Need help for current measurement...

Discussion in 'The Projects Forum' started by bhargav shankhalpara, Nov 5, 2013.

  1. bhargav shankhalpara

    Thread Starter Member

    May 9, 2010
    18
    0
    Hello everyone...

    i am new in current measuring concept, and i make one of control application type project...

    actually i am controlling one ac induction motor using microcontroller (ATTINY88). and i want to add one extra function into it is over-current protection.(when current more than 6 amp, automatically gets turn off by microcontroller) for that i decide to use current transformer for current measurement. so i need to interface it with microcontroller.

    i have current transformer with 1 (one) turn of primary winding and 350 turn of secondary winding. i know that to convert secondary current into voltage i need to connect burden resistor across it. i need to obtain voltage between 0-5v DC from that to apply microcontroller. also for that i need to signal conditioning for that before apply it to microcontroller.

    problem is that...

    i don't now that which value of burden resistor is best for my application and after obtaining well voltage signal condition circuit require which include (rectifier and amplifier).

    after searching about signal conditioning circuit i found this document and circuit.

    http://tinyurl.com/oqr52d3

    in this circuit i understand about all resistor and op-amp but initial two zener diodes and at last RC time constant make question in my mind that why its here and if here than what should be its value.

    please help me in this project...

    thank you...
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,052
    3,244
    What is the current rating and maximum output voltage rating of your current transformer?

    The zeners are just to prevent overvoltage from high current transients. They can be 5.1V.

    The time constant must be at least high enough to filter the rectified signal to the desired ripple level.
     
  3. bhargav shankhalpara

    Thread Starter Member

    May 9, 2010
    18
    0
    Hi crutschow...

    Thanks for reply...

    as i mention in post my current transformer have 1 primary turn and 350 secondary turn.

    maximum current passing through primary in my case is 7 AMP. and according to that secondary current will produce. and by burden resistor according voltage.

    thanks
     
  4. crutschow

    Expert

    Mar 14, 2008
    13,052
    3,244
    My question was "what is the current rating of the transformer and maximum output voltage rating of the transformer?". The winding ratio doesn't tell me that.
     
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