211EC3377

IMPLEMENTATION OF ONLINE TEMPERATURE
CONTROLLER BASED ON LabVIEW
Thesis submitted in partial fulfillment
of the requirements for the Degree of
Master of Technology
in
Electronics and Instrumentation Engineering
By
Abhyarthana Bisoyi
Roll No: 211EC3377
Department of Electronics & Communication Engineering
National Institute of Technology, Rourkela
Odisha- 769008, India
May 2013
IMPLEMENTATION OF ONLINE TEMPERATURE
CONTROLLER BASED ON LabVIEW
Thesis submitted in partial fulfillment
of the requirements for the Degree of
Master of Technology
in
Electronics and Instrumentation Engineering
By
Abhyarthana Bisoyi
Roll No: 211EC3377
Under the Supervision of
Dr. Umesh Chandra Pati
Department of Electronics & Communication Engineering
National Institute of Technology, Rourkela
Odisha- 769008, India
May 2013
Department of Electronics & Communication Engineering
National Institute of Technology, Rourkela
CERTIFICATE
This is to certify that the Thesis Report entitled “IMPLEMENTATION OF ONLINE
TEMPERATURE CONTROLLER BASED ON LabVIEW” submitted by Ms.
ABHYARTHANA BISOYI bearing roll no. 211EC3377 in partial fulfillment of the
requirements for the award of Master of Technology in Electronics and Communication
Engineering with specialization in “Electronics and Instrumentation Engineering”
during session 2011-2013 at National Institute of Technology, Rourkela is an authentic
work carried out by her under my supervision and guidance.
To the best of my knowledge, the matter embodied in the thesis has not been submitted
to any other University / Institute for the award of any Degree or Diploma.
Dr. Umesh Chandra Pati
Place:
Associate Professor
Date:
Dept. of Electronics and Comm. Engineering
National Institute of Technology
Rourkela-769008
Dedicated to my
Family and friends
ACKNOWLEDGEMENT
The satisfaction and euphoria on the successful completion of any task would be incomplete
without mentioning the people who made it possible whose constant guidance and
encouragement crowned out effort with success.
I would like to express my heartfelt gratitude to my esteemed supervisor, Dr. Umesh
Chandra Pati for his technical guidance, valuable suggestions, and encouragement
throughout the experimental and theoretical study and in preparing this thesis. It has been my
honour to work under his guidance, whose expertise and discernment were keys in the
completion of this project.
I am grateful to the Dept. of Electronics & Communication Engineering, for giving me the
opportunity to execute this project, which is an integral part of the curriculum in M.Tech
programme at the National Institute of Technology, Rourkela.
Many thanks to my friends who are directly or indirectly helped me in my project work for
their generous contribution towards enriching the quality of the work. I would also express
my obligations to Prof. S. K. Patra, Prof. K. K. Mahapatra, Prof. S. Meher, Prof. T. K. Dan,
Prof. S. K. Das, and Prof. Poonam Singh.
This acknowledgement would not be complete without expressing my sincere gratitude to my
family for their love, patience, encouragement, and understanding which are the source of my
motivation and inspiration throughout my work. Finally I would like to dedicate my work and
this thesis to my parents and my brother.
Abhyarthana Bisoyi
Date:
Roll No: 211EC3377
Place:
Dept. of ECE
NIT,Rourkela
i
ABSTRACT
LabVIEW (Laboratory Virtual Instrumentation Engineering Workbench) is the software
which gives virtual existence of hardware, reduces its cost and hence termed as Virtual
Instrumentation. This thesis presents the implementation of ON/OFF and PID controller for
controlling the temperature of a heating element inside a wooden box with the help of
LabVIEW. In this software, DataSocket Protocol and Transmission Control Protocol (TCP)
are used for developing an online transmission process between client and server. Client has
control over the set point and Server has control over the temperature. With the help of
internet protocol, client provides the value of set point according to which the control actions
are taken by the server. The paper also includes discussions regarding the advantages and
disadvantages of TCP/IP.
Written communication in LabVIEW refers to communication via internet where the
user can write messages to another user. Generally written communication is not found in any
programming related software but LabVIEW makes this possible using internet protocol.
This helps in easy and fast transmission of data in form of messages between the client and
server PC(s). After the transmission process gets over, the transmitted data is used for
implementing PID controller. The various responses in PID controller are obtained by
varying the tuning parameters. The responses are with respect to three conditions in the
controller. On studying the response curves, parameters like setting time, rise time and
maximum overshoot are obtained. A comparison table is obtained for these parameters and
helps in deciding to choose the values for tuning parameters of the controller.
ii
TABLE OF CONTENTS
Particulars
Page No.
Acknowledgements……………………………………………………………………..
i
Abstract…………………………………………………………………………………
ii
Table of Contents……………………………………………………………………….
iii
List of Figures…………………………………………………………………………..
vi
List of Tables……………………………………………………………………………
viii
Abbreviations……………………………………………………………………………
ix
1.
2
INTRODUCTION .............................................................................................................. 2
1.1
Overview ..................................................................................................................... 2
1.2
Motivation of Work..................................................................................................... 3
1.3
Background Literature Survey .................................................................................... 4
1.4
Objective of Work ....................................................................................................... 5
1.5
Thesis Outline ............................................................................................................. 6
THERMAL PROCESS....................................................................................................... 8
2.1
Proposed System ......................................................................................................... 8
2.2
Temperature Controllers ........................................................................................... 11
2.2.1
2.3
ON/OFF Controller ................................................................................................... 12
2.3.1
2.4
Steps to control temperature .............................................................................. 11
Application of ON/OFF controller..................................................................... 14
PID Controller ........................................................................................................... 14
2.4.1
Proportional........................................................................................................ 15
2.4.2
Integral ............................................................................................................... 16
2.4.3
Derivative ........................................................................................................... 16
2.4.4
Stability .............................................................................................................. 16
2.4.5
Manual tuning .................................................................................................... 16
2.4.6
Characteristics of PID controller ....................................................................... 17
iii
3
2.4.7
Steps for designing a PID controller .................................................................. 17
2.4.8
PID palette in LabVIEW .................................................................................... 18
IMPLEMENTATION OF DATASOCKET PROTOCOL............................................. 20
3.1
3.1.1
Front panel ......................................................................................................... 20
3.1.2
Block diagram .................................................................................................... 21
3.2
DataSocket Overview ................................................................................................ 22
3.3
Using DataSocket in LabVIEW ................................................................................ 22
3.3.1
DataSocket open ................................................................................................ 23
3.3.2
DataSocket close ................................................................................................ 24
3.3.3
DataSocket write ................................................................................................ 24
3.3.4
DataSocket read ................................................................................................. 24
3.4
Internet Communication Using DataSocket Protocol ............................................... 25
3.4.1
Server DataSocket program implementation ..................................................... 25
3.4.2
Client Data Socket program implementation..................................................... 25
3.4.3
Algorithm for implementation of ON/OFF controller ....................................... 25
3.4.4
Algorithm for manual tuning of PID controller ................................................. 27
3.5
4
VI in LabVIEW ......................................................................................................... 20
Results and Discussion .............................................................................................. 27
3.5.1
Implementation of ON/OFF controller using Data Socket Protocol ................. 27
3.5.2
Implementation of PID controller using DataSocket protocol .......................... 33
3.5.3
Implementation of multiple client-server communication ................................. 37
IMPLEMENTATION OF TCP/IP ................................................................................... 41
4.1
Internet Protocol ........................................................................................................ 41
4.2
User Datagram Protocol ............................................................................................ 41
4.3
Transmission Control Protocol.................................................................................. 41
4.3.1
Using TCP connections in LabVIEW ................................................................ 41
4.3.2
Algorithm for using TCP/IP: ............................................................................. 43
iv
4.3.3
Advantages of TCP/IP ....................................................................................... 44
4.3.4
Disadvantage of TCP/IP .................................................................................... 44
4.4
Online Written Communication ................................................................................ 44
4.4.1
4.5
5
Algorithm for written communication ............................................................... 44
Results and Discussion .............................................................................................. 45
4.5.1
Implementation of ON/OFF controller using TCP/IP ....................................... 45
4.5.2
Implementation of PID controller using TCP/IP ............................................... 46
4.5.3
Implementation of online written communication ............................................. 48
CONCLUSION ................................................................................................................ 51
5.1
Limitations of the Thesis ........................................................................................... 51
5.2
Scope for Future Research ........................................................................................ 52
References…………………………………………………………………………………
54
Dissemination……...……………………………………………………………………… 56
v
LIST OF FIGURES
Figure No.
Page No.
Figure 1.1: Block diagram of a control system .......................................................................... 2
Figure 2.1: Block Diagram of the Proposed System.................................................................. 9
Figure 2.2: Flow Diagram of the project ................................................................................. 10
Figure 2.3: General Block Diagram ......................................................................................... 12
Figure 2.4: Basic block diagram of a conventional PID controller ......................................... 15
Figure 2.5: PID Palette ............................................................................................................. 18
Figure 3.1: Front Panel of LabVIEW ...................................................................................... 20
Figure 3.2: Block Diagram of LabVIEW ................................................................................ 22
Figure 3.3: DataSocket Server ................................................................................................. 23
Figure 3.4: DataSocket Open ................................................................................................... 23
Figure 3.5: DataSocket Close .................................................................................................. 24
Figure 3.6: DataSocket Write .................................................................................................. 24
Figure 3.7: DataSocket Read ................................................................................................... 24
Figure 3.8: Simple DataSocket Protocol Implementation ....................................................... 28
Figure 3.9: Output when SP<PV and PV is Within Limit ....................................................... 28
Figure 3.10: Output when SP<PV and PV is Out of Limit ...................................................... 29
Figure 3.11: Output when SP>PV and PV is Within Limits ................................................... 30
Figure 3.12: Output when SP>PV and PV is Out of Limits .................................................... 31
Figure 3.13: Output when SP=PV ........................................................................................... 31
Figure 3.14: Upper portion of the block diagram of server ..................................................... 32
Figure 3.15: Lower portion of the block diagram of server ..................................................... 32
Figure 3.16: Front Panel of PID controller .............................................................................. 33
Figure 3.17: Front panel of client (PID controller) .................................................................. 34
Figure 3.18: Block diagram of client (PID controller) ............................................................ 34
Figure 3.19: Graph showing under damped response.............................................................. 35
Figure 3.20: Graph showing critically damped response......................................................... 36
Figure 3.21: Graph showing over damped response................................................................ 36
Figure 3.22: Flow of data among 2 clients and a server .......................................................... 37
Figure 3.23: Front Panel of Server ........................................................................................... 38
Figure 3.24: Front Panel of Client1 ......................................................................................... 38
Figure 3.25: Front Panel of Client2 ......................................................................................... 39
vi
Figure 4.1: TCP/IP Listen Icon ................................................................................................ 42
Figure 4.2: TCP/IP Write Icon ................................................................................................. 42
Figure 4.3: TCP/IP Read Icon.................................................................................................. 43
Figure 4.4: Front Panel of ON/OFF controller Server ............................................................. 46
Figure 4.5: Block Diagram of ON/OFF controller Client........................................................ 46
Figure 4.6: Front Panel of PID controller Server ..................................................................... 47
Figure 4.7: Front Panel of PID controller Client ..................................................................... 47
Figure 4.8: Front Panel of Communicating Server .................................................................. 48
Figure 4.9: Front Panel of Communicating Client................................................................... 49
vii
LIST OF TABLES
Table No.
Page No.
Table 2.1: Effect of PID Controllers on Closed-Loop System ................................................ 17
Table 3.1:Comparison between response curves ..................................................................... 37
viii
LIST OF ABBREVIATIONS
LabVIEW
Laboratory Virtual Instrument Engineering Workbench
DAQ
Data Acquisition
DAS
Data Acquisition System
PC
Personal Computer
DS
Data Socket
TCP
Transmission Control Protocol
UDP
User Datagram Protocol
IP
Internet Protocol
VI
Virtual Instrument
PV
Process Variable
SP
Set Point
DSTP
Data Socket Transfer Protocol
NI
National Instrument
PID
Proportional Integral Derivative
PI
Proportional Integral
PD
Proportional Derivative
FTP
File Transfer Protocol
ANFIS
Adaptive Network-Based Fuzzy Inference System
NCS
Networked Control System
OLE
Object Linking and Embedding
OPC
OLE for Process Control
HTTP
Hyper Text Transfer Protocol
LAN
Local Area Network
DNS
Domain Name System
TC
Temperature Controller
CGI
Common Gateway Interface
ix
Chapter 1
Introduction
Overview
Motivation
Background of Literature Survey
Objective of Work
Thesis Outline
1. INTRODUCTION
1.1 Overview
Control system is a system that controls a variable by using error-sensing through a closed loop.
The variable is known as controlled variable that must be maintained or controlled at some
desired value. The desired value of the controlled variable is known as set point. The variable
used to maintain the controlled variable at its set point is known as manipulated variable. A
closed loop refers to the condition in which the controller is connected the process comparing the
set point with the controlled variable and determining corrective action. The objective of a
control system is to use the manipulated variable and to maintain the controlled variable at its set
point despite of disturbances. Disturbance is any variable that may cause controlled variable to
deviate away from set point. Figure 1.1 represents the block diagram of a control system.
Figure 1.1: Block diagram of a control system
The basic controllers used to control a process variable at its set point are ON/OFF, P, PI,
PID and PID fuzzy. There are various networking protocols used in LabVIEW (Laboratory
Virtual Instrument Engineering Workbench) such as DS (DataSocket Protocol), TCP
(Transmission Control Protocol), and UDP (User Datagram Protocol) which provides online
facilities to the users. These are the basic tools for communication over internet.
2
Mainly controllers with combination of Proportional, Integral and Derivative are more
effective than other controllers. As conventional controllers such as P, PI, PD, PID, OttoSmith, all their different types and realizations, and other controller types have been
counted on years. It is important for all conventional controllers to know a mathematical model
of the process in order to design a controller. Unconventional controllers develop new
approaches in the controller design where mathematical model of a process is generally is not
needed. Examples of unconventional controller are a fuzzy controller and neuro or neuro-fuzzy
controllers.
LabVIEW is a graphical programming environment which reduces the cost by giving a
virtual existence of hardware, and hence termed as Virtual Instrumentation. This environment
best suits for high-level or system-level design. The basic difference between “natural
instrumentation” and “virtual instrumentation” is the software part of a virtual instrumentation.
The software replaces complex and expensive equipment by simple and less expensive hardware.
The program in this software consists of two parts: front panel and block diagram. Front panel
shows the control and indicator while the main programming part is done in the block diagram
which is usually kept up to user. Controls are the inputs and indicators are the outputs. Various
operations have been done relating these controls and indicators.
1.2 Motivation of Work
In the academic and industrial communities, remote real-time control of processes is receiving
considerable attention. In industries, when an instrument acquires some quantity and then
measures it, its value has to be kept at some limit otherwise it may cause some problem. Hence
the controllers are needed to solve the purpose. The controllers may function in controlling
controlled variable such as temperature, pressure, flow, level, humidity, etc. Using LabVIEW
software it becomes easy to design a controller. In earlier years, much research has been done on
the controllers but not on the various internet protocols found in LabVIEW. The internet
protocols can be used in order to develop communication among the users.
Data Acquisition (DAQ) is the process of measuring and processing any electrical or
physical quantity such as voltage, temperature, humidity, pressure, etc. A “server-client”
relationship is formed using these protocols. A server is a user who acquires and measures the
3
variable, performs operations and if requires any help then sends a request to the client. Client is
a user who accepts the request from server and provides service in return. The protocols help in
long distance communication by making it very easy and fast. The combination of controllers
and protocols is more helpful in industries. The client and server are connected using DAQ.
Depending upon the system to be controlled, the user will choose the type of control for the
process. Among the controllers, ON/OFF controller is the basic one that has been implemented
followed by PID in order to compare. PID controller is best suited for industrial application since
it gives zero offset because of I-component and better stability because of other components.
Various technologies are developed in order to perform real time control using internet based
technology. LabVIEW is one of the software packages used in process control application. It
uses various protocols such as TCP/IP, DataSocket, etc. that allows remote control using
internet. Many universities have developed internet based process control laboratories for the
students that would be helpful for distance education.
1.3 Background Literature Survey
The literature survey begins with study of ON/OFF controller. In 2003, E. Rézaei [1] and in
2009, K. Prerna [2] proposed a system where the temperature of a bulb inside a wooden box has
been controlled by using ON/OFF controller, with the help of DS Protocol and also developed
the algorithm. In 2011, A.O. Neaga, et al. [3] proposed a system to control liquid nitrogen to its
set point using ON/OFF controller, but there are certain defects in the control loop. In 2011, R.
Dutta [4] proposed a system where the temperature of a set of light bulbs inside a wooden box is
controlled using DS Protocol and digital temperature sensor. In 2007, S. Murthy [5] described in
their paper about protocols and the way these protocols help in improving networking
capabilities of many measurement and automation applications. LabVIEW encourages such
protocols in control applications.
In 2007, S. Zhong, et al. [6] proposed a self-tuning algorithm for PID parameter using
method of recursion least square. In 2009, A. Nazir, et al. [7] presented a genetic algorithm for
tuning PID parameters which reduced the computational requirement. In 2009, J. Liu, et al. [8]
presented a real time development system showing the control of position in a dc servo motor
using PID controller. He described about various PID algorithms to control position using DAQ.
4
In 2010, S. Ravi, et al. [9] developed an ANFIS controller for plastic extrusion system which
gave better performance than fuzzy logic and PID controller. F. Faizan, et al. [10] implemented
a discrete PID on pendulum with an idea to balance an inverted pendulum using PIC
microcontroller. In 2011, S. K. Sahoo, et al. [11] discussed in their paper regarding the
modulus hugging approach for designing PI and PID controller in order to control the speed
of DC motors using various algorithms. In 2011, V. Kumar, et al. [12] discussed a
comparative study on performance of various fuzzy PID with other fuzzy controllers. In
2011, J.H. Zhang, et al. [13] proposed an acquisition diagnostic system for remote ground
equipment using LabVIEW. Hai-bo Lin [14] introduced an intelligent temperature controller
where the simulation results show intelligent temperature controller has good control
performance and higher accuracy using PID algorithm.
In 2010, S. Mohammadi, et al. [15] developed a fuzzy based PID controller that
helps in reducing the packet loss while TCP communication. In 2003, D. Poulton, et al.
[16] discussed in their paper about the fading effects of rain on TCP/IP packet based
satellite links and proposed a PID delay controller based on non-uniform sampling
filtering. In 2006, A. Wei, et al. [17] discussed in their paper about TCP in Networked
Control System (NCS) and performance of different types of data result. In 2011, F.
Xiao, et al. [18] introduced in their paper about CAN-TCP/IP gateway showing the
application of webserver in that field. In 2012, Y. Li, et al. [19] described about
vulnerabilities of TCP/IP by exposing it to attacks.
1.4 Objective of Work
The objective intends to measure and control the temperature of a heating element inside a box
using controllers. This is performed by using LabVIEW software, by developing a “Client” and a
“Server”. They communicate using DataSocket and TCP protocol where the server controls the
temperature using ON/OFF and PID controller and the client has an option to decide the set
point. The various advantages of internet protocols in LabVIEW have been discussed. The
advantages include communication like chatting, sending information, etc. Client and server are
two users that communicate using TCP/IP for sending their data. These data are used further in
implementation of controllers. Here PID controller has been implemented and the various
5
conditioned outputs are obtained. A comparison table is obtained with different outputs of the
controller.
1.5 Thesis Outline
Including the introductory chapter, the thesis is divided into 6 chapters. The organization of
the thesis is presented below.
Chapter 2 - Thermal Process
The proposed system has been discussed in this chapter. The flow diagram of the process has
been described with brief explanation on it. Introduction to the two controllers has been given.
Chapter 3 - Implementation of DataSocket Protocol
In this chapter, the control of temperature using DataSocket protocol has been discussed. The
implementation algorithms of the two controllers have been described. The simulation
results have been discussed. Communication of two clients with one server has been
discussed.
Chapter 4 - Implementation of TCP/IP
In this chapter, the control of temperature using Transmission Control Protocol has been
discussed. The implementation algorithms for the protocol have been described. The chapter
also includes the simulation results obtained.
Chapter 5 – Conclusion
The overall conclusion of the thesis is presented in this chapter. It also contains some
limitations of the thesis and future research topics.
6
Chapter 2
Thermal Process
Proposed System
Temperature Controllers
ON/OFF Controller
PID Controller
2
THERMAL PROCESS
This chapter discusses the proposed system, introduction to the two controllers, ON/OFF and
PID controller and their algorithm.
2.1 Proposed System
The main objective is to maintain the temperature inside a wooden box which is heated by a
heating element i.e. a bulb, at some desired value of set point which is selected by Client. The
heating element is covered by a wooden box and on heating; the temperature is sensed by
temperature sensor and is transmitted to the server PC with the help of DAQ card. Since, the
output of sensor is in voltage form, the server PC converts it to temperature using Equation 2.1.
PV = 6. Vin + 60
(2.1)
Where, PV is Process Variable
Vin is voltage measured by sensor
This value of temperature i.e. process variable (PV) is sent to client PC. The client PC on
receiving PV sends set point (SP) value to the server PC. Depending upon the SP, ON/OFF and
PID controller take necessary actions. The actions are in the form of signals that control the
operation of fan. When the temperature crosses the neutral zone, controller turns a fan ON or
OFF accordingly. Neutral zone is the zone bounded by low and high limit.
Figure 2.1 shows the proposed system block diagram. It shows the client server relationship
along with the communication path between them.
8
Figure 2.1: Block Diagram of the Proposed System
Figure 2.2 shows the flow diagram of the project including the involvement of proposed system.
The transmission of information between client and server has been done by using TCP/IP and
DataSocket Protocol. The approach for the goal can be easily summarized by a flow chart by
which we can see the further proceedings. It just gives a generalized view but not specific for
each controller. There is a difference between the two paths after “Data received by PC/Server”
block. The first path can be used when hardware modeling is involved. The second path has been
implemented in the software part.
9
Figure 2.2: Flow Diagram of the project
10
2.2 Temperature Controllers
Temperature controller (TC) is an instrument that controls temperature. The temperature sensor
senses the temperature and the value is given as an input to the TC. The temperature controller
has an output that is connected to a control element for instance a heater or fan.
In order to accurately control a process temperature without an operator involvement, a
temperature control system depends upon a controller, which uses a temperature sensor
(Thermocouple or RTD) as an input. It compares the observed temperature with the desired
temperature (set point), and obtains an output to a control element. The controller is just a part of
the whole control system, but the entire system is after selecting the proper controller. The
following points should be noted while selecting a controller:
•
Type of sensor and the temperature range.
•
Type of output required.
•
Control algorithm needed.
•
Number of output and its type.
In various applications, the above points will not be enough to measure a quantity. So it is
needed to control a quantity. Either the quantity has to stay constant at some fixed value or the
quantity can be varied in some manner decided by user. The control action has to be decided
first.
2.2.1
Steps to control temperature
The temperature is the physical quantity that has to be controlled. The following steps are carried
out in order to control temperature:
•
The first step for controlling temperature is to measure it and to observe the value it has.
So it is important to know the temperature.
•
The Second step after measurement of temperature is to compare it with the desired
temperature (Set Point) that is the temperature needed. It is essential to verify if the value
is too high or too low and check the range.
•
The last step after comparison is the decision of control action to be taken. There are
various ways to control a variable.
11
When a control system is build up, it is useful to visualize how the signals are produced and the
way it affects the system. The designers of a control system design a block diagram to show the
signals flow in a control system. Figure 2.3 shows the block diagram of a typical control system.
Figure 2.3: General Block Diagram
The block diagram consists of the following components:
•
Process
•
Measurement
•
Error Detector
•
Controller
•
Control Element
2.3 ON/OFF Controller
An ON/OFF controller is a basic temperature controller. The output from the controller is either
ON or OFF without any middle state. An ON/OFF controller will respond to the output only
when the temperature deviates from the set point. An ON/OFF controller drives the manipulated
variable from a fully closed condition to fully open depending upon the position of the controlled
variable with respect to the set point. For controlling heat, the output is on when the temperature
is less than the set point, and off when above SP. Since the temperature deviates from the set
12
point in order to change the output response, the temperature of the process will be monitored
continuously.
If sudden actions are taken by heating switches turning ON and OFF at the instant the
measured temperature deviates from the set point, then the system starts “chattering” repeatedly
and then the system wouldn't last for a long time. In order to avoid this, practical ON/OFF
controllers have a dead band around the set point. The dead band is also known as proportional
band. When the measured value lies within this band the controller does not take any action. But
when the value moves outside this band the action is taken. The reason behind this is to introduce
set of oscillation for the value of controlled variable, which means that at larger dead band the
amplitude obtained is higher and frequency is lower.
ON/OFF differential prevents chattering or making fast, if the deviation above and below
the set point occurs very rapidly. The difference in temperature needs exceeding the set point by
a certain amount before the output turns OFF or ON continuously. The demerit of ON OFF
Controller is the occurrence of “Hunting”. This “ON and OFF” switching continues all the time,
around the set point temperature. After the “Overshoot” and “Undershoot” the process
“stabilizes” and “oscillates” around the Set point value. This is called “Hunting”. To prevent
“oscillation” at set point Temperature the ON and OFF switching point are NOT the same.
Otherwise the controller would not know if it has to switch ON or OFF at set point. The
difference between the ON-switching point and the OFF point is called the “Hysteresis”. It is
represented in equation 2.2.
u(t) = �
Where:
Umax ;∀ e(t)>0
Umin ;∀e(t)<0
(2.2)
e(t) – control error (for unit feedback).
u(t) – control signal (controller output).
ON/OFF controller have only two possible control signal values irrespective of the
value of control error. Hence this controller is the simplest one among other temperature
controllers. Depending on the error, whether it is positive or negative, the control signal u(t) can
13
have two values, Umax (high level) or Umin (low level). The objective behind this way of
control is that the two control levels attain desired value of controlled variable in shortest time
possible. When the process has a positive static gain, high level control signal (Umax), will
increase the value of controlled variable. A drawback of control is that the control signal on
oscillating may cause control variable to oscillate around the set point and at times there is no
solution to this problem. The process is forced to oscillate since u(t) is never zero, it is
either Umax or Umin. The only way to avoid these forced oscillations is to reduce the gain
for small values of error, e(t) which can be achieved by introducing a proportional mode that
remains active for certain values of error.
2.3.1
Application of ON/OFF controller
ON/OFF controller is mostly used where an accurate control is not demanded. It is implemented
in systems which cannot handle heavy amount of energy to turn ON and OFF, where the mass of
the
system
more,
that
temperatures
change
extremely
slowly.
One
special kind
of ON/OFF management used for alarm could be a limit controller. This controller uses a
latching relay that should be manually reset, and is employed to close up a method once an
exact temperature is reached.
2.4 PID Controller
PID controllers are the foremost widely-used style of controller for industrial application. It
is conjointly referred to as “Three-term controller”. They are structurally easy and exhibit strong
performance over large varies of operating conditions. Within the absence of the entire data of
the method these varieties of controllers are the foremost economical of selections. The three
main parameters concerned are Proportional (P), Integral (I) and Derivative (D). The
proportional half is liable for following the required set-point, whereas the integral
and derivative half accounts
for the
buildup of
past
errors and
therefore
the rate
of modification of error within the method severally.
Derivative mode improves stability of the system and allows increase in gain Kp and
decrease in integral time constant Ti, that will increases speed of the controller response.
PID controller is employed once coping with higher order electrical phenomenon processes once
14
their dynamic is not like a dynamics of an integrator.
There are various methods for tuning a PID controller:
1. Manual Tuning.
2. Ziegler-Nichols Method
Figure 2.4: Basic block diagram of a conventional PID controller
For the PID controller represented in Figure 2.4,
Output of PID controller is represented by equation (2.3),
t1
u(t) = Kpe(t) + K i � e(τ)dτ + K d
0
Where,
de(t)
dt
(2.3)
Error, e(t) =Set point- Plant output
Kp = proportional gain, Ki = integral gain, Kd = derivative gain
Problem in structure of a controller arises during designing a control system, defining structure
and controller parameters and tuning them.
2.4.1
Proportional
The proportional term is given by equation 2.4,
Pout = K p e(t)
15
(2.4)
If K p is high then the system becomes unstable. If it is too low then control action may
not be effective for responding to disturbances.
2.4.2
Integral
The integral term is given by equation 2.5,
t
Iout = K i � e(τ)dτ
(2.5)
0
The integral term eliminates the steady-state error by the movement of the process
towards set point. But it may cause overshoot so an additional component is required.
2.4.3
Derivative
The derivative term is given by equation 2.6:
Dout = K d
de(t)
dt
(2.6)
The derivative term reduces the overshoot and improves the stability of the process. But
it slows the transient response of the controller.
2.4.4
Stability
If the tuning parameters of PID controller are not chosen properly, the process may become
unstable and the instability is caused by excess gain. PID controller algorithm is given by
equation 2.7,
t1
1
de(t)
u(t) = K �e(t) + � e(τ)dτ + Td
�
Ti
dt
0
Or,
2.4.5
K
t
u(t) = Ke(t) + T ∫0 1 e(τ)dτ + KTd
i
(2.7)
de(t)
dt
Manual tuning
The proportional, integral and derivative terms must be individually adjusted or "tuned" to a
particular system using trial and error. It provides accuracy and stability for the process.
16
2.4.6
Characteristics of PID controller
Table 2.1 shows the comparison between rise time, overshoot, settling time, steady state error for
different tuning parameters of PID controller. . Effects of each of controllers Kp, Kd, and Ki on a
closed-loop system are summarized in the table shown below. Changing one of these variables
can change the effect of the other two. For this reason, the table should only be used as a
reference while determining the values for Ki, Kp and Kd.
Table 2.1: Effect of PID Controllers on Closed-Loop System
PARAMETERS
RISE
OVERSHOOT
TIME
SETTLING
S-S
TIME
ERROR
Kp
Decrease
Increase
Small Change
Decrease
Ki
Decrease
Increase
Increase
Eliminate
Kd
Small Change
Decrease
Decrease
Small Change
A proportional controller can reduce the rise time and steady-state error but cannot remove it.
An integral controller eliminates the steady-state error, but makes the transient response worse.
A derivative controller improves the stability of the system, reduces the overshoot, and improves
the transient response
2.4.7
Steps for designing a PID controller
While designing a PID controller for a given system, the following steps are followed in order to
obtain a desired response.
•
The open-loop response is obtained.
•
Kp is added to improve the rise time.
•
Kd is added to improve the overshoot.
•
Ki is added to eliminate the steady-state error.
•
Each of Kp, Ki, and Kd is adjusted until a desired overall response is obtained.
17
2.4.8
PID palette in LabVIEW
The figure 2.5 shows the functions of the PID Palette. Following functions are found the Control
Palette:
Figure 2.5: PID Palette
18
Chapter 3
Implementation of
DataSocket Protocol
VI LabVIEW
DataSocket Overview
Using DataSocket in LabVIEW
Internet Comm. Using DataSocket
Results and Discussion
3
IMPLEMENTATION OF DATASOCKET PROTOCOL
LabVIEW is different from other software packages as it uses symbols rather than any textual
language for programming purpose. LabVIEW programs are called Virtual Instruments (VIs)
because replaces original instruments with the blocks which carry the same operation as that of
the instrument. Any instrumentation application will have two components, namely, the user
interface and the underlying code.
3.1 VI in LabVIEW
The VI consists of two divisions as follows:
•
Front Panel
•
Block Diagram
3.1.1
Front panel
The front panel of LabVIEW is known as “panel” in short. It is a LabVIEW term for user
interaction interface. The panel contains two objects namely controls and indicators. The control
is a LabVIEW front panel entity which takes an input to the code while the indicator is an entity
which displays the output from the code. Figure 3.1 shows the front panel of a VI.
Figure 3.1: Front Panel of LabVIEW
20
In short the front panel of LabVIEW has got the following features,
•
Provides user interface.
•
Shows Controls or Indicators.
•
Highly customizable.
3.1.2
Block diagram
The block diagram of LabVIEW is otherwise known as “diagram” in short. It is the “backplane”
of the LabVIEW program where the actual code resides. Any control or indicator placed on the
front creates an icon on the block diagram which acts as a connection between them. The main
programming part of VI is done here. The controls can be differentiated from the indicators by
their thicker border and contains an arrow on the right side of the block.
Even the software gives facility to make sub VI(s) by which the efficiency and optimization
increases. National Instruments provides various toolkits by which a user can understand the
software easily. Figure 3.2 shows the block diagram of a VI where the sum of two numbers is
found out.
In short the block diagram of LabVIEW has got the following features,
•
It consists of the actual program.
•
This part is invisible to user.
•
User reads from left to right just like a book.
21
Figure 3.2: Block Diagram of LabVIEW
3.2 DataSocket Overview
DataSocket is a TCP/IP tool developed by National Instruments for networked data transfers. It
is an online programming technology based on TCP/IP that makes an easier way of data
exchange between computers and applications. In earlier days, various protocols, hardware and
software were developed for the applications. Usually in testing and manufacturing industries
problems arise due to the integration of hardware and software component of a system. This
problem forced a programmer to link between the protocols to transfer data, which required lots
of development, time and resources. As a solution to this, National Instruments developed
DataSocket. It helped in publishing/sharing live data over a network and provides an interface
for many protocols.
3.3
Using DataSocket in LabVIEW
The tool that is devised by NI for networked data acquisition is Data Sockets. With development
in LabVIEW for networking and distributed control, Data Sockets helped in the recent versions
of LabVIEW. However, it does not form a part of the standard networking tools. So in order to
use Data Socket in LabVIEW the user has to start the DataSocket Server in the data socket
network. Figure 3.3 shows the DataSocket server.
22
Figure 3.3: DataSocket Server
DataSocket is compatible with any form of data type. The DataSocket sub-palette is the Data
Communication menu for a user. There are four functions found in this palette and they are:
•
DataSocket Open
•
DataSocket Close
•
DataSocket Read
•
DataSocket Write
The natural sequence of the program will be Open, Close, in between a series of read and write
operations. The variant sub menu is used to handle data transfers with variants in a bidirectional
manner. Variant is a special type of data type that is created for Data Socket operations. It has got
close relation with String data type.
3.3.1
DataSocket open
This block can be used only once in each VI. Figure 3.4 shows the block for DataSocket Open.
Figure 3.4: DataSocket Open
The inputs and outputs of the block can be seen in the diagram. The URL is the site for the
connection, for host system dstp://localhost can be used. The mode is an integer which defines
the mode of connection, ‘1’ is for write, ‘2’ is for read, ‘3’ is for buffered read and ‘4’ is for
buffered read/write. The output of the blocks is connection ID that is generated.
23
3.3.2
DataSocket close
This block can be used only once in each VI. Figure 3.5 shows the block for DataSocket Close.
Figure 3.5: DataSocket Close
The connection ID generated from DataSocket Open is given as an input to this block. The output
timed out is optional.
3.3.3
DataSocket write
Figure 3.6 shows the block for DataSocket Write.
Figure 3.6: DataSocket Write
The connection for this block can be defined either through a string or the connection id. This
block writes the data to the variable that is present on the other side connected in.
3.3.4
DataSocket read
Figure 3.7 shows the block for DataSocket Read.
Figure 3.7: DataSocket Read
The output of this block is data where the value of variable is assigned. The input to this block is
connection in where the data exchange process is carried out.
24
3.4 Internet Communication Using DataSocket Protocol
Data Socket (DS) is a communication protocol in LabVIEW. It permits reading, writing, and
sharing of live data between applications and/or different data sources and destinations. DS uses
an URL format similar to http, which is called dstp (Data Socket Transfer Protocol). Dstp allows
two way communications and data exchange between applications. This protocol is used in
both server and client applications. LabVIEW has several built-in Sub VIs that can be used
within systems have permission to write, create, and read data on the DS Server.
3.4.1
Server DataSocket program implementation
The Data Socket protocol based program in the server computer opens bi-directional
communication using DS Open Connection sub VI. The server with URL given as
dstp://localhost/file_name receives set point value from the client. The server sends the
process temperature value to the client. The Low-Limit and the High-Limit of the temperature
control neutral zone are also set from the server front panel. The client controls the set-point on
the server.
3.4.2
Client Data Socket program implementation
The client computer also opens a communication using DS Open sub VI. The server with URL
as dstp://ip_address of server/file_name is selected which allows connection between clients and
the server using DS protocol to interchange the information. The client sends set-point
information to the server as a double precision value. The server sends the process temperature
value to the client computer. The Data Socket connection is closed using the DS Close
Connection sub VI.
3.4.3
Algorithm for implementation of ON/OFF controller
The logic behind the implementation of ON/OFF controller using DataSocket Protocol is
described as follows:
1. The calculated error is compared with upper limit and lower limit.
2. Accordingly, the indicators show the state and action that has been taken. The state is seen
through the “Within Limit” and “Out of Limit” indicator. The “Fan ON” and “Fan OFF”
25
indicators show the control action that is to be taken.
3. The comparison has been done with following three conditions.
A). If Error > 0 AND PV > Low Limit then the indicators states are:
Cooling Fan ON: OFF
Cooling Fan OFF: ON
Within Limit: ON
Out of Limit: OFF
Digital I/O: OFF
If condition is not satisfied, then the indicators states are:
Cooling Fan ON: ON
Cooling Fan OFF: OFF
Within Limit: OFF
Out of Limit: ON
Digital I/O: ON
B). If Error < 0 AND Tout< High Limit, then the indicators states are:
Cooling Fan ON: ON
Cooling Fan OFF: OFF
Within Limit: ON
Out of Limit: OFF
Digital I/O: ON
If condition is not satisfied, then the indicators states are:
Cooling Fan ON: OFF
Cooling Fan OFF: ON
Within Limit: OFF
Out of Limit: ON
Digital I/O: OFF
C). If Error = 0 then the indicators states are:
Cooling Fan ON: OFF
Cooling Fan OFF: OFF
Within Limit: ON
Out of Limit: OFF
26
Digital I/O: OFF
If condition is not satisfied, then the indicators states are,
Cooling Fan ON: OFF
Cooling Fan OFF: ON
Within Limit: OFF
Out of Limit: ON
Digital I/O: OFF
3.4.4
Algorithm for manual tuning of PID controller
Using the following steps, manually the PID tuning parameters has been set and the output
response is obtained.
1. First Ti and Td values has been set to zero.
2. K C has been increased until the output of the loop oscillates.
3. K C has been set to approximately half of that value for a "quarter amplitude decay" type
response.
4. Ti has been increased until any offset is corrected for the process.
5. K C has been increased if required but too much K C causes excessive response and overshoot.
3.5 Results and Discussion
The various simulation results of implementation of ON/OFF and PID controller using Data
Socket protocol are discussed in this section.
3.5.1
Implementation of ON/OFF controller using Data Socket Protocol
Figure 3.8 shows the front panel and block diagram of a client server communication using Data
Socket Protocol. The client1 VI acts as server and client2 VI acts as client. The server is run first
followed by client so that the client responds to the request of the server. The URL given by
server for sending Process Variable (PV) is dstp://localhost/client1 and for receiving Set Point
(SP)
is
dstp://localhost/client2.
The
URL
27
given
by
client
for
sending
SP
is
dstp://localhost/client1 and for receiving PV is dstp://localhost/client2.
Figure 3.8: Simple DataSocket Protocol Implementation
Figure 3.9: Output when SP<PV and PV is Within Limit
Figure 3.9 shows the front panel of server on left side and client on right side. The lower and
28
upper limit for temperature has been chosen as 40 and 60 respectively by the server PC. The Vin
is 0, corresponding PV obtained is 60. The client sets the SP as 50 and the value of error has
been calculated as -10.The output is obtained for the condition SP<PV and PV is Within Limit.
The state of the indicators can be seen in the figure. Even if the PV is within limit still it is
deviated from the set point. So the Cooling Fan is turned ON in order to bring back to its desired
value.
Figure 3.10 shows the front panel of server on left side and client on right side. The lower
and upper limit for temperature has been chosen as 40 and 60 respectively by the server PC. The
Vin is 5, corresponding PV obtained is 90. The client sets the SP as 50 and the value of error has
been calculated as -40.The output is obtained for the condition SP<PV and PV is Out of Limit.
The state of the indicators can be seen in the figure. Since the value of PV is not in the range the
“Out of Limit” is turned ON while others remain OFF.
Figure 3.10: Output when SP<PV and PV is Out of Limit
Figure 3.11 shows the front panel of server client for the condition when SP>PV and PV is
within the limit. The Vin is -2, corresponding PV obtained is 48. The client sets the SP as 50 and
the value of error has been calculated as 2.The output is obtained in the form of indicators that
can be seen in the figure. Since the value of PV is within limit but has not crossed SP, the
cooling fan remains OFF.
29
Figure 3.11: Output when SP>PV and PV is Within Limits
Figure 3.12 shows the front panel of server client for the condition when SP>PV and PV is
out of limit. The Vin is -5, corresponding PV obtained is 30. The client sets the SP as 50 and the
value of error has been calculated as 20.The output is obtained in the form of indicators that can
be seen in the figure. Since the value of PV is below the lower limit the “Out of limit” indicator
turns ON while the other remain OFF.
Figure 3.13 shows the front panel of server client for the condition when SP=PV. The SP set
by client is 60, Vin is 0, corresponding PV obtained is 60. Since the client has set the SP to 60,
the value of error calculated is 0.The output is obtained in the form of indicators that can be seen
in the figure. Since there is no deviation of PV from the SP, no control actions are taken. Only
the “Within limit” indicator turns ON since the PV does not lie outside the dead band set by the
server. Other indicators remain OFF.
30
Figure 3.12: Output when SP>PV and PV is Out of Limits
Figure 3.13: Output when SP=PV
31
Figure 3.14: Upper portion of the block diagram of server
Figure 3.15: Lower portion of the block diagram of server
Figure 3.14 shows the upper portion of the block diagram of server while figure 3.15 shows the
lower portion. The combination of both figures forms the complete block diagram of server. The
upper portion shows the operation of ON/OFF controller and lower portion shows the
connections for Data Socket protocol communication with client.
32
3.5.2
Implementation of PID controller using DataSocket protocol
Figure 3.16 shows the front panel of PID controller using DS protocol. The URL for sending PV
to client is dstp://localhost/PID_DS_SER and that of receiving SP is dstp://localhost/client2. The
SP set by the client is 60. In order to obtain response curve, the tuning parameters are set to
different values. In the given figure the value of PV is controlled up to 60.02. This is a close
approximation obtained.
Figure 3.16: Front Panel of PID controller
33
Figure 3.17: Front panel of client (PID controller)
Figure 3.18: Block diagram of client (PID controller)
34
Figure 3.17 shows the front panel of the client and figure 3.18 shows its block diagram. The
communication of client and server is similar to that of the ON/OFF controller. The only
difference lies in the operation of controller.
There are three conditions of response and they are, critically damped, over damped and under
damped. These responses have been obtained using manual tuning of PID tuning parameters.
WhenK C , Ti and Td have been tuned to 3, 0.006 and 0 respectively, underdamped response have
been obtained. The graph is shown in Figure 3.19. The value of process variable obtained was
60.05. An overshoot peak is observed and immediately follows undershoot which tries to
stabilize the curve.
Figure 3.19: Graph showing under damped response
Figure 3.20 shows the critically damped response of PID controller. This is the manual
tuning results where the values of tuning parameters of PID controller,K C , Ti and Td have been
tuned to 3, 0.048 and 0 respectively. It is clearly seen that the PV is controlled to its SP value
with less time. The value of process variable obtained was 60.
When K C , Ti and Td have been tuned to 3, 0.08 and 0 respectively, overdamped response
have been obtained. The graph is shown in Figure 3.21. The value of process variable obtained
was 60.06. For individual response, their corresponding rise time, settling time, peak overshoot
35
have been obtained.
Figure 3.20: Graph showing critically damped response
Figure 3.21: Graph showing over damped response
Table 3.1 shows the comparison between the three response curves with respect to their curve
36
characteristics. So, the final values for PID parameters were chosen as 3, 0.048 and 0
respectively.
Table 3.1:Comparison between response curves
Output at different conditions
Response Curve
Rising
time
Critically damped
Over-damped
Under-damped
3.5.3
21
Settling
time
Maximum
Overshoot
40
0
35
72
0
10
56
12
Implementation of multiple client-server communication
Multiple communications refers to a relation where more than one connection is present. In this
case, two client users are present and they communicate with a single server. Figure3.22 shows
the flow of data among the three users acting as clients and server. The server at first initiates the
request for data.
SERVER
CLIENT 2
CLIENT 1
Figure 3.22: Flow of data among 2 clients and a server
37
Figure 3.23 shows the front panel of server. The server sends the value of PV to client1 and waits
for value of SP from client 2.
Figure 3.23: Front Panel of Server
Figure 3.24: Front Panel of Client1
38
Figure 3.24 shows the front panel of client1. The client receives the value of PV from server and
then sends the value low limit to client 2. The function of client 1 is to decide the value for lower
limit of temperature band.
Figure 3.25: Front Panel of Client2
Figure 3.25 shows the front panel of client2. This client receives the value of lower limit from
client 1 and then sends the value set point to server. The function of client 2 is to decide the
value for upper limit of temperature band as well as the set point. The value of upper limit is
obtained by the following formula,
Upper limit= Lower limit + Dead band
(3.1)
On obtaining upper limit, the client has got both the limits and can decide the set point.
39
Chapter 4
Implementation of
TCP/IP
Internet Protocol
User Datagram Protocol
Transmission Control Protocol
Online Written Communication
Results and Discussion
4
IMPLEMENTATION OF TCP/IP
The two controllers are already described briefly in chapter 3. The algorithm and the basic
operations remain same as discussed earlier. This chapter deals with implementation of these two
controllers using TCP/IP.
4.1
Internet Protocol
The various tools for communication over networks are Internet Protocol (IP), User Datagram
Protocol (UDP), and Transmission Control Protocol (TCP). A datagram contains of data and a
header containing source and destination addresses. IP develops the path for the datagram to
transmit over the network and reach to the specified destination. IP is not reliable and provides
duplicity in transmission of data. A programmer usually prefers TCP or UDP over IP.
4.2
User Datagram Protocol
UDP provides simple, low-level communication between processes on computers. Processes
communicate by sending datagrams to a destination computer or port. A port is the location
where data has to be sent. IP handles the computer-to-computer delivery. Once the datagram
reaches the destination computer, UDP moves the datagram to its destination port. If the
destination port is not open, UDP discards the datagram. UDP shares all the delivery problems of
IP. UDP is used in applications where reliability is not critical.
4.3
Transmission Control Protocol
TCP/IP is an Internet Protocol (IP). The TCP part of the name refers to Transmission Control
Protocol. TCP/IP provides a reliable way of transmitting and receiving data over a network.
4.3.1
Using TCP connections in LabVIEW
In order to use TCP/IP the following steps have been followed in LabVIEW.
•
A TCP/IP Listen has been established. This is found on the Functions Communication
TCP palette. Figure 4.1 is the icon for the TCP/IP Listen.
41
Figure 4.1: TCP/IP Listen Icon

The TCP/IP Listen listens over the network for another computer trying to
connect over the port specified in the integer input at the left side of the
icon. That port number must be a number not used by other parts of the system,
and here port number 2055 has been used arbitrarily.

When the TCP/IP Listen hears another computer trying to connect over the
correct port, it establishes a Connection ID, and an Error Signal, and those outputs
are used in later TCP/IP vi blocks.

Another TCIP/IP Listen cannot be used with the same port number once the
connection has been established.
•
User can use either of the following vi(s).

TCP/IP Write - which writes data to the other computer over the network. Figure
4.2 is the icon.
Figure 4.2: TCP/IP Write Icon
 The TCP/IP Write uses the Connection ID, which it also passes to the next
vi, and the Error signal which it also passes to the next vi.
 The input is a string so it is necessary to convert it to a string.
 User can specify a timeout, and can get information on the number of
bytes written over the network with this vi.

TCP/IP Read - which reads bytes from the remote computer. Figure 4.3 is the
icon.

There are the usual inputs, the Connection ID and the Error Signal.
42

The integer input (blue line at left) is the number of bytes that the user
wants to read.

The output is the string composed of the bytes that are read.
Figure 4.3: TCP/IP Read Icon
4.3.2
Algorithm for using TCP/IP:
By convention, the “client” is the user that initiates the call and requests for information, and the
“server” is the user that answers the call and dispenses information. But this is a general not a
rule, the connection can work both ways.
Next target is to obtain the server’s IP number for the client. If it is a local area network
(LAN), the address is fixed as (192.168.xxx.xxx) and a constant is stored somewhere.
Following are the Vis found in a TCP palette:
•
TCP Open Connection
•
TCP Close Connection
•
TCP Write
•
TCP Read
•
TCP Create Listener
•
TCP Wait on Listener
For the client side,
•
In Client PC, TCP Open has been called with the IP Number, the port number that has
been connected with a suitable timeout.
•
For TCP Write, a string and Connection ID has been provided that is obtained from TCP
Open.
•
The SP that is in integer format has been converted to string by using typecast. TCP Read
has been called and is provided with the connection id (obtained from TCP Open), a
mode, and a number of bytes to read.
43
•
When transmission is over, TCP Close has been called to close the connections.
For the server side,
•
The TCP Create listener has been called and this provides a listener id. In a while loop;
TCP listener has been called using the listener id that is just obtained.
•
When a connection comes in, the listener becomes active, then the TCP Read and TCP
Write has been called.
•
When transmission is over, TCP Close has been called, and the loop is repeated, to wait
for another connection to come in.
4.3.3
Advantages of TCP/IP
•
Variable length messages allows clients to negotiate the transfer of information
•
Data that is transferred is buffered by receiver
•
Servers can be built where desired
4.3.4
•
Disadvantage of TCP/IP
At times it can be complicated to setup
TCP provides the most reliable data transmission and allows multiple and simultaneous
communications.
4.4 Online Written Communication
Chatting has been always done via internet but not in any software. LabVIEW offers the facility
to chat and communicate in software. Here the internet protocol helps in communication that is
TCP). The main objective is to show the various advantages of internet protocols in LabVIEW.
The advantages include communication like chatting, sending information, etc. Client and Server
are two users that communicate using TCP/IP for sending their data.
4.4.1
Algorithm for written communication
The following steps have been taken to send a single string.
44
•
At first, the length of the string has been found out.
•
The length of the string is a number, and that number is converted to a string so that it can
be sent further.
•
This length is sent to the user using a TCP/IP Write.
•
Then, the string is sent.
•
When the transmission is over, connection has been closed.
The following steps have been taken to receive a single string.
•
The first string received has the data for the string length of the string needed. The length
of the first string received has been assumed to be 2.
•
The length of the string is a string; it is converted to a integer and is used in the second
TCP/IP Read.
•
4.5
When transmission is over, connection has been closed using TCP/IP Close Connection.
Results and Discussion
The various simulation results of implementation of ON/OFF and PID controller using TCP/IP
are discussed in this section.
4.5.1
Implementation of ON/OFF controller using TCP/IP
The front panel of the ON/OFF controller server is shown in Figure 4.4 and the block diagram is
shown in Figure 4.5. In this case, the value of PV is greater than SP, the calculated error is
positive and hence the “fan OFF” indicator is turned ON. Since PV is less than the high limit, the
“within limits” indicator is turned ON while the rest two indicators remain OFF.
The TCP/IP icons can be seen in the block diagram. The port address is 2055 which is
given as input to the TCP OPEN CONNECTION in Client side and as input to TCP LISTEN
icon in Server side.
In this case, the value of PV is greater than SP, the calculated error is positive and hence
the “fan OFF” indicator is turned ON. Since PV is less than the high limit, the “within limits”
indicator is turned ON while the rest two indicators remain OFF. The TCP/IP icons can be seen
in the block diagram. The port address is 2055 which is given as input to the TCP OPEN
45
CONNECTION in Client side and as input to TCP LISTEN icon in Server side.
Figure 4.4: Front Panel of ON/OFF controller Server
Figure 4.5: Block Diagram of ON/OFF controller Client
4.5.2
Implementation of PID controller using TCP/IP
The front panel of the PID controller server using TCP protocol is shown in Figure 4.6 where the
46
set point is set to 60. The front panel of PID controller client is shown in Figure 4.7. In this case,
also the PV value is sent to the client and the client sets the SP. This is the manual tuning results
where the values of tuning parameters of PID controller,K C , Ti and Td has been tuned to 3, 0.048
and 0 respectively. It is clearly seen that the PV is controlled to its SP value with less time.
Figure 4.6: Front Panel of PID controller Server
Figure 4.7: Front Panel of PID controller Client
47
4.5.3
Implementation of online written communication
The front panel of communicating server is shown in Figure 4.8. The server on finding the value
of PV sends it to client by writing a message as “PV=50” in “Server Typing” box found in the
front panel. On pressing enter while running condition, this message can be seen in “Server’s
Message” which shows the message server typed. This message is sent to client with port
number 6342 and can be seen in “Server’s Reply” box. The next message sent by server is
“SP=?” and on pressing enter reaches client.
Figure 4.8: Front Panel of Communicating Server
The front panel of communicating client is shown in Figure 4.9. The client on receiving the
value of PV sends the value of SP to server by writing a message as “SP=60” in “Client Typing”
box found in the front panel. On pressing enter while running condition, this message can be
seen in “Client’s Message” which shows the message you typed. This message is sent to server
with port number 6342 and can be seen in “Client’s Reply” box.
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Figure 4.9: Front Panel of Communicating Client
49
Chapter 5
Conclusion
Limitation of the thesis
Scope for future research
5
CONCLUSION
The thesis shows the applications of internet protocols in LabVIEW, to control the temperature
of a heating body. The software has got wide applications in industries for various purposes
including generation of C and VHDL code. It is very easy to use since it provides blocks which
give a virtual existence of instrument. This chapter concludes the thesis, provides the limitations
and the future scope of the project. In chapter 3, algorithm for the two controllers has been
discussed. The implementation of these algorithms has been properly done and corresponding
simulation results has been obtained.
DataSocket is an extremely powerful way to transfer data and to create easy connections
between computers. The DataSocket Read and DataSocket Write VIs support various protocols
including DSTP, OPC, Lookout, HTTP, FTP and File retrieval. Through the use of front panel
Datasocket connections, a user can quickly and easily establish a connection to a data item. This
capability will improve the networking capabilities of many measurement and automation
applications. DataSocket is an easy-to-use, high-performance programming tool that is designed
specifically for sharing and publishing live data in measurement and automation applications
between different applications and between machines across the Internet. DataSocket for
LabVIEW simplifies live data exchange between different applications on one computer or
between computers connected through a network.
Although ON/OFF is a very cheap form of control, it is rarely used in process control
applications because of the oscillation which causes in the controlled and manipulated variables.
In a connected process these oscillations would propagate right through the system and causes
problems. The thesis brings the applications of LabVIEW to perform online operations. In
chapter 4, online written communication that is “Chatting” has been discussed.
5.1 Limitations of the Thesis
The limitations of the thesis can be the following:
•
The simulation results are obtained in software only, no hardware is involved.
•
New technology for controllers is not implemented.
•
Techniques like FTP, HTTP; etc which is now-a-days used for fast online transmission of
51
information is not implemented.
5.2 Scope for Future Research
A continuous development of new control algorithms insure that the time of PID controller has
not past and that this basic algorithm will have its part to play in process control in foreseeable
future. It can be expected that it will be a backbone of many complex control systems. The work
can be extended to following areas,
•
Implementation of hardware which would help in industrial application.
•
Controlling temperature by using fuzzy PID controller.
•
The application of TCP/IP can be extended to multiple accesses by client and server,
service tasks, etc.
The graphs obtained can be published in web browser using HTTP, can be sent from one user to
another by using FTP (File Transfer Protocol), e-mails, etc.
52
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55
Journals:
1.
DISSEMINATION
Abhyarthana Bisoyi and U. C. Pati, “Implementation of ON/OFF and PID controller
using TCP Protocol Based on Virtual Instrumentation”, Published for International
Journal of Advanced Computer Research, Mar. 2013.
2.
Abhyarthana Bisoyi and U. C. Pati, “Online Written Communication using Internet
Protocol based on Virtual Instrumentation”, Accepted for publication in Journal of
Instrument Society of India, Sep. 2013.
Conference:
1.
Abhyarthana Bisoyi and U. C. Pati, “Implementation of ON/OFF and PID controller
using TCP Protocol Based on Virtual Instrumentation”, Proceedings of International
Conference on Advance Computing and Communication, Ranchi, pp. 23-27, 16-17 Mar.
2013. (Published)
56

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