F31118 — Encoder 1: Speed change not plausible

F31118 is raised by Encoder 1 when an HTL/TTL encoder delivers a speed change that is not plausible: the S120/S150 manual titles the code Encoder 1: Speed change not plausible, the G130/G150 manual the equivalent Encoder 1: Speed difference outside the tolerance range. In both cases the condition is the same — the measured speed change (difference) has exceeded the maximum value in p0492 over several sampling cycles. The change of the averaged speed actual value, where one exists, is monitored in the current controller sampling time. Encoder 1 is involved here in its role as motor encoder; for this case the manual notes that the fault response can be a changeover to encoderless operation. Depending on the drive configuration, the same condition can also be issued as an alarm (A) or with no reaction (N).

• For an HTL/TTL encoder, the speed change has exceeded the value in p0492 over several sampling cycles (the G130/G150 manual words the same condition as a speed difference outside the tolerance range in p0492).
• The change to the averaged speed actual value — if applicable — is monitored in the current controller sampling time.

1. Check the tachometer feeder cable for interruptions.
2. Check the grounding of the tachometer shielding.
3. If required, increase the maximum speed difference per sampling cycle in p0492.

• The drive stores the fault value in r0949; interpret it as a decimal number. The manual publishes no decoding — the value is intended only for internal Siemens troubleshooting.

• p0492 — maximum speed difference per sampling cycle: the threshold monitored by this fault; F31118 trips when the speed change of Encoder 1 exceeds this value over several sampling cycles, and the manual's remedy permits increasing it if required.
• p0491 — Motor encoder fault response ENCODER: cross-referenced for this fault; it sets the fault response that takes effect when Encoder 1 is used as motor encoder, including the changeover to encoderless operation mentioned for this code.
• r0949 — fault value: read the decimal fault value of F31118 here; per the manual it serves only internal Siemens troubleshooting.

F31118 is acknowledged once the drive has inhibited its pulses (pulse-inhibit acknowledgment); afterwards the drive can be restarted. When the same condition is configured as an alarm (A) or with no reaction (N), the manual specifies neither a reaction nor an acknowledgment.