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Re: filtering question
---------- Forwarded message ----------
Date: Mon, 29 Sep 1997 20:28:51 +0300 (EET DST)
From: Harri Suomalainen <haba-at-cc.hut.fi>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: filtering question (fwd)
On Sun, 28 Sep 1997, Tesla List wrote:
> Concerning RF filtering in the power cabinet itself, I have a Sprague
> Electric RF Interferance Filter Model No. JN10-1501F1. It is a 3x40amp
> 240v RFI filter.
> It is labeled "Load" side, and "Line" side. I am assuming that this was
> designed to remove RF eminating from the line side, before going to the
> load, hence it's orientation. Of course, in our situation, it is the load
> that is producing the RF, so should the orientation be reversed, or does it
> matter?
The ones I've run across (the most typical model) is usually like this:
at line side a larger cap, then a common mode choke, then smaller caps.
This is obviously a low-pass filter having better protection to the noise
coming from the side smaller caps are (ie. load). The most usual case is
that the apparatus is making noise and it should be filtered so that
it won't enter the line.
In this case reversing the filter is no answer, actually it is better
*not* to reverse it!
The connection type makes a lot more info. Some types have caps at the
load side connected to earth making a viable rf feedpath for common
mode noise to the earth if connected that way.
> And will this provide adequate line filtering?
Common mode choke does not filter all noise. It depends weather noise
is common mode noise or differential mode noise.
Yes, some models of filters have many stages and filter perhaps both
common mode and differential mode noise. As I'm not familiar with
perticular type Sprague filter I cannot help further.
Anyway, I'd always like to be on the safe side with the heavy kick-back
a pole big can give. I'd filter both common and differential mode noise
very heavily. I'd have heavy MOV's there too.
--
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Harri.Suomalainen-at-hut.fi - PGP key available by fingering haba-at-alpha.hut.fi