This post was authored by Joel Don, ISA's social media community manager.

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.

The span, in inches of water, of a differential pressure transmitter used to measure the full level of a tank that is 5 feet, 6 inches 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
e) none of the above

Click Here to Reveal the 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 feet, 6 inches.

The height translates to 66 inches 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 0.9 the SG of water. Figure the correct answer by multiplying 0.9 times 66 to get 59.4.

The correct answer is B.

About the Author
Joel Don is the community manager for ISA and is an independent content marketing, social media and public relations consultant. Prior to his work in marketing and PR, Joel served as an editor for regional newspapers and national magazines throughout the U.S. He earned a master's degree from the Medill School at Northwestern University with a focus on science, engineering and biomedical marketing communications, and a bachelor of science degree from UC San Diego.

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