Calculate 4-20mA from Process Variable

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

Formula :

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

Where,

X is Process Variable

LRV is Lower Range value

URV is Upper Range Value

Example:

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