Date:         Sun, 20 Jan 2002 20:14:47 -0600
Reply-To:     Larry Alofs <lalofs@ENTERACT.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Larry Alofs <lalofs@ENTERACT.COM>
Subject:      Re: AFM upgrade using 16 volt tantalum capacitor
Comments: To: David Beierl <dbeierl@ATTGLOBAL.NET>
Content-Type: text/plain; charset=us-ascii

David Beierl wrote:
>
> At 09:22 AM 1/20/2002, Larry Alofs wrote:
> >Someone ought to reverse-engineer one of these things to see what the VW
> >solution really consists of.  The service bulletin says something about
> >"active components" (transistors).
>
> It's an active low-pass filter.  I don't know the time constants.  The
> capacitor approximation was arrived at experimentally by people trying 10
> uF and deciding that 20 worked better.  Dunno whether they did any math in
> the process.  In general you want something that passes say five Hertz and
> blocks say fifty.
>
> david
>
> --
> David Beierl - Providence, RI
>   http://pws.prserv.net/synergy/Vanagon/
> '84 Westy "Dutiful Passage"
> '85 GL "Poor Relation"

It seems to me that the resistances in the AFM are around 1K. With a
capacitor of 10 MFD you get an RC time constant of .01 seconds, with 20
MFD about .02 s.  It appears that we could go to 50 or perhaps 100 MFD
and the signal would still change fast enough to follow the movement of
the vane in the AFM.
 Whaddaya think?

Larry A.