Finding process variable from 4-20 mA signal using Fraction measurement
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Finding process variable from 4-20 mA
We will explain this by solving one question here.
Q# If the pressure range of process variable is 5-10 bar of transmitter and having electronics signal 4-20 mA. What will be pressure if current 14 mA?
There is few steps to follow
Signal span = 20 mA – 4 mA = 16 mA
Process Span= 10 bar – 5 bar = 5 bar
Live zero = 4 mA
Output signal = 14 mA
1) Finding fraction of measurement
Fraction change signal= (output signal-live zero) / signal span
= (14-4)/16= 0.63
2) Actual process change = fractional change × process span
= 0.63×5= 3.15
3) Actual process value = actual process change + initial value of process
= 3.15+5= 8.15 bar
This will be the output pressure when current signal is 14 mA.