signal lines and sensor information, refer to manual in appendix 10-A. DAQ
assistant is accessible from MAX or LabVIEW to configure virtual channels and
measurement tasks. We will use and configure it in LabVIEW in the next chapter as a
part of G-Programming.
Figure 6-7: Device self test. A success message will be displayed if device pass the self test as shown.
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6.6 SUMMARY In this chapter we discussed the national instruments USB data acquisition
device selection criteria in detail according to the project requirements and future
enhancements and described in detail that how a USB DAQ device is configured for
proper operation by mentioning different steps of hardware setting, device recognition,
and self test and how sensors/signal lines are attached with the device. Then provided
complete features of selected NI USB-6008 multifunction DAQ card. In addition the
self indigenously data acquisition card was also discussed briefly giving its designing
techniques.
Figure 6-8: Attaching sensors/signal lines with the device to the selected channels and setting up timing and triggering from software.
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INTRODUCTION
Human machine interface is the aggregate of means by which peoples (the
user) interact with a particular machine, device, computer program, or other complex
tool (systems). The interface provides means of
• Inputs: Allowing the users to manipulate a system
• Outputs: Allowing the system to produce the effects of the users' manipulation.
To work with a system, the users need to be able to control the system and
assess the state of the system. User interfaces has great significance in the industrial
instrumentation and automation. All the parameters which have to be measured are
displayed on the computer based interfaces in the control rooms in every modern
industry which refers to the graphical, textual and auditory information the program
presents to the user, and the control sequences (such as keystrokes with the computer
keyboard, movements of the computer mouse, and selections with the touch screen)
the user employs to control the program, provided articulated graphical output on the
computer monitor. There are at least two different principles widely used in GUI
design: Object-oriented user interfaces and application oriented interfaces.
Under the hood, there are several software components that work together to
do the job like visual basic, C/C++, matlab etc. We have developed our project HMI
on the industry standard LabVIEW. This chapter deals with the programming
environment, advantages and applications of LabVIEW and provides comprehensive
sketch of the developed HMI.
7.1 LabVIEW
The National Instruments LabVIEW graphical development environment helps
create flexible and scalable design, control, and test applications. With LabVIEW,
engineers and scientists can interface with real-world signals; analyze data for
meaningful information; and share results through intuitive displays, reports, and the
Web.
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Short for Laboratory Virtual Instrumentation Engineering Workbench is a
platform and development environment for a visual programming language from
National Instruments. The graphical language is named "G". Originally released for
the Apple Macintosh in 1986, LabVIEW is commonly used for data acquisition,
instrument control, embedded design and industrial automation on a variety of
platforms
7.1.1 DATAFLOW PROGRAMMING
The programming language used in LabVIEW, called "G", is a dataflow
language. Execution is determined by the structure of a graphical block diagram (the
LV-source code) on which the programmer connects different function-nodes by
drawing wires. These wires propagate variables and any node can execute as soon as
all its input data become available. Since this might be the case for multiple nodes
simultaneously, G is inherently capable of parallel execution. Multi-processing and
multi- threading hardware is automatically exploited by the built-in scheduler, which
multiplexes multiple OS threads over the nodes ready for execution.
Figure 7-1: Screenshot of a simple LabVIEW program [Courtesy of NI website]
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Screenshot of a simple LabVIEW program in figure 7-1 that generates,
synthesizes, analyzes and displays waveforms, showing the block diagram and front
panel. Each symbol on the block diagram represents a LabVIEW subroutine (subVI)
which can be another LabVIEW program or a LV library function [13].
7.1.2 GRAPHICAL PROGRAMMING LabVIEW ties the creation of user interfaces (called front panels) into the
development cycle. LabVIEW programs/subroutines are called virtual instruments
(VIs). Each VI has three components: a block diagram, a front panel and a connector
pane. The latter may represent the VI as a subVI in block diagrams of calling VIs.
Controls and indicators on the front panel allow an operator to input data into or
extract data from a running virtual instrument. However, the front panel can also serve
as a programmatic interface. Thus a virtual instrument can either be run as a program,
with the front panel serving as a user interface, or, when dropped as a node onto the
block diagram, the front panel defines the inputs and outputs for the given node
through the connector pane. This implies each VI can be easily tested before being
embedded as a subroutine into a larger program.
The graphical approach also allows non-programmers to build programs by
simply dragging and dropping virtual representations of the lab equipment with which
they are already familiar. The LabVIEW programming environment, with the included
examples and the documentation, makes it simpler to create small applications. This is
a benefit on one side but there is also a certain danger of underestimating the expertise
needed for good quality "G" programming. For complex algorithms or large –scale
code it is important that the programmer possess an extensive knowledge of the
special LabVIEW syntax and the topology of its memory management. The most
advanced LabVIEW development systems offer the possibility of building stand -
alone applications. Furthermore, it is possible to create distributed applications which
communicate by a client/server scheme, and thus is easier to implement due to the
inherently parallel nature of G-code.
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7.1.3 ADVANTAGES
One benefit of LabVIEW over other development environments is the
extensive support for accessing instrumentation hardware. Drivers and abstraction
layers for many different types of instruments and buses are included or are available
for inclusion. These present themselves as graphical nodes. The abstraction layers
offer standard software interfaces to communicate with hardware devices. The
provided driver interfaces save program development time.
Peoples with limited coding experience can write programs and deploy test
solutions in a reduced time frame when compared to more conventional or competing
systems. Many libraries with a large number of functions for data acquisition, signal
generation, mathematics, statistics, signal conditioning, analysis, etc., along with
numerous graphical interface elements are provided
A main benefit of the LabVIEW environment is the platform independent
nature of the G code, which is portable between the different LabVIEW systems for
different operating systems (Windows, MacOSX and Linux).
7.2 DATA ACQUISITION TASKS In NI-DAQmx and LabVIEW, a task is a collection of one or more channels,
timing, triggering, and other properties that apply to the task itself. Conceptually, a
task represents a measurement or generation you want to perform. For example, you
can create a task to measure temperature from one or more channels on a DAQ device.
Traditional NI-DAQSpecific VIs for performing:• Analog Input• Analog Output• Digital I/O• Counter operations
NI-DAQmxNext generation driver: • VIs for performing a
task• One set of VIs for all
measurement types
Figure 7-2: Data acquisition task in LabVIEW [courtesy NI website]
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The main advantage of data acquisition task in LabVIEW is that just a single
set of VIs used to perform analog I/O, digital I/O, and counter operations where as
other application software requires different platforms for each operation.
According to the project requirement we have to develop a task which should
be the combination of three analog inputs for displaying all parameters, one analog
output to control the servo valve position and a digital output to actuate the water
pump at desired level.
1. Select the DAQ Assistant Express VI, shown in figure 7-3, on the Input
palette and place it on the block diagram. The DAQ Assistant launches and a Create
New dialog box appears.
2. Click the Analog Input button to display the Analog Input options.
3. Select Voltage to create a new voltage analog input task.
The dialog box displays a list of channels available on DAQ device installed.
The number of channels listed depends on the number of channels you have on
the DAQ device. Here it will show eight channels for NI USB-6008.
4. In the My Physical Channels list box, select three physical channels to
which the signals are connected, as ai0 for valve position, ai1 for liquid level, ai2 for
furnace temperature, and then click the Finish button. The DAQ Assistant opens a new
DAQ assistant express VI is used in G-
programming to develop the DAQ task. It
interacts with the device through NI DAQmx. It
quickly and easily programs the DAQ device by
creating a local task. Most of the application can
use this express VI. As it is placed in the block
diagram from palate it will automatically pop up
the configuration window. Now just follow these
simple steps to develop the required task
Figure 7-3: DAQ assistant express VI
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window, shown in Figure 7-4, which displays options for configuring the channel you
selected to complete a task.
5. In this configuration window select the input range of the signal from -10v
to +10v; rename the selected channels, set the terminal configuration as single ended.
In the timing section provide the acquisition mode as continuous samples ant fed 1K
samples to read. Here we can select maximum 10K samples to read as supported by
our device.
Figure 7-4: DAQ device physical channels configuration window
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Now this DAQ assistant express VI has been configured for the analog inputs.
Place two more express VIs for analog and digital output respectively in the task.
Repeat same procedure as discussed for configuration.
7.3 DEVELOPED HMI (THE FRONT PANEL) In the front panel different virtual instruments are developed for visual as well
as numeric displays, for controlling parameters and giving diverse indications as well.
The meter gauge, liquid tank and the thermometer are placed for displaying
visually, the servo valve position, height of liquid in the tank and furnace temperature
respectively and all are calibrated according to the original mechanical model and real
conditions. In addition to all these graphical VIs the numeric displays for all the three
parameters in the units of closing percentage, millimeters and Celsius are also shown.
Different indicators are placed which will alert the upper and lower limits of level and
temperature.
For controlling purpose a knob is positioned to feed up the reference position
for servo controlled valve. An indicator for the water pump on/off status is sited also
while the status is controlled by the upper and lower limits automatically through
programming.
There is an additional feature for database storage is developed on the front
panel. This will store all the readings with respect to time in a file in the document
format whenever and until the user wants to store the data in order to keep the record
or taking printouts and graphs.
A complete snap of the front panel is shown in figure 7-5 below where all the
VIs placed can be viewed.
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7.4 BLOCK DIAGRAM PROGRAMMING The graphical G-programming of LabVIEW was already discussed. The block
diagrams of the programming are shown on the next page in figure 7-6 which is
composed of different express VIs as listed under with their function description.
1. Split Signal Express VI:
This express VI is used to split the different signals which are routed on
the same line. Since DAQ assistant express VI yields only one output
therefore it is required to split all the three signals for individual
process and analysis.
2. Scaling and Mapping Express VI:
Figure 7-5: The front panel of developed HMI on LabVIEW.
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It is used to calibrate the acquired signal according to the real word.
3. Mathematical Comparison Express VI:
Used for comparing scaled signals with the preset values in order for
indicating different status and taking decisions for the controlling
operations.
4. Write Measurement File Express VI:
It is used for making database of the acquired information in different
formats with many options.
5. Display Message to User Express VI:
This express VI is used to display the messages to the user during run time
under different conditions as programmed like if user wants to open the valve more
than 100% then it will automatically pop up the massage of invalid range.
Besides these express VIs different Boolean and mathematical operations are
utilized for manipulating and process the acquired signal and information as shown in
figure 7-6 which gives a complete look of block diagram programming. Here it can be
seen that all the express VIs and operations are placed within a loop named as while
loop.
This loop is always placed before starting the program and all the express VIs and sub
pallets are placed within this loop to ensure the continuous operation otherwise either
it will stop immediately or will not execute.
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7.5 SUMMARY In this chapter first we described about the industry standard instrumentation
software the LabVIEW and introduce its programming environment, discussed its
applications and advantages over other programming languages. Then a complete
scheme for configuring the data acquisition devices within LabVIEW was provided
and created the local task to meet the project requirement using DAQ assistant express
VI after which we acquired all the signals for further process, analysis and
manipulation.
The developed HMI is then discussed including its front panel and block
diagram programming in detail, giving description of all the express VIs and
Figure 7-6: Block diagram programming of developed HMI using LabVIEW G-programming environment.
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operations used in its programming and the VIs that were customized in the front
panel. All the features of HMI were provided.
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Our project began in July 2007 and at that time we did not even know
where to start from! What kind of resources and effort are required to accomplish such
tasks! But we took it as a challenge and from the day one we went through rigorous
research and analysis, encountering a totally new and confusing problem at every step
but by the grace of Allah we did not stop at any point and solved every problem on our
own.
Therefore, today we have achieved in this short span of six months what
most people around us in this field have achieved in years. And we are proud of our
effort.
As explained earlier our task was to develop DAQ card and its HMI. To
simulate this project practically we also require some input parameters so development
of transducer to measure different physical parameters also become a part of our task.
So we selected temperature, level and position as our physical parameters. We made
different calculations to find out our required sensors and their signal conditioners and
electronic devices for DAQ card. The details about these requirements are given in
previous chapters.
.WHAT WE ACHIEVED IN THIS PROJECT
Indigenously development of transducers which gave us knowledge of internal
working of industrial transducers. We developed J-type thermocouple of industrial
standard which gave us knowledge that how industrial thermocouples are
manufactured and what are the key points about which we have to care during
thermocouple calibration for required output temperature reading. Our designed level
transducer was not of industrial standard because cost was also our primary concerned
but this designed transducer can replace industrial transducer for short time as it has
no impact of high temperature and pressure environment. But finally we succeed in
getting the industrial water column level transmitter which also provide us the hands
on experience of calibrating and implementing the industrial transducers. Servo
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motors are widely used in the industry for lot of processes for position control. It has
complex function but during our project we learned it thoroughly.
Future of the industrial monitoring is the virtual instrumentation, the
combination of customizable software (LabVIEW) and modular hardware (NI USB-
6008), is the most powerful tool for data acquisition and virtual instrumentation as it
provides most user friendly environment, cost effective and quick to use. During the
configuration of DAQ card and development of HMI on the LabVIEW we have faced
a lot of problems; the main was unavailability of both the hardware, software and the
peoples who worked on it. Till now it used rarely in our industries but during
development of HMI we learned a lot about LabVIEW which will consequently help
us in the future market.
ENHANCEMENTS
There is common saying “nothing is permanent except change.”
Therefore there are always the possibilities of improvements and enhancements in
the previous design according to the current requirement and available resources and
technology.
We have made lot of efforts in designing our project in order to meet the peak but
there are enhancements which can be carried out in the future.
• This project can be converted into wireless communication based monitoring
system.
• This project can be enhanced for the hundreds of inputs by using data
networking communication protocols like Modbus, Ethernet etc.
• Since our primary concern was the monitoring of parameters but we not only
performed the instrumentation but also designed the control actions for
position and pump control. But the DAQ has many vacant analog and digital
IOs. These IOs can be employed by extending the mechanical assembly for
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more process parameters and control actions and modifying a little in the
software.
86
REFFERENCES [1] Application note NO: 369 for thermocouple signal conditioning, www.analog.com
[2] Basic concept about designing of hardware display, http://www.electronics-
lab.com/projects/test/014/
[3] Components data sheet, http://www.datasheetarchive.com
[4] Distributed control system, http://www.answers.com/topic/distributed-control-
system?cat=technology
[5] Floyd, Electronic Devices 6th Edition, Pearson Education, 2003
[6] Francis H Raven , Automatic Control engineering, McGraw-Hill, 1994
[7] HMI tutorials, http://www.iec.org/online/tutorials/hmi/
[8] Human Machine Interface, www.wikipedia.com./wiki/hmi
[9] Industrial Text and Video Co., Electrical relay and Diagram Symbols
Instrumentation Symbols and Identifications, www.industrialtext.com
[10] ITS-90 Table for J-Type Thermocouple, ISE Incorporation http://iseinc.com
[11] James W. Dally, Instrumentation for Engineering Measurement 2nd Edition, John
Wiley & Sons Incorporation, 1993, p-110,124
[12] LabVIEW, www.wikipedia.com/wiki/labview
[13] LabVIEW developer zone, www.ni.com/labview
[14] Mohammad Ali Mazidi and Janice Gillispie Mazidi, The 8051 Microcontrollers
and Embedded systems 8th Edition, Pearson Education, 2004,
[15] Omega Engineering Technical Refference, Introduction to level Measurment,
http://www.omega.com/toc_asp/sectionSC.asp?section=K&book=green&flag=1, 2006
[16] Ramakant A. Gaykwad, op-amps and Linear Integrated Circuits 3rd Edition,
Prentice hall International, 1993
[17] Reference table of all types of thermocouples, http://instrumentation-
central.com/pages/thermocouple_reference_table.htm
[18] Richard C. Dorf and Robert H. Bishop, Modern Control Systems 7th Edition,
Addison Wesley
[19] Robert T. Paynter, Introductory Electronic Devices and Circuits 4th Edition,
Prentice hall Inc, 1989
[20] Scott Mackenzie, the 89c51 Microcontroller 2nd & Upgrade Edition
87
[21] Servo motors, http://www.epanorama.net/links/motorcontrol.html
[22] Thermocouple modeling, web.cecs.pdx.edu/~gerry/epub/pdf/thermocouple.pdf
[23] Group Discussion, www.groups.yahoo.com
[24] Instrumentation, http://en.wikipedia.org/wiki/Instrumentation
[25] Virtual Instrumentation, http://en.wikipedia.org/wiki/Virtual_instrumentation
[26] Virtual & Traditional Instruments, http://zone.ni.com/devzone/cda/tut/p/id/4757
[27] Glossary, www.tdt.com/WebHelp/OX_FlashHelp/UserGuide/TipsTricks/Glossary.htm
[28] Future of virtual instrumentation, http://www.scientific-
omputing.com/scwmayjun04james_truchard.html
[29] Virtual Instruments in Engineering process
http://zone.ni.com/devzone/cda/tut/p/id/4752
[30] Modern vs. Traditional Instrumentetation
http://zone.ni.com/devzone/cda/tut/p/id/4757
[31] http://zone.ni.com/devzone/cda/tut/p/id/2964
[32] LabVIEW, http://www.ni.com/labview/whatis/
APPENDIX-B ASSEMBLEY CODE FOR 89S51 FOR DIGITAL SCANNER
; START PROGRAM ORG 00H LJMP MAIN
;**************************** ; INTERRUPT 1 STARTS ORG 0013H
CHK_STRT: JB P2.0,CHK_INCR CALL DELAY_12MS JB P2.0,CHK_INCR RETI
;**************************** ; MAIN PROGRAM STARTS ORG 30H
MAIN: MOV R5,#3 MOV P2,#0FFH MOV IE,#10000100B
AGAIN_01: MOV A,#01H
AGAIN: MOV P1,A CALL DELAY INC A CJNE A,#04H,AGAIN JMP AGAIN_01
;***************************** ; SUBROUTINE FOR INCRESING SCANNING TIME CHK_INCR: JB P2.1,CHK_DECR CALL DELAY_12MS JB P2.1,CHK_DECR INC R5 JNB P2.1,$ JMP CHK_STRT
;****************************** ; SUBROUTINE FOR DECRESING SCANNING TIME CHK_DECR:
JB P2.2,POS_1 CALL DELAY_12MS JB P2.2,POS_1 DEC R5 CJNE R5,#1,CONT_DEC MOV R5,#2
CONT_DEC: JNB P2.2,$ JMP CHK_STRT
;************************** ; SUBROUTINE FOR JUMPING AT POSITION 1 POS_1:
JB P2.3,POS_2 CALL DELAY_12MS JB P2.3,POS_2 MOV A,#01H MOV P1,A JMP CHK_STRT
;************************** ; SUBROUTINE FOR JUMPING AT POSITION 2 POS_2:
JB P2.4,POS_3 CALL DELAY_12MS JB P2.4,POS_3 MOV A,#02H MOV P1,A JMP CHK_STRT
;************************** ; SUBROUTINE FOR JUMPING AT POSITION 3 POS_3:
JB P2.5,CHK_STRT CALL DELAY_12MS JB P2.5,CHK_STRT MOV A,#03H MOV P1,A JMP CHK_STRT
;************************** ; DELAY SUBROUTINE FOR SCANNING INC/DEC DELAY:
MOV 31H,R5 Z: MOV R4,#5 Y: MOV R3,#200 X: MOV R2, #250 DJNZ R2 , $ DJNZ R3 , X DJNZ R4, Y DJNZ 31H , Z
RET;************************ ; DELAY SUBROUTINE FOR MINIMIZING PUSH BUTTON BOUNCING DELAY_12MS:
MOV R1,#25 T: MOV R0,#250
DJNZ R0,$ DJNZ R1,T
RET END
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APPENDIX-D: PROJECT MANUAL
MIDAS Multiplexed Industrial Data Acquisition System
I. SIGNAL CONDITIONING AND CONTROLLING CARD FOR SERVO VALVE
INSTRUCTIONS
1) Only 0V to 5V should be given to reference for min. and max. Position of
valve.
2) Adjust lower limit that is 0V output by varying Pot.1.
3) Adjust upper limit that is 5V output by varying Pot.2.
4) Adjust proportional gain by varying Pot.3.
NOTES:
The above card not only used to measure position but also used for
controlling the position of valve.
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II. LEVEL TRANSMITTER AND TEMPERATURE SIGNAL CODITIONING CARD
INSTRUCTIONS:
1) Pot.1 is used for adjusting load impedance for current out put transmitters.
2) Pot.2 is used for adjusting the gain of signal conditioned output of
thermocouple.
3) Pot 3. is used as positive feedback gain for decreasing the non-linearity errors.
4) Pot 4. is used for adjusting the negative feedback gain during removing non-
linearity in thermocouple voltage.
5) Pot.5 is used for adjusting the ambient temperature. First short the
thermocouple input and then adjust the ambient temperature.
6) Whenever thermocouple becomes open or power supply becomes higher than
recommended then RED LED shown will automatically blinks.
__________________________________________________________________ PCSIR - Institute of Industrial Electronics Engineering, IIEE ST-22/C, Block-6 Gulshan-e-Iqbal, Karachi – 75300
III. SCALING FOR DIGITAL SCANNER
INSTRUCTIONS:
1) Pot.1 is used for adjusting the upper limit of first quantity which is Level here.
2) Pot.2 is used for adjusting the upper limit of second quantity which is
temperature here.
3) Pot.3 is used for adjusting the upper limit of third quantity which is Position of
servo controlled valve here.
NOTE:
You can use any three quantities whose upper range falls within 999.
__________________________________________________________________ PCSIR - Institute of Industrial Electronics Engineering, IIEE ST-22/C, Block-6 Gulshan-e-Iqbal, Karachi – 75300
IV. DIGITAL SCANNER
INSTRUCTIONS:
1) Pot.1 is used for adjusting the A/D conversion rate of scanner.
2) Pot.2 is used for adjusting the lower limit of the reading that is 000.
3) Pot.3 is used for same purpose as Pot.2 but it is more precise.
NOTES:
Selection panel control the appearance of each parameters. scanning time can be
increased or decreased by pressing button T+ or T- (500ms for each time) and can be
jumped at any particular quantity by first pressing stop button and then required
position. All three quantities after scaling is given at scanner input.