Hi guys, Recently I have added a desktop into the garage dedicated for the CNC. However I can not get the probe function to work with the desktop. I am constantly getting the Error 9 and Alarm 4 code. I'm using a generic xyz probe made from an aluminum block. Double checked my wiring and should be all correct. Somehow the probe is being triggered instantly when the clip from the probe connects to the spindle. I can't figure out how, here is what I figured out so far: 1. The machine probe function works with the laptop that was connected to it before. 2. Probe function works with the desktop if the VFD power is disconnected. 3. Probe gets triggered if I connect a wire from the PC case to the CNC machine with the VFD power disconnected. Any suggestions would be appropriated!
Short between AC EARTH And DC GND somewhere in your system From the symptoms, desktop PC shorting either in PSU, or motherboard shorting to case
Any recommendation on how to identify the short? Also is it normal for the multi-meter to read that the probes are shorted when they are not touching and the laptop is reading the probe as open?
Normal. No. Short inside desktop. Fine on laptop - pointing finger at Desktop. Fixing: replace desktop PSU, or look for shorts (chaffed through cables touching inside case, motherboard screwed onto wrong standoffs, somewherr DC GND is touching AC EARTH (metal PC case is earthed usually)
I did some more digging and this is what I found. Stripped the desktop out of the case and ran it as a testbench, same issue. I tried a second high-end desktop with the issue. Both systems were using an EVGA PSU. I determined the laptops does not connect to AC Earth which is why it's working The frame and spindle are grounded to AC Earth, this is necessary. Desktop PSU links the DC GND and AC Earth which seem like a common standard. Multi-meter indicate all the pins from the USB port are linked to AC Earth. I believe this is normal. Once I plugin the USB to the blackbox, the probe gnd is linked to AC Earth. At this point the entire frame of the machine is DC grounded and AC Earthed. I don't know what power supply I could get to eliminate this problem. Also read usb voltage isolator could potentially help.
Here is my wiring to the vfd just in case I did anything wrong. The spindle ground and the power plug ground share the same ground terminal.
AC "ground" (I prefer the term mains EARTH to distinguish them) should NEVER be connected to DC ground. It is potentially dangerous as a fault in the mains wiring or insulation could result in a lethal voltage being present on low voltage equipment. Mains earth is not necessarily free of voltages relative to the low voltage equipment - remember voltage is a RELATIVE measurement and the output of low voltage power supplies is usually "floating" - ie NOT related to a true earth. Alex.
As both PCs do it, any chance you used the same monitor? Does unplugging cable between PC and Monitor open the short? (HDMI's DC GND and USBS DC GND is the same, so Monitor could be source of GND to Earth short) Anything else plugged into the test bench setup that also has a main plug?
I tested the monitor previously and it's not that either. I received the usb voltage isolator today and that seem to solved the probing issue!
(; Seem to "work around" more like it. The short is still present and someday could cause mains leaking into the DC domain damaging controllers, computer and even becoming a safety risk. Isolators are a band-aid.
Haha ideally I would like to pin point the source of the issue but I tried everything else I could think of. I am pretty sure the desktop PSU is linking the ground and earth. All my systems uses EVGA power supplies and 2 systems behave the same. I could try another brand of PSU, I guess.
