4–20 mA Pressure Signal Scaling

Translate a linear 4–20 mA pressure transmitter reading to its configured kPa range.

How this calculation works

A linear 4–20 mA transmitter maps its lower configured pressure to 4 mA and its upper pressure to 20 mA. Enter the measured loop current and both calibrated endpoint pressures in kPa. The calculator removes the 4 mA offset, divides by the 16 mA signal span and applies that fraction to the pressure range. It reports both pressure and percentage of transmitter span. Endpoint pressures must use the same gauge or absolute reference, and the upper endpoint must exceed the lower one. Currents outside the calibrated interval are extrapolated and flagged because they may indicate a fault rather than a valid measurement. Manufacturer-specific fault codes and nonlinear or square-root signal processing are not interpreted by this linear conversion.

Inputs and units

Measured loop current (mA)
Pressure at 4 mA (kPa)
Pressure at 20 mA (kPa)

Method and formula

Fraction of span = (I in mA − 4)/16; pressure = P4mA + fraction × (P20mA − P4mA).

Worked example

Example inputs

Measured loop current: 12 mA
Pressure at 4 mA: 0 kPa
Pressure at 20 mA: 1000 kPa

Calculation steps

Remove the live-zero offset and divide by signal span: fraction = (12 − 4)/(20 − 4) = 8/16 = 0.5.
Apply the pressure range: pressure = 0 + 0.5 × (1000 − 0) = 500 kPa.
Express the reading as percentage of span: 100 × 0.5 = 50%.

Example results

Scaled pressure: 500 kPa
Transmitter span reading: 50 %

Assumptions

Linear increasing pressure transmitter; endpoint pressures use the same gauge or absolute reference

Limitations

Does not interpret manufacturer-specific fault currents or nonlinear/square-root extraction
Extrapolated values are not reliable measurements

Sources

NI: How Can I Scale My 4–20 mA Sensor Data?: Two-point linear conversion and 4/20 mA endpoints