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  1. #1

    Bench testing flame sensors?

    I have a hand full of f/s . Was just wondering can they be tested out of a furnace with just a flame (torch or lighter) and meter? Kind of like testing a t-couple on a bench? If not I will just check them on the shop furnace.

    Thanks

  2. #2
    Join Date
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    I would think that if you simulate a flame rectification circuit by sending like 90 to 120 volts through the flame sensing rod and having it ground out on something similar to a burner face with flame in between and your meter hooked up, in theory that should work.
    I would expect you would only get accurate results if the flame used was similar to a burner flame though; and the ground similar to 2, or a used burner.
    I'm really just guessing here though

    Sent from my GSIII on Tapatalk

  3. #3
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    Quote Originally Posted by DeHeatify View Post
    I would think that if you simulate a flame rectification circuit by sending like 90 to 120 volts through the flame sensing rod and having it ground out on something similar to a burner face with flame in between and your meter hooked up, in theory that should work.
    What! am I missing something here?
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  4. #4
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    Probably not... I may be missing a few screws! Maybe i shouldn't answer things first thing in the morning. . : }

    In rereading.. it should say "and the ground similar to a burner.. or use a used burner" so I guess that would basically be saying. No...why bother.

    Sent from my GSIII on Tapatalk

  5. #5
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    A flame sensor is not a magical device it is nothing but a metal rod with a ceramic or porcelain insulator. If you have continuity from the tip to the electrical connection, clean from excessive dirt and the insulator is not cracked it is good.

  6. #6
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    Does anyone know what voltage is used in a typical furnace flame rectification circuit? Is it actually 120VAC? If so, I'm glad I never tried to touch the sensor while a furnace was try to ignite. I've measures many flame rectification circuits with my meter but have never be bitten by one.
    "The bitterness of poor quality remains long after the sweetness of low price is forgotten". --Benjamin Franklin
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  7. #7
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    Depends on the control board air1. Put one meter lead on the flame sensor wire and the other to ground and check a few. It only takes a second. BTW the voltage is not only present when it's trying to light. Many boards send constant voltage to the flame sensor,checking for flame when there should not be one.

  8. #8
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    You can test flame rectification with most any voltage. I know of fireplaces that use a 3vdc system. It is the microamperage that counts. In order to test a flame rod in addition to a stable flame that closely approximates that of the subject appliance, you would need a ground that has a mass at least 4x that of the rod. Note that a rod which tests ok out of the unit does not guarantee it will work once installed so I see little benefit to this bench testing. As long as ceramic insulators are not cracked, there isn't much else to go wrong other than the actual electrical connections.

  9. #9
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    Interesting thread

    Could you mount it next to a burner flame and use the diode checking function on your meter, testing between the burner ground and flame rod lead?

    That may be a simple test, but I have never tried it

    You have sparked my curiosity though

  10. #10
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    Quote Originally Posted by hearthman View Post
    As long as ceramic insulators are not cracked, there isn't much else to go wrong other than the actual electrical connections.
    I was always told that flame sensors had a coating on them that helped the flame rectification, and that if it was damaged, it would not pass through the correct flame signal

    Is this accurate? Or was somebody misinformed

  11. #11
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    It is just a metal rod. This is somewhat oversimplified, but it just completes a circuit through the flame itself to prove ignition.

  12. #12
    Join Date
    Dec 2012
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    columbus, OH
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    I can't get a uA reading on my home furnace at all. Its an janitol with a spark igniter. flame sensor is coming from ignition module i know its good if i unplug it durners shut down and spark starts up and i know my meter is good ive tested the sensors at my school the same day. This has been bugging me can anyone please give me an explanation?

  13. #13
    Maybe I'm doing something wrong but I haven't replaced maybe a dozen flame sensors in 25 years

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