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
Brüel & Kjær
18
Fig.2.12 Frequency response of the preamplifiers when used as an integrator
Fig.2.12 shows the frequency response of the preamplifiers when used as an integra-
tor. This is achieved by combining the response characteristics of both the low- and
high-pass filters to achieve the ideal frequency response characteristics of an integra-
tor.
As shown,
F
HP
is set to equal
F
LP
–
the frequency at which integration of the signal is
to begin. In order to optimise the overall preamplifier response, the damping coeffi-
cient

and the cut-off frequency
F
HP
of the low-pass filter can be changed. Further-
more, a single-pole, low-pass filter is needed to achieve the necessary roll-off rate of
20 dB for integration.
Note: It is not recommended to integrate complex signals, such as single shocks, and
impulses.
See section 2.6.1 , section 2.6.2 and section 2.6.3 on dealing with the steps necessary
to change the preamplifiers to an integrator.
2.6.1 Changing the Low-pass Filter
The low-pass filter must be changed from a two-pole to a single-pole filter to obtain
the roll-off rate of 20 dB/dec. This is done by replacing the two resistors
and
by a single resistor
R
L
as shown in Fig.2.13 .
The value of resistor R
L
is determined by F
LP
and is obtained from the formula
printed on the preamplifier shield:
10 Hz 100 Hz
0 dB
-5 dB
-10 dB
-15 dB
-20 dB
20 Hz 50 Hz 200 Hz
500 Hz
1 Hz 2 Hz 5 Hz
5 dB
892066/1e
-3 dB
FHP = FLP = 10 Hz
Damping
ζ
= 0,37
2 pole high-pass filter
Integrator Response
Single pole
filter gives
roll-off rate = 20 dB/dec
R
L
1
R
L
2
F
LP
1.59 10
8

R
L
-------------------------- Hz
 
=