1 April 2005

ISA Certified Control Systems Technician (CCST) Program

This question is from the Level I study guide, Domain 1, Calibration.

Level l represents a professional who has a 5-year total of education, training, and/or experience.

CCST question

The span, in inches of water, of a differential pressure transmitter used to measure the full level of a tank that is 5 ft, 6 in high and contains a process material with a specific gravity of 0.9 should be:

A. 73.3

B. 59.4

C. 66.0

D. 5.6

CCST answer

First, recall the definition of span, which is the algebraic difference between the upper and lower range values. In this problem, that difference is the height of the tank, or 5 ft, 6 in.

The height translates to 66 in of water. The process material, however, has a different density than water, and therefore its specific gravity is different too. The specific gravity of a liquid is the density of that liquid compared to the density of water.

The problem says the material has .9 the SG of water. Figure the correct answer by multiplying .9 times 66 to get 59.4, answer B.

Nicholas Sheble (nsheble@isa.org) explains the answers to CCST questions. For information about the CCST program, go to www.isa.org/ccst.