Frequenzfilter english.pdf - Frequency Filter(Hardware and...

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Frequency Filter (Hardware and Software) For the analysis of digital signals, it is absolutely necessary to suppress high-frequency signal components, which could lead to misinterpretations. This includes all frequencies that are higher than the predetermined limit from the Nykist theory 2 max Sample Signal f f this is only possible with a hardware filter. By using low-pass filtering at too high frequencies, various problems arise. 1) Since frequency filters have different qualities of amplitude attenuation in the stop band of the filter, make sure you keep a big enough distance to the cutoff frequency, as this frequency is by definition where the signal has weakened by 3 dB, or about 30%. To get the desired results, the amplitudes and frequencies, of the signal that is to be filtered, as well as the progression of the amplitude attenuation of the filter must be known. 2) The unwanted frequencies can in principle also be filtered by software, which is of course much cheaper and more convenient than using a hardware filter. In addition to possible differences in quality you should also consider that, The sample rate of an analog-digital converter is limited With the sample rate the amount of data increases linearly In this respect it is always good advice to look at the first analog signals, or when using only digital technology, at least at the entire relevant frequency range, before being digitized for analysis with a limited sample rate. To illustrate, which errors can be caused, if filtering is not properly executed, take the following as an example: in LabVIEW a program was written, that records the signal over a data acquisition board and in addition a hardware filter (1100 SCXI) and displays both unfiltered and filtered signals.
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