An electronic transmitter with an output of 4 – 20 mA is calibrated for a pressure range of 7 – 10 MPa(g). What pressure is represented by a 12 mA signal?
Solution
Signal Span or Span of transmitter 20 mA – 4 mA = 16 mA
Output Signal = 12 mA
Live Zero = 4 mA
Base Point = LRV of Range = 7
Process Span = URV -LRV = 10 – 7 = 3
Fraction of Measurement Change = 12 – 4 / 16 Â = 0.5
Actual Process Change = (Fractional Change) x (Process Span)
Actual Process Change = 0.5 x (10 – 7 MPa) = 1.5 MPa
Actual Process Value  = Base Point + Process Change
Actual Process Value = 7 + 1.5 MPa = 8.5 MPa(g)
Result :
Pressure at 12 mA is 8.5 MPag
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