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Electromagnetic Interference problem

Electromagnetic Interference problem

(OP)
I am performing vibration analysis on a motor that is around 50 feet away from the control panel.

The output of the data translation module I am using has a USB output, therefore I had to install A USB over CAT5 converter to run it out to the control panel (since the limitation on USB is 16.4 feet)

The only problem is that the contractor ran the cat 5 converter box right under a soft starter in the control room and now my program freezes every time I run the motor while connected inside the control room.

I need to leave a PC inside the control room for a few months and be able to remote into it for recording purposes.

I believe that the soft starter is causing Electromagnetic Interference with the USB to CAT5 converter and in turn causing my analysis software on my computer to freeze.

Would a Faraday cage solve this problem?

Are there any kind of EMI shielded USB cables out there? Or am I right about the USB to CAT5 Converter's circuitry receiving a massive spike from the soft starter?

RE: Electromagnetic Interference problem

It is difficult to say without seeing the installation and perhaps also do a few measurements. But it is more often common-mode voltages than EMI that causes the problem.

First of all, I usually try to connect all power supplies to an outlet that has the same ground as the system I am recording signals from. That usually reduces common mode voltages so that the data transmission works.

Second, I use rather heavy HF ferrite toroids on the USB cable. Put as many turns as you can through the toroid.

If that doesn't help, get someone used to this kind of problems to help you. A Faraday - I do not think that will help. And it isn't practical to arrange in an effective way either. If it helps, it is usually because you will bond the different equipment together when you install it in a Faraday's cage.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Electromagnetic Interference problem

Quote (Cyanogen281)

The only problem is that the contractor ran the cat 5 converter box right under a soft starter

This is a bit unclear. Is the box under the soft starter, or just the CAT5 cable?

In any event,

1. Is your USB to CAT5 converter in a metal box?
2. Shielded ethernet cable is available. Is yours shielded?

If you've got a plastic box and unshielded cable, the noise from the soft starter has two different paths into your system.

PS - please don't post the same question in more than one forum, unless you do so as described in the forum policies.

Best to you,

Goober Dave

Haven't see the forum policies? Do so now: Forum Policies

RE: Electromagnetic Interference problem

(OP)
I should have been more specific...

I am measuring data from a motor 50 feet away.

I am using a USB of CAT5 ethernet converter to get around the USB length limitations (16.4 ft)

The data translation module is powered by the USB port on the PC (Which goes over the CAT5 until right inside the control room where it is converted back to USB, Coincidentally right under the soft starter)

The Converter box itself I think is getting Electromagnetic Interference from the soft starter right above it...

Any advice would be greatly appreciated.



The converter looks something like this Link

RE: Electromagnetic Interference problem

You were specific enough in the OP.

It is very seldom that such a converter is disturbed by emission "through the air". It is usually HF common-mode voltages/currents that cause the trouble.

You can illustrate that the "air" emission is miniscule by introducing a screen (copper plate or steel plate) between the two devices, ground the plate and see if anything changes. You do not need a complete "cage" to remove 20+ dB of interference, but you will probably still have the interference left in your system.

And, if that actually works - fine, there's your solution.

Did you try to increase the distance between culprit and victim?

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Electromagnetic Interference problem

(OP)
We tried bringing the USB cable outside of the control room (effectively increasing the distance) to see if that had any effect on the EMI and the vibration analysis software worked great.

It's only when the converter is inside of the control room that this problem occurs.

I have looked through the settings in the software and there is no type of filter option.

I am looking into something called Mu-Metal tape that might be the solution to my problem.


RE: Electromagnetic Interference problem

Mu-metal is only for magnetic fields. Not so much for electro-magnetic interference. It requires special care and lots of experience to be applied correctly. Did you try the other tips?

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Electromagnetic Interference problem

(OP)
We cannot move the computer outside of the control room.

Would this be an option for wrapping around the USB over CAT5 Converter? Link


Thanks for all the help guys.

RE: Electromagnetic Interference problem

Ground your aluminum foil too.

Best to you,

Goober Dave

Haven't see the forum policies? Do so now: Forum Policies

RE: Electromagnetic Interference problem

You can try moving the Cat 5 to USB converter to a different location. That should not be too much trouble.

RE: Electromagnetic Interference problem

(OP)
The converter needs to be in the same room as the computer with the vibration analysis software on it.

If I use the copper tape I linked in the post above, I assume I should ground it to something outside of the control panel where the soft starter is located.

I have attached a picture of what I have going on and the predicament I am in.


(Yes I know my artistic skills are pathetic at best)


Thanks for all the help guys!

RE: Electromagnetic Interference problem

Ground whatever you're using to the metal can that it sits in. That enclosure is surely grounded well.

Remember, shielding the thing is just an experiment as Gunnar mentioned above. It may or may not prove to be your solution.

Best to you,

Goober Dave

Haven't see the forum policies? Do so now: Forum Policies

RE: Electromagnetic Interference problem

(OP)
Can anyone think of anything else (other than EMI from the soft starter) that could be causing this issue with the vibration analysis program?

The program freezes when the soft starter kicks on but after I close out of the program and open it back up (with the motor still running) if functions as it should.

Any other ideas/opinions on this would be greatly appreciated.

RE: Electromagnetic Interference problem

There are plenty of USB extenders which operate over fibre. Fibre doesn't care a damn about magnetic fields, grounding problems, or pretty much anything other than physical damage. Electrically, little short of a direct hit by lightning would bother it.

RE: Electromagnetic Interference problem

Use a desktop machine instead of a laptop... might have better grounding and not freeze the system.

Dan - Owner
http://www.Hi-TecDesigns.com

RE: Electromagnetic Interference problem

Or...

Use a laptop (powered by battery alone, isolated on a wood table) instead of a desktop. If a ground loop is the issue, then the complete lack of grounding should break the loop.


PS: It's too bad that EMI isn't fuzzy red lines as shown in the sketch. It'd be so much easier if it were visible like that. smile

RE: Electromagnetic Interference problem

(OP)
I have tried using battery power on the laptop only (holding it in my hands) and the vibration analysis program still freezes.

I thought it might be a ground loop issue so I installed a UPS powered HP PC out there a week ago and still the same problem exists...

Which leads me back to the USB over CAT5 Converter...

The CAT5 cable is UTP (Unshielded Twisted Pair) The USB is unshielded, and the Converter is a plastic box likely to have sensitive integrated circuity in it.

RE: Electromagnetic Interference problem

(OP)
I have thought about going and buying a hundred feet of CAT6 just to ensure that it isn't the Ethernet cable causing problems with my system.

Could anyone explain to me how a USB to Ethernet converter works? Could I use a USB to Ethernet converter on one end and just run the cat5 straight into my computer? Basically taking out the converter under the soft starter?

Are there any conflicting protocols I should be aware of?


Again, thanks for all the help guys.

RE: Electromagnetic Interference problem

That would depend on your software, but it's certainly doable in the general sense: http://www.usb-over-ethernet.com/, but you probably need a software driver as marketed by that site, since normal Ethernet drivers only understand TCP/IP, which would not be what's coming out of your ethernet cable.

TTFN
FAQ731-376: Eng-Tips.com Forum Policies

Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers

RE: Electromagnetic Interference problem

If I have this right in my head:

You have a vibration analyzer on the motor, and its output is USB. Your PC is in the control room. So out by the motor is a USB-to-ethernet converter and in the control room is an ethernet-to-USB converter for plugging into the pc?

Why not try a long USB extension and keep the active (repeater) portion outside of the room?

http://www.newegg.com/Product/Product.aspx?Item=N8...

Best to you,

Goober Dave

Haven't see the forum policies? Do so now: Forum Policies

RE: Electromagnetic Interference problem

I agree with Gunnar when he said that ground loops are a common (mode, LOL) problem; but you've probably eliminated that possibility with your hand held laptop experiment.

How about just getting some very large (2-inch wide) braid and shielding the entire cable including the dongle?


Beware one problem doesn't exclude the other. Be prepared to repeat the hand held laptop experiment in case it's both ground loop and EMI.

RE: Electromagnetic Interference problem

There is such a thing as shielded Cat 5/6 cable. I don't think that going from Cat 5 to Cat 6 cable will make any difference. Instead try going to a shielded type of cable. You will also need special shielded RJ-45 connectors. I still don't know why you can change the location of the converter within the control room. Mount it as far as possible from the soft-starter and as close to your computer as possible.

RE: Electromagnetic Interference problem

How about unbolting the converter from the wall and temporarily setting somewhere else like on the floor, just as a troubleshooting method.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Electromagnetic Interference problem

Your USB to Ethernet adapter is going to be a microprocessor/microcontroller with a USB port and an Ethernet port. The firmware initializes both ports and then passes the data through. You can easily do this in your controller if it has the proper ports.

Z

RE: Electromagnetic Interference problem

you've stated nothing regarding how your

1."data translation" hardware is grounded or isolated from ground
2. how the cable is routed (tray, conduit), or it's degree of isolation from adacent power wiring.

sounds like a ground loop issue, there is test equipment for isolating gound loops, have youused such hardware?

RE: Electromagnetic Interference problem

(OP)
Our data translation hardware is grounded next to the motor that we are measuring the vibration from.

When we move the computer (Laptop for this application) away from the motor and begin the vibration analysis everything works as it should.

The CAT5 cable that is run into the control room is, unfortunately, ran in the same conduit as the power wiring.

We have isolated the problem to the USB to Ethernet converter and it only seems to freeze the program when the USB/CAT5 converter is inside the control room.

Is a Faraday cage completely out of the question at this point? Wouldn't that shield the USB/CAT5 converter? Perhaps some copper tape wrapped around the device, then grounding the tape?

RE: Electromagnetic Interference problem

Quote:


The CAT5 cable that is run into the control room is, unfortunately, ran in the same conduit as the power wiring.

You've now lost whatever money _that_ saved, just in your time.

A separate conduit for the signal cable basically amounts to a Faraday cage, without the expense of trying to pull a foil-wrapped signal cable in with the unshielded one.

Mike Halloran
Pembroke Pines, FL, USA

RE: Electromagnetic Interference problem

An optical fibre doesn't know or care about EMI, regardless of how bad it gets. Run your USB data over fibre.

RE: Electromagnetic Interference problem

You can get a good sheet metal guy to Faraday-ize your USB/Ethernet converter, or just wrap the heck out of it (and also the cables next to it) with aluminum foil and see if it really works.

I like ScottyUK's suggestion the best.

Best to you,

Goober Dave

Haven't see the forum policies? Do so now: Forum Policies

RE: Electromagnetic Interference problem

(OP)
An Optical Fiber cable converter is around $800 for the entire setup for my particular application.

Being as the (CAT5) data cable has already been run in the conduit with the power wires, I am thinking of simply replacing the UTP (Unshielded Twisted Pair) CAT5 cable with a shielded version of it and hopefully that will fix the problem. If not I don't see the harm in simply wrapping the USB/CAT5 Converter in something like aluminum foil essentially creating a Faraday cage for testing purposes.

Any other advice or suggestions would be greatly appreciated.

Thanks for all the help guys.

RE: Electromagnetic Interference problem

Foil, whether aluminum or copper, is pretty much a waste of time, Mu-Metal slightly less so.

A simple steel box will be superior to any of them, every time.

Mike Halloran
Pembroke Pines, FL, USA

RE: Electromagnetic Interference problem

That does depend whether your problem is capacitive (E-field) or magnetic (B-field) coupling. Any earthed metal will knock capacitive coupling right down. Magnetic coupling is best dealt with by increasing separation, followed by mu-metal and the like.

RE: Electromagnetic Interference problem

Are you still discussing this? What is this - an academic exercise?

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Electromagnetic Interference problem

The CAT5 cable that is run into the control room is, unfortunately, ran in the same conduit as the power wiring.

move it

The CAT5 cable is UTP (Unshielded Twisted Pair)

go spend $2.60 and buy shielded cat5 cable

www.KilroyWasHere.com

RE: Electromagnetic Interference problem

Another reason to move the signal cable to a separate conduit, on a planet where the NEC applies, is that the Cat5 cable probably isn't rated for voltages as high as the motor voltage.

Mike Halloran
Pembroke Pines, FL, USA

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