PCB Piezotronics Vibration Division ICP 086C01, Инструкция по установке и эксплуатации

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7
20 dB below initial low frequency force levels.
4. Change hammer tips and/or mass to modify its behavior if necessary:
a. For higher frequency response, use a stiffer tip and no extender.
b. For better low frequency response, use a softer tip and install the extender.
c. To increase motion signal energy, increase impact velocity and/or hammer
mass.
IMPORTANT: When using the Model 086D80 Mini Impact Hammer with the Model
084A17 Hammer Handle, best results are achieved when also using the Model 084Al3
Extender Mass. The Model 084Al7 is designed for use in frequency ranges lower than
those reached when using the Model 084Al4 Handle Cable Assembly. The use of the
Model 084Al3 Extender Mass improves the low frequency content of the force input to
the structure, and improves the
“
feel
”
of the hammer by offsetting any effective mass
added to the handle base by an attached cable.
5. Repeat steps 1 and 4 until adequate results are obtained.
Generally speaking, the impact tips affect the hammer impulse frequency content, and the
extender affects the signal energy level. Frequency content and energy level are
interrelated, so both will be affected by different hammer structures. Hammer velocity at
impact will also affect both. In general, massive structures with lower stiffness require
the use of the extender and soft impact tip to adequately excite low frequency resonances.
During testing, occasionally check and tighten the electrical and mechanical connections.
Repeated impacting tends to loosen them, which may result in erratic and noisy signals.
Although modal tuning has done much to eliminate this possibility, bouncing (multiple
impacts) or penetration may still occur when using too heavy a hammer on too light a
structure, or section of a structure. This will appear as an oscillatory component
superimposed on the spectrum in your data. Reject such data. Some skill and practice
may still be required when testing lighter structures.
PCB's newest ICP
®
power units providing greater than 10 volts positive signal range
(three x 9 volt batteries) prevent undetected overloads in the power unit. Distortion,
undershoot, and oscillation of the impulse time history as viewed on the analyzer display
is caused by ringing of the analyzer's anti-aliasing filters, which is their normal behavior.
To view the correct impulse waveform, switch the analyzer to a high-frequency range.
5.0 CALIBRATION
Calibration involves testing the functional transfer behavior (sensitivity) of the sensor
structure in controlled transactions and environments.
Different hammer structures have different sensitivities, because the test structure
experiences a force greater than the crystal-sensing elements. The force of impact on the