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TEMPERATURE CONTROL SYSTEM

Objectives:

To design PID controller based on Open loop method and to apply it on a temperature control

system.

Block Diagram:

Specifications:

Temperature sensor:

Type RTD PT-100

Mounting BSP

Temperature transmitter:

Type RTD PT-100

Output 0-5V DC

Range 0-1000C

Process tank:

Capacity 0.5 lit

Material SS 304

SP

Flow meter

TT

Input flow

Thyristor

Heater

Controller

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Heater:

Capacity 1.5 KW

Rotameter:

Range 100 LPH

Make Eureka

Overall size: 500L 700D 500H

Weight(approximate): 30 Kg

Control panel: All extruded with switches, power supply, indicators make presidents.

ADC/DAC card: 12 bit resolution

Software: for experimentation, PID control, data logging, trend plot, offline analysis and

pricing

Theory:

In the reaction curve method of controller design, one needs to open the control loop just

before the final control element and create a small sudden step change in process input. From

the shape of the resulting reaction curve obtained, the controller parameters are calculated by

simple equations. From the curve, Slope (R) and Dead time (L) are calculated. Where R is the

slope of line drawn tangent to the point of inflection and L is the time between the step change

and the point where tangent line crosses the initial value of the controlled variable.

Procedure:

Condition the equipment, set the water flow to the apparatus as 40 LPH by using

rotameter control.

Switch on the control module and switch on the computer also.

Open the temperature control trainer, select suitable port and start the process.

Select the control (Open loop)

The controller mode is selected as manual mode

Log on and enter the filename

Change the output (give a step change) by changing the corresponding field.

Press F3 key to display the trend.

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Wait till steady state conditions achieved

Press F6 key to record the process response values on time basis in computer in present

file

Give a step change to process by changing the output (by say 30-40% which is taken as

P) by using the following keys

For 10% change Page up or Page down

For 1% change + or -

For 0.1% change Insert or Delete

After the process value becomes steady, press F6 key to stop the data logging in

computer

Come out from the online mode.

Now, choose offline mode, open the file in which the data is stored. Press F4 key to see

the table.

Plot the graph of Process variable Vs time.

Find out the slope of the tangent drawn at the point of inflection and find the value of

dead time also.

Process reaction curve method suggests the following values for PID parameters using R,

L and P. (P is the step change applied in % i.e. initial output-final output of the

controller)

Mode Proportional Integral Derivative

P 100 RL/P

P+I 110 RL/P 0.3/L

P+I+D 83 RL/P 0.5/L 0.5L

Select the controller in the PID mode and the control in closed loop and check the

process response for a step change in the set point.

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Observations:

Tabulate the experimental values as shown below. Take the readings till the process variable

settles to a finite a value (in a band).

Calculations:

The dead time and the slope of the tangent are found out. The values are

Dead time, L =

Slope of tangent, R =

Process output change, P =

Model Graph:

Sl. No. Time Process variable

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Summary and Conclusions:

PID controller settings are calculated based on open loop data. The controller is loaded with the

PID values and the process is run with a step change in the set point. It is seen that the process

variable tracks the set point.