Electromagnetic Interference problem

[Cyanogen281]

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?

 

[Skogsgurra]

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

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[DRWeig]

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

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[Cyanogen281]

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

 

[Skogsgurra]

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

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[Cyanogen281]

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.

 

[Skogsgurra]

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

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[Cyanogen281]

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.

 

[MacGyverS2000]

Grab some tin foil from the local supermarket...

Dan - Owner

http://www.Hi-TecDesigns.com

 

[DRWeig]

Ground your aluminum foil too.



Best to you,

Goober Dave

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[djs]

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

 

[Cyanogen281]

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!

 

[DRWeig]

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

 

[Cyanogen281]

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.

 

[ScottyUK]

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.

 

[MacGyverS2000]

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

Dan - Owner

http://www.Hi-TecDesigns.com

 

[VEBill]

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.

 

[Cyanogen281]

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.

 

[IRstuff]

Can you use Cat6 cable instead?

TTFN
faq731-376

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[Cyanogen281]

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.