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sponse of a mini shaker ( 481 0)
driven by the BFO output of the
2010 at a low vibration level.
The upper curve was recorded
with
the
analyzer
in
the
linear
mode. It shows that the signal level
is of the same magnitude as the
background noise and cannot be re-
corded without using narrow band
analysis. The lower curve shows
the same signal recorded with the
analyzer
in
the
selective
mode
(3, 16Hz bandwidth). Only the fun-
damental originating from the BFO
is recorded, thus the influence of
noise, spurious vibration and har-
monic distortion is rejected.
Frequency Analysis of Mechanical
Vibrations
The 201 0 finds wide application
in the field of mechanical vibration.
Fig .8 shows a set-up for analysis of
mechanical vibrations
.
The transducer which
is
mounted
on the part of the structure (a small
electric motor) where the vibration
is to be measured, picks up the ac-
celeration and converts it to an elec-
trical signal which is fed to the
preamplifier 2626 for amplification.
The 2626 is a preamplifier of the
charge type which means that it
measures the change in charge ap-
pearing over the transducer. As the
2626 is only sensitive to charge
changes the connecting cable be-
tween
the
transducer
and
the
preamplifier may be of considerable
length.
From the preamplifier the
amplified signal is fed to the
input
of the 2010 for analysis.
In connection with the recording
in Fig. 9 a bandwidth of 10Hz and a
frequency range of 20Hz to 20kHz
was chosen. The Level
Recorder
2307 which was connected to the
201 0 by a flexible shaft supplied
the drive
for
the frequency sweep.
The range potentiometer of the re-
corder was a 75 dB potentiometer.
The curve recorded shows that the
acceleration
is
greatest
around
40Hz with additional peaks around
100Hz and 300Hz.
In order to make a detailed
inves-
tigation of the peak appearing at
300Hz the settings of the 2010 and
the recorder 2307 were changed.
The
bandwidth
was
changed
to
3, 16Hz to get as accurate a fre-
quency determination as possible,
the frequency range was changed
to the 2Hz to 2kHz range in order
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100
200
500
1000
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10000
20000
40000
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Fig.7. Recording of frequency response of mini-shaker driven at low vibration level
171106
Analyzed
signal to
be
recorded
173256/
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Fig.8. Example of instrument set-up for recording vibration spectrums
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QP 1124
10
20
Hz
!10
100
200
Multiply Freq-
Sea,.
by
500
1000
2000
500f
Z.....t...l:
Fig.9. Recording of frequency analysis of the vibrations of a small electric motor
200Hz
300Hz
400Hz
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171108
Fig.1 0. Enlarged section of frequency analysis in Fig.9. The top of the chart shows the event
marker frequency calibration
9
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