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

A transmitter is calibrated for +40 to +140 inches of water for a level application. This is a ________ zero range.

A. suppressed
B. elevated
C. nominal
D. biased

CCST Answer

The correct answer is A,“suppressed.” If an instrument is mounted below a vessel, it senses a total head. This head includes the head developed by the distance from the instrument location to the bottom of the vessel and does not represent the true level in the vessel. The head due to the distance below the vessel must be compensated for by calibrating the transmitter using zero suppression techniques. This technique ensures the head due to the distance below the vessel is set as the zero point for the level measurement, thereby removing it from the determination of the actual level.

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