Glad to hear the problem is fixed!
It often means barking up a few incorrect trees before finding the solution. At least you are interference free again.
73 - Rob VK2GOM / GW0MOH
Yet another interference problem
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GM3SEK
Re: Yet another interference problem
Many congratulations for sticking with it until the problem was fixed, Erwin. "Fixed" also means that there isn't much I can addVK3MEB wrote:Ian,GM3SEK wrote:.. you need to focus on the short, direct bonding connections between the different parts of the appliance....
Talk about "earthing" is just dragging your focus away from what really needs to be done.
73 from Ian GM3SEK
that's exactly what I took from the articles you referenced in your earlier post and that's what I've tried to implement. You are right in pointing out that I shouldn't call it "earth" but old habits die hard! In my own mind I now differentiate between "Protective Earth" and "RF Earth", thanks to the EMC journal article.
As you can see in the photos I have used the stud on the enclosure as a central connection point for my RF Earth wires with short pieces of 6 sqmm wire connecting it to the gear tray and the other parts of the cabinet. I'm trying to prove a path back to the metal part of the VSD (the back wall).
The motor cable shield is currently terminated at the EMC gland (due to the type of gland) but I have already got a "Through-Shield" type of EMC gland which will allow me to run the shield all the way to the VSD. Currently the motor cable is unshielded between the gland the the drive.
I'd appreciate your comments on the RF earth wiring shown in the photos to point out where I've gone wrong with putting the theory into practice.
Changing the controller has obviously removed most of the interference at source, but what you did with the wiring has also helped to prevent whatever was left from being radiated. However, I don't think that the green/yellow wires are actually helping very much with RF interference.
High-frequency currents will follow the path of least inductive reactance, which will be your 'structural' bonding between the big, broad metal backplate and the metal box itself. You already told us that the powder coating has been removed to give large areas of metal-to-metal contact, which also was exactly the right thing to do. The green/yellow wires are connected in parallel with all of that direct structural bonding, but relatively RF little current will flow through those wires because they are much longer and thinner, so they will have a much higher inductive reactance.
However, the green/yellow bonding wires are probably still needed as a backup to the structural bonding. Safety inspectors always like to see those green/yellow wires as proof that correct procedures have been followed.
There are a few other little things that you might have done differently... but what the heck, you did all the big things right! Go and enjoy some radio now, Erwin - you've well earned it.
73 from Ian GM3SEK
PS... did you notice, I never once mentioned "Earth"
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VK3ERW
Re: Yet another interference problem
GM3SEK wrote: There are a few other little things that you might have done differently...
PS... did you notice, I never once mentioned "Earth"
Ian,
many thanks for your comments.
I'm getting the hang of it (slowly) … "RF Bonding" … not "Earth"
Although the problem is solved I would still like to use this a learning experience as I work with VSD's every day, albeit mostly in industrial environments where RFI seems to be accepted.
I would greatly appreciate you thoughts on the other little things I could have done differently.
Many Thanks
73
Erwin (VK3MEB)
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GM3SEK
Re: Yet another interference problem
You are seriously asking me to pick nits?VK3MEB wrote:Although the problem is solved I would still like to use this a learning experience as I work with VSD's every day, albeit mostly in industrial environments where RFI seems to be accepted.
I would greatly appreciate you thoughts on the other little things I could have done differently
You did all the big things right: solid, low-inductance connections between the backplate and the box, and you used a shielded cable to the VFD with 360deg cable glands. Compared with that, almost everything else is a detail... but sometimes those small details add up.
With hindsight, it would have been better to make more space in the crowded area to the right of the controller, and then to keep the different kinds of wiring more separate from each other.
There are large currents at many different frequencies flowing inside this box, so the general aim is to avoid creating magnetic pickup loops. For a start, the master "earthing" stud inside the box should be very close to the entrance hole, so that the incoming green/yellow wire of can make a very short, direct connection. All the other green/yellow wires should then be tucked away flat against the walls of the box to avoid creating open loops.
Mains wiring should have the line and neutral (blue and brown) wires twisted together for as much of their runs as possible - yet again, to reduce the risk of magnetic coupling - and mains wiring should also be kept separate from the control wiring.
By all means make everything neat and tidy using cable ties - but use them to tie different kinds of wiring apart, not together!
The big problem with EMC is that we don't know in advance how helpful these little details might be. The only workable strategy is to try to do everything right in the first place. Good wiring layout doesn't cost anything extra (except a bit of thought) and it certainly won't do any harm... but it might possibly do a lot of good.
73 from Ian GM3SEK
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VK3ERW
Re: Yet another interference problem
Hi Ian,
thanks for your comments - I see what you mean. Although it may not make any difference, I might clean up my wiring just to have it look right.
73
Erwin
thanks for your comments - I see what you mean. Although it may not make any difference, I might clean up my wiring just to have it look right.
73
Erwin
Re: Yet another interference problem
Shielding is an interesting topic.
The device about might tease out some thinking about shiedling. It is a RF current sampler where a voltage proportional to the current on the coax inner conductor is developed across the BNC output terminals.
Click on it for a bigger picture.
The ferrite core is the core of a transformer, the secondary is 30 turns of enamelled wire.
If you look carefully, you will see the right hand end of the braid is connected to a 'ground' lug on the coax connector, and on the left side, the jacket emerges from the ferrite core and the braid is cut at the jacket end. The coax inner conductor connects between the two coax connector inner pins.
Why does this work (and it does work) since there is a 'shield' between the current carrying inner conductor and the ferrite core and every ham knows that the shield on a coax prevents the escape of electric and magnetic fields due to current on the inner conductor? Try to answer it without using the word Faraday, answer it in terms of how magnetic flux is developed in the ferrite core due to the coax inner current.
Owen
The device about might tease out some thinking about shiedling. It is a RF current sampler where a voltage proportional to the current on the coax inner conductor is developed across the BNC output terminals.
The ferrite core is the core of a transformer, the secondary is 30 turns of enamelled wire.
If you look carefully, you will see the right hand end of the braid is connected to a 'ground' lug on the coax connector, and on the left side, the jacket emerges from the ferrite core and the braid is cut at the jacket end. The coax inner conductor connects between the two coax connector inner pins.
Why does this work (and it does work) since there is a 'shield' between the current carrying inner conductor and the ferrite core and every ham knows that the shield on a coax prevents the escape of electric and magnetic fields due to current on the inner conductor? Try to answer it without using the word Faraday, answer it in terms of how magnetic flux is developed in the ferrite core due to the coax inner current.
Owen