Q for Jim Weir or others: solid state fuel level probes?

"Evan Carew" wrote in message
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Isn't this just a capacitance meter on a chip?

Evan

Yes and no. It's not meant to measure absolute capacitor values. It compares
a relatively large fixed capacitance (reference capacitor) to a much smaller
external capacitance. The external capacitance can be two metal strips
attached to the tank, right next to eachother. The air around the strips,
the plastic of the tank and the fuel inside the tank form the dielectricum
for the small capacitor. When flying, the fuel slowly gets replaced by air,
so the capacitor changes value. The chip translates this into digital
information or a PWM signal, depending on which chip you select. PWM is easy
to convert to a voltage, and can drive standard fuel gauges.

The full inner working is a bit more complex and includes

I have used some of their other chips (QT60040) for solid state keypads and
they work quite well. I have ordered a couple QT300's to play with, if it
works out I'll post results here. Possible issues are stability over
temperature, and maybe radio interference. These chips use some kind of
pulse burst system which may introduce noise.

Rob

Jim Weir wrote:

I think the chips themselves are worth investigating. I do have a prejudice
against UK semiconductor manufacturers, having had a major one and a minor one
simply stop producing parts that rendered several tens of thousands of dollars
of hardware and engineering time down the drain.

I realize that they are not ALL like that, but the only two that have screwed me
thus far in 40 years have been UK based.

Jim

-If you want to do some tinkering of your own (legal disclaimer here..) you
-may want to look at sensor chips from QProx (www.qprox.com). They have a
-couple of capacitive level monitor chips like the QT300/301 or QT117L that
-may provide real-time non-contact level information. If you have a non-metal
-tank you may be able to just attach two strips on the side of the tank and
-be done.
-
-Jim, what do you think?
-
-Rob
-

Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

I've used the QT114 for a single point fluid (alcohol) level control in
a one liter plactic cylinder. Precise within fractions of a mm. I also
used the QT110 for an isolated (behind a glass display window) proximity
switch for one of our students' Physics class projects. The QT117 or
QT300 might work for a tank level gauge. They even have "slosh" filter
software built in,