I have a couple of proximity sensors that came without documentation. I'm planning to use them as home sensors for a CNC router.
The label says that they're NPN sensors, 6-36 VDC, 200mA. There are three wires, which I understand to be +V (brown), -V (blue) and output (black). My expectation was that, since these are NPN, they would be current current sinking, and that there would be no electrical connection between brown and black. What I found was that if I apply +V to brown, I get +V on black, with a resistance of 10K Ohms. It seems like there's an internal pull-up resistor between +V and output. As expected, if the sensor comes within 2mm of metal, output is connected to -V (with 10 Ohms resistance). Am I interpreting this correctly?
Any recommendations on the simplest safe way to wire these sensors up to a parallel port input? Although the label says 6-36V, they seem to work with as little as 4V, though obviously that's out of spec. I had been expecting to supply my own pull-up resistor between output and +5V.