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Thread: New Low Fuel Alarm Sensor

  1. #1
    Senior Member Eric Page's Avatar
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    Default New Low Fuel Alarm Sensor

    In an earlier thread, we discussed existing low fuel alarm sensors, and I mentioned that I found an alternative that might work. It's an ultrasonic liquid sensor that detects the presence or absence of fuel by shooting high-frequency sound pulses through the wall of the tank and measuring reflections. I bought the sensor from this Amazon listing, which was the lowest price I could find, by half.

    The sensor is 1.1" diameter x 0.75" thick. It has an 18" long 4-conductor pigtail with a 4-pin connector (JST XH-series). The four wires coming from the sensor are:

    • black (ground)
    • red (12V)
    • yellow (active high output)
    • white (active low output)

    When the sensor detects liquid, the active high output provides 12V and the active low output pulls to ground. It comes with three small plastic vials containing acoustic gel for testing, epoxy resin for mounting and hardener for the epoxy.

    DS1603NF.jpg SensorEpoxy.jpg

    I plugged most of the bungs on a Kitfox aluminum header tank and filled it ~3/4 full of water, then I mounted the sensor to the back of the tank with acoustic gel and tape. During testing I tilted the tank along the plane of its back face to move water behind the sensor. The sensor is rated for a power supply of 10-36V. I powered it with 12V from a bench supply and it consumed 13 milliamps (0.013 amps).

    It doesn't like to be mounted near the edge or corners of the tank; I'm guessing that the extra metal in those locations interferes with sensing. After some trial and error, I ended up mounting it ~2" down from the top edge, between two of the top-side bungs. In that location it detected changes as I tilted the tank very reliably, and I never saw it miss. Sensing a change of state takes about one second, at most.

    From my testing, I'd say it's a winner. It's dirt cheap, it's small and lightweight, it mounts outside the tank and it doesn't require an additional tank, hoses or fittings. I'm going to go ahead and use it. I'll design a small interface board to make it easy to connect to ship's wiring. Once that's done and tested, I'll post details in case anyone else is interested.

    One note: I don't know that the sensor location I tested is feasible once the tank is mounted to the airframe, so I'm planning to mark areas with no interference on the tank and re-test, when I get to that point.
    Eric Page
    Building: Kitfox 5 Safari | Rotax 912iS | Dynon HDX
    Member: EAA Lifetime, AOPA, ALPA
    ATP: AMEL | Comm: ASEL, Glider | ATCS: CTO
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  2. #2
    Senior Member rv9ralph's Avatar
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    Default Re: New Low Fuel Alarm Sensor

    The sensor you found has promise. My question is what are you using to display the reading. I have a simple, few electronics panel.

    Ralph

  3. #3
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    Default Re: New Low Fuel Alarm Sensor

    Good Deal! I was hoping it was going to work out.

    I'll be ordering one soon.

  4. #4
    Russell320's Avatar
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    Default Re: New Low Fuel Alarm Sensor

    How long will the acoustic gel remain in place after installation?
    Russ
    Model IV Speedster
    912UL IVO IFA
    RV6A
    Needle, Ball and Airspeed
    Maybe a little GPS

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

    Quote Originally Posted by Russell320 View Post
    How long will the acoustic gel remain in place after installation?
    It's only used for testing. Permanent installation is with the provided epoxy, though I suspect that a thin skim of Hysol would work just as well.
    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. #6
    Senior Member Eric Page's Avatar
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    Default Re: New Low Fuel Alarm Sensor

    Quote Originally Posted by rv9ralph View Post
    My question is what are you using to display the reading. I have a simple, few electronics panel.
    I'm going to use an alarm input to a Dynon EFIS, but using the sensor with an old-school instrument panel would be pretty easy too.

    I didn't mention it in my first post, but I plan to design two versions of the interface board to use with the sensor. One will be very basic, to support EFIS inputs, and the other will incorporate a dead-simple LED flasher circuit for less complex panels, like yours.

    I'll post more on those once I've designed and tested them, but it'll be a little while. I'll try to keep the assembly as simple as I can; I know some folks aren't very comfortable with board-level soldering.
    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

  7. #7

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    Default Re: New Low Fuel Alarm Sensor

    I have two of these, one for each wing tank. I'll install warning lights on my, yet to be built, panel. I have a float switch for my header tank to tell me that I really messed up with fuel management.

  8. #8
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    Default Re: New Low Fuel Alarm Sensor

    I ordered a couple of them. One for a spare. I'm thinking running to a small green LED light for full header tank, and a red LED light for low fuel in header tank. Thanks for posting these sensors up. JImChuk

  9. #9
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    Default Re: New Low Fuel Alarm Sensor

    There's some Arduino circuits out there for using with that sensor. But for header you only really need to know
    continuous low fuel, since the header always has a bubble in it working out exact volume would not be of much
    value

    Jeff

  10. #10
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    Default Re: New Low Fuel Alarm Sensor

    Quote Originally Posted by avidflyer View Post
    I ordered a couple of them. One for a spare. I'm thinking running to a small green LED light for full header tank, and a red LED light for low fuel in header tank. Thanks for posting these sensors up. JImChuk
    The header tank should always be full of fuel I would think under normal situations. I would have the sensor as high as possible on the header tank. And as I understand this sensor to work, is it will send current down the one wire if the sensor is reading fuel. That in my thinking would go to the green light, which will maybe also tell me everything is working with the sensor. If header tank starts to run empty, the sensor should then send a current down a different wire to the red warning light. Maybe I've got it all wrong, but that is what my plan was based on how I thought it could work. Am I wrong? JImChuk

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