Author Topic: Help with noise problem  (Read 1058 times)

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Offline jordiboronat2017

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Help with noise problem
« on: February 14, 2017, 07:14:48 AM »
Hi,

Trying to get some help here with a noise problem I´m having on my homebuilt 8 x 4 cnc machine.

Machine is up and running at the moment, no issues and smooth path without input signals for limits but as soon as these are connected the Y axis gains steps when the VFD it´s on.

The machine runs on nema 34 3:1 reduction, with leadshine drivers and ZP5A breakout board. All the electronics are on a metal case (including VFD), running shielded cable to a XLR connector on the case and shielded from there to steppers, and all the shields to a common star ground (metal case and from there to earth ground).

I can run wires from the breakout board to the XLR connector and run the machine correctly as long as the XLR is not in contact with the case. As soon as the XLR connector (with the sield connected to it) is in contact with the metal case and therefore with the star ground, the Y axis gains steps.

I´m fairly confident it´s a noise problem but not sure how to deal with it....any help will be appreciated!

Jordi

Offline Tweakie.CNC

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Re: Help with noise problem
« Reply #1 on: February 14, 2017, 07:31:22 AM »
Quote
As soon as the XLR connector (with the sield connected to it) is in contact with the metal case and therefore with the star ground, the Y axis gains steps.

From what you have described it sounds like you have created an earth loop.
All shields should be connected to the Star Earth at the controller end only.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline jordiboronat2017

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Re: Help with noise problem
« Reply #2 on: February 14, 2017, 08:03:12 AM »
Hi Tweakie,

I´m connecting the cable shield to the XLR connector and this screwed into the metal case acting as a ground point. Shields are connected only at one end. Would this create ground loops?

Sketch would be:

Breakout board--------------------------->XLR FEMALE- METAL CASE (all shields here) - XLR MALE --------------------->Stepper/limit

How can I identify ground loops?

Offline Tweakie.CNC

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Re: Help with noise problem
« Reply #3 on: February 14, 2017, 08:35:45 AM »
Hi Jordi,

Sorry, but without looking in detail at you installation I can only guess but here are some points to consider...

Earth and GND should be treated as entirely different circuits.
All metal parts, that can be touched (of a machine which is connected to mains electricity) must be properly connected to protective Earth.
VFD driven spindle motor cable should be shielded.
All inputs (limit / home switches, EStop, probe, etc.) cable should be shielded.
All cable shields should be connected to one star Earth point at the controller end only.
If you are connecting the same thing to Earth in two different places then that is an Earth loop and should be avoided.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.