NAMUR NE 43 and NE 107 are both recommendations from NAMUR, the process-industry user association, and both deal with a field device telling the control system something is wrong. They work on different layers. NE 43 is an analog convention: on a 4-20 mA loop, a current below 3.6 mA or above 21 mA is failure information, not a measurement, so a dead or faulted transmitter is detectable from the wire alone. NE 107 is a diagnostics classification: whatever a smart device's internal diagnostics find is mapped to four standardized status signals, delivered over the digital layer and shown as standard symbols on the host. One guards the signal. The other grades the device's health.
Key takeaways
- NE 43 defines fault currents on the analog 4-20 mA layer: below 3.6 mA or above 21 mA means fault, never measurement.
- NE 107 defines four device status signals: Failure, Function Check, Out of Specification, Maintenance Required.
- NE 43 needs no digital communication. NE 107 needs a digital path, HART or a fieldbus, and a host that supports it.
- NE 43 enable is a per-loop fact for the I/O list. NE 107 routing is an alarm-philosophy and maintenance decision.
- The two are complementary, and a modern smart transmitter is normally configured for both.
NE 43 in one paragraph
NE 43 turns the live zero of the 4-20 mA signal into a fault detector. A healthy transmitter never drives outside 3.8 to 20.5 mA, so a defined fault current, commonly 3.6 mA low or 21 mA or more high, cannot be confused with a reading. The input card recognizes the out-of-band current, takes the value out of control, and raises an instrument-fault alarm instead of feeding a false measurement to the controller. The classic failure it prevents: a level transmitter loses power, the card would otherwise read bottom of scale, and the controller would fill the vessel.
NE 107 in one paragraph
NE 107 answers a different question: not "is the signal valid right now" but "how healthy is the device." Smart transmitters run internal diagnostics, and every vendor's diagnostics differ. NE 107 makes the result usable by mapping all of it to four standardized status signals with fixed symbols, so an operator or maintenance tech sees the same four states regardless of brand. The status travels over HART or a fieldbus into the DCS and the plant asset-management system, where it drives maintenance prioritization under the plant's alarm management regime rather than a trip.
| NE 107 status | Meaning |
|---|---|
| Failure | Output invalid, the device or its sensor has failed |
| Function Check | Output temporarily invalid, work in progress on the device |
| Out of Specification | Operating outside specified conditions, measurement uncertain |
| Maintenance Required | Output still valid, wear reserve nearly exhausted |
Side by side
| Aspect | NE 43 | NE 107 |
|---|---|---|
| Layer | Analog 4-20 mA current | Digital diagnostics, HART or fieldbus |
| What it signals | Signal invalid, hard fault on the loop | Graded device health, four categories |
| Needs digital comms | No | Yes |
| Where configured | Transmitter fault-current setting plus AI card | Device diagnostics mapping plus host and asset management |
| Typical response | Instrument-fault alarm, value out of control | Maintenance action, prioritized by category |
How they pair on one loop
On a well-configured loop the two recommendations divide the work. NE 43 is the floor: even if the digital layer is down or the host ignores HART, a hard failure still announces itself on the current. NE 107 is the early warning: a transmitter drifting toward its wear limit reports Maintenance Required weeks before it ever drives a fault current. The failure modes meet in the middle, and the loop specification should say how, which is the same per-loop discipline that decides everything else on the I/O list.