F270 / F437 Endress+Hauser — 4-20mA signal out of range (below 3.8mA or above 20.5mA)
At a glance
- Severity
- FAULT STOP
- Domain
- INSTRUMENTATION
- Reference standard
- NAMUR NE 43 / IEC 60770
- Product / context
- Current output failure — Proline / Cerabar
What it means
The 4-20mA analog transmitter is providing a signal outside the NAMUR NE 43 limits: current below 3.8mA (low fault indication) or above 20.5mA (high fault indication or saturation). The PLC or control system detects the value as out of range and triggers a diagnostic alarm. The associated process measurement is unreliable.
Probable causes
- Broken wiring or loose terminal in the 4-20mA loop (causes current <3.6mA or 0mA).
- Transmitter internally faulty (damaged output electronics).
- Insufficient loop supply voltage: voltage across the transmitter below the minimum required (typically 12-15V DC).
- Primary sensor faulty (e.g., load cell, pressure sensor, level probe) forcing the transmitter into saturation.
Reference values
| loop 4 20mA | {"live_zero":"4 mA = 0% of span","broken_wire":"< 3.6 mA","overrange":"> 21 mA","supply":"24 VDC ±10%","max_loop_resistance":"≈ 600 Ω with 12 V at the transmitter"} |
|---|
Where to start
Measure the loop current with a multimeter in series (or use the PLC mA function if available). Is the reading 0mA or very close to zero?
Full guided diagnosis in the app
The diagnostic tree for this fault has 9 guided steps with measurements, checks and resolutions. You'll find it in ElectraIQ, one of the four IndexOS apps: free, works offline.
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More Endress+Hauser codes
- F041 — PT100/PT1000 probe faulty (open circuit or short circuit)
- HART Comm Error — HART communication impossible (no response from transmitter)
- S140 / S141 — Noisy analog signal (electromagnetic interference)
- S972 / M972 — Transmitter out of calibration (offset or span error)