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capacitive fuel gauge for petrol

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angus:
the one i have removed is a magnetic float and 9 reed switches, just as you decribed... problem is 2 fold, the float is not as buoyant in fuel as it would be in water, so only just floats, and i suspect sink on harsh cornering, even though it is in a dip tube with small hole top and bottom
also 9 reed switches leaves gaps between them, there isnt physical room in the tube for more, and it is sometimes a few miles before i sees the first switch on the journey
the arduino that currently runs it, has damping programmed in for corners, but obviously isnt so good on first switch on...

its in a lotus 7 style kit, so is quite often subject to harsh cornering, hence the baffled tank
 

hermetic:
I think I would go for a better float, or see what you can find available to read fuel pressure (weight) in the tank as tank contents.
Phil

AdeV:
IMHO the problem with floats is they can end up not floating (which is not TOO bad, at least they end up reading "empty" all the time; worse if the mechanism jams & it reckons you have fuel when you don't... Plus, it's an electromechanical system, and on cars, anything mechanical will eventually break...

Weight's no good, because the weight transfer as the car moves around on the road, goes up/down hills and bumps, will always be throwing off the readings. Hit a big bump with a 1/2 full tank and one moment it'll read full, the next empty, then full again until all the oscillations in the suspension and the fuel itself damp down...

Nah, I have to say, I like the idea of a capacitive sensor. No moving parts, once the capacitance range is determined, and any temperature offset compensated for; it should be extremely reliable, long lasting, high resolution and very accurate. The 2nd tube idea is great, if there's room in the tank for it, but it should still be possible to use an arbitrary off-the-shelf capacitor which, once the circuit is tuned, should be just as good as a 2nd tube, and also much cheaper and smaller.

awemawson:
Another approach is is sonar technology as used in domestic central heating oil tanks . The Watchman Sonic is an example.

A sonic burst is transmitted towards the oil surface and the reflected sound is detected. The transit time is a function of tank level. Now obviously a lot of averaging would be needed in an automotive application  but the technology works (I have three oil tanks here on the farm monitored by them)

The averaging could simply be a tube with only a small hole at the bottom, and having the sonic sender in the top

angus:
Trouble with sonic devices, they need as gap between the liquid level and the sensor head... the ones we use at work need 12"

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