This automation industry quiz question comes from the ISA Certified Control Systems Technician (CCST) program. Certified Control System Technicians calibrate, document, troubleshoot, and repair/replace instrumentation for systems that measure and control level, temperature, pressure, flow, and other process variables. Click this link for more information about the CCST program.
A controller is being tuned for a fast control loop. It has proportional action and the gain has been adjusted for a value by the technician.
As reset action is added to the loop, which of the following will need to take place?
The technician will need to:
a) add derivative
b) increase the gain
c) decrease the gain
d) increase the dead time
e) none of the above
Click Here to Reveal the Answer
The correct answer is C, decrease the gain. Both gain and reset (integral action) act upon the error in the same direction, per the simplified proportional, integral, derivative (PID) control algorithm:
= Gain Term + Integral Term
= Kc (E) + Kc · E(t) / Ti
If integral action is added, it is often necessary to reduce Kc, the gain, in order to keep the resulting tuning from being too aggressive.
Reference: Goettsche, L.D. (Editor), Maintenance of Instruments and Systems, 2nd Edition