Siemens alarm F31118: Encoder 1: Speed difference outside the tolerance range

What it means

For HTL/TTL incremental encoders the speed derived from the pulse train changed faster than allowed across sampling cycles - the threshold is set in p0492. Physically this occurs when pulses drop out at speed (loose connection, marginal signals) making the computed speed jump, or genuinely during extreme accelerations. Check tacho/encoder cabling and grounding before raising p0492.

Likely causes

• interrupted or intermittently contacting encoder/tachometer cable
• poor shield grounding injecting noise into pulse lines
• p0492 threshold too tight for real dynamics
• failing encoder output stages dropping pulses

Replacement parts

We supply the following units for this alarm — tested, warranty-backed:

• 6FX2001-… encoder cable

  cable · Common cause

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