Hi guys. I got questions regarding sensor and how to properly interface them since I am designing an interface card. I have a PLC unit (OMRON CP1L M40DT-D). Now the big question now is i've got these sensors.. Hall Effect Switch -> I don't know if it is NPN or PNP? How do i determine this with a multimeter? There is no code written on it and is epoxy sealed. I tried to open up 1 unit to see the insides for code or manufacturer. No luck. Encoders.. I got three types of encoders. Type 1. RE-30 Dunker motor encoder. I downloaded their datasheet but to no avail what output is given? It simply says output via a photo transistor. But how do I determine if this is an open collector este a PNP or NPN type via a multi tester? Type 2. Hengstler Encoder.. I got 2 channels A and B. Are both NPN or PNP? Again same question how to test via a multimeter. Type 3. Hall Effect as limit switches... I got a bunch of them and burned a few guessing the polarity. This time I got it right.. Pin config... pin 1 -> VCC pin 2 -> Gnd pin 3 -> Vout Same as above how to determine if its NPN or PNP type... Generally I know how to figure out a transistor if its PNP or NPN. But I am unsure with sensors. The manufacturer of dunker and hengstler never replies... And I need to know what configuration I should use (High or Low side). My plc does both but only has 1 common rail so in general an interface card is required. Switching speeds are very slow and low voltage.