4-20mA Formulas

As seen in the accompanying image, the voltage output of a 4–20 mA transmitter can be transformed to a specific range, from 0 to a maximal amplitude Vmax:

I [mA] = ( ( (V − Vmin) / ( Vmax − Vmin) ) × 16 ) + 4 (Voltage to Current)

V [Voltage] = ( (I − 4 ) / 16) × ( Vmax − Vmin ) + Vmin (Current to Voltage)

PV [units] = ( (I − 4 ) / 16) × ( PVmax − PVmin ) + PVmin (Current to Process Variable)

Where,

I is the current.
V is the voltage.
PV is the Process Variable.
min is the Lower Range Value of the respective signal.
max is the Upper Range Value of the respective signal.

Keep in mind that the min and max values and units must match.

For Voltage to Current, As an illustration, The output voltage of an analog output card is 3V, and its total range is 0–6V. Determine the corresponding 4–20 mA current value.

I = ( ( (V − Vmin) / ( Vmax − Vmin) ) × 16 ) + 4

I = ( ( (3 − 0) / ( 6 − 0) ) × 16 ) + 4

I = 12A

Reference : Instrumentationtools