Hello Graham,
No, you need to separate the voltages. My board has optoisolated inputs and outputs.
Here is how Mr. Duncan of CNC4PC explains it.
An optoisolator is an integrated circuit that transmits the signal through an encapsulated LED and
phototransistor. When the signal is on, the LED lights up, the phototransistor captures it and
relays the signal. In that way, your computer’s electronics are completely isolated from your
circuitry. The signals are transmitted through light and not through physical connections. In
this way, a power surge has no way of reaching your computer.
black and brown are power and blue is signal.
I've never seen a 24V prox. that the signal is blue. I do not know if this is a set in stone standard or not. I have replaced a blue million switches, different manufacturers, styles, etc. The signal has been black on all of these. Blue=neg. brown=pos. black=signal.
Hope this helps.
Brett