Ground voltage difference

[WayneC]

I'm chasing a problem with my system where it intermittently resets Mach 3 during operation. In checking wiring and ground voltages, I found a .25 voltage difference between ground on my Controller and ground on the spindle sheild wiring. The spindle shield wiring is connected directly to the rest of the grounds, and so is the controller. When I measure voltage to the main ground common connection point, either component will measure zero. But when I measure from the spindle shield to the controller chasis ground I get a .25 volts.

Is this enough difference to worry about? How can I get rid of this?

Thanks. I hope my explanation is adequate.

Wayne C

[KIMFAB]

Did you measure this with a scope or a meter? If measured with a meter .25 volts should be enough to disrupt your computer with the mach 3. Check it with a scope - you might find spikes far larger than the .25 volts.
It helps if you have a single point ground.Connect your ground to the center of a 1/4 " copper bar and put your computer and your control circuits on one end and your spindles and other motors on the other end and try it again.
The power supply of the computer or control could also cause these problems.

[WayneC]

Thanks, I'll sure try that. I don't have a scope, so I'll assume that the short time length spikes are enough to trigger a reset in Mach 3.

What can cause this sort of voltage difference? I suspect its in my controller, as the computer doesn't have any measureable diff from the spindle.

Also, how can I fix this if the ground bar doesn't solve it?

Thanks again for your help.

Wayne C

[Al_The_Man]

If you have a central ground point set up, try grounding from the common at the PC parallel port to the central point, rather than allowing it to ground through the mother board.
The service ground should also be at this central point.
Al.

[WayneC]

Hi Al. Thanks for your help. Is the shell of the connector considered ground? Or do I need to use the pin on the connector that is the common?

Wayne C

[Al_The_Man]

Pins 18 to 25 are common (ground) IIRC.
I would connect any or all to the common point, in fact what I usually do also is bring out the common of the PC from one of 'Hard Drive' connectors and take that to the common Earth Ground point to by pass the MB.
Al.