Fuel level sensor

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Askov
Posts: 2
Joined: Sat Nov 23, 2019 10:21 pm
Location: Denmark

Fuel level sensor

Post by Askov »

Has anyone tried using high precision pressure transmitters instead of the conventional lever type?
There are a few benefits from using pressure transmitters. Low weight, no moving parts and accurate measurements from full tank to empty.
But what am I missing since I can’t find anyone doing it?

https://www.apgsensors.com/pressure-tr ... ransducers

https://www.kelleramerica.com/pressure- ... itter.html
Building a TSi High Wing in spe
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lutorm
Posts: 76
Joined: Fri Jan 28, 2022 11:00 pm
Location: Sweden

Re: Fuel level sensor

Post by lutorm »

This is an old post, but I was curious so I went looking at those datasheets. I think the problem is that the pressure you need to measure is quite low. The ballpark pressure from a full tank would be about 1 kPa or 0.15psi. Let's say we want to measure the fill level to 1%, then you need an accuracy of 10Pa. Since the ambient pressure in the tanks change depending on altitude, you need a differential sensor that can measure 10Pa on top of a 100kPa background. Not impossible (it's actually about the measurement range and accuracy of the pitot-static airspeed sensor) but not trivial, especially not when one side of the measurement is gas and the other liquid. The measurement will also be affected by acceleration, i.e., how many G you pull, but you could probably average that out. The pressure difference also depends on the density of the fuel, so it would be affected by the temperature of the fuel as well as whether it's avgas or mogas.

It can clearly be done -- liquid-fueled rockets measure their propellant level this way -- but, being somewhat familiar with the complexities of that method, a capacitative probe seems more straightforward and also has no moving parts.
Blog of various projects: https://blog.familjenjonsson.org/blog/
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