I would like to know what he AD7794 sigma delta samples at. the clock is 64 kHz but I could not find the actual sample rate in the datasheet.
I have misinterpreted your query - you are asking about the sampling rate at which the analog input is sampled but I answered with the output data rate.
Anyway, the modulator operates at 64 kHz but samples the input on both clock edges. So, the sampling rate is 128 kHz.
The update rate of AD7794 can vary from 4.17 Hz to 470 Hz. You can find this specs on the 1st page (features of the product) of the datasheet. Its RMS noise and effective number of bits versus the gain and update rate can be found in Tables 11 and 12 on Page 15 of the datasheet.
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