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A year or so ago I built a simple gauge for the fuel oil tank in my basement using a MaxSonar-EZ ultrasonic distance sensor. At some point, it stopped working, and when I removed it from the tank today, I found that there's quite a bit of black … uh, "stuff" on portions of the PCB, wires, and pads. I'm assuming it's corrosion of some kind. Although it's not outside of the realm of possibility, I don't believe the sensor got splashed and I know it wasn't submerged. I don't know if the transducer is itself damaged. I never liked that sensor much, so I've got a Parallax one that I intend to put in it's place. I'd like to find a way to make this sensor more resistant to the environment (assuming it's the environment that's caused the MaxSonar unit to die), or find a better replacement. I'm fairly confident that I can protect the Parallax sensor's PCB from the air in the tank with some acrylic sheet and Permatex gasket maker, but the transducers will necessarily be exposed. I'm not sure this is sufficient, however. I'd appreciate other suggestions on how to make a more durable gauge!

Thanks, Brian

blalor
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  • You put the PCB and electronics in openly in the tank? I hope you took serious precautions against any possible sparking... – Mark Sep 02 '11 at 23:42
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    @Mark - I do believe that most fuel-oil will not burn openly. You have to atomize it and heat it to get it to combust. – Connor Wolf Sep 03 '11 at 06:35
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    @Mark - Fake is right. You can't compare fuel-oil with gasoline. You have to heat the oil's surface with an open flame to get it burning, and even then it may not combust immediately if the flame has a rather low temperature. A spark won't do anything. – stevenvh Sep 03 '11 at 07:12
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    The liquid is not the concern, its not even the concern with gasoline, you can actually throw a lit match into a very well ventilated tub of liquid gasoline and it will simply go out. The vapors however, are another story. An example MSDS sheet for No. 2 home heating oil reads: "Vapors may be ignited rapidly when exposed to heat, spark, open flame or other source of ignition. When mixed with air and exposed to an ignition source, flammable vapors can burn in the open or explode in confined spaces..." Vapors can and do build up in tanks and most are not evacuated of oxygen. – Mark Sep 03 '11 at 18:02

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http://en.wikipedia.org/wiki/Conformal_coating

You can use a conformal coating on the PCB at least. Not sure about the sensor.

dext0rb
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I'm not sure how well it would work, but I would think ultrasonic sound waves would penetrate a baggie.

Could you just put the sensor in a zip-lock bag (or similar)?

MaxBotix, if you ignore their offensive Christian PCB-imagery, makes a "Outdoor" ultrasonic transducer that is hermetically sealed, and weather rated.
They also offer "F-Option for Chemical Resistance - Fluorocarbon sealant for our Outdoor Ultrasonic Sensors"

Connor Wolf
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  • That's not a bad idea. I wanted to get away from the MaxBotix product, however, since its minimum range is 6 inches, and that accounts for a non-trivial amount of fuel in the tank. The Parallax PING reads down to 0.8 inches. – blalor Sep 03 '11 at 11:29
  • "but I would think ultrasonic sound waves would penetrate a baggie" -- most likely some major attenuation at the interface. Worth a try but I'm skeptical. – Jason S Sep 03 '11 at 15:57