Hi
I'm looking for a way to record fluctuations in earth voltage. We currently are using laptop soundcards, but it suffers from a lot of noise. Thinking of going to a USB type device for recording to a laptop.
Data is recorded for 1second after triggering at a sampling interval of
50ms. The sampling frequency is therefore 20kHz. Typical signal measurements are on the order of 1mV to 0.001mV. Any sample code available for signal recording, stacking and filtering?Regards
The sampling frequency is not "therefore" anything determinable by any other parameter you mentioned. And if data is recorded for 1 second, then the sampling interval is one second, not some other value. A sampling *rate* of 50 *microseconds* would be the same as saying the sampling frequency was 20KHz. Code is simple: set up an array of the appropiate size and start with the pointer to the array (or index if you prefer that terminology) to the first element. Take a sample and advance the pointer (or add one to the index); repeat until the total desired number of samples has been taken. Stacking? What is that? Filtering? What do you want? What kind(s)?
The duration of measurement is 1 second, with a voltage and time value recorded every 50ms for a period of 1second. During stacking, the values obtained during different 1second measurements are averaged to remove noise. With filtering further noise removal can be accomplisehd through the removal of e.g. powerline noise 50hz / 60hz.
If you keep all of the data acquired during a given period, then transform it from the time domain to the frequency domain via a FFT, then one could easily remove the line frequency "spikes" (fundamental and harmonics) without disturbing the signal data. Furthermore, if the signal has a repetitive waveform, those aspects could be enhanced and non-related aspects could be de-emphasized. However, care must be taken to preserve modulation in the carrier frequencies.
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