Troubleshoot

Troubleshoot 4–20 mA Loop Field Diagnostic Walkthrough
⚠️ For authorized, trained personnel only. Improper handling of live electrical terminals can cause equipment damage, injury, or death. Follow your site’s safety procedures and lockout/tagout policy.

Step 1 — Check the Transmitter Display

Does the transmitter have a display, and is it showing something?

Tap an option above to continue.

Step 2 — Check the Terminals

Can you safely remove the cover and check the terminals? Only do this if you are trained, authorized, and it’s safe to do so.

Check a wire count above to continue.
Wiring Diagram
2-wire transmitter wiring diagram: Power Supply + and - to Transmitter + and - to PLC/DCS Analog In IN+ and IN-
Check a wire count above to see the matching wiring diagram.

Step 3 — Check Voltage

With the loop still powered, set your multimeter to DC Volts and measure directly across the two power terminals (meter leads in parallel with the terminals — no need to disconnect anything). Expect roughly 24V minus the wiring/device drop, or the value on your loop drawing.

If you read no voltage: check the power supply output, check the fuse or breaker feeding the loop, and check the terminals for a loose or corroded connection. A missing wire is the most common cause.

If voltage looks correct: the transmitter is getting power — move on to checking current below.

Step 4 — Check Current

Set your multimeter to DC mA. If your terminal block has a built-in test/disconnect jack, use that to insert the meter in series — that’s what it’s there for. Otherwise use a clamp-on mA meter so you don’t have to break the loop. Expect a steady reading between 4 and 20 mA.

If voltage is present but current is 0 or stuck: the transmitter itself may be faulted, there may be an open wire further down the loop, or the transmitter could be stuck in a fixed test/simulation mode — check its local configuration.

A fuller guided walkthrough for loops without test terminals is coming soon.