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ADS131A04: How to set the filter for 50hz and 60hz

Kevin Raman
Prodigy 60 points
Part Number: ADS131A04
Other Parts Discussed in Thread: ADS1261, ADS1220, ADS124S08, ADS1258

Tool/software:

Hi, I saw that there is a configurable notch filter that is controlled by OSR and Fmod.

I'm not clear on how to calculate the best OSR for 50 and 60hz Filter. Also, I am unsure on how to understand the normalised graphs provided in the datasheet.

Our Fmod is 4.096MHz. Is there a step-by-step guide on how we can calculate the OSR to be chosen for either 50Hz and 60Hz filter? I appreciate any input, thanks. 

  • 0
    TI__Mastermind 47451 points

    Hi Kevin Raman,

    A plot like the one shown below means that the frequency response nulls occur when the ratio of the input frequency to the selected data rate = 1. So, if fIN = 50 Hz, then fDATA (the sample rate) should equal 50 SPS. To get both 50 and 60 Hz rejection, you would need to operate at 10 SPS because this is the largest number that is a factor of both 50 and 60 Hz. To set the data rate, you need to choose an ADC clock (CLK), then set the CLK_DIV bits, then the ICLK_DIV bits, and finally the OSR to the desired value.

    Also, I should point out that the ADS131A04 is designed to measure 50/60Hz frequencies because it is generally used for metrology or other energy measurement applications. So this might not be the best device to use if you are trying to get rid of these frequencies

    If you can share more about your application perhaps we can offer a more suitable device

  • 0 in reply to Bryan Lizon86
    Prodigy 60 points

    We are using the card for power monitoring in a machine. Hence, we would need to remove the 50/60 Hz noise from the AC power line if possible. I read that the datasheet's AC performance test conditions are at 50 and 60HZ hence I thought it could filter out the 50/60Hz. Do help to suggest a similar ADC that can filter out these AC input frequency.

  • 0 in reply to Kevin Raman
    TI__Mastermind 47451 points

    Hi Kevin Raman,

    What are your signals of interest then? Are you only interested in a DC voltage and current measurement?

    How fast do you want to sample, how many inputs, etc.?

    The more info you can provide the better recommendation we can provide

    -Bryan

  • 0 in reply to Bryan Lizon86
    Prodigy 60 points

    Hi, we are only interested in DC voltage and current measurement.

    We will be using 8 input channels. Our sampling speed will be varied due to the varying OSR setting I believe.

  • 0 in reply to Kevin Raman
    TI__Mastermind 47451 points

    Hi Kevin Raman,

    You could check out devices such as the ADS1220, ADS124S08, ADS1261, or ADS1258. These devices are multiplexed delta-sigma ADCs that are listed in order of increasing max sample rate. The first three devices offer a dedicated filter type for removing 50/60 Hz, though these filters can only operate up to a maximum of 20 SPS (I am not sure what your max sample rate is for your application)

    -Bryan