Renishaw TP-20 Probe Connection

Thanks to both for the info there, thats interesting that it supplies 12v.

I think I have found a way to do this, which actually was quite easy, I still need to actually test this circuit however!

Using the circuit shown here - electronics.stackexchange.com/questions/...g-5v-microcontroller

I have attached my revised circuit that should trigger the 24v input with the same transistor.

Yes, that should work, but why not run the whole circuit off of 24V? It just needs a higher-voltage op-amp and making R4 proportionally bigger.