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I want to know how to determine the signal sampling rate required to reconstruct electrical signals whose frequency components are unknown, such as, for example, signals of charge/discharge voltage on a capacitor. I want to design a system capable of scanning this type of signal in real time.

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  • $\begingroup$ You really can’t do that. You can only make educated guesses $\endgroup$ – Stanley Pawlukiewicz Jul 24 '18 at 5:00
  • $\begingroup$ educated guesses? $\endgroup$ – AmnSyn Jul 28 '18 at 19:07
  • $\begingroup$ google.com/… $\endgroup$ – Stanley Pawlukiewicz Jul 28 '18 at 20:19
  • $\begingroup$ I know what that means. I just don't know what criteria or specifications I should take into account to make a "educated guess" that actually works in practice. $\endgroup$ – AmnSyn Jul 29 '18 at 0:08
  • $\begingroup$ to select a sample rate, you need to know the frequency content. If you don’t know the frequency content, you have to make an educated guess. There is no general criteria for selecting a sample rate other than the frequency content of the signal. There must be a reason for sampling your signals, something you want to measure. Consider what frequency content that signal feature would manifest. You could also Google for what other people doing similar things have used. Make an educated guess. There are all sorts of capacitors. Do some modeling and simulation. $\endgroup$ – Stanley Pawlukiewicz Jul 29 '18 at 1:04
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Sampling a signal requires that it should be bandlimited. When it's not, you should apply a preprocessing analog bandlimiting (aka anti-aliasing) filter to enable its proper sampling. There are various concerns on how to choose the most practical anti-aliasing filter. The most important concern is the filter cutoff frequency which determines the minimum sampling rate to record the signal.

Your application is about capturing capacitor charge/dischage signals which are of spiky nature and hence posses very large bandwidths; quite large sampling rates might be necessary. In very rough terms, the dischaging signal's bandwidth is inversely proportional to the time-constant of the discharging network, assuming a first order simplified model.

If you know this time constant, then you should select the lowpass filter whose time constant is smaller than that. This will make sure that the anti-aliasing filter's bandwidth will be larger than the signal of interest's bandwidth.

So you should firt determine the time cosntat of your observed network, to predict a first order estimate of the minimum sampling rate required.

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