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## AutoQuiz: How to Calculate Steady State Gain for a Standard Pneumatic Instrument Loop

The post AutoQuiz: How to Calculate Steady State Gain for a Standard Pneumatic Instrument Loop first appeared on the ISA Interchange blog site.

AutoQuiz is edited 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.

### You have a standard pneumatic instrument loop with a span of 200 units. What is the steady state gain?

a) 0.06 psig/unit
b) 0.07 psig/unit
c) 0.08 psig/unit
d) 0.12 psig/unit
e) none of the above

The correct answer is A, 0.06 psig/unit.

Gain is defined in control theory as the change in input divided by the change in output. In this case, the gain can be calculated as follows:

Gain = (full range change in input) / (full range change in output)

= (15 psig – 3 psig, for a pneumatic loop) / 200 units of change

= (15 – 3) / 200

= 12 / 200

= 0.06 psig/unit

Reference: Goettsche, L.D. (Editor), Maintenance of Instruments and Systems, 2nd Edition