How to get a good fuel reading (sloshing problem)
How to get a good fuel reading (sloshing problem)
(OP)
I plan to use a capacitive fuel probe to detect the level of fuel in commercial vehicles. The principal is simple, the probe provides a frequency (or voltage) that is proportionate to the level of fuel. Doing the math based on tank geometry is also OK.
But what I am wondering about is hot to get a proper reading with all the sloshing that is going on in the tank.
What is the best approach to designing an algorithm to do this?
Also, how long does it usually take the fuel tank to settle once the vehicle comes to a stop? (idea would be that rather than taking measurements while vehicle is moving, they could be taken only when standing).
Thanks





RE: How to get a good fuel reading (sloshing problem)
If you time- average a decent number of samples over a period exceeding the natural slosh period, you shouldn't have to worry about, or detect, whether the vehicle is in motion.
Doing the measurement quasi- continuously also saves you from embarrassment over truncated and inaccurate readings associated with operators who shut down every system as soon as the vehicle comes to rest.
Mike Halloran
Pembroke Pines, FL, USA
RE: How to get a good fuel reading (sloshing problem)
Thanks Mike. Well, the idea to measure while stopping was, well, just an idea.
From what I have read so far, and I am still Googling, of course averaging is the way to go. But what type of average... there are many.
By the way, a related issue is that, the idea is not to provide data logging of continuous level monitoring. That would require way too much storage and anyway I don't see the benefit. My idea is to log regular intervals (say every 1 liter drop) and of course irregularities (like fueling or siphoning).
Any thoughts?
Thanks
RE: How to get a good fuel reading (sloshing problem)
Regards
Pat
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RE: How to get a good fuel reading (sloshing problem)
Thanks patprimmer but I cannot modify the tank other than to make the hole for the probe to go in.
RE: How to get a good fuel reading (sloshing problem)
My questions:
Are capacitive sensors anywhere near linear with fuel level?
What dynamic range is the raw signal?
If the sensor uses charge/discharge time to measure capacitance, how often will its output change anyway? No point in sampling faster than that.
Mike Halloran
Pembroke Pines, FL, USA
RE: How to get a good fuel reading (sloshing problem)
My concern is as I mentioned the sloshing of fuel in the tank as the vehicle moves and getting a good reading. I know/assume it amounts to averaging, but not sure exactly how.
RE: How to get a good fuel reading (sloshing problem)
No matter; just sample periodically, stuff the data into a ring buffer, and report the level as the AA of the last N samples, where N is the size of the ring buffer. You can work out the time delay/ phase error associated with this sort of reporting, and compare it with any specs you have for step function response, which you didn't mention.
Mike Halloran
Pembroke Pines, FL, USA
RE: How to get a good fuel reading (sloshing problem)
Mike Halloran
Pembroke Pines, FL, USA
RE: How to get a good fuel reading (sloshing problem)
Why are you reinventing the wheel?
Cheers
Greg Locock
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RE: How to get a good fuel reading (sloshing problem)
Are you an engineer or a student.
Regards
Pat
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RE: How to get a good fuel reading (sloshing problem)
RE: How to get a good fuel reading (sloshing problem)
What size hole can you have in the tank?
As someone associated with fuel delivery and level sensing for motor vehicles, I worked with many 'clever' electronics and software engineers that spent plenty money and plenty time trying to devise the perfect indicator and never got much further than the performance of a baffled reservoir with a resistive sensor.
Bill
RE: How to get a good fuel reading (sloshing problem)
RE: How to get a good fuel reading (sloshing problem)
In fact, I distrust a level indicator that _doesn't_ do it.
Mike Halloran
Pembroke Pines, FL, USA
RE: How to get a good fuel reading (sloshing problem)
Regards
Pat
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RE: How to get a good fuel reading (sloshing problem)
Linearisation of any sensor is easy if there are no vehicle dynamics to be taken into account. As soon as the tank starts moving, all bets are off until the general relationship between a typical vehicle 'mission' and the reaction of the liquid bulk is studied.
Bill