Dynomotion

Group: DynoMotion Message: 9788 From: fchopinqc Date: 7/14/2014
Subject: EMF Issues

I  Tom and every body else, I'm trying to setup a KSTEP and KFLOP system and I have some issues with EMF emission toward one of my friendly HAM neighbors. My setup is composed of a aluminum not grounded CNC, both encoder and motor cables from the KSTEP to my CNC are shielded . KSTEP and KFLOP are connected together by JP7 and a flyover 2 inch long ground wire connected the ground terminal on both board.


Earth ground (safety ground) is connected to the control box panel, the EMF 120V  filter enclosure and cables shield's. The shields cable are not connected to anything at the motor ends... and my CNC is not grounded.  I'm still thinking on if it's a better idea to put a Ground Fault Circuit Interrupter on the power supply, maybe both...


For the moment digital VSS and analog commun are note tied to earth ground and the shields... 


should I link all the grounds EARTH, VSS, analog commun and the shields together?


Any suggestion or general guides lines for setting up a CNC  regarding the EMF disturbance ?



Thanks!
Group: DynoMotion Message: 9789 From: Tom Kerekes Date: 7/14/2014
Subject: Re: EMF Issues
Hi,

Are you able to determine the source?  The most likely source is the KSTEP voltage chopping circuit.  If you disable KSTEP and/or the motor supply does the interference go away?

Can you hear it on an AM radio?

The other possibility may be the 200MHz DSP.

Is KFLOP+KStep in a metal box?

I would think you would want to connect the motor wiring shield to the motor body and connect the shield to Earth GND.

Is the motor wiring twisted pair (one pair for each coil)?

Is the motor Supply wiring shielded?

Regards
TK


Group: DynoMotion Message: 9790 From: fchopinqc Date: 7/14/2014
Subject: Re: EMF Issues
Hi Tom. the EMF interferences are emitted by the motor drive power amplication no  question.    No drive no problem aka if motor KStep enable=off but KLOP is on no problem.

No cable are not twisted pair. 4 wires in a shielded gaine one for each motor...

**********
I would think you would want to connect the motor wiring shield to the motor body and connect the shield to Earth GND.
***********
In this case my CNC table will be grounded, I've tried on one motor but no difference was noted...


My question was should I link together the digital ground/Analog ground and the electrical earth ground?
Group: DynoMotion Message: 9791 From: Tom Kerekes Date: 7/14/2014
Subject: Re: EMF Issues
Hi,

There may be a difference between earth grounding the CNC Table (and motor body) and connecting the motor cable shield to the motor body.

Regarding : should I link together the digital ground/Analog ground and the electrical earth ground?

Sorry I'm no expert, but I think it may be more a question of how and where.  Not sure what you mean by Analog GND.  I'm thinking that the more Earth GND connections you make the more you should reduce EMI, but the more chance there is of creating GND loops and causing problems with KFLOP operation (including possible damage).

Are you running KSTEP in fully Isolated mode with a separate isolated +5V supply?  My thinking is that even if you have all the Motors, Motor wiring, Supply, supply wiring enclosed in a Faraday cage.  If there is a Motor Supply GND connection to KFLOP GND then EMI can leak out through that GND connection and radiate out all of KFLOPs cabling, USB, PC, etc..  So ideally if KSTEP was isolated and KSTEP, KSTEP +5V Power supply, Motor Power Supply, Motors, and related wiring was all enclosed in a Faraday cage there would be little emission.

If 3 motors are emitting you may not notice a difference if only 1 is prevented from emitting.

Regards
TK

From: "fchopinqc@... [DynoMotion]" <DynoMotion@yahoogroups.com>
To: DynoMotion@yahoogroups.com
Sent: Monday, July 14, 2014 2:11 PM
Subject: Re: [DynoMotion] EMF Issues

 
Hi Tom. the EMF interferences are emitted by the motor drive power amplication no  question.    No drive no problem aka if motor KStep enable=off but KLOP is on no problem.

No cable are not twisted pair. 4 wires in a shielded gaine one for each motor...

**********
I would think you would want to connect the motor wiring shield to the motor body and connect the shield to Earth GND.
***********
In this case my CNC table will be grounded, I've tried on one motor but no difference was noted...


My question was should I link together the digital ground/Analog ground and the electrical earth ground?
Group: DynoMotion Message: 9792 From: carlcnc Date: 7/15/2014
Subject: Re: EMF Issues
Do you have the neg [-] of your power supply tied to a star ground at the case?
I have always tied ac ground and the dc [motor supply] together
but NOT the logic supply
Carl
 
Group: DynoMotion Message: 9793 From: Dan Date: 7/15/2014
Subject: Re: EMF Issues
I am not sure this attachment will come through. But it is a PDF from AB on grounding. It is fairly informative and might help in this situation. National Instruments has a good write up too but I don’t have a copy saved.
 
2 rules I typically go with
1.Ground everything to 1 location
2. Ground a shield at the end the signal originates from. So for an analog out of a KANALOG card it is the KANALOG card end, for a analog signal coming into a KANALOG card it is at the device generating the analog signal.
 
 
Dan
 
Sent: Tuesday, July 15, 2014 1:24 PM
Subject: Re: [DynoMotion] EMF Issues
 
 

Do you have the neg [-] of your power supply tied to a star ground at the case?
I have always tied ac ground and the dc [motor supply] together
but NOT the logic supply
Carl
 

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