Low frequency sampling rate high resolution systems still need a good LP filter for all the reasons mentioned above.If I sample a thermocouple at a slow rate such as 1 Hz, do I need Low Pass Filters? I'm not aware of any noise sources that are that low in frequency, and since I'm sampling so slowly, does this by default eliminate noise contributions in the high frequency ranges?
https://www.ti.com/lit/ds/symlink/ads1220.pdf section 9.1.2 on page 45
https://www.analog.com/en/analog-dialogue/articles/practical-filter-design-precision-adcs.htmlMany sensor signals are inherently bandlimited; for example, the output of a thermocouple has a limited rate of
change. In this case the sensor signal does not alias back into the pass-band when using a ΔΣ ADC. However,
any noise pick-up along the sensor wiring or the application circuitry can potentially alias into the pass-band.
Power line-cycle frequency and harmonics are one common noise source. External noise can also be generated
from electromagnetic interference (EMI) or radio frequency interference (RFI) sources, such as nearby motors
and cellular phones. Another noise source typically exists on the printed circuit board (PCB) itself in the form of
clocks and other digital signals. Analog input filtering helps remove unwanted signals from affecting the
measurement result.
A first-order resistor-capacitor (RC) filter is (in most cases) sufficient to either totally eliminate aliasing, or to
reduce the effect of aliasing to a level within the noise floor of the sensor. Ideally, any signal beyond f(MOD) / 2 is
attenuated to a level below the noise floor of the ADC. The digital filter of the ADS1220 attenuates signals to a
certain degree, as illustrated in the filter response plots in the Digital Filter section. In addition, noise components
are usually smaller in magnitude than the actual sensor signal. Therefore, using a first-order RC filter with a
cutoff frequency set at the output data rate or 10x higher is generally a good starting point for a system design.
https://www.physicsforums.com/threads/power-from-the-super-moon.765429/post-5224011
https://forum.allaboutcircuits.com/threads/50nv-resolution.130468/post-1073894
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