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AGILENT 35670A
Supplemental Operator’s Guide
32
Section 12 : Hammer Test Setup Without a Force Transducer
Hammer testing for modal analysis without a force transducer can yield usable
results if an accelerometer is placed on the hammer and used to trigger the
measurement. Although frequency response functions acquired with this technique
will be affected by the dynamic characteristics of the hammer assembly and also its
mass-loading effects, approximate mode frequencies and mode shapes can still be
computed using modal analysis software.
On the other hand, power spectra obtained by measuring the single-channel response
to a non-instrumented hammer strike may also provide information regarding modal
frequencies and shapes, but success is too dependent on the consistency of the
hammer strike, and therefore this technique is not recommended.
Setting Up the Hammer Test Without a Force Transducer
Attach an accelerometer to the hammer using cement or wax, and connect this
transducer to Channel 1. Attach the response accelerometer to the desired location
on the structure, and connect it to Channel 2. Preset the analyzer and set up
transducer parameters as described in the section “Measuring with Transducers.”
Then proceed with the test in accordance with the proceeding section on “Modal
Testing with a Hammer and Accelerometer.”
Avg
[FFT]
Type: RMS Number: 5
Update Rt: 5 Overlap: 0 %
Date: 10-02-96 Time: 09:24:00 PM
X:656 Hz Y:939.573 e-3
0Hz 3.2kHzAVG: 5
A: Freq Resp2/1 X:656 Hz Y:444.409
1
e+3
10
e-3
LogMag
5
decades
B: Coherence2/1
1
0
Real
100
e-3
/div
0Hz 3.2kHzAVG: 5