So I'm trying to figure out how to get an accurate RPM reading on our Colombo spindle. I'm walking into a job that was left 1/2 done and I admit I'm not an expert, I'm just the guy that it falls to make it work.
Firstly, the spindle is brand spankin new, old one burnt out as the guys that did the 'retrofit' didn't know that the air wasn't cooling the spindle, so at least I know that the spindle is good and the sensors are in working condition.
Now here's my problem, the sensor is listed as a NAMUR, which a quick google told me is an inductive pickup sensor.
The spindle should be sending 2 pulses per rotation, so I set it up to send 5v to the sensor and the return to lucky 13 on the input and told Mach 4 control and ESS that is the spindle RPM sensor pin.
Well, it's getting........something?
Speed reading is bouncing all over the place at rest and has no real relation to actual spindle speed (checked by running spindle directly from VFD at lowest speed and watching readout).
So what am I missing? Sensor power range is listed as 5-30vdc, but later notes in the manual state +24vcc for all the sensor power needs. Does this mean I'm going to have to puzzle out a step down or some other means for the system to read the sensor?

I haven't used the ESS in quite some time; so I'm not the best to help you on this, however, I do know that when I was using the ESS all the signal voltages are 5VDC, so you should be fine there.  The two pulses shouldn't be an issue either, you will just have to double your feedback since I'm pretty sure the ESS is only for single point feedback. 
If you're getting readings that are all over the place, you may be having noise issues from your VFD.   Again, someone that uses the ESS regularly will need to hop on here and help you out more with this.

Words

Hey, a starting point is better than nowhere. I'm just happy that is not caught fire since the guy doing the retrofit quit working on it.
I wish I was joking about that, it happened more than once.

So, for the folks curious and following along I read the manuals again and looked at what was on the machine.
The wiring and circuit for the RPM sensor and tool changer are all gone.

The inductive sensors are all PNP and should have resistors and a circuit to pulse the input to the board, so time for some math and circuit board design. I wanted to cut out all the bus bars in the thing and make it tidier anyway, so not a bad thing to need to do.