Integrator's first pass on the part
The Square D / Telemecanique XU2S18PP340D is an 18 mm threaded tubular thru-beam photoelectric sensor in the XU2 series, designed to pair an emitter and a receiver across a sensing distance of 8 m on a 12 to 24 VDC supply. It carries a 1 millisecond response and a 500 Hz switching frequency, which is the bandwidth ceiling the receiver will hold on a high-speed conveyor or indexing table before the output starts to miss transitions. Output is PNP (light/dark selectable) into a maximum load current rated for typical 4-wire DC sensor service, terminated through an M12 4-pin DC micro male connector — the standard drop-in wiring pattern on most PLC digital input cards. The body is nickel-plated brass, threaded M18, sealed to IP67 with a PMMA lens, and the approvals on the data plate are UL, CSA and CE — which is what an inspector looks for when a sensor ships onto a washdown line or into a UL-listed panel.
What the headline ratings decide
8 m sensing distance is the number that sets the application envelope: anything wider calls for a different XU receiver or a laser-class sensor, anything narrower is comfortably inside this part's range with margin to spare. 500 Hz switching frequency at 1 millisecond response is what decides whether this part fits a high-speed indexing application — it does; for slower presence detection it's simply more headroom than you'll use.
Same-function cross-shop
The closest functional alternative in the same XU2 thru-beam family is XU2S18PP340WD: same 8 m range, same 12 to 24 VDC, same PNP, same M12 4-pin DC micro male connector, same 500 Hz switching and 1 millisecond response — the only documented difference in the data is a 90 deg side sensing head orientation versus the axial head on the XU2S18PP340D, which is a panel-layout call rather than an electrical one.