> -----Original Message-----
> From: Jeremy Darling [SMTP:jdarling@ASKPIONEER.COM]
> Sent: Thursday, July 17, 2003 2:21 PM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Re: [OT]: Basic theory of a fuel gauge
>
> Well hate to argue, but I've worked and built many car's and truck's
> And while the gauge was positivly fed it is typically fed off of a
> simple solution that is composed of magnet wire wrapped around some
> sort of (depending on age) cardboard center.
>
The difference being I am used to tearing apart components made by Lucas
(Prince of darkness) over here in the UK. It's very likely the US
manufacturers took a different approach.  Having said that I have seen some
older French and italian gauages that used the same hot wire method. Most
lot of them use a coil of resistance wire wrapped around a bi-metalic strip
rather than the classic hot wire type guage.


>  Then an arm moves up
> and down via a float in the tank.  This was common in the 50's and
> 60's.  In the 70's they started using baffles in the tank as it was
> found that the sender could (and will) change too rapidly in quick
> accelerations, breaking, and tight turns.  Mid 70's to late 80's it
> was common to find a solution that was closer to what you are
> describing, but usually the tank still had some sort of baffling
> system incorporated into it (look at your tank, their are these
> dents in it that are very uniform) the new baffling system also
> worked well to hold the tank straps at uniform positions.  Late
> 80's until today they use many different types of senders (thou
> most are still based on the same idea) and typically the buffering
> occurs either in the onboard computer (witch tells the gauge
> where it should be) or in the gauge itself.  Want to see a perfect
> example tear apart the gas tank on a VW bug some time.  Even today
> if you tear down a tank their will be a float connected to a
> plastic cylinder open the cylinder and you find a simple wire wrap
> solution.
>
Most modern senders don't use a wound resistance wire per se, but have a
printed element on a ceramic substrate, a technique also used in some flap
type air flow meters and throttle position sensors.

Mike


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