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D-Sub EMI Filters

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kkinney

Joined: 11 Jan 2006
Posts: 42

Posted: Wed Jan 17, 2007 8:32 am Post subject: D-Sub EMI Filters

I'm still learning about electronics and avionics.  EMI still leaves me in the dark, though I'm learning about it too.



Assume someone were to have a noisy radio: Would EMI shielded D-sub connectors help with this in any way?  For example - http://specemc.com/series100.asp



How applicable would this be to correcting that problem?



Regards,

Kevin Kinney



--

Non-Parent - I don't see how you can raise children & stay sane.

Parent - You don't.  You pick one and go with it.

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nuckollsr(at)cox.net
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Posted: Wed Jan 17, 2007 11:21 am Post subject: D-Sub EMI Filters

At 11:27 AM 1/17/2007 -0500, you wrote:



 	  Quote: 	
		  

I'm still learning about electronics and avionics.  EMI still leaves me in 

the dark, though I'm learning about it too.



Assume someone were to have a noisy radio: Would EMI shielded D-sub 

connectors help with this in any way?  For example - 

http://specemc.com/series100.asp



How applicable would this be to correcting that problem?



Regards,

Kevin Kinney


	


   Check out the chapter on noise in the 'Connection.



   The short answer to your question is, "Yes, filters

   may be useful in mitigating noise problems."



   The facts one needs to secure before selecting any

   noise mitigation tool or technique are:



   (1) who is the victim?



   (2) who is the antagonist?



   (3) what is the propagation mode for coupling

       the noise between 2 and 1?



   One then needs to evaluate one or a combination

   of (1) reduce noise from antagonist, (2) increase

   ability of victim to operate satisfactorily with

   noise presented and/or (3) consider ways to

   attenuate if not eliminate the propagation mode(s).



   It may well be that the filter connector you've cited

   will help . . . but simply adding such a device as

   an experiment is commonly called "Swaptronics . . .

   let's replace or add things until something good

   happens."



   If this sounds like a daunting task, don't feel bad.

   It CAN be an engineer's worst nightmare. To date,

   I've not worked a noise problem we couldn't

   fix . . . but some of them have been exceedingly

   $time$ consuming. For example, see:



http://www.aeroelectric.com/Pictures/Misc/Too_Close.jpg



   Here's a photo of a ground fault detection

   transformer on a biz jet that's mounted too close

   to a bleed air tube that is excited by field flux

   leakage from a starter generator.



   A variety of techs spent 4 weeks chasing this

   one before they moved the airplane to Wichita.

   Our techs fought it for a week before one of

   them joined me during the xmas holiday and an

   ice storm to struggle with the beast. We found

   the propagation mode by accident. I still don't

   know root cause. The airplane was 13 years old

   and something changed to allow coupling of the

   starter generator to the engine and ultimately

   generate an AC magnetic field around the bleed

   air tube.



   The "fix" was to build an adapter plate to

   increase clearance between tube and transformer

   to 1" . . . i.e. we broke the propagation mode.

   Now, we COULD have chased down the change to the

   engine but after the airplane was down for 6 weeks,

   nobody was to eager to let me take the engine

   apart. We COULD have substituted a modern torroidal

   transformer but that would have generated a

   certification effort. So . . . moving the transformer

   turned out to be the practical solution.



   Since the first happenstance of this condition,

   a second airplane presented with the same problem

   and the spacer kit fixed it too.



   It's useful to consider the LONG answer. Not necessarily for

   examples of things to keep in one's bag of tricks for

   noise mitigation. The long answer is an illustration of

   the variabilities one might encounter. It further

   illustrates the fact that systems can become troublesome

   after a long history of satisfactory performance.



   The likelihood that a filtered D-sub will fix a problem

   in the field is low. It's rare that supplier of

   a product has failed to design their electro-whizzy

   to live in the real world. If a device using d-sub

   connectors presents with a noise problem, it's more

   likely that the solution will not include addition

   of a filtered d-sub connector.



   Bob  . . .

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