Is it possible to have 2 probes connected on the same pin of the controll board?   When both are connected,  none will activate the digitize led  so I need to unplug one.  Both  probe (z probe and touch probe) are NC.

The motion card is the usb r motion card running mach 3

Thank you

Yes if both probes are active low open-collector and the input has a pullup.

Yes if both probes are active low open-collector and the input has a pullup.

   open collector = open circuit? And what is a pullup?

Thank you

OC means that when the probe triggers it connects the input to ground - like a tool contacting a touch plate.  The input is "active low" so is activated when the input is grounded - to detect this it has to be high level beforehand so is "pulled up" with a resistor, typically 10k ohms.  If your touch probe works the same way, for example if it just uses an isolated tip which is grounded when it touches a metal workpiece, you can just connect the probes in parallel and each will work independently as long as the other isn't touching. 

However the classic Renishaw type touch-trigger probe goes open circuit when triggered but is closed before that.  Would therefore need an "inverter" to convert it to "open collector" to allow it to be parallel connected.  Th low-cost probes now available can be bought with different options.  The Renishaw style is "fail safe" in that if the connection becomes open circuited e.g. by the cable breaking or the operator forgetting to plug it in the machine thinks the probe is activated and stops moving. The probes can also detect both side and end contact so you don't need a separate touch plate provided you know the tool and probe offsets.  If you operate by setting each tool to a known height with a touch plate during machining though this won' work.