AutoQuiz: How Do You Measure Tank Levels with Differential Pressure Transmitters?

AutoQuiz is edited by Joel Don, ISA’s social media community manager.

Today’s 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, AutoQuiz-tank-levels-differential-pressure-transmittersflow, and other process variables. Click this link for information about the CCST program. This question is from the Level I study guide, Domain 1, Calibration. Level I represents a professional who has a five-year total of education, training, and/or experience.

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.

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