How to Calculate 4-20mA current loop from Process Variable value of a field transmitter. Check the formula to find out equivalent 4-20mA signal from Process Variable.
Calculate 4-20mA from Process Variable
First calculate equivalent percentage from the process variable
Percentage = ( X – LRV / URV – LRV ) . 100
Then calculate equivalent 4-20mA signal from percentage
4-20mA = ( Percentage + 25 ) / 6.25
X is Process Variable
LRV is Lower Range value
URV is Upper Range Value
A Flow transmitter has a range of 0 to 2500 m3/hr and it is displaying flow rate of 1500 m3/hr. calculate the transmitter output current.
Process variable = 1500 m3/hr
Lower Range Value, LRV = 0 m3/hr
Upper Range Value, URV = 2500 m3/hr
Note: units must be same for process variable, LRV & URV
Percentage = (1 500 – 0 / 2500 – 0 ) . 100 = 60 %
4-20 mA Signal = (Percentage + 25) / 6.25 = (60 + 25) / 6.25 = 13.6 mA
Also you can use online Instrumentation Calculator for Automatic calculations. Click Here.