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4–20 mA scaling calculator

Scale a linear current-loop signal to engineering units, or find the current for a target engineering value.

01Inputs

Conversion direction

A label only; changing it does not convert values.

Engineering range
bar

bar

The 20 mA endpoint must be greater than the 4 mA endpoint.

mA

Nominal range: 4 to 20 mA, inclusive.

Result

Engineering value

— bar

Enter values and select Calculate.

Rounded to 6 decimal places; small and large values use scientific notation. Verify the unrounded calculation for your application.

Nominal linear scaling only. Out-of-range signals are rejected. This tool does not interpret fault currents or transmitter diagnostics.

Formula

E = L + ((I − 4) / 16) × (H − L)

I = 4 + ((E − L) / (H − L)) × 16

I = loop current in mA; E = engineering value; L = engineering value at 4 mA; H = engineering value at 20 mA. The current span is 16 mA. E, L and H use the same engineering unit.

Units

Enter current in milliamperes (mA), not amperes. Both engineering endpoints and the engineering input must use the selected unit. The unit selector changes the label only; it does not convert numerical values.

How it works

  1. Set the engineering values corresponding to 4 mA and 20 mA from the transmitter configuration.
  2. Choose a direction and enter either the measured current or the target engineering value.
  3. The calculator finds the fraction of the 16 mA span and maps it linearly to the engineering span, or applies the inverse.

Example: for a 0–200 psi transmitter, 4 mA = 0 psi, 12 mA = 100 psi, and 20 mA = 200 psi.

Reference

NI: How Can I Scale My 4-20mA Sensor Data? ↗

Two-point linear scaling; NI’s 0–200 psi example is used in the reference tests. Use your transmitter’s configured endpoints. Nonlinear and square-root extraction modes are outside this calculator’s scope.