AC Voltmeter

Discussion in 'General Electronics Chat' started by olvine, May 20, 2014.

  1. olvine

    Thread Starter Member

    Mar 10, 2014
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    Hey

    I want to make AC voltmeter using microcontroller. To feed this voltage to microcontroller first I need to scale this AC voltage to controller's input voltage range. For that what should be methods to do this. Or what are the options ?
    voltage range: 0-500Vpp.
    Method in consideration: Simple voltage divider.
    what else ?
     
  2. olvine

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    Mar 10, 2014
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    PIC16F887 or PIC16F1827 are available
     
  3. inwo

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    Nov 7, 2013
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    What value and wave form do you want to measure?
     
  4. studiot

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    Nov 9, 2007
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    The division ratio will depend upon frequency and may need compensation.
    Have a look in the service manual for an oscilloscope and see how they do it.
     
  5. olvine

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    Mar 10, 2014
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    range is 0-1000Vpp and sine wave
     
  6. olvine

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    Mar 10, 2014
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    Need to make a digital AC voltmeter. simple resistive network can do the task but I want to know other methods for scaling of AC signal
     
  7. studiot

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    You may have misunderstood my comment, which is why you have not told us what frequency range you are working in.

    A resistive divider may be appropriate, the actual topology will depend upon source and load (voltmeter) impedences.

    But if your voltmeter is going beyond mains frequencies, even only audio, then you will need some compensation.
     
    Last edited: May 20, 2014
  8. olvine

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    Mar 10, 2014
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    This simple circuit works fine with 10kHz sine 1000Vpp.

    But the frequency is 60Hz for which I would be designing a meter.
     
  9. studiot

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    So what is the capacitor doing in your divider?

    Is this a real exercise or just a theoretical one in a simulator?
     
  10. olvine

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    Mar 10, 2014
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    Kinda compensation.

    and without capacitor I am getting the same results
     
  11. studiot

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    But wasn't that in a simulator?
     
  12. olvine

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    Mar 10, 2014
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    Yes it is in simulator.
    I suppose proteus not a good simulator then
     
  13. studiot

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    It is not that, it is that components, particularly resistors, are 'ideal' and the circuit cannot add a random amount of stray capacitance or lead capacitance.

    Do you understand why (and therefore when) compensation is needed?

    As already said, you will not need compensation at 60Hz.
     
  14. olvine

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    Mar 10, 2014
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    Yes understood. Thank you

    Can you please help me out with some other method to attenuate the AC signal to controller's ADC input level ?
     
  15. studiot

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  16. olvine

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    Mar 10, 2014
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    transformer increase cost and that's why it can't be considered.

    I have also considered capacitor voltage divider but may be we need to consider the frequency too.
    Their are other methods like using thermocouple and hall effect sensor but I don't think they are good enough to implement.
     
  17. studiot

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    How about a valve voltage follower with fractional gain?
     
  18. olvine

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    Mar 10, 2014
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    This is something new...lemme check this
     
  19. studiot

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    This was a common trick in the old days using a cathode follower probe.

    You could do it a transistor, but 1000volt transistors are not so cheap.
     
  20. olvine

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    Mar 10, 2014
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    Are you considering that I need to make a digital AC voltmeter and for that some analog external circuit is required to attenuate the AC signal of higher voltage to microcontroller's allowable voltage ?
     
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