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Motion Device Grounding
« on: December 31, 2019, 03:58:57 PM »
I’m using a PoKeys57CNC Ethernet CNC motion controller and a PoKeys57E Ethernet I/O device powered by a 12 volt isolated power supply. That is the 12 volt common (Vo) is not connected to machine or earth ground. I will not be using any input signals that connect to machine ground like some probes do. Is it best to ground  it anyway or let it float which would reduce the risk of ground loops?
Thanks for any help,

Tony
« Last Edit: December 31, 2019, 04:11:03 PM by Tony Bullard »

Offline smurph

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Re: Motion Device Grounding
« Reply #1 on: January 03, 2020, 02:07:04 AM »
Floating isn't bad.  Also, there is ZERO risk in ground loops if you don't create them.  And when I say ground loop, I mean a loop between devices/components.  Say like a motion controller, the PC, and a VFD. 

Let's see if I can do some ASCII art for the win here...  :)
Good (D is for device):

D   D   D
\    |    /
     |
     G

Bad:
D - D - D         D - D - D
|                      \    |    /
|               or         |
G                          G

Steve
Re: Motion Device Grounding
« Reply #2 on: January 03, 2020, 05:35:14 AM »
Tony
just interesting me why you use 57E and not the porelay cards?
Re: Motion Device Grounding
« Reply #3 on: January 03, 2020, 09:39:49 AM »

Thanks Steve, I’ve been worried about this for a long time.
None of the devices/components NEED a common between them. The PC, PoKeys57E control panel I/O and the PoKeys57CNC motion controller communicate through Ethernet so they don’t use a ground or common. All other components like limit switches, VFDs, servo drives and solenoids are either optically coupled, galvanic isolated or relay controlled.

Katz, I use the PoRely8 driven by the PoKeys57CNC controller which is in the machine control cabinet. I use the PoKeys57E in the control console for digital and analog inputs from switches and pots. For control console outputs I use 2 open collector PoExtBusOC16s for the illuminated pushbuttons. The control cabinet and control console are 10 feet apart an this Hurco KM3P mill retrofit with Mach4 and Gecko G320X servo drives. One Ethernet cable communicates between the two.

Some pictures under construction attached:


Re: Motion Device Grounding
« Reply #4 on: January 04, 2020, 04:23:42 PM »
how did you connect the "PoKeys57E" i didn't see the Ethernet cable?
Re: Motion Device Grounding
« Reply #5 on: January 04, 2020, 04:46:26 PM »
I took the picture while I was wiring it. The cable was not plugged into the PoKeys57E at that time. Three Ethernet cables connect the PC, PoKeys57E and the PoKeys57CNC to a router. The PC and the PoKeys57E are in the console and the PoKeys57CNC and the router are in the control cabinet.
Re: Motion Device Grounding
« Reply #6 on: January 04, 2020, 05:59:48 PM »
i asked because i use to use cat7 and cat 7 already have also the ground ,so in this case its like the bridge of ground between devices that Steve advice to avoid

Re: Motion Device Grounding
« Reply #7 on: January 05, 2020, 08:21:47 AM »
I don't know what I'm talking about but I think the ground you are referring to is the Ethernet transmit and receive common (ground) which is independent of the PC or Pokeys power ground. There is no connection between the Pokeys RJ45 contacts and the Pokeys power ground.