RE: [SI-LIST] : EMI due to fans

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From: Jim Muccioli (jastech@ameritech.net)
Date: Fri Oct 13 2000 - 23:27:50 PDT


Ken,
I have written several papers on small dc motors, ITEM UPDATE 2000 (shipping
first week of November) will be publishing a paper "Broadband Testing of
Low-cost Filter Solutions for DC Motors" that I will be presenting at the
"Electrical Manufacturing & Coil Winding Association EXPO 2000", November 1,
2000 at Cincinnati, OH. After the paper is presented I will put it up on my
web site. http://www.jastech-emc.com or http://www.x2y.com. If you need an
advance copy please sent me an E-mail.
Best Regards,
Jim Muccioli

-----Original Message-----
From: owner-si-list@silab.eng.sun.com
[mailto:owner-si-list@silab.eng.sun.com]On Behalf Of Ken Cantrell
Sent: Thursday, October 12, 2000 10:49 AM
To: Michael Nudelman; Sunil Kumar
Cc: Patrick Lawler; si-list@silab.eng.sun.com
Subject: RE: [SI-LIST] : EMI due to fans

Which is why I think you have a global grounding problem. You are unable to
shunt the noise to ground. You are on the edge, and just about anything you
do will tip you over. Hypersensitivity (being microphonic) is a red flag
for global grounding issues. Are you in a metal chassis?

-----Original Message-----
From: owner-si-list@silab.eng.sun.com
[mailto:owner-si-list@silab.eng.sun.com]On Behalf Of Michael Nudelman
Sent: Thursday, October 12, 2000 11:01 AM
To: Sunil Kumar
Cc: Patrick Lawler; si-list@silab.eng.sun.com
Subject: Re: [SI-LIST] : EMI due to fans

Are DC fans collector-type ? Then you have sparks, and so you are bound to
have
some EMI.

Sunil Kumar wrote:

> Patrick.
>
> Yes, DC fans are being used. I have already tried that. I had powered up
> fans from separate power supply. But still I did see increase in jitter.
>
> Sunil
>
> On Thu, 12 Oct 2000, Patrick Lawler wrote:
>
> > If a DC fan is being used, the pulsating current load current may be
> > feeding back through the power supply into the logic circuitry.
> > This applies whether the fan is brush or brushless.
> >
> > If this is your situation, try powering the fan from a separate power
> > supply to see if the symptom goes away.
> >
> >
> > On Thu, 12 Oct 2000 11:41:55 +0500 (GMT+0500), Sunil Kumar
> > <sunilb@cdotb.ernet.in> wrote:
> > >I am measuring cycle-to-cycle jitter in clock in a system, where clock
> > >(PECL, 50MHz) is going from one PCB (card) to other through twinax
> > >cable. In the second card clock is converted into TTL and then
distributed
> > >to various ICs. I am looking at the clock just before the PECL-to-TTL
> > >convertor. Both the cards are in the same backplane. The system is
> > >equiped with a set of fans for cooling, which are kept below the card
> > >frame. Now what I have observed is, when the fans are not on, jitter is
> > >much much less in comparision of the jitter when fans are on. I think,
the
> > >fans are generating EMI, which is disturbing the planes in the
backplane
> > >and the cards, and hence jitter is increased. Any explanations?
> > >
> > >One more thing which I have observed is, the PECL-to-PECL clock
> > >fanout buffer (no PLL inside) is reducing jiiter (with fans off), i.e.
> > >jitter at input is more than that at output. Can anybody explain this?
> > >
> > >Is there any PECL-to-TTL clock fanout buffer which adds very low
> > >jitter? The PECL-to-TTL buffer which I am using, is adding lot's of
> > >jitter.
> >
> >
>
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