ISA Certified Control Systems Technician (CCST) Program

InTech, Jul 2004 by Sheble, Nicholas

CCST question

Dividing the density of the process fluid by the density of _____ gives a dimensionless number called specific gravity.

A. mercury or mercury vapors

B. oil or natural gas

C. water or air

D. any known liquid or gas

CCST answer

Specific gravity (SG) is the ratio of the density of a solid or liquid to the density of water at 4°C. It also refers to the ratio of the density of a gas to the density of dry air at standard temperature and pressure. This specification is seldom used. Specific gravity is a dimensionless quantity, which is to say it has no units as density does.

The utility of SG is that it translates into any system units-SI, CGS, or American Engineering. Standard materials and properties tables use SG, leaving the conversion to density to the individual user.

Water has a specific gravity equal to 1. Materials with a specific gravity less than 1 are less dense than water and therefore will float in water. Substances with a specific gravity greater than 1 are denser than water and will sink.

The correct answer is C.

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.

Nicholas Sheble writes and edits the CCST department. Contact him at nsheble@isa.org. For information about the CCST program, go to www.isa.org/ccst.>

Copyright Instrument Society of America Jul 2004

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