Quote Originally Posted by Graeme View Post
A NPN output is simply just a switch to 0V.
The datasheet is a bit scant... I'd verify that there aren't any pull-up resistors attached to the output of that NPN switch (which would see the supply voltage on the output if the switch is in the open state)....therefore to test, just provide it with its supply voltage & see what voltage is on it output (if any)