The Festo SMTSO-8E-NS-M12-LED-24 is a magneto-inductive proximity sensor designed for T-slot mounting on pneumatic actuators — the standard cylinder profile across Festo and most ISO/VDMA-compliant tie-rod cylinders. It detects the piston position through the slot wall without mechanical contact, so no wear on the seal or the sensor body. The NPN switching output (the "NS" in the code) pulls the load to ground when the magnet passes, which matters if your PLC input card or relay logic expects a sinking signal.
NPN vs PNP — the deciding factor against the sibling
The closest functional peer is the SMTSO-8E-PS-M12-LED-24, which is the PNP (sourcing) variant. Same housing, same T-slot fit, same M12 connector, same magneto-inductive principle. The only difference is the output polarity: NS = NPN sinking, PS = PNP sourcing. If your panel was wired around the PNP version, dropping in the NS means rewiring the load side — the sensor itself bolts into the same slot and uses the same cable. For a panel OEM standardizing on NPN inputs, this is the correct pick; for a line-down swap where the original was PNP, order the PS variant instead.