Lesson 8 - Process Control and Instrumentation End of Unit SAQ
This lesson allows you to test yourself on the material covered in the Process Control and Instrumentation unit and determine the level to which you have met the learning outcomes.
Suggested Response - Q4
*** What are the effects of increasing controller gain, integral time constant, and derivative time on P, PI, and PID controllers? Use diagrams to help explain this.
Response:
For P controllers, increasing controller gain will reduce offset and increase oscillations:
Figure: The effect of gain on proportional controller action and offset
For PI controllers, controller gain and integral time constant both have an influence. Increasing integral time constant reduces the effect of the integral term. Increasing controller gain will cause oscillations if the gain is taken too high. Integral time constant will have little effect if it is too high and could also cause oscillations if at too high a level. These two must be optimised together.
Figure: Relative effects of changing gain and integral time constant
Increasing derivative time can reduce the magnitude of the oscillations. However, it can also add to the noise of the process.
Figure: Effect of derivative time on controller action