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Controlling air core meters

Discussion in 'Electronic Design' started by Jeroen, Apr 29, 2004.

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  1. Jeroen

    Jeroen Guest


    I'm in the process of designing an air core meter controller using a few
    opamps and two DAC's. I'm wondering if it's better to use open loop voltage
    or current mode feedback control. The angle of deflection only depends on
    the ratio of the current through the windings, but not both windings are
    exactly the same, so voltage control would be less ideal, though errors
    could be could corrected by the software.
    I've looked into the Philips SA5775, but these are difficult to get hold of
    in very small quantities.

  2. I don't seem much reason not to use voltage drive. That's what the
    Philips chip does, and it's good enough for automotive meter.

    Using voltage drive, there is an additional error (linearity error)
    source from the self-heating of one coil relative to the other and the
    tempco of the coils +4000ppm/K. This could be avoided using a
    regulated supply and current drive, but it may not be significant in
    your application.

    Where did you get the air core movements in "very small quantities" ?

    Best regards,
    Spehro Pefhany
  3. Jeroen

    Jeroen Guest

    Just using parts from junked instrument panels. I have not yet succeeded in
    finding a supplier :(

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