Hi all....

I've just taken delivery of a fuel tank sensor and display for the car I'=
m
building next week :)
However, the sensor has got me thinking.... Many moons ago, there was a
long thread on this list about sensing fuel levels in containers. I seem
to remember optical solutions where popular. Most people shyed away from
anything involving electricity within the fuel tank. So when I took recei=
pt
of my sensor I was rather surprised to find an open potentiometer- a floa=
t
arm actuates the wiper (all this under petrol or in the vapours). This le=
ads
to believe me that
1) the company that produces this is heavily insured :)
2) I may have pre-warmed petrol and/or a free afterburner function
3) the meter limits the current going down the sensor.

I tested the resistance and it was fairly linear 0-300 ohms. The meter ap=
pears
to be moving coil/iron but it's sealed so I can't peak inside. Any ideas
on how the internals of the meter work? I'm also curious how they stop th=
e
petrol guage from being adversely affected by the car battery voltage (9-=
15v)....


I'd probably be tempted to use the R as part of a RC oscillator circuit
going into a F/V converter. Hopefully that way I'd limit the current thro=
ugh
the potentiometer. I'm not sure what heat dissapation I'd be happy with
in my petrol tank though!! If I was going to invent it from afresh I'd us=
e
a platic bowden cable off the float arm and have it actuate an external
potentiometer.... But any ideas how they do it in the real world??

Ben

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