FUSION AUTOMATE TOOLS / AUTOMATION TOOLS

4–20 mA Loop Calculator

Check available loop voltage and transmitter headroom. Fast, browser-local and free to use.

A 4–20 mA loop needs enough voltage for the transmitter after the PLC input, cable, and any barrier have taken their voltage drop. This check uses the worst case: 20 mA.

Loop supply voltage (V)Transmitter minimum operating voltage (V)PLC analog input burden (Ω)Barrier / isolator burden (Ω)Total cable resistance, out + return (Ω)

PLC burden: find this in the analog-input datasheet; 250 Ω is common for a 1–5 V input.

Cable resistance: include both wires. At 20 mA, every 100 Ω causes a 2 V drop.

Total loop burden

270 Ω

PLC + barrier + cable

Voltage drop at 20 mA

5.4 V

Burden × 0.020 A

Voltage at transmitter

18.6 V

Supply − loop drop

Voltage headroom

6.6 V

Available − transmitter minimum

Loop status

OPERATES

Transmitter has enough operating voltage.

The loop has 6.6 V spare voltage at 20 mA.