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Magnetron fail & empty oven detection

Discussion in 'General Electronics' started by Mark rainess, Jun 5, 2007.

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  1. Mark rainess

    Mark rainess Guest

    I am building a machine that uses a microwave oven. I need a simple and
    cheap way to reliably determine 1) that the magnetron is operating, and
    2) that the oven cavity is not empty.

    My first attempt was a diode RF sensor on a board mounted outside the
    cavity with a short probe projecting inside through a hole. The food
    item being heated moves relative to the probe and causes the response to
    increase and decrease as it acts on the E field. When I see the changing
    response I know the magnetron is working and the oven is not empty. This
    works fine if the food is by itself; but, the food rests on ceramic
    which moves. The ceramic material influences the E field to a large
    degree and makes it impossible to detect the food item. I can't
    eliminate the ceramic or change to another material. It seems I need an
    entirely different approach.

    If I put two RF probes in the waveguide spaced one-quarter wavelength
    apart, I think the phase relationship between the two probes will change
    when the oven is empty.

    I want to avoid the expense of adding a secondary waveguide in order to
    make a directional coupler.

    Does anyone have an idea for a simple cheap way to detect that the oven
    is empty.

  2. Robert Baer

    Robert Baer Guest

    Try adding a low value resistor in series with the maggie supply to
    sense load current.
    If the maggie is not working at all, the current will be zero.
    The load current, in most cases, will be rather low with an empty
    oven, and much higher (and possibly varying due to rotating items) if
    the oven is not empty.
  3. Jasen

    Jasen Guest

    ceramic is something, therfore the cavity is not empty,

    what do you really want?
    probably won't work either.
    define empty.

  4. neon


    Oct 21, 2006
    use thermocouple wire and monitor the output
  5. Graham

    Graham Guest

    I feel the above might be a fruitful approach.
    I would be inclined to put the series resistor in the
    transformer secondary rather than the Magnetron
    cathode thus avoiding the voltage doubling effect
    of the hv rectifier/capacitor/magnetron configuration.

    I doubt if monitoring the transformer primary would
    work too well, as oven transformers work near

    FFS be careful.

    I remember doing something similar years ago and
    used a torch-bulb and ORP12 arrangement as
    a HV opto-coupler.

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