Glossary · 4-20 mA
What is 4-20 mA signal?
The most widely used analogue signal in industrial measurement: 4 mA is the bottom of the range and 20 mA the top, and current, unlike voltage, is not affected by cable length.
Starting at 4 rather than zero lets you detect a broken wire (0 mA) and power the transmitter from the same loop. NAMUR NE43 treats below 3.6 mA or above 21 mA as a failure signal.
Scaling is linear: value = LRV + span × (mA − 4) / 16. Use the 4-20 mA calculator in the workshop.
Related terms
- HART protocol
- A digital protocol carried on top of the 4-20 mA signal itself, allowing transmitter configuration, reading and diagnostics without interrupting the analogue measurement.
- Intrinsic safety (Ex i)
- A protection concept that limits the electrical energy in a circuit so it cannot produce an igniting spark or heat, even under fault conditions.
- Programmable logic controller (PLC)
- An industrial computer built to control machines and processes: it reads sensors and switches, runs the control program, and drives motors and valves, repeatedly and reliably.