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Highpass filter - HP/04 - Lowpass filter LP/04

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6 switched corner frequencies : 7 pole Butterworth high pass 2, 5, 10, 20, 50, 100Hz

7 pole Butterworth low pass 100, 200, 500, 1k, 2k, 5kHz

HP/04

Provides brick wall type minimalisation of spurious low frequency phenomena that may otherwise invalidate data from piezo-electric sources.

Supposed  vibration acceleration signals may contain thermal and strain induced noise elements, both constrained to the low frequency end of the spectrum by reason of thermal mass and the 1/fo2 relationship between acceleration vs. displacement respectively.

The filter of course acts as the boundary fo, between valid data (>fo) and this type of noise.

LP/04

If low pass complement of HP/04, provides selectable upper frequency boundary, removing unwanted signal components and noise. White noise content of overall signal is proportional to   bandwidth, hence LP/04 willproduce significant signal/noise improvementwhere upper frequency can be constrained.

GENERAL

Applications may be as individual filters or bandpass pairs to quasi steady state wideband signals.

Signal recovery can be near absolute in the presence of stop band noise up to  60dB higher but two octaves removed from the corner frequency, although this idealised performance may be negated to some extent by nonlinearity modulation products. 7 pole Butterworth response is maximally flat (no ripple) in the pass band, stop band attenuation is 42dB/octave. Filter transient response is damped oscillatory which colours the response to impulsive type signals.

IMPLEMENTATION

Each filter provides 6 switched corner frequencies (-3dB) covering an overall 50 : 1 frequency range. Passband gain is unity ; a DIRECT switch bypasses the filter.

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highpass-filter-hp04-schematic

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