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P51PressureMeasurement-Slide4

Air weighs 14.7 psi at sea level which is defined as 1 atmosphere. Therefore, a psia unit will read 14.7 psia at sea level. At full vacuum it will read 0 psia. Both psis and psig units will read 0 psig at 1 atmosphere. Expanding on this example, using a 0 to 100 psia sensor with a 4 – 20 milli amp output, at 0 psia the transducer output will be 4 milli amps. At 100 psia, which is the same as 85.3 psig or psis, the transducer output will be 20 milli amps. A 100 psig or psis transducer is measuring the same full scale output pressure as a 114.7 psia transducer. There is an offset, or difference of 14.7 psi between psia and either psig or psis. In other words, 100 psig or psis is equal to 114.7 psia.

PTM Published on: 2011-01-24