Control system-lab

1
DEV BHOOMI INSTITUTE OF TECHNOLOGY
CHAKRATA ROAD,NAVGAOUN
MANDUWALA,UTTARAKHAND
Programs: B.TECH. (Electrical and Electronics Engineering)
CONTROL SYSTEMS LAB
Laboratory Manual
PREPARED BY
ASHISH KUKRETI,
ASST.PROFESSOR,
ELECTRICAL ENGINEERING DEPARTMENT

2
LIST OF EXPERIMENTS
CONTROL SYSTEMS LAB(EE332)
1. To study P, PI and PID temperature controller for an oven and compare their
performance.
2. To study and calibrate temperature using resistance temperature detector (RTD)
3. To study DC position control system
4. To study synchro-transmitter and receiver and obtain output V/S input characteristics
5. To determine speed-torque characteristics of an ac servomotor.
6. To study performance of servo voltage stabilizer at various loads using load bank.

3
Experiment No-1
Theory and Concept
Objective: To study P, PI and PID temperature controller for an oven and compare their
performance .
Apparatus : - Temperature measurement system
Solid-state relay for driving heater bulbs
Micro controller based control unit
LCD display
Theory: This set up is designed to demonstrate the working of a typical temperature controller
using PID mode of operation.
Proportional controller is a mode of control action in which there is a continuous linear
relationship between values of deviation and manipulated variable.
In order to remove the offset associated with proportional action , combination of P+I is widely used,
As a result of integral action, the offset error is almost reduced to zero but the transient response is
adversely affected.
A derivative control action may be added to proportional control to form P+D action. Derivative
control action may be defined as control action in which the magnitude of the manipulated variable
is proportional to the rate of change of error.
P+I+D action produces smallest maximum deviation and offset is eliminated because of integral
action. The derivative action provides improved transient response against load variations. In short
PID approach to control problem can be summarized in terms of
The mathematical equations governing the operation
A simple analysis would show that the derivative block essentially increase the damping ratio of the
system and therefore improves dynamic performance by reducing overshoot, the integral action
eliminates the steady state error. Representation of controller monitoring the plant:
Dev Bhoomi Institute Of Technology
Department of Electrical & Electronics Engineering
LABORATORY MANUAL
PRACTICAL INSTRUCTION SHEET
EXPERIMENT NO. 1 ISSUE NO. : ISSUE DATE:
REV. NO. : REV. DATE : PAGE: 3
LABORATORY Name & Code: PEE-652 control system Lab SEMESTER: VI

4
Ref input Temp
-
PID PLANT
CONTROLLER
Procedure:
For Proportional Control(P)
1. Keep SW3 in Test mode.
2. Keep SW2 in Mode Check
3. Then Keep KI=0 &KD=0, now system will be configured for proportional mode
4. Make proper connection for heater cable, RTD cable &fan cable.
5. Now select system as SW3 in TEST
SW2 in Normal
SW1 in PID side.
6. If selection is kept as above you will be able to set temperature with the help of P1. You will
see display as ST= AT=
7. Now select system as SW3 in START
SW2 in NORMAL
SW1 in PID
8. Now system will start in proportional mode
For P+I mode:
All procedure is same as described for proportional mode
Only at pt(3) keep KP>0, KI>0 &KD=0 then system will be configured for P+I mode.
For P+I+D mode:
All procedure is same as described for proportional mode.
Only at pt(3) keep KP>0, KI>0 &KD>0 then system will be configured for P+I+D mode.
NOTE: For Modes: You can take observation with fan load on/off or by varying fan speed for
creating disturbances on the system.
Fan provided acts as load on the system by taking more/less away from the modes

5
Observation:
Sl.
ACTUAL
TIME in
TEMPERATURE
No. Seconds
in Deg C
FlowChart:
Characteristic:
The Typical PID characteristic for different settings may be as follows

6
Temp set pt
Time
Result: Temperature of oven is controlled by using PID controller. By varying P,I,D values two
graphs of temperature vs time is plotted.
Discussion of Result:
1. The steady state error may be reduced by proper setting of Integral controller setting.
2. The transient state is improved by adjustment of Kp & Td.
3. For different settings of P I D different response Curves may be obtained.
4. The response Characteristics of P+I+D controller exhibit SECOND ORDER
CHARACTERISTIC.

7
Experiment No-2
Theory and Concept
Objective: To study and calibrate temperature using resistance temperature detector
(RTD).
Appratus required: RTD sensor,Thermistor,,Precisethermometer,Digital multi-meters .
Theory: Among the methods use to measure the temperature is utilizing the fact that for some
materials the electric resistance changes with the temperature. RTD stands for Resistance
Temperature Detector
in which the resistance of the RTD increases almost linearly with temperature. A good example
material which use extensively is platinum. For other materials such as semi-conductor, the
electric resistance inversely changes with the temperature. These materials are known as
Thermistors.
The basic relation for the electric resistance variation with temperature for RTD is given by
[1 ( )] RTD o o R = R +α T − T (1)
where
RRTD is the electric resistance of the RTD, [Ω]
Ro is the electric resistance of the RTD at the reference temperature To, [Ω]
T is the temperature, [°C]
To is the reference temperature, [°C]
α is the temperature coefficient of resistively, [1/°C]
Typical example of α for platinum is 0.00385 1/°C. Notice that the sensitivity coefficient for RTD
is given by
α RTD o K = R (2)
Again for typical platinum RTD, the sensitivity coefficient is bout 0.4 Ω/°C, which means that the
sensitivity is very small i.e. for 1°C change, the resistance changes by 0.4Ω . For this reason, in
order to measure the resistance RRTD correctly, Wheatstone bridge is use. A typical Wheatstone
bridge is shown on Figure 1 below.
LABORATORY MANUAL

8
The bridge is balanced when the voltage between the point A and B in figure 1 is null. This can be
achieved by changing the variable resistance R. When the bridge is balanced the four resistance
are related together by the following equation
Notice that if R1=R2, then RRTD=R.
It is to be noted that some RTD sensors come with three or four wire leads to reduce the effect of
self heating when measuring the RTD resistance. For our experiment since we have short leads,
the resistance RTD will be measured directly using a precise digital multi-meter.
The relationship on the other hand for the thermistor resistance with temperature is given by
where
RT is the thermistor resistance at temperature T, [Ω]
Ro is the resistance at the reference temperature To, [Ω]
T is the temperature at which the resistance is RT, [K]
To is the reference temperature, [K]
β is the material constant [1/K]
Unlike RTD there is no need to use Wheatstone bridge when measuring the resistance of the a
thermistor RT. Also to be noted that the variation of the thermistor resistance with temperature is
not linear as can be seen from equation 4.
In this experiment, the values of α, and β will be determined, along-with fundamental equations
similar to equations 1 and 4 above for RTD and the thermistor respectively.

9
Procedure
The experiment setup is shown in Figure 2 below. The temperature of the constant temperature
bath can be set to be any desire temperature as long as it is in the range of operation of the unit.
[For laboratory experimental bath such the one we have in our laboratory the operational
temperature range is between 10 and 80°C]. There is an indicator on the bath that shows the set
point temperature and the actual fluid temperature. The procedural steps for the experiment are:
1-Insert the RTD sensor and the thermistor sensor inside the constant temperature bath
2-Take the RTD leads (only two will be used) to the Digital multi-meter to measure the RTD
resistance, RRTD. Do the same thing for the thermistor to measure the thermistor resistance RT
using another digital multi-meter.
3-Turn on the constant temperature bath on. Set the liquid temperature to 10 °C.
4-When the liquid temperature reaches the set point temperature as indicated on the temperature
display, measure RRTD, and RT. In case a precise thermometer is available, insert it in the proper
hole on the top of the liquid bath and record also the thermometer reading when steady state
condition is prevailed. Record the measured data in Table 1 below.
5-Change the setup fluid temperature to another temperature and repeat step 4. It is recommended
to start with a temperature of 10°C, and increase T by 5°C each step for 7 to 8 readings.

10
Data Analysis
1-Plot the variation of RRTD/Ro with T-To. Let To be the lowest temperature [in our case To=10°
C].
For your information usually manufacturers take To=0°C at which R=Ro [Typically for platinum
Ro=100 Ω at 0 °C]
2-Use Trendline in Excel to curve fit the data, and find α (the temperature coefficient of
resistivity).
3-Calculate the uncertainty of the curve fit equation for the RTD
4-For the thermistor plot ln(RT/Ro) vs. (1/T-1/To). Again take To to be the lowest temperature you
have reached. Note that T and To must be in Kilven.
5-Use Tendline in Excel to find the curve fit equation for RT/Ro
6-Calculate the uncertainty for the curve fit of the thermistor
7-From the developed equation what is the value of β for this thermistor?
Additional requirements
1-What is the sensitivity of the RTD
2-Calaulcte the sensitivity of the thermistor at T=40°C
3-Do an internet search and fill table 2 to show the characteristics of different temperature measuring
Sensors.

12
Theory and Concept
OBJECTIVE: To study D.C position control system.
Apparatus: D.C position control system unit.
THEORY: The D.C Position control system is so called because the D.C signals exist in the system.
For example if the reference input and the controlled output are constant values a straight line can
graphically represent the actuating signal.
The signals in the other part of the system can be represented in the similar manner. For D.C voltage
controlled system, the actuating signal e [t]is a D.C voltage. In the simplest form the output position
and the reference position o1and 02 are measured and compared by a potentiometer pair whose
output voltage is proportional to error in the angular position. The error voltage is amplified and
applied to servomotor whose positions the load and the output potentiometer such that the error is
reduced to zero.
NEED FOR STABILIZATION
With switch SW1in open position and the step change in the input shaft, the output shaft exhibits an
oscillating behaviour. This happens because of the system elements, which are capable of storing
energy i.e. capacitance, inductance inertia of moving components like rotor, load, gear train etc. Once
the system is excited by change in the input signal, the various elements begin to store energy, even if
the error voltage falls to zero. The stored energy causes the output shaft to move in the same
direction. This creates an error of opposite polarity and the system is again instructed to work in the
opposite direction. In this way, energy storing elements tend to produce overshoots and undershoot in
the system. In the experimental setup, output Derivative Feedback is used for stabilization of the
output.
The Tachogenerator, which is coupled to the motor, generates an output voltage, which is
proportional to the rate of change of displacement. This voltage is coupled to the input of error
amplifier, either in the regenerative mode or degenerative mode.
By the adjustment of potentiometer P4ampunt of derivative feedback can be adjusted, while DPDT
switch is meant for selection of mode of stabilizing feedback.
HOW DERIVATIVE FEEDBACK WORKS
When switch SW1 is closed [i.e. inTACHO IN position] and the degenerative feedbacks are suitably
adjusted, we observe that the output shaft follows the input shaft in a smooth fashion without any
unwanted oscillations.
If the mode of feedback is regenerative, then the output never reaches the stable state. Instead it keeps
on oscillating around the desired position.
LABORATORY MANUAL

13
In short, for degenerative feedback, the damping factor of the system is decreased, thus resulting in
breaking action on the moving components, prior to their final desired position. For a greater amount
of feedback voltage, damping becomes excessive and the system exhibits a very sluggish response,
settles to a final position. The tendency for oscillations is found to be dependent on the amplifier gain
setting.
OPERATION WITH STABLIZING FEEDBACK
1. Now put the SW switch in lower position i.e. tacho in position, SW2 must be in downward position
i,e degenerative mode. Keep P4 in fully anticlockwise direction.
2. The system can be tested for operation as follows
3. Now take the pot P1to 180 position& effect the step input change in one of the directions, output
again indicates oscillations. Now advance the pot in P4 in clockwise direction and the output now is
observed to follow the input in a smooth fashion without oscillation. If the P4 pot is too much
advanced, the output now follow input in a sluggish fashion indicating over –damped system. Now
take the pot P1 to 180 positions.
4. Now put the switch SW2 in upward position i.e. regenerative mode. Now if the pot P1 is disturbed
the output pot P2 is found to oscillate continuously around the desired position. As the amount of
feedback is adjusted the frequency and the amplitude of output is observed to vary.
DO NOT OPERATE THE D.C POSITION CONTROL IN THE REGENERATIVE MODE FOR A
LONG TIME.
Block Diagram Of DC Position Control System:

14
Procedure:
1. Before switching on the main panel, see that the switches SW3, SW4 {on the LHS panel} are
in the downward position i.e. ON position.
2. Ensure that SW1&SW2are in the off position i.e upward position.
3. Keep the input position P1 in 10 positions
4. Potentiometer p3 [amplifier gain adjustment] should be in mid position.
5. Now switch on the main unit LED ‘Rand LED ‘G” should glow.
Operation without feedback [SW1in off position i.e. Tacho Out}
6. Now slowly advance the i/p potentiometer P1 in clockwise direction. The o/p potentiometer
along with load will be seen to be following the change in the i/p potentiometer.
7. When the i/p is disturbed the null indicator will be showing some indication but when the o/p
reaches desired positions, again the null indicator indicates almost zero. It may be noted that when i/p
POT is moved in anti-clockwise direction, the o/p POT also moves in the reverse direction.
Step change in input
8. Now change the i/p POT in a step fashion (in fact approximating step input). The output will be
observed to change in oscillatory mode.
Observations:
Plot the output angle v/s input angle for both the system i.e. without and with stabilizing feedback.

15
Precautions:
1. Please do not cross zero degree position by moving POT P1 i.e. do not operate between
350 deg and zero deg.
2. Do not try to rotate output POT by hand .this may damage the potentiometer
Result: The output angle v/s input angle characteristics for both the system i.e. without and with
stabilizing feedback are to be observed.
Discussion of the Result:
1. Student should be able to understand the effect of amplifier gain. Higher the gain, smaller
is the error.
2. Student should be able to understand the function of output potentiometer.

16
Theory and Concept
OBJECT: To study synchro-transmitter and receiver and obtain output V/S input
characteristics.
Apparatus : Synchro setup, Digital Multimeter, Connecting wires.
THEORY:
A synchro is an electromagnetic transducer commonly used to convert an angular position of a shaft
into an electrical signal. The basic synchro is called synchro transmitter. Its construction is
similar to that of three phase alternator. Let an A.C voltage Vr(t)= Vr sinwct (1)be applied to the rotor
of the synchro transmitter. This voltage causes a flow of magnetizing current in the rotor coil which
produces a the air gap along the stator periphery. Because of transformer action, voltages are induced
in each of the stator coils. As the air gap flux is sinusoid ally distributed, the linking any stator coil is
proportional to the cosine of the angle between rotor and stator coil axis. Let Vs1n, Vs2n,Vs3n
respectively be the voltages induced in the stator coils S1,S2,S3 with respect to the neutral.
Then with respect to the rotor position as shown in the fig[rotor makes an angle degrees with
stator S2]
Vs1n= Kvr Sin wct cos [ +120] …..(2)
Vs2n= Kvr Sin wct cos ( ……… (3)
Vs3n= Kvr Sin wct cos [ +240] …..(4)
Three terminal voltages of the stator are
Vs1s2= Vs1n-Vs2n
=3 KVr sin ( +240)sin wct….(5)
Vs2s3= Vs2n-Vs3n
=3 kvr sin ( +120)sin wct…..(6)
Vs3s1= Vs3n-Vs1n
=3 kvr sin ( )sin wct……….(7)
LABORATORY MANUAL

17
When =0 from equations 2 &3 it is seen that maximum voltage is induced in the stator coils S2
while it follows from equation [ 7 ] that the terminal voltage Vs3s1 is zero. The position of the rotor
is defined as ELECTRICAL ZERO.POSITION.
Schematic diagram of synchro transmitter

18
Procedure:
1. In this part of experiment, we can study, because of transformer action the angular position
of the rotor of synchro transmitter is transformed into unique set of stator voltage.
2. Connect the mains supply to the system with the help of cable provided, do not connect
any patch cords to the terminals marked S1, S2, and S3.
3. Switch on the main supply for the unit.
4. Starting from zero position, note down the voltages between stator winding terminals in
a sequential manner.
5. Enter the reading in the tabular form and plot the graph of rotor voltages of all the three
phase voltages.
Tabular column:
Expected graph.
Stator voltage

19
Theory and Concept
OBJECT:To determine speed-torque characteristics of an ac servomotor.
Apparatus: AC servomotor setup Multimeter connecting wires
THEORY: - A pair of precision servo potentiometers is working as an error detector. The
potentiometer marked as INPUT POTENTIOMETER translates information regarding the desired
angular position into a proportional A.C voltage. The potentiometer marked OUTPUT
POTENTIOMETER converts the information regarding the present position of mechanical load into
a proportional A.C voltage. Note that this pair of input And output potentiometers is excited by a 6
volts 50 Hz supply. {V {t}}.
Any difference of potential between the wiper contacts of servo potentiometer is amplified by means
of A.C power amplifier. The power amplifier output activates the control winding of the A.C
servomotor {2 phase}.The other is activated {reference winding} by means of fixed AC voltage. The
load to be positioned is coupled to the output shaft of the output servomotor and gear train
combination. The same shaft is also coupled to the output potentiometer.
This position control system works to make the output shaft position identical to the input shaft
position. When the output shaft is being positioned, the mechanical load is also moved to a new
desired position thus making error voltage always zero. The system works to make the error voltage
zero after disturbance.
Block diagram of A.C position Control System:
LABORATORY MANUAL

20
Procedure:-
1. Switch ON the AC main supply, Switches SW1, SW2 and SW3 should be in the ON position.
2. Observe that the input and output potentiometers come in alignment.
3. Keep the gain pot in almost in maximum gain position { Almost fully clockwise position}
4. Take the input potentiometer to the starting position i.e. very near to the zero position. The output
potentiometer will also follow the input potentiometer till the null indicator indicates null
position.
5. Enter the observations in the tabular column given below. You may repeat the observations with
lower amplifier gain, to observe that there is greater error, with higher gain {i.e. maximum gain}
you may note that the output pot indicates sustained oscillations.
6. You may use the test points black, TP1, TP2, TP3 a.TP1- Black- Excitation voltage for
potentiometer system.b.TP2-black –Variable point p otential for I/P pot.c.TP3- Black-variable
point potential for O/P pot. Note that EXCITATION point {TP1-black} for O/P pot is floating
with respect to the main ground.
7. Green terminal on the left hand side indicates main ground of the system. You may connect
C.R.O across the TP4 and ground {green terminal}, TP5and ground to observe the A.C
preamplifier output and servo amplifier output respectively.
8. Please note that the switches SW1 SW2 and SW3 are in series with A.C preamplifier, servo
amplifier output and at the input of the A.C servomotor reference and control winding
Observation:

21
Precautions:
1. If the Red LED is not glowing, check for the front panel fuse {D.C fuse}.If it blows again; do
not switch ON the unit.
2. The Switch SW3 is connected in series with A.C servomotor windings. The same may put in
OFF condition when the unit is not being used.
3. Do not try to rotate the o/p by means of the knob by hand.
Result- Ac position control is studied for various gains and it is observed that error is high for low
values of gain and error is less fo high values of gain.
Discussion of Result: This position Control system works to make the output shaft position
identical
to the input shaft position. When the output shaft is being positioned ,the mechanical load is also
moved to a new desired position thus making error voltage always zero.

22
Theory and Concept
OBJECT: To study performance of servo voltage stabilizer at various loads using load bank.
Appratus required: kit of servo voltage stabliser.
THEORY: Servo Voltage Stabilizer save the life of costly appliances, CNC machines, electrical
equipment, medical equipment’s, motors, lab equipment etc. by correcting the voltage fluctuations
in the incoming AC voltage and bringing and keeping it at the desired voltage levels. The principal of
operation of servo stabilizer The control circuit controls the servo motor. The motor is mechanically
attached to the arm of a continuously variable auto transformer which feeds to the primary of a
series control buck boost transformer. The stabilizer output voltage is compared with the reference
voltage & resultant error signal controls the servo motor which corrects the voltage by bringing it to
the preset voltage. Operating Instructions: A. MANUAL Operation: Put the control mode switch on
the front panel in the manual position, adjust the output voltage too the desired level with
RAISE/LOWER switch which rotates the motor that in turn adjusts the variable voltage transformer
in such a way as to give the desired output. Needless to say that this output voltage will change with
input variation. This has to be manually adjusted again to the desired voltage level in case of
fluctuating input supply voltage. The manual control has been basically provided to obtain
uninterrupted output voltage. even when control circuit develops a fault or is being replaced or
checked. B. AUTOMATIC Operation: Put the control mode switch in auto position to recheck
whether the input and output connections are properly made as described above. In auto mode the
unit is giving stable output as specified by automatic correction for input voltage or load
fluctuations.
LABORATORY MANUAL

23
Fig:Circuit diagram of Servo Voltage Stabilizer
PROCEDURE:
a) Connect the variable load with ammeter to the output of servo stabilizer.
b) Connect the input of servo stabilizer to the mains 220 volt, 50 hertz and adjust the output voltage
at 220 volt.
c) Now vary the load at steps to maximum load and record the output voltage and current and find
out the percentage load regulation.
CALCULATION:
RESULT: It is observed that the specified output voltage is almost remain same even if we increase
the load or there are fluctuations in the supply.

24
Precaution:
1. While studying the load characteristics the maximum current should not exceed the current
rating specified.
2. The output socket of the transformer must never get short circuited even momentarily.

Control system-lab

More Related Content

Similar to Control system-lab (20)

Recently uploaded (20)

Control system-lab