F33118 — Encoder 3: Speed change not plausible

F33118 is an Encoder 3 monitoring fault: for an HTL/TTL encoder, the drive has established that the speed change exceeds the tolerance in p0492 over several sampling cycles. The S120/S150 manual titles the message Encoder 3: Speed change not plausible, while the G130/G150 manual titles it Encoder 3: Speed difference outside the tolerance range; both describe the same condition. Where an averaged speed actual value is used, the drive additionally monitors the change of this averaged value within the current controller sampling time. 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 of Encoder 3 has exceeded the value in p0492 over several sampling cycles.
• Where an averaged speed actual value exists, the drive also monitors the change of this averaged value 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, to be interpreted as a decimal number. Per the manual, this value is only for internal Siemens troubleshooting; no decoding is published.

• p0492 — square-wave encoder max. velocity difference per sampling cycle: the tolerance whose exceedance raises F33118 on Encoder 3; the remedy is to increase it if required.
• r0949 — fault value: where the drive places the fault value of F33118, to be interpreted as a decimal number.

The fault is acknowledged with pulse inhibit; once the cause has been remedied and the fault acknowledged, the drive can be restarted. When the drive is configured to issue the same condition as an alarm or with no reaction, neither a reaction nor an acknowledgement applies.