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Automatic Microwave Plasma Waveguide Tuner

Discussion in 'Electronic Design' started by O5O, Jul 11, 2006.

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  1. O5O

    O5O Guest

    Does anyone here have any experience with an automatic microwave tuner
    circuit?

    I was considering using a 3-3/4" stroke push / pull solenoid coupled to an
    LVDT. Where I would put a microwave detector diode in the waveguide near the
    dummy load, and when reflected radiation is detected, move the tuner via the
    solenoid and LVDT to scan for the position that minimizes reflected power.

    The planned application is regarding a microwave plasma jet that will inject
    glassy ceramic material into the flame to be melted and deposited. I suspect
    that varying rates of material deposition will change the load impedance and
    require continuous tunning. Thus the requirement for an automatic tunning
    circuit seems plausible.

    --
    Christopher R. Thompson
    Student of Mechanical Engineering
    California State Polytechnic University, Pomona
    CSUHome: http://www.csupomona.edu/~cthompson1/
    MyHome: http://christoffur.hopto.org/
    Email: mailto:
     
  2. Guest

    It might work. A 3.75" push-pull solenoid is not a good way of
    generating this sort of travel - the usual solution is a rotating
    stepper motor with a lead screw threaded through the axis. Go to

    http://www.mclennan.co.uk/index.html

    and check out "linear actuators" for some examples. You can buy some of
    their stuff ex-stock from Farnell and RS Components.

    Proper linear stepping motors - no lead screw - are more fun, but
    harder to get hold of. I've got one on my desk at the moment, but it
    cost $US2000 and it took four months from enquiry to delivery.

    The LVDT is a nice position sensor, but bulky and a lot longer than the
    travel you are measuring. Heidenhain used to be the major supplier of
    linear messuring systems - and may still be for all I know.

    http://www.heidenhain.com/

    A lot depends on the precision and resolution that you need.
     
  3. O5O

    O5O Guest

    Ok Bill. Thanks a lot.

    I don't think that I really know what is going to happen when I start
    feeding various materials into the plasma. I am guessing that a certain
    amount tunning will be necessary, and would like to make that process as
    automatic as possible.

    What we are really after is minimum reflected power, and the position of the
    tunning element is only for reference. The circuit is either tunned or not,
    and there are only two directions of travel. If the circuit is tunned then
    movement in either direction will increase the reflected power, and if the
    circuit is un-tunned then one direction will increase the reflected power
    and the other will decrease it. I would think that your linear actuator with
    a stepper motor will work out quite nicely.

    I will keep your advice in mind as I trudge on, and I have added your links
    to mine own.

    Thanks again from,
    Chris.
     
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