VS ERR

+_
S
VF

Pragna
MICRODESIGNS

INSTRUCTION AND OPERATION

MANUAL
FOR

PID CONTROLLER

Designed and Manufactured by:

PRAGNA MICRODESIGNS
No. 34, Karekallu, Kamakshipalya,
Basaveshwaranagar post, Bangalore – 560 079.
Ph: 23482492 Telefax: 23285123
E-mail: pragnamicrodesigns@yahoo.com
 CONTENTS

1. INTRODUCTION INTRODUCTION
2. DESCRIPTION OF THE UNIT
PID Controllers are Very often used in industrial process control to ensure that a
3. FRONT PANEL DETAILS
Parameter such as speed temperature flow etc is maintained to be a constant
4. EXPERIMENTS
desired value. P-I-D stands for Proportional Integral Derivative control, as the

controller uses all these in the feedback. One can also have P control, PI or PD

controllers depending on the requirement. All these are feedback controllers with

variable values for P, I and D.

To enable training of students in all these aspects, a PID controller with builtin set
point generation, controller and simulated process are provided for studying the
performance of the controller in closed loop.

1) PROPORTIONAL CONTROLLER:

A Proportional control feeds back a value proportional to the measured value, to

establish a constant value for the measured value of the parameter, against
incidental disturbances in a system.

The first stage of the controller error amplifier is a differential amplifier that
establishes the difference between the set value and the measured value. This error is
then amplifiers and feed back to control the parameter. This amplification is
proportional to P-Gain, a low gain means loose control and high gain means tight
control. Proportional controllers always have a finite steady state error.

Vs V s-Set voltage
Error =
1+G
2. INTEGRAL CONTROLLER:

The rate of change of the output from the integral controller is proportional to

the error.
dVo 1 Verror
= Ki Verror =
dt Ti
Ti is integral time constant. When there is a large error the controller output
changes rapidly to correct the error. As the error gets smaller, the controller
output changes more slowly as long as there is an error. The controller output will
continue to change. Once the error is zero, the output change also goes to zero.
This means the controller holds the output which eliminates the error. The
Transfer function of integral controller is Vout Ki
Verror S
The integral controller has very poor dynamic response.

3) DERIVATIVE CONTROLLER:

The output of the derivative controller is proportional to the Rate of change of

error. Vout = Kd =

The derivative controller responds to changes in error to overcome the process

inertia. It produces an output only for changes in error and hence it is mostly used

in combination with other type of controllers. Generally it is combined with PI

Controller to improve the dynamics of the process.

4) PROPORTIONAL + INTEGRAL CONTROL
This is one of the most popular forms of control, since in this case, the finite error is
=
always zero. However one has to ensure that proper P-and I gain are choosen,
appropriate for the delays encountered in the control.

With non optimised P and I the response may show an overshoot, or in certain cases,
the system may itself become unstable - oscillatory.
Proportional + Integral controller
D verror is an effort to combine the advantages of both

dtfrom proportional and error dimination from integral

good transient response

controller. The transfer function of PI - controller is ( Kc + Ki )

s
5) PROPERTINAL + DERIVATIVE CONTROL

In many P Controllers, the system delays might make the final response poor for a

step change in the set value. In these cases, one can resort to controlled derivative

feedback to improve the step response and dynamic performance of the loop.

6) P-I-D CONTROL

In P-I Controllers, derivative feedback may be employed to bring in stability of the

system or to improve the dynamic performance. All these are feedback controllers, with
variable values for P, I and D.
 DESCRIPTION OF THE UNIT
1. AIM : To Study the performance characteristics of an analog PID controller
using simulated systems.

2. CONTROLLER UNIT: This is a vary well designed unit to study the PID Controllers. This
unit consists of signal sources, a digital voltmeter, a PID controller, Different process
with builtin stabilized DC supply.

3. SIGNAL SOURCES : This part consists of variable low frequency square wave and
triangle wave generator with variable amplitude.
The square wave is used as command input to the system. The square wave is treated as repeated
step input. The triangular wave is used for external x-deflection in the CRO.

4. POWERSUPPLY AND DIGITAL VOLTMETER: This unit is with builtin

regulated power supply of +12V and –12V. A variable DC 0-12V is available on the panel
and be used as a dc input or set voltage. A 3 ½ digit digital voltmeter of + 19.99 volt is
provided on the panel to measure different steady state voltages like set voltage, feedback
voltage and output voltage.

5. ERROR DETECTOR : The error detector is a unity gain adder which adds the set
voltage with the feedback voltage.

6. INVERTING AMPLIFIER: It is unity gain inverting amplifier. This amplifier he

inserted in the loop, if required to ensure –ve or +ve
feedback. We can check the effect of +ve feedback.

7. CONTROLLER : The controller is an analog proportional - Integrate -Derivative

(PID) in which the PID parameters are adjustable. The values can
be set with in the following range through 10 turn calibrated
Potentiometers with dial.

Proportional Gain – Kc - 0 to 20
Integral gain - Ki - 0 - 1000
Derivative gain - Kd - 0-0.01

8. PROCESS : In practical the process or plant is the part of the

system which produces the descried response under
the influence of command signal.

In this unit the process is an analogue simulation of

Different blocks.
 PID CONTROLLER

FRONT PANEL DETAILS:

1. MAINS : Mains ON/OFF Switch with builtin indicator

2. SQUARE : Variable Square wave output – 0 – 2V

3. LEVEL : Potentiometer to vary the amplitude of square wave

and Triangle wave

4. FREQUENCY : Potentiometer to vary the frequency of square wave

and triangle wave

5. TRIANGLE : Triangle wave o/p for triggering purpose in x – y mode

6. AMPLITUDE : Potentiometer to vary the DC voltage from 0-12V

7. DC : Variable DC o/p – 0- 12V

8. GND : Ground Terminal.

9. DPM : 3 ½ digit DC Voltmeter to measure DC Voltage at

different points.

10. Vin : +ve input of error detector – Set voltage

11. Vf : -ve input of error detector – feedback voltage

12. Ve : Error Voltage

13. P : 10 turn potentiometer to vary the proportional gain

from 0 to 20 with indicating dial.

14. I : 10 turn potentiometer to vary the integral gain from

10 to 1000

15. D : 10 turn potentiometer to vary the derivative gain from 0 to 0.01

16. CONTROLLER : PID Controller with variable PID Parameters
17. ON/OFF : ON/OFF Switch for P, I, D individually.
18. + : Adder
19.INV AMP : Unity gain inverting amplifier to find the effect of
positive feed back
20. PROCESS
 First Order System : First order system with time constant of -3 msec.
 Second Order System : Second order system with time constant of ..5 msec.
ά : Damping factor can vary from 0 to 2 by varying R.
 Time Constant : 1 msec – suitable for – square wave input
 Integrator : 2 msec time with 180˚ phase shift.
 BLOCK DIAGRAM OF THE SYSTEM
COMMAND
COMMAND PROCESS OR RESPONSE
CONTROLL PLANT
ER RESPONSE
+
-

P I D CONTROLLER
P I D CONTROLLER

Kc

E(s) M(s)

Ki
+ - S +

SKd
 P I D CONTROLLER

LEVEL SQUARE

FREQUENCY TRIANGLE
CONTROLLER

AMPLITUDE DC

INV. AMP
MAINS

FRONT PANEL
 EXPERIMENTS

1) PROPORTIONAL CONTROLLER – OPEN LOOP :

Make the connections as given in the figure. Connect DC voltage of 0.5

volts to PID input. Connect feedback input to ground. Vary the proportional gain
pot. ( 10 turn pot with dial indicator) Total proportional gain is 20. So, 10
corresponds to gain 20 and 1 corresponds to gain – 2. Switch ON P Controller and
keep I and D controller at OFF position. Vary the proportional gain pot and note
down the output voltage and entered in an tabular column. Here, it works as simple
amplifier.

Sl.No Vin Gain Vout

1 0.4 1 0.37
2 0.4 2 0.78
3 0.4 5 2.02
4 0.4 7 2.84
5 0.4 10 4.08
6 0.4 15 6.14
7 0.4 20 8.21
 2) INTEGRAL CONTROLLER :- (Open Loop)

Make the connections as given in the circuit diagram. Connect a small voltage of
O.2Volts to the input. Connect feedback input to Ground. Switch OFF P and D
controller - switch ON I controller. Set t to some value and observe the output with
the digital voltmeter. We can observe that the output builds up as a ramp till it
reaches saturation voltage. We can also check this by connecting square wave of
small amplitude and we can observe a triangular wave at the output.

3) DERIVATIVE CONTROLLER (Open Loop):-

Make the connections as given in the circuit diagram. Connect DC Voltage to

input, connect feedback input to ground switch OFF PI controller and switch ON
D Controller. We can observe that the output changes only when input level keep
on changing. The output depends on rate of change of error voltage. This can be
observed by varying the input DC supply. We can also observe the derivative
controller by giving triangular wave as input. We can see the square wave at the
output.

4) PROPORTIONAL CONTROLLER – Closed Loop:-

Make the connections as given in the circuit diagram. Keep I and D controllers at
OFF position. Connect DC supply to Vin. Connect First order plant in the loop.
Note down Vin, Vf, Verror for different P - gain and entered in the tabular column.
We can observe that the error voltage = Vs
l+G

Check with the Theoretical value and the practical result.

TABLE

Sl.No P-Gain – Set voltage – Feedback Error Calculated

G Vs voltage – VF volter – Vs error
1 1 1 0.48 0.52 0.5
2 2 1 0.65 0.35 0.33
3 4 1 0.79 0.21 0.2
4 6 1 0.85 0.15 0.14
5 10 1 0.90 0.10 0.09
6 14 1 0.93 0.07 0.066
7 16 1 0.94 0.06 0.058
8 18 1 0.94 0.06 0.052
9 20 1 0.95 0.05 0.047
Next connect Second Order System in the loop. Repeat the experiment as above.
In this case note down time vis error and entered in the tabular column.and also
connect Square wave input and keep the Damping factor of Second order system
constant and observe the wave form at Vf by varying P-Gain.You can observe
that as the P-Gain

5) DRAW THE GRAPH OF TIME V/S. ERROR.

Sl.No T – sec Verror

Next Connect Integrator in the loop. Integrator has 1800 phase shift. When we
connected directly to the feedback input, then it works as positive feedback, now
the feedback added with the set voltage and the .error voltage will reach its
maximum. This is the effect of positive feedback on the closed loop system. To
make it -ve feedback connect integrator output to the Feedback input trough
inverting amplifier as shown in the figure. Since the plant itself is an integrator, the
error will be automatically zero, without I controller also.

6) INTEGRAL CONTROLLER:

Make the connections as given in the circuit diagram. Keep P and D controller at
Off position - connect DC supply to V in. Repeat the same procedure for first order
system, Second Order System and integrator we can observe that the system shows
zero offset error but very poor dynamic performance. Enter the results in the tabular
column.
7)PROPORTIONAL+INTEGRAL(PI)CONTROLLER:
Make the connections as given in the circuit diagram - Keep D Controller at
off position. Connect DC supply to Vin. Repeat the same procedure for first
Order System, Second Order System for different Values of P and I gain.
Enter the results in the tabular column.

8) PROPORTIONAL + INTEGRAL + DERIVATIVE CONTROLLER (PID) :

Make the connections as given in the circuit diagram connect DC supply to V in.
Repeat the same procedure for First Order Plant, Second Order Plant. Enter the
results with tabular column.

9) TESTING WITH CRO :

P-I-D Controller can also be tested with square wave input. And observe the
response on a regular CRO. For testing the PID controller for square wave
(Step input) connect time constant block only in the loop. Do not connect First
Order System, Second Order System and integrated in the loop, as there blocks
time constant is more compare to the time period of the square wave input. We
can also connect the CRO in X- Y mode and verify the results. Connect X-
input to triangle waveform and Y -input to feedback input - V F.

Draw the re" 'ts for P, PI, PID Controllers and for different P-I-D
gains.
PROPORTIONAL / INTEGRAL / CONTROLLER DERIVATIVE – OPEN LOOP
P I D CONTROLLER – CLOSED LOOP
PID CONTROLLER FOR SQUARE WAVE INPUT
P I D CONTROLLER FOR INTEGRATOR LOOP