Exp. No.
: 2 Date: 08-01-
2025
LEVEL CONTROL TRAINER
AIM
To study the performance of different controller (Proportional controller)
APPARATUS REQUIRED
1. Process station
2. Data acquisition card
3. Process control software with PC
4. Path chords
5. compressor
THEORY
Two position control applied in a process station results in a continuous oscillation in
the quantity to be controlled. This drawback was overcome by a continuous action
which could be maintained by a continuous balance of the input and output. The
continuous control modes include proportional, derivative or integral control modes or
a combination of these modes.
PROPORTIONAL CONTROLLER
In this control mode, the actuating signal for the control action is proportional
to the error signal. The error signal being the difference between the set point and the
feedback signal. The output of this control mode can be represented as:
u(t)=Kp e(t) + u0
u(t)=controller output at any time
e(t)=actuating error signal
Kp= proportional gain between error and controller output
The range of errors to cover the 0% to 100% controller output is called the
proportional band.
LEVEL CONTROL
PROCEDURE
1. Ensure the availability of air and water.
2. Interface the PC with process station and check whether all the patching is
closed.
3. Switch on process station, water pump (by adjusting round knob), air input,
and PC and data acquisition card.
4. Maintain G pressure at 20 psi by adjusting air regulator knob.
5. Position HV1 valve in a partially opened mode and HV2 valve in a slightly
opened mode
6. Open process control software in PC and select ‘Trainer>>Level’.
7. Then select ‘control >>ONN-OFF
8. Then check the performance of P with different controller selection in
‘control’ menu.
9. Select Kp, Ki and Kd values by tuning process or trial and error method.
10. Save the optimum parameter values and process curves.
GRAPHS:
SET PARAMETER VALUES
Sl.No Controller type Set point KP KD KI
1 P 13 2 0 0
2 PD 13 2 1 0
3 PI 13 2 0 0.01
4 PID 13 2 1 0.01
5 ON/OFF 13 Differential gap: 2
RESULT
The performance of various controllers [P, PD, PI, PID and ON/OFF] controllers has
been studied by obtaining plots for PV (cm) [level] Vs. Time and C.P (%) [controller
response] Vs. Time for each controller respectively.
INFERENCE
● The graph between primary variable (PV1) & & time (s) the following
conclusions can be made:
● PROPORTIONAL CONTROLLER- Responds faster than PI & PID
Controller but lower than PD controller.
As the set point is 15 cm it is clearly observed that P controller has residual error in its
response and cannot eliminate the error effectively.
● PI CONTROLLER :
The response is slowest and initial the response reaches comparatively higher values
than the set point 15 cm and then gradually decreases and follows oscillatory path to
approach the set point.
The overshoot is higher compared to PD & PID controller.
● PD CONTROLLER →Relatively faster response.
→Never reaches the set-point value as it lacks integral action which helps to
eliminate steady state error but derivative action reduces overshoot.
● PID CONTROLLER:
Relatively faster response and the overshoot is minimum Steady state error is also
minimized .The steady state error elimination has facilitated it to reach the set point
value. Thus, it is the best response.
● ON/OFF CONTROLLER: It attains overshoot at higher value than set point &
then approaches set point in uniform sinusoidal response. These oscillations continues
thus it is undamped system .It works by switching on and off the controller completely
depending upon the error. Overshoot is higher and steady state error exists. Set point
value is never reached accurately.
