Measurement-computing WBK18 Manuel d'utilisateur télécharger pdf (Page 11)

Using the 2-pole Filter and Bypass

2-pole Filter Mode

For applications where the signal of interest is entirely AC in nature, the low-pass filter mode of 8-pole is

the best choice. Vibration signals coupled through an ICP accelerometer are an example of this. However,

for applications where the DC component of the input signal is also of importance, 2-pole mode may

provide better results. Proximity sensor measurements are an example of this. This is because the 8-pole

switched capacitor filter, while providing excellent attenuation characteristics, does not process DC signals

with a high level of accuracy. For accelerometer applications this is not a limitation, as there is no

information in the DC component of the input signal. The 2-pole filter, in contrast, is formed by two 1-

pole RC filters in series. This filter provides excellent passband accuracy, at the expense of a more gradual

roll-off characteristic, as detailed below.

Gain of 2-pole Filter Mode

-80

-70

-60

-50

-40

-30

-20

-10

0 102030405060708090100

FIN/FC

Gain (dB)

Gain of 2-pole Filter Mode

-25

-20

-15

-10

-5

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Gain (dB)

FIN/FC, Zoom-In to Filter Cutoff Frequency Region

WBK18, Dynamic Signal Input Module

926896

WBK18, pg. 11

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Measurement-computing WBK18 Manuel d'utilisateur Page 11