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Sweep Random
1042
Sweep Random Generator
1042
Slave Filter 2021
Test Specimen
i
Control
Accelerometer
Vibration Meter
2502
Accelerometer Preamplifier
2622
Fig.5.3. Example of test arrangement for multiple sweep random testing
The number of narrow band generators necessary to perform the proper
test will depend upon the number of important
frequency
regions.
The arrangement can be extended to include more generators whenever
required.
In this way capital investment required to perform adequate
random vibration testing is reduced to a minimum and a very flexible test
system is obtained.
5.3. MULTIPLE-EXCITER VIBRATION TESTING
Testing of large specimens can involve many problems in the design of a
suitable fixture. These problems are
reduced
if multiple-exciter systems are
used. A two-exciter system is shown in Fig.5.4. The test specimen is large
and may have independent and different resonant frequencies causing
irregular overall motion. Thus, four feedback control accelerometers are
used, and the Control Signal Selector Type 4410 allows the control signal to
be selected. It can choose any channel, the highest, the lowest or the average
of the channels. If the test specimen was a dead mass, a single accelerometer
feedback could be employed.
The signal source used is a Sweep Random Generator Type 1042 driving
into Power Amplifiers Type 2707. Each Power Amplifier drives an exciter
Head/Body combination. Either the Mode Study Head Type 4814, the Big
44
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