Wire break / Overrange flicker Siemens — Noisy analog signal (electromagnetic interference)
At a glance
- Severity
- DEGRADED
- Domain
- INSTRUMENTATION
- Reference standard
- IEC 61326-1 / NAMUR NE 21
- Product / context
- Unstable signal on AI module — ET 200SP / S7-1500
What it means
The 4-20mA or 0-10V analog signal exhibits oscillations, spikes, or noise superimposed on the actual measurement. The PLC reading is unstable, with rapid variations that do not correspond to the process dynamics. Noise can cause false alarms, control loop oscillations, and unreliable readings.
Probable causes
- Signal cables routed in parallel with power cables (motors, VFDs, heating resistors) without adequate separation.
- Signal cable shielding missing or shield not grounded (or grounded on both sides creating a ground loop).
- VFDs or drives nearby generating conducted and radiated high-frequency interference.
- Plant grounding not equipotential: potential difference between panel ground and field ground.
Where to start
Disconnect the signal cable from the transmitter and connect a 4-20mA calibrator in place of the transmitter. Is the signal read by the PLC now stable?
Full guided diagnosis in the app
The diagnostic tree for this fault has 7 guided steps with measurements, checks and resolutions. You'll find it in ElectraIQ, one of the five IndexOS apps: free, works offline.
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The same fault on other brands
More Siemens codes
- 0xE900 / 0xE901 — IO-Link communication lost (device not responding)
- HART: No Reply — HART communication impossible (no response from transmitter)
- 6EP1333-4BA00 — Unstable PLC power supply — cyclic restarts
- 6ES7521-1BL00-0AB0 — Digital input module — input not reading (stuck at 0)
- 6ES7522-1BL01-0AB0 — Digital output module — output not activating
- 6ES7531-7KF00-0AB0 — Analog input module — full-scale reading or error
- ANSI 50/51 — Overcurrent Protection 50/51 Trip
- COMM LOSS — Supervision Network Loss