VFD interference problem

[eurikain]

This is how the cabinet is set. All hight voltage power cables are on one side of the cabinet. Signal cables are close to the BOB, there is only 5V power cables that run next to them.

I'll get rid of the ribbon cable, but that doesn't solve my ground loop. Why would I have a ground loop while other don't ? Is it the computer that's the problem ?

[komatias]

This is how the cabinet is set. All hight voltage power cables are on one side of the cabinet. Signal cables are close to the BOB, there is only 5V power cables that run next to them.

I'll get rid of the ribbon cable, but that doesn't solve my ground loop. Why would I have a ground loop while other don't ? Is it the computer that's the problem ?

I think it is down to the fact that many use metal cabinets to house the electronics and also for the machine frame. Spurious currents then have an easier path to earth.

[eurikain]

I confirm that it is a ground loop. I changed the parallel port today using a PCI card I have. Same noise issue. Disconnecting the PC fixes the issue.

[komatias]

I confirm that it is a ground loop. I changed the parallel port today using a PCI card I have. Same noise issue. Disconnecting the PC fixes the issue.

have you got an oscilloscope to probe the parallel port?

[eurikain]

Nope, sorry ! I have a voltmeter though :) Probably won't be of any help huh :'(

[Clive S]

Have you tried a new pp cable yet?

[Clive S]

I confirm that it is a ground loop. I changed the parallel port today using a PCI card I have. Same noise issue. Disconnecting the PC fixes the issue.

How can you confirm that it is a ground loop problem!! Have you confirmed that your PP cable is not just a printer cable (not all printer cables are the straight though type) You can check it with a multi meter

[magicniner]

Is there a reason why you don't have an RFI filter on the VFD power lines close to the VFD?

[eurikain]

Well, after trying to sort things out again with Graeme, we came to the conclusion that there was no ground loop. The PP cable is straight through, and there is nothing wrong with the 0V connections. So, I decided to take everything out of the control box, and next week I'll wire it step by step and check for interferences at each step.

[Clive S]

Well, after trying to sort things out again with Graeme, we came to the conclusion that there was no ground loop. The PP cable is straight through, and there is nothing wrong with the 0V connections. So, I decided to take everything out of the control box, and next week I'll wire it step by step and check for interferences at each step.

Put in all in a metal box if you can