I was wondering what type of sensor would work with my g540 drive. I am confused on how to hook one up because the g540 seems to call for the signal to be connected to ground for the input to work. I can't imagine a reed switch could respond to 20K rpms or more. I would assume some sort of optical pick-up, but those have a output of 5volts or more. The g540 is somewhat popular, so i am guessing there is someone who has a spindle speed setup that works. Please help if you can. Thank you.

You need a sensor with an 'NPN' type output. Connect the sensor's power supply DC Common to the G540 DC Common and the sensors output to the G540's input. The sensors output will pull the G540's input to DC Common.

Will something like this work?
https://www.alliedelec.com/Images/Products/Datasheets/BM/OMRON_ELECTRONICS_INC/834-0205.PDF
If so, I will go ahead and purchase it. Thank you.

You have the right idea, but the response frequency is too low on that one:

Response frequency *2 50 Hz min. (Average: 500 Hz)

It won't work much past 500 RPM...

Do you have any suggestions? My power supply is 24v, but if I have to, I can put a voltage regulator on it.

Will something like this work?
https://www.alliedelec.com/Images/Products/Datasheets/BM/OMRON_ELECTRONICS_INC/834-0205.PDF
If so, I will go ahead and purchase it. Thank you.

Yes, this will work fine. I've had one on my Taig mill for about 10 years now. Works up to 6000rpm without issue

Cheers,

Peter

I see Peter is right, I should have spent a bit longer looking at the data sheet and kept all the time units consisatnt.

500Hz = 500 cycles/second so 500 cycles/second * 60 seconds = 30,000 cycles / min (or 30K RPM).

Good catch Peter!