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Thread: Low Fuel Sensor

  1. #41
    Senior Member Eric Page's Avatar
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    Default Another Option for Low Fuel Sensing?

    I'm investigating an idea for low cost, non-contact low fuel level sensing.

    After pondering this thread for a couple of days, I started searching for fuel level sensors. Most of the results were float switches, but I also found some optical sensors like the one Jerry showed. Many of them aren't cheap and all of them require contact with fuel, which means a hole in the tank and the possibility of plastic deterioration.

    Then I got to thinking... some time ago I built a project using an ultrasonic distance sensor. I recalled that while searching for that sensor I also found liquid sensors, but I couldn't remember any details. It took some online sleuthing, but I finally came up with the sensor manufacturer's website (Chinese).

    There are basically four versions of this company's sensor:

    • DS1603L - RS-232 output
    • DS1603DA - RS-485 output
    • DS1603AQ - analog voltage output
    • DS1603NF - "switch" output (pulls to 12V or to ground)

    The first three are of little use to us, primarily because interfacing them to an EFIS or panel indicator would be a bit of a hassle. However, the last version is more interesting. It has a simple high-low output, which will talk to a digital or alarm input on an EFIS, or it could drive an LED indicator directly (like one of these flashing LEDs, perhaps).

    I ordered one of the DS1603NF sensors, and I have a new aluminum header tank on order from Kitfox. When those items arrive I'll run some tests and report back here. Stay tuned...

    -----

    P.S. For anyone who's interested in how these sensors work, this Texas Instruments application note gives a useful overview.
    Eric Page
    Building: Kitfox 5 Safari | Rotax 912iS | Dynon HDX
    Member: EAA Lifetime, AOPA, ALPA
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  2. #42
    Senior Member PapuaPilot's Avatar
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    Default Re: Low Fuel Sensor

    Anything that switches or has a variable (analog) output can be connected to the Garmin G3X and probably a Dynon. I have 3 or 4 user programed inputs to my G3X touch of things that were not already included inputs of the GEA. These come up as a CAS warning.

    As an example, I added a starter warning with a small wire connected to the starter solenoid output incase the solenoid were to stick. I had it happen once on an amphibious C-206 and it destroyed the started because it was still engaged. After starting my Kitfox I always check the CAS warnings to make sure the "STARTER" warning is off. I also hooked up the warning wire from my EarthX battery.
    Phil Nelson
    A&P-IA, Maintenance Instructor
    KF 5 Outback, Cont. IO-240
    Flying since 2016

  3. #43
    Senior Member 109JB's Avatar
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    Default Re: Low Fuel Sensor

    Why not use a thermistor based sensor like cars have had for at least 50 years?
    John Brannen
    Morris, IL
    Sonerai IIL (Single Seat)
    Kitfox 3/4 1050 - Rotax 582 (Back Flying and sold)
    Kitfox IV 1050 - Rotax 582 (sold)
    Kitfox IV 1200 Speedster - Rotax 912 UL (project)
    Piper Twin Comanche (Sold)
    Glasair 1 FT (Waiting to start)

  4. #44

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    Default Re: Low Fuel Sensor

    I'm using this sensor:

    https://www.aircraftspruce.ca/catalo...clickkey=17718

    with an AN 867-4 Bung welded into the header tank: I have the round header tank that is mounted behind the baggage sack:

  5. #45
    Senior Member Eric Page's Avatar
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    Default Re: Low Fuel Sensor

    Quote Originally Posted by PapuaPilot View Post
    Anything that switches or has a variable (analog) output can be connected to the Garmin G3X and probably a Dynon.
    That's pretty much what I figured, given my quick perusal of the Dynon installation manual, but I didn't want to make a blanket statement that it would work with every EFIS. I'm glad to hear that Garmin supports direct analog inputs, and I'd be very surprised if MGL weren't similar.

    Quote Originally Posted by 109JB View Post
    Why not use a thermistor based sensor like cars have had for at least 50 years?
    A thermistor based sensor would still require a hole in the tank and contact with fuel. Also, it would likely require significant signal conditioning to reliably convert a tiny resistance change into a binary logic flip without nuisance indications caused by changes in ambient temperature or refueling.

    Quote Originally Posted by 4Hummer View Post
    I'm using this sensor:

    https://www.aircraftspruce.ca/catalo...clickkey=17718

    with an AN 867-4 Bung welded into the header tank.
    No doubt that system works well, and I wouldn’t suggest that anyone who already has a working sensor take it out or replace it.

    I’m trying to come up with a solution for aircraft that don’t already have a low fuel alert. Hopefully one that weighs a few ounces and doesn't require any modification to the fuel system.

    Maybe the sensor I found won't work, but for the price it seems like it's worth a try. Easy and cheap might entice owners who otherwise wouldn't have installed a low fuel sensor, and that can only improve the safety of the fleet!
    Eric Page
    Building: Kitfox 5 Safari | Rotax 912iS | Dynon HDX
    Member: EAA Lifetime, AOPA, ALPA
    ATP: AMEL | Comm: ASEL, Glider | ATCS: CTO
    Map of Landings

  6. #46
    Senior Member 109JB's Avatar
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    Default Re: Low Fuel Sensor

    A thermistor based sensor only needs a bulb and 12V to work.

    https://youtu.be/UEmbRJKlSeI?t=328
    John Brannen
    Morris, IL
    Sonerai IIL (Single Seat)
    Kitfox 3/4 1050 - Rotax 582 (Back Flying and sold)
    Kitfox IV 1050 - Rotax 582 (sold)
    Kitfox IV 1200 Speedster - Rotax 912 UL (project)
    Piper Twin Comanche (Sold)
    Glasair 1 FT (Waiting to start)

  7. #47
    Senior Member rv9ralph's Avatar
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    Default Re: Low Fuel Sensor

    Belite radiant instruments have a series of light instruments, including several fuel sensor products that could fit your needs... if you don't want to use the Kitfox Aircraft factory recommendations.

    Belite can be found at: https://radiantinstruments.com/bingo-4-liquid-detector/

    Ralph

  8. #48
    Senior Member Eric Page's Avatar
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    Default Re: Low Fuel Sensor

    That detector uses exactly the sensor I listed above. They blacked out the part number in the demo video, but it looks identical and the QR code on the label confirms that it's the DS1603L.

    The product description mentions a "USB port" but it doesn't explain how that's supposed to be used. RS-232 is not USB, so they would have to add a bridge IC and a USB connector, but why bother? If it were plugged into a USB port on an EFIS, it would be ignored unless the EFIS had been programmed to recognize the sensor and do something with the data. So, what is the sensor supposed to connect to, other than the LED indicator module they sell for it, and why do they sell the sensor by itself? Very strange.

    At $129.95, their markup on the sensor is eye-watering. They sell individually for as little as $10 delivered, and probably less in quantity.

    At least this is evidence that the sensor has already been tested and works for this purpose.

    Good find, Ralph. Thanks.
    Eric Page
    Building: Kitfox 5 Safari | Rotax 912iS | Dynon HDX
    Member: EAA Lifetime, AOPA, ALPA
    ATP: AMEL | Comm: ASEL, Glider | ATCS: CTO
    Map of Landings

  9. #49
    Senior Member Eric Page's Avatar
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    Default Re: Low Fuel Sensor

    The ultrasonic liquid sensor arrived yesterday. I didn't have time this weekend to test it, but I'll power it up soon and post the results.

    DS1603NF.jpg

    It came with three small plastic vials. The first is unlabeled and contains a clear, odorless gel substance, which I'm guessing is an acoustic coupling gel used for testing, similar to the stuff that medical technicians smear on patients while doing an ultrasound. The second is labeled "R" and contains what smells and feels like the resin half of a two-part adhesive, so I presume the third vial (unlabeled) must be the hardener.
    Eric Page
    Building: Kitfox 5 Safari | Rotax 912iS | Dynon HDX
    Member: EAA Lifetime, AOPA, ALPA
    ATP: AMEL | Comm: ASEL, Glider | ATCS: CTO
    Map of Landings

  10. #50
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    Default Re: Low Fuel Sensor

    I have the poly header, and sensor in it. I had to cover the header with hvac metal tape to block out
    extraneous light from making it false alert. It does flicker a bit when you get around 1/2-1/4 fuel and
    tends to flicker more and more as you get lower on fuel. So I sort of like it, but you kind of have to get
    used to that it's not a hard off/on in function, at least until you have a fuel stoppage ...

    I don't have any fuel leaks, but I can still smell fuel in the plane when it's been sitting, and as far as I
    can tell the odor of avgas (I run 100LL) is all that gets through the tank ...

    Jeff

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