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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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