Electrical Reference
4–20 mA Scaling
Convert loop current to engineering units with transparent math.
Map 4–20 mA linearly to the transmitter’s lower and upper range values.
Formula
- Percent span = (mA − 4) ÷ 16.
- Engineering value = lower range + percent span × (upper − lower).
Checks
- Confirm active/passive loop, supply polarity, burden, scaling endpoints, and units.
Common mistakes
- Dividing by 20 instead of the 16 mA span.
- Ignoring square-root extraction configured in a transmitter or control system.
Verify
- Check at 4, 12, and 20 mA and compare transmitter, loop indicator, and PLC/DCS values.