Convert an analog signal between milliamps/volts, engineering units, and PLC raw counts — in any direction.
A transmitter sends a 4-20 mA signal that represents a process value across its range. Your analog input card converts that current to raw counts, and your PLC program scales those counts to engineering units with a linear equation. This calculator runs that math in any direction.
Engineering value = EUmin + (raw − rawmin) × (EUmax − EUmin) / (rawmax − rawmin). Most platforms also provide a scaling instruction — Allen-Bradley SCP/SCL, Siemens NORM_X/SCALE_X — covered in our analog input scaling guide.
The signal starts at 4 mA, not 0, so the PLC can tell a real 0% reading from a broken wire (which reads 0 mA). That "live zero" is the heart of the 4-20mA current loop — and the reason analog wiring is so reliable on the plant floor.
Free PLC simulator
This is the math your PLC does every scan. Learn to wire and scale a 4-20mA loop, then practice the ladder and Structured Text free in your browser.