Grounding for touch probe, G540
I have a DIY cnc router. It uses an Ethernet Smoothstepper, a G540 (rev8) fed from a Mean Well 48v power supply driving 4 Nema 23 steppers. The spindle is a water cooled 2.2kw spindle connected to a Huan Yang VFD. Everything is working beautifully - no noise or other issues. The G540 is providing PWM speed control and this is also working well. The 220v VFD input and the 110v input to the 48v power supply and a small 5v power supply for the ESS all have their green wire ground tied together at a single point - star ground, also tied to the cnc chassis. The spindle is grounded using the 4th wire which is connected internally in the spindle.
I would like to add a touch off probe using the G540 input 4. Inputs 1-3 are my X,Y,Z home switches, each wired NO with the common wired back to the -V terminal of the 48v power supply. These also work well.
I have seen two approaches to wiring the touch probe. Some use two wires, one connected to the input pin on the G540 and the touch surface, the other wire connected to the -V terminal of the 48v power supply, and the other end having an alligator clip that needs to be attached to the bit in the spindle. Note my spindle (and the bits) already have continuity to my star ground point (verified), but do not have continuity back to the -V teminal of the 48v power supply.
The other approach is to use only one wire connected to the input pin, and also connect the -V terminal of the power supply to my star ground point, so the input is brought low upon contact to the bit.
I would prefer to not need to connect the alligator clip to the bit, and am concerned that this just creates a long ground loop. Either method is going to result in connecting -V to my star ground. Is one of these ways preferred? Is there any potential issue in tying -V to "earth" ground? With the alligator clip it will only be temporary during the probe, the other method would have a permanent connection, but directly to the star point, with a short wire.
Thanks
Richard
Tubular latex pressure vessel configuration engineer