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Signal ground / Earth ground
« on: November 27, 2013, 08:13:03 AM »

Signal ground / Earth ground

In reference to ground loops as a source of “noise”:

Quote from Tweakie.

“Also check for GND loops - in particular the LPT cable shield should not be connected to GND at both the computer end and the machine frame if they are both, in turn, connected to earth etc.”

Interesting Tweakie, what about the signal grounds like pins 18-25 on a DB25 connector? can that be grounded at both ends? I hope.


Hi Tony,

Yes, the 18-25 is common signal GND between the PC and the controller but remember that this is signal GND, it is not Earth.


I believe the LPT signal grounds are connected to the computer chaise which is also the -5V and -12V power supply GND which in turn is connected to earth ground through the AC power card. Is this correct?

Is it OK to have the signal grounds be connected to earth ground at both the computer and a controller which is grounded at the machine?

Thanks for any help.


Offline Tweakie.CNC

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Re: Signal ground / Earth ground
« Reply #1 on: November 27, 2013, 10:44:45 AM »
Re: Signal ground / Earth ground
« Reply #2 on: November 27, 2013, 11:51:29 AM »
Thanks Tweakie,

That is a help. I don't appear to have any noise issues with my plasma machine but do see where I don't have perfect "star" connections and someday should make them better.