BRUEL & KJAER 4809 - Cross-Motion Characteristics for Calibration

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3. CHARACTERISTICS
3.1. FREQUENCY RESPONSE AND RESONANCE
In Fig.3. 1 is shown a plot of the frequency response of a Type 4809
Exciter. The acceleration in g is plotted with respect to frequency for a
constant voltage.
~~~ ~~~ ~~~
ODOOOODCDDDDCDDOOOOOOOOOOOOODDOOOODDODOOOOOOOODOOD
BrUel & Kjcer
50 25
Potentiometer Ranv- :____50___d8 Rectifier :~ LOIIINI' lim. Freq.: _20___Hz 'Wr. Speed : _____lLmmfs-c. Paper SpMd :__L_ ~Mc .
1 0 75
Copenhagen :
dB dB
.W~2C 316
Moasu•l"ll Obj.:
Vibration
Exciter Ty ~
..1§QL__3C 15 100
Constant
Voltage = 5 V
~~~ = Typ_L 20 10 31 .6 g
4343
accelero-
meter
~m
- ---~51 m
~
~
Slgn.: __ o o
Qp 1124 10 20 Hz 50 100 200
*Multi ply Frequency Scale by
' dB dB
860
2 15
0 0
500 1000 2000
5000 10000 20000 40000 D A B C Un.
Zero level:
1612/2112 A B C Lin.
Fig.3. 1. Frequency response of the Type 4809
The acceleration level increases with frequency to a damped peak at
about 150 Hz. This is the suspension resonance of the Exciter. The acceler-
ation level then remains constant from 700 to 5000 Hz, after which it
climbs sharply to a peak at 16 kHz. This peak is the major axial resonance
of the moving element itself. It can be seen that the Exciter could be
operated in the range 700 to 5000 Hz without using a compressor loop to
control the oscillator. However, the use of a compressor loop is generally
recommended, since resonances from the test object also enter in.
3.2. RATED FORCE AND LIMITS
Fig.3.2 shows a diagram of loading limits with respect to frequency for
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