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A traducer's analog output is generated by its DAC as seen in the below plots. The plots are from the same data with increasing zoom. Plots obtained by using a DAQ. It seems like the DAC outputs 3 voltage values per second(see the last plot). But it is raw and not filtered and thus not smooth. It looks like this transducer doesn't filter/smooth the DAC output. It is in discrete steps not smooth as you see(created by samplehold of DAC).

I have couple of questions:

1-) Is a smoothing filter needed if I am only interested in the mean value of the voltages? Is filter only needed in applications like sound outputs?

2-) I'm sampling this DAC output by a DAQ device(sampling rate 500Hz) and obtain the below plots. What would you say about the noise here? Is that something to do with sampling rates or DAC being not smoothed?

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  • \$\begingroup\$ Theoretically speaking, you generally want a reconstruction filter on the output of your DAC; a simple example, say you know your Max DAC output frequency will be 500Hz, you can put a simple low-pass filter on the output to suppress harmonics / HF noise \$\endgroup\$ – Krunal Desai Apr 13 '16 at 23:32
  • \$\begingroup\$ are the harmonics coming from sampehold of the DAC? \$\endgroup\$ – user16307 Apr 13 '16 at 23:45
  • \$\begingroup\$ what R C values would you recommend for low pass? \$\endgroup\$ – user16307 Apr 13 '16 at 23:46
  • \$\begingroup\$ @KrunalDesai: For some purposes, frequency component above Nyquist is undesirable and should be squelched. For other purposes, however, one wants an output which switches quickly between discrete values. What kind of filter one should use will depend upon what one wants the output to do. \$\endgroup\$ – supercat Apr 14 '16 at 6:29
  • \$\begingroup\$ @supercat in which purpose one may want output with switching discrete values? \$\endgroup\$ – user16307 Apr 14 '16 at 7:18
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A good calculator page for RC filter and analytics is: http://sim.okawa-denshi.jp/en/CRlowkeisan.htm

Better yet, go for an active filter using an opamp. A Salen Key calculator is: http://www.calculatoredge.com/electronics/sk%20low%20pass.htm

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  • \$\begingroup\$ What is the advantage of active filter compring. to passive filter? \$\endgroup\$ – user16307 Apr 14 '16 at 7:16

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