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measuring power factor

Discussion in 'Electronic Design' started by Pinchy, Sep 24, 2004.

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  1. Pinchy

    Pinchy Guest

    I intend to design a device to measure the power factor without the
    use of a microcontroller. In the design, the measured angle will be
    given by a simple DC voltage, e.g. 30° = pi/6 rad = 0.523 V

    A problem that occurs is calculating the cosine of this voltage. In a
    discrete setup, I will use Taylor series and realise it with analog
    multipliers and a few operational amplifiers.

    Before starting this, I would like to know if a single IC exists that
    can make this calculation at once, eg 0.523 V IN results in cos(0.523)
    = 0.866 V OUT

    Thanks for help

    (designer has a degree of engineer in elektronics)

    Geert
     
  2. Check these out:

    http://www.analog.com/library/analogDialogue/bestof/pdf/06_3.pdf
    http://www.analog.com/UploadedFiles/Data_Sheets/737468486AD538_c.pdf

    not sure if either is still available...
    (Maybe designer should learn to use microcontroller)

    Best regards,
    Spehro Pefhany
     
  3. John Fields

    John Fields Guest

    ---
    Why on earth would you want to do that?
    ---
    ---
    Sure.

    Vin>----[ADC]---[ROM]---[DAC]--->cos(Vin)

    The single IC is the ROM, a Read-Only-Memory with a cosine lookup
    table burned into it.
     
  4. Tim Wescott

    Tim Wescott Guest

    Power factor can either be defined as pf = cos(theta_v - theta_i), where
    theta_v and theta_i are the phases of the voltage and current,
    respectively, and we assume that all waveforms are pure sinusoids.

    I better definition in my mind is the one that goes:

    Power to Load
    pf = -----------------.
    (V_rms)*(I_rms)

    This definition accommodates all sorts of situations where the "pure
    sinusoid" definition doesn't, like pulsed currents (even on a DC line),
    harmonic currents from rectification, or anything else you can dream up.

    If you are not bent on measuring the sign of the reactive vars, then you
    can build your power factor meter with a couple of RMS chips and a few
    multipliers, all from ADI.

    And you won't have to mess with trig functions.
     
  5. Ken Smith

    Ken Smith Guest

    Why are you using such a messy way of doing it?

    I suggest:

    Run the voltage into an AGC

    Run the current into a comparitor.

    Use the output of the comparitor to sync. demod. the AGCed voltage.
     
  6. New definition of "Single" today, John?

    Hello!
    Zuzej Maaya
     
  7. You could use an ADuC832 or something like that, and get single chip
    with the above block diagram, eh?

    Best regards,
    Spehro Pefhany
     
  8. Pooh Bear

    Pooh Bear Guest

    Given the loads today on the AC network, It would seem foolish to measure
    power factor by the old fashioned phase angle approach.

    Your definition is much more appropriate.


    Graham
     
  9. Ken Smith

    Ken Smith Guest

    Use one of the Cygnal micros and you get the ADC the table and the DAC all
    in one chip. That would do it.
     
  10. The Phantom

    The Phantom Guest

    You haven't told us what accuracy you require.
     
  11. Tom Seim

    Tom Seim Guest

    Yeah, a Microchip PIC micro w/ADC.
     
  12. John Fields

    John Fields Guest

     
  13. keith

    keith Guest

    Because his professor asked the question, and he's been skipping class?
     
  14. Tom Seim

    Tom Seim Guest

    He asked if there existed a single IC that can do this, and there is.
     
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