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jtprouty

Fuel Level Sensor Success!

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Hi All,

I'm relatively new to electronics but have had some success that you might be interested in. I've been trying to find a way to monitor fuel levels but couldn't find anything on the market that looked like it would work. After searching around and doing a lot of reading I've come up with a circuit that actually works!

It's done using a Quantum QT301-D processor (http://www.qprox.com/products/qt300_301.php) and some very basic circuitry. The biggest challenge was coming up with probes to actually measure the fuel since it measures the capacitance of the fuel. I ended up using copper sheet on the outside of the tank and a piece of small copper tubing inserted through the top of the tank. Now that the system is working I can tell exactly where the fuel level is by looking at my voltmeter. I'll but outputting that information to the ground station via an ADC.

I can post pictures if anyone is interested.

Happy flying,

Jim

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Very cool. One of the things that you need to observe is that the calibration is often affected by fuel brand, oil type, and alcohol/nitro content.

At least that is what I ran into. The fix is easy -- just create different profiles in your software for the fuel types you use and allow access to them at the field.

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Hi Mike,

I found that two strips outside the tank were too sensitive to outsite fields and cause too much interference. The copper tube inside the tank works very well right now. Installing it in the plane on Tuesday and hope to flight test it during the week.

Happy flying,

Jim

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Hi Guys,

I'm attaching a couple of pix to these posts as I'm not sure how to upload pix to this board. This post include on of the fule probes made of copper tubing. The tubing I used in the fuel tank is 1/16" with the ends soldered closed to keep fuel out.

post-6-1097270346_thumb.jpg

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This picture is of the entire unit. The box on top contains the circuit and will only be used during testing. Unfortunately the only electronics supplier that we have here is Radio Snack and the push buttons that I purchased were too big to mount on the board. I'm ordering some surface mount push buttons and will get rid of the box once they come in. Probably goop the circuit to the tank.

In this shot you can also see the copper plate that's been taped to the side of the tank. Note that the copper must run from the bottom of the tank to the top level that you want to measure. If the fuel level in the tank goes above the top of the plate the systems will reach its saturation point and you'll get erroneous readings at that end. Same goes for the bottom measurement.

post-6-1097270821_thumb.jpg

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This picture shows the calibration buttons for the fuel levels. They are set up with common power from the circuit with the low calbration connected to pin 2 on the QT301-D and high going to pin 7.

post-6-1097270987_thumb.jpg

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This final picture shows the calibration markings I used to verify that the circuit was working properly. The tank is a 50oz Du-Bro tank and as luck would have it, measures 10cm from top to bottom (we mount it sideways in our UAV). I made marks every centimeter and then calibrated the circuit. Voltage range was 0-4V so voltage change expected between marks was .4V. Sure enough, I got .4V and can now read my fuel level via a voltmeter. :)

We did make two modifications to the basic circuit. We addes a capacitor and a resistor to pin 6 and to bring up the voltage and to help with averaging. The other mod was to add an OpAmp to allow for lower voltage drop along long wire runs.

Hope this information is helpful. It's nice to be able to help out for a change! :-p

post-6-1097271338_thumb.jpg

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I found that two strips outside the tank were too sensitive to outsite fields and cause too much interference.

Believe me, I spent waaaaaay too many hours with the external strip sensing and had mixed success in developing a commercial offering. Fuel type, content, etc plays a huge role in setup. Not exactly practical for selling an easy to install solution that fits all roles. Obviously, the goal was not to start drilling holes in a tank, but there's really no way around it for some cases (metal tanks,etc). I was also unsuccessful in sensing gasoline or kerosene from the external strips. Senses water well though ;)

Good luck with flight testing.

Michael

Edited by Mluvara

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Hi Michael,

I'm actually using this one to sense gasoline and have found it to be pretty accurate. I've been able to get consistant results outside of the aircraft and will be trying it inside the plane on Tuesday and hopefully flying it on Wednesday. I'll post results once I've done some more testing.

Happy flying,

Jim

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Yes, but it appears that you have a tube inside of the tank. I couldn't get it to work with just a capacitive measurement through the tank wall. The idea was to be non-intrusive to the tank and just add a sensor. It should work fine if you are sensing it with a tube touching the fluid. Nevertheless, it is a touchy circuit and takes some time to implement as you have found.

Michael

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I didn't want to use the tube either but with some B-1/2 sealer (it's an aircraft grade sealer) you can seal the hole very quickly and permanently. I've just used shoe goo temporarily on this one but will break out the sealer once I know everything is working well.

Happy flying,

Jim

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