BEI Industrial KH25D‑SS‑1000‑ABZC‑28V/V‑SM18 (part 01002‑8291) is an optical incremental rotary encoder used in servo drive and motor control systems, offering 1000 ppr with a heavy‑duty cast‑metal housing and IP66 sealing. Common failure modes for this class include loss of signal due to broken optical tracks or misalignment, contact degradation on the 2.5″ flange mount, and electrical shorts from damaged wiring harnesses. First‑check diagnostics: verify that the supply voltage (28 VDC) is within spec and stable; inspect the encoder shaft and housing for mechanical damage or contamination; confirm that all signal leads are intact and properly terminated, then review any error codes from the host drive for missing quadrature pulses or index errors.[oss-gpt-20b]