September/October 2012

ISA Certified Control Systems Technician (CCST) program

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 loop diagram typically includes all of the information indicated below, except for:

A. Tag numbers of instruments connected to the loop as shown on the P&IDs and depicted by the loop diagram.

B. Conduit size and material in which the wires are run for the loop.

C. Wire numbers for all wires and terminal numbers for all connections depicted in the loop diagram.

D. Indication of the interrelation to other instrumentation loops, including overrides, interlocks, cascaded set points, shutdowns, and safety circuits.

CCST answer

The correct answer is B. Tag numbers (A), wire numbers and terminal numbers (C), and indication of the interrelation to other instrumentation loops (D) are three of the essential elements of a loop diagram. They define the "blueprint" for wiring of the components in the loop shown on the loop diagram. The size of the conduit and the material of the conduit (B) are not usually shown on the loop diagram because these items are generally not required for design review, installation, or maintenance.

Reference: Maintenance of Instruments and Systems, 2nd Edition, Goettsche, L.D. (Editor), (2005), ISA