Siemens alarm 20002: [Channel %1: ] Axis %2 zero mark not found

What it means

The reference cam was found correctly, but no encoder zero mark occurred inside the search window that follows the cam edge. The axis stops and remains unreferenced until the measuring system delivers a plausible reference pulse.

Likely causes

• contaminated or damaged encoder scale/disc so the zero-mark track fails
• zero-mark search window (MD 34080 REFP_MOVE_PLUS/_MINUS area) too small
• incremental encoder configured although distance-coded/absolute behavior expected
• encoder cable shielding or connection intermittent
• encoder electronics marginal, especially at higher traverse speeds

Replacement parts

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

• 6FX2001 series motor encoder (EnDat/incremental)

  encoder · Common cause

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• 6FX5002 series encoder signal cable

  cable · Common cause

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