Is this a new unit? It should have make/markings on it.
The three wire kind require power, common, and output, they can be PNP or NPN, this decides how the output is connected.
The common connections are Brown +, Blue Com, Black load.
But there are variations out there, this is why you need to refer to the manufacturers info and the machine schematic to find out if the device switches to + or common (Sink or Source).