Newsgroups: comp.robotics
Path: cantaloupe.srv.cs.cmu.edu!das-news2.harvard.edu!fas-news.harvard.edu!newspump.wustl.edu!news.ecn.bgu.edu!vixen.cso.uiuc.edu!howland.reston.ans.net!ix.netcom.com!netcom.com!nagle
From: nagle@netcom.com (John Nagle)
Subject: Re: Stretch sensors?
Message-ID: <nagleD8Bqs8.JAw@netcom.com>
Organization: NETCOM On-line Communication Services (408 261-4700 guest)
References: <3oblel$m48@linda.teleport.com> <3omvlt$7ro$1@mhadg.production.compuserve.com>
Date: Tue, 9 May 1995 18:45:43 GMT
Lines: 22
Sender: nagle@netcom6.netcom.com

Steve Ranzinger <70672.113@CompuServe.COM> writes:
>How about using a spring and measure the variation in capacitance 
>generated between the coils of the spring as it is stretched to 
>different lengths?  I think this approach would give you very 
>precise measurements.  If you've ever tried to build a simple FM 
>transmitter, and made your own coils, it doesn't take much 
>movement in the loops of the coil to really change the frequency!

      Measuring the capacitance between two plates, one of which can move,
is a common sensor technique.  It's also used for liquid level sensors;
the liquid can be either the other plate or the dielectric.  This is for
short distances, the shorter the better.  Things like solid-state
accelerometers use this approach.  Generally, it's used for separations
under 1mm.

      For longer movements, you need something with better external noise
rejection, like a LVDT transducer, which is a kind of split transformer.

      Anybody find a source of conductive elastomers yet?

					John Nagle
     
