For a pneumatic transmission system for instrumentation purposes, if a pneumatic pressure indicator has a calibrated scale of 0 to 1000 psig, what would be the actual measured pressure if the transmitted pneumatic signal pressure to the indicator is 9 psig, assuming the industry standard of 3 to 15 psig is used for instrument air?

Question

Accepted Answer

Option B: 500 psig. Using the 3-15 psig standard, the signal span is 12 psig. A 9 psig signal represents 50% of the span ( (9-3)/(15-3) = 0.5 ). Applying this to a 0-1000 psig range, 50% of the full scale equals 500 psig, which is the measured process pressure.