Sensors with pnp output are rather designed for a PLC environment, the inputs of PLCs usually react to the presence of a certain voltage level with the detection of a logic HIGH state and will detect LOW level when there is no voltage, i.e. if they are disconnected.Most, if not all, DAQ and other PC interface cards I have seen rather have TTL compatible inputs which need a certain voltage level to detect a logic HIGH state and must be tied to GND level (or at least close to it) to detect a logic LOW level. Since a PNP output cannot tie anything to GND you will need some interface circuitry. The most simple one will be a simple transistor circuit with an NPN transistor, with the base tied to your sensor output via a current limiting resistor, the collector connected to +5VDC (many cards provide an auxiliary +5VDC output) via a load resistor, and the emitter tied to GND. A resistor should be tied between the base of the transistor and GND to sink the leakage current of the PNP output to GND. A TTL compatible signal can be obtained directly from the collector of the transistor. The collector will be close to GND (i.e. logic LOW level) when the sensor output is switched on, and will be at logic HIGH level when the sensor output is switched off.
