01 February 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

A plant has a 30-foot-high water tank mounted on top of a 70-foot platform. What is the water level in the tank, measured in feet, if a pressure gage on the first floor, height 5 ft, reads 40 psi?

A. 22.3

B. 27.3

C. 30

D. 10


CCST answer

One has to be heads up on this problem. InTech initially thought all the platform heights and tank numbers and distances hither and yon were red herrings and that this was a straight conversion problem. However, 40 psi translates to 92.3 feet of water, which won't work in a 30-foot-high water tank and isn't one of the answer choices either.

This means that the 40 psi measurement did not transmit down to that five-foot level, but that there is an actual physical device and system stretching that distance from the bottom of the water tank to that point five off the ground, below the platform.

The correct answer is B. There's 92.3 feet of water, subtract the 70 feet of platform height, add the five feet above the floor where the meter measurement happens and one ends up with 27.3 feet.

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