The Omron EESX951R1M is a transmissive photomicrosensor from the EE-SX95 series, built for through-beam detection of objects passing through a 5 mm gap. It uses an infrared LED light source and outputs an NPN open-collector signal, switching on either light or dark condition depending on the wiring configuration. Supply range is 5 to 24 VDC, and the output sinks up to 50 mA — enough to drive a PLC input or small relay directly.
The 5 mm sensing distance is the slot width — the object must break the beam inside that gap. This is a fixed-gap sensor, not a proximity type; alignment is mechanical, not electrical. The NPN output is common for Japanese-origin PLCs; if your input card expects a PNP signal (sourcing), you will need a level shifter or a different sensor. The infrared LED is invisible to the eye, so a test jig or a reflective card helps during commissioning.