Instrumentation · Signal Conversion
4-20mA Calculator
Convert a 4-20 mA transmitter current to engineering units, or an engineering-unit process value back to milliamps — with NAMUR NE43 fault-zone checking on every result.
IEC 60381-1 · NAMUR NE43
Worked example
A pressure transmitter is ranged 0–10 barg. The DCS shows a loop reading of 14.4 mA. What is the actual process pressure?
EU = 0 + ((14.4 − 4) / 16) × (10 − 0) = 6.5 barg (65% of span)
The form above is pre-filled with these exact numbers — press Calculate to reproduce this result, or change the inputs for your own loop.
Frequently asked questions
What is the 4-20 mA current loop standard?
IEC 60381-1 defines 4-20 mA as the standard analog transmission range for process instrumentation. 4 mA represents 0% of the measured range and 20 mA represents 100%. Current, not voltage, is transmitted because current stays constant along a wire regardless of cable resistance or run length, so a receiver 1 km away reads the same value as one sitting next to the transmitter.
How do I convert a 4-20 mA signal to engineering units?
Subtract 4 from the current reading, divide by 16 (the span of the signal), multiply by the engineering-unit span (range max minus range min), then add the range min. This calculator does that math for you and also checks the reading against NAMUR NE43 fault zones.
What do NAMUR NE43 fault zones mean?
NAMUR NE43 reserves the area just outside 4-20 mA for diagnostics: below 3.6 mA or above 21 mA signals a failed transmitter or broken wiring, while 3.6-4.0 mA and 20-21 mA flag a fault condition such as an out-of-range process value. A healthy loop stays within 4-20 mA at all times.
Why is current used instead of voltage for transmitter signals?
Voltage drops along a cable in proportion to its resistance, so a receiver far from the transmitter would see a different voltage than one nearby. A current loop forces the same current through every point in the series circuit, so cable length and resistance do not affect the reading at the receiving end (within the loop's voltage budget).
Can this calculator convert engineering units back to milliamps?
Yes. Switch the direction selector to "Engineering Units → mA", enter the process value and the range, and the calculator returns the corresponding loop current. The value must fall within the range min and max to produce a valid current output.