Form factor and sensing principle
The XUM9APXBL2: This is a tubular background rejection photoelectric sensor from the Telemecanique XUM series, meaning the emitter and receiver sit in the same cylindrical housing and the sensor discriminates the target from the background by the angle of the returned light. The tubular form factor (M18 or similar barrel) suits machine guarding zones where a rectangular block would interfere with tooling or where the sensor must mount through a bracket hole rather than on a flat face.
Peer form-factor delta
The closest functional peers — XUK8TAE2MM12, XUK8TAE1MM12, and XUK8APSML02M12 — are block/rectangular background rejection sensors, not tubular. The sensing principle is the same (background rejection), but the XUK block housing requires a flat mounting surface and occupies more panel depth than the XUM9APXBL2 barrel.