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ADS7951: measuring of average voltage value

Vladimir Naumenkov
Prodigy 120 points
Part Number: ADS7951
Other Parts Discussed in Thread: ADS7128

Dear Sir, please answer

I need to measure “average voltage value” - let's call it like that, because this value cannot be called RMS.

 I have signal source, figure 1. Signal frequency – 50 Hz. I feed it to operational amplifier rectifier and have signal figure 2. I feed then it to operational amplifier integrator and have signal figure 3. (amplifiers are powered by  plus 5 V and  minus 5V). I feed signal to ADC then. ADC has 5V reference.

 I need now to use +5V power only, and I have +2.5 V reference (or  +5 V) for ADC operation.

 I can generate the following signal using operational amplifier – figure 4.

QUESTION: how can I use ADC like ADS7951 in order to get as a result something like, what I got before?

I understand this: do I need to take signal samples at intervals of about 0.1 - 0.2 ms and then calculate the average value?

What ADC circuit to apply?

Please, see figures 1 - 4 in attach.

TIA

Sincerely,

Vladimir Naumenkov

  Letter 1_ ADC_figures.docx

  • +1
    TI__Genius 17857 points

    Vladimir,

    We have an ADC similar to the ADS7951 that does a true RMS calculation internally (ADS7128).  You may want to review this device to see if this would be a good option for you.   With any ADC you can do post processing mathematics on your results.  So, if you wanted to implement the exact method you did with the amplifier in post processing, you would do the following:

    1. Invert signals less than zero.

    2. Mathematically integrate the modified signal.  There are many methods for mathematical integration (search Trapezoidal integration for one common approach).

    I hope this helps!

    Best regards, Art

  • +1 in reply to Art Kay
    Prodigy 120 points

    Dear Art, thank you

    Sincerely,

    Vladimir Maumenkov