ISA Certified Control Systems Technician (CCST) program

CCST

Certified Control System Technicians (CCSTs) calibrate, document, troubleshoot, and repair/replace instrumentation for systems that measure and control level, temperature, pressure, flow, and other process variables.

CCST question

Which of the following is a valid form of the PID algorithm?

A. Proportional and derivative modes on error, integral on measurement
B. Proportional and integral modes on measurement, derivative on error
C. Proportional, integral, and derivative modes on error
D. Proportional, integral, and derivative modes on measurement

CCST Answer

The correct answer is C, “Proportional, integral, and derivative modes on error.”

The standard PID algorithm is configured so that each of the three terms operates on the error (SP – PV). Proportional and derivative actions can also be configured to operate on PV (measurement), but not integral. Integral requires a reference against which to integrate (i.e., SP as a reference, and error as the quantity over which to integrate).

Answers A, B, and D all include “integral on measurement,” and therefore are not valid forms of the PID algorithm.

Reference: Goettsche, L.D. (Editor), Maintenance of Instruments and Systems, Second Edition, ISA, 2005.