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ADC design with the ADC124S101

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mariush:

--- Quote from: antonmi97 on April 18, 2019, 03:56:58 pm ---
The post processing time isn't relevant since I only need results every 5 seconds for example. How could I save 8 readings of 11 bits into 9 bytes of memory??


--- End quote ---

You can't, i was stupid. For some reason in my mind I was thinking 10bit instead of 12bit, and 9 bit instead of 11 bit. I apologize for confusing you.
You'd use 11 bytes for 8 values ... 3 bit x 8 = 24 bits or 3 bytes + 8 bytes

antonmi97:

--- Quote from: MasterT on April 18, 2019, 05:29:21 pm ---A lot depends on application, for power metering usually 20 x ac frequency  = 20x 50(60) = 1000  (1200) Hz sampling rate is o'k.
Number of bits defined by accuracy,  1% in all 0.02 - 16A range demands 17-bits.

Type of adc doesn't matter, as long as INL strictly specified in DS.  Sigma-Delta type, same like audio codecs is fine .
SAR ADC may run at higher sampling rate, to simplify anti-aliasing filter design.

 For Hall current sensor, based on my experience, it's quite complicated to get noise-free small current measurements w/o  heavy filtering data.

--- End quote ---

Are you sure about the sampling rate? I currently use the ADS1015 (12-bit 3.3kHz) and I'm quite sure you can't get all the high frequency components in the current wave form for example from SMPS, microwaves, and other appliances that have non-sinusoidal current wave forms. 1200 Hz would be enough if the wave form was more/less a nice sine wave, but for most of the things it won't be.

That's why I wanted to ask you guys what sampling rate is enough to cover it all within like +/- 1%. I guess the quite high frequency components at 200 kHz are so insignificantly short (narrow) that I don't even have to bother with them. Right?

MasterT:

--- Quote from: antonmi97 on April 18, 2019, 10:38:57 pm ---
--- Quote from: MasterT on April 18, 2019, 05:29:21 pm ---A lot depends on application, for power metering usually 20 x ac frequency  = 20x 50(60) = 1000  (1200) Hz sampling rate is o'k.
Number of bits defined by accuracy,  1% in all 0.02 - 16A range demands 17-bits.

Type of adc doesn't matter, as long as INL strictly specified in DS.  Sigma-Delta type, same like audio codecs is fine .
SAR ADC may run at higher sampling rate, to simplify anti-aliasing filter design.

 For Hall current sensor, based on my experience, it's quite complicated to get noise-free small current measurements w/o  heavy filtering data.

--- End quote ---

Are you sure about the sampling rate? I currently use the ADS1015 (12-bit 3.3kHz) and I'm quite sure you can't get all the high frequency components in the current wave form for example from SMPS, microwaves, and other appliances that have non-sinusoidal current wave forms. 1200 Hz would be enough if the wave form was more/less a nice sine wave, but for most of the things it won't be.

That's why I wanted to ask you guys what sampling rate is enough to cover it all within like +/- 1%. I guess the quite high frequency components at 200 kHz are so insignificantly short (narrow) that I don't even have to bother with them. Right?

--- End quote ---

 There are standards for power measuring, I'm sure for North America ANSI defines bandwidth up to 20-th harmonics of the AC waveform. So 1200 Hz is a band, sampling rate is a different species. MInimum is x2 by Nyquist = 2400 samples per second. Period.
 Pushing this rate up makes sense for a number of reasons:
 - simplify anti-aliasing filter design;
 - to do oversampling for increasing resolution of the adc;
 - to run a software LPF, reducing noise getting into measurements band.

From the analog.com

--- Quote ---ADC Output Pass Band (0.1 dB) 0.672 kHz
ADC Output Bandwidth (−3 dB) 1.6 kHz
--- End quote ---
https://www.analog.com/media/en/technical-documentation/data-sheets/ade9153a.pdf

antonmi97:

--- Quote ---There are standards for power measuring, I'm sure for North America ANSI defines bandwidth up to 20-th harmonics of the AC waveform. So 1200 Hz is a band, sampling rate is a different species. MInimum is x2 by Nyquist = 2400 samples per second. Period.
 Pushing this rate up makes sense for a number of reasons:
 - simplify anti-aliasing filter design;
 - to do oversampling for increasing resolution of the adc;
 - to run a software LPF, reducing noise getting into measurements band.

From the analog.com

--- Quote ---ADC Output Pass Band (0.1 dB) 0.672 kHz
ADC Output Bandwidth (−3 dB) 1.6 kHz
--- End quote ---
https://www.analog.com/media/en/technical-documentation/data-sheets/ade9153a.pdf

--- End quote ---

So with the adc output bandwidth of 1.6 kHz, a good enough sampling rate would be 10*bandwidth = 16 kSPS? I’ll have a more detailed look at the datasheet, but 1 MSPS seems definitely like a overkill for now.

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