Voltage Sources/ AC measurements

Discussion in 'The Projects Forum' started by dtow1, Apr 27, 2010.

  1. dtow1

    Thread Starter New Member

    Apr 27, 2010
    24
    0
    Hello,

    I am a new member here. I am working on a project to measure ac values using an ADC. I am using a voltage divider to scale down the AC line voltage into the acceptable ranges for my ADC. My ADC cannot accept negative voltages with being damaged and I am attempting to put in a dc offset.

    So far I am trying to use a summing amplifier to sum the ac signal with the dc offset.

    I am getting my DC offset from elsewhere in the circuit where there is a regulated 18Vdc. I am using a voltage divider to scale it down to 1.5 volts and a buffer/follower op amp circuit to keep it at that constant 1.5 volts, since the follower keeps the other stage from affecting this voltage.

    The problem I am running into is that the AC signal keeps going through the follower/buffer into the DC divider which is a huge issue in this circuit as the DC values supply other circuits as well.

    If anyone can point me in the right direction so that I can sum the DC and AC signals without having the AC signal traveling back into the DC voltage divider I would greatly appreciate it.

    Dtow1
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Why not use a precision rectifier to insure your AC becomes DC, with all peaks positive? A further suggestion is to filter the rectified AC and convert that smoothed DC, so you don't need to make a zero crossing detector to aid in synching the conversion to the waveform.
     
    dtow1 likes this.
  3. dtow1

    Thread Starter New Member

    Apr 27, 2010
    24
    0
    Hello beenthere,

    Thank you very much for your reply. I had not thought of that, If I am following you I could use the rectified AC signal, which would just be the positive peaks, which would allow me to get the peak voltage. I like that approach, thank you for the feedback, I think your suggestion will work much better than what I am trying to do, and it certainly requires far fewer components. Thanks!
     
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