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Digital Low Pass Filters

A test series e.g. a raw file) can be viewed as a superposition of signals plus noise. Since a Fourier transform is additive, the frequency spectrum of a measurement is the sum (superposition) of the signal frequency spectrum and the noise frequency spectrum. If a reflection can be fitted by a Pearson VII profile (Chap. 4.7) and if the maximum of this even function is put in x = 0, [Pg.96]

That is, for a steady signal the share of higher frequencies approximates zero whereas the frequency response of the noise stays more or less constant. Therefore, above a certain frequency only the noise will contribute. If one suppresses this high-frequency part by multiplication with 0, after the reverse transform into the amplitude domain the signal is kept unchanged, only slightly disturbed by the low-frequency part of the noise. [Pg.99]

Instead of the application of a low pass filter in the frequency domain itself (multiplication with 1 in the low-frequency range and above that with 0, i.e. multiplication of the frequency response with a rectangle function), one can use in the amplitude domain (i.e. for the measurement itself) the mathematically fully equivalent convolution with the Fourier transform of that rectangle function. [Pg.99]

Numerically the convolution of a step scan is merely the application of a sliding weighted mean (e.g. like the Savitzky-Golay method). The Fourier transform of the rectangular function has the shape of sin(nv)/(nv) (whereby n is inversely proportional to the width of the rectangle) and unfortunately approaches 0 only very slowly. To make do with a small number of points for a convolution, one must tolerate a compromise and renounce the ideal rectangular shape of the low pass filter (in the frequency domain). [Pg.99]


In that case, after each newly generated derivative, the noise must be eliminated with a digital low-pass filter (Fig. 3-43). [Pg.71]

The signal before digitization is sufficiently low-pass filtered so that noise is below 1 mV at the digital volt meter (DVM). [Pg.231]

The microhotplate temperature is measured using a polysilicon resistor as temperature sensor (Ry). The resistor is biased with a temperature-independent current source (Free). The voltage drop across the resistor is low-pass filtered and converted to the digital domain using a 10-bit successive-approximation ADC from the analog library of austriamicrosystems (Unterpremstatten, Austria). The inputs of the digi-... [Pg.66]

Sample rates for the majority of digital controllers are adjustable and range from 1 sample every 5 s to 10 samples per second. Some controller designs have fixed sample rates that fall within the same range. Hardwired low-pass filters are usually installed on the analog inputs to the controller to help protect the sampler from aliasing errors. [Pg.72]

The ISFETs are connected to a source-drain follower, and the output of this amplifier is connected to a digital oscilloscope. For presentation purposes, the curves are filtered with a software low-pass filter using a cutoff frequency of 40 Hz for elimination of the 50 Hz main supply interference, which has a top-top amplitude of typically 0.2 mV. [Pg.400]


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Digital filtering

Filtering low-pass

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