Lesson 7 - Process Control Mechanisms SAQ
This lesson allows you to test yourself on the material covered in the Process Control Mechanisms lesson and determine the level to which you have met the learning outcomes.
Suggested Response - Q4
** Consider the following figure showing a pressure control loop:
a) Is this an open or closed loop system?
b) Is the controller direct acting or reverse acting?
c) What are the issues with the PID loop and how would you improve it?
Response:
a) The system is closed loop, as the output signal responds to changes in the process variable and setpoint.
b) This controller is reverse acting as the output goes down as the process variable goes up.
c) With regards to the PID loop, there is much overshoot and oscillation, along with a large offset, which suggests this is proportional control only. The controller gain should be reduced, and a large integral term should be added by way of a low integral time constant. No derivative should be added as this is a pressure control loop and derivative action will add noise and potentially oscillations.