BRUEL & KJAER 2663, Technical Documentation Manual

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Chapter 2 — Operation
Circuit Adjustment for Velocity Measurement
Preamplifiers Types 2663 and 2663 B
User Manual
BE 1068 – 12
17
2.6 Circuit Adjustment for Velocity Measurement
The preamplifiers are preset to operate over a wide frequency range and use their
high- and low-pass filter pair to give a typical operating-frequency range as shown in
Fig.2.11 . It can also be used as an integrator which converts the acceleration signal
into a velocity signal. This is achieved by changing the operating characteristics of
the high- and low-pass filter stages of the preamplifier. The purpose of this section is
to explain how to change the filter stages of the preamplifier to integrate the signal.
Fig.2.11 Preset frequency response Types 2663/2663 B
Fig.2.11 shows the preset frequency response of the preamplifiers, which is obtained
from combining the responses of the low- and high-pass filter pair. The low-pass filter
determines the high frequency cut-off
F
LP
of the preamplifier and is preset to 33 kHz.
A filter roll-off rate of 40 dB/dec. is necessary to achieve a sharp attenuation beyond
cut-off and is obtained by using a two-pole filter. The high-pass filter determines the
low frequency cut-off and is preset to 0.5 Hz. The damping factor

and cut-off fre-
quency
F
HP
are chosen to obtain a linear response and to suppress low frequency
noise.
030070/1
10 dB
0 dB
-10 dB
-20 dB
-30 dB
-40 dB
-50 dB
-60 dB
-70 dB
-80 dB
0.1 Hz 1.0 Hz 10.0 Hz 100.0 Hz 10000.0 Hz
Type 2663
Type 2663 B
1000.0 Hz
100000.0 Hz