In the case, if you do not have the task-specific software “Shaker systems calibration”, you can perform all the necessary measurements using ZETLAB Software package. The program “DC voltmeter” is used for the purpose of vibration acceleration measurements (figure 1)
Figure1. “AC voltmeter” program: vibration acceleration measurements
Figure 2. “Frequency meter” program: signal frequency measurements
In accordance with the applicable standards, for the purpose of vibration acceleration non-uniformity control, it is recommended to use operation mode with the automated sweep of the signal (in the case if such mode is available) and maintenance of the set acceleration level at the control point. The system for vibration exciters calibration provided by ZETLAB Company includes such mode in the case if the user has the shaker controller (in our particular example – VCS ZET 017-U). To use it, turn on the VCS ZET 017-U, start the program “Feedback generator (Sinusoidal vibration)”, set the frequency range, necessary acceleration level and sweep time (or velocity).
Figure 3. “Feedback generator (Sinusoidal vibration)” program
In this case, the frequency sweep range should be equal to the nominal frequency range, while acceleration and displacement should be 0,7 from the top level of the nominal ranges limit. If the frequency sweep rate is from 0,5 up to 1,0 octave per minute during the maximum possible duration of shaker system’s uninterrupted operation, then the acceleration value is measured at the transition frequency or at 400 Hz frequency at equal time intervals specified above. The program “Feedback generator (Sinusoidal vibration)” automatically maintains the set acceleration value at the control point throughout the frequency range.
The program “Feedback generator (Sinusoidal vibration)” can be used for producing the signal with an automated frequency sweep. The program also allows to set a complex test profile (figure 5) with the maintenance of the set displacement value at low-frequency range, velocity at medium frequency range, acceleration at the high-frequency range.
Figure 4. The program “Feedback generator (Sinusoidal vibration)”. Tests process
Figure 5. Vibration tests profile
It is also preferable to use the automated frequency sweep mode since it allows to evaluate vibration acceleration non-uniformity in the dynamic operation mode of the vibration exciter (shaker) as the specified frequency range is approached by the signal. When using the program “Feedback generator (Sinusoidal vibration)” in the calibration procedure, it is also convenient to use the function “Signals recorder” for producing the test report. This function enables tracking the changes of frequency and acceleration values of the reference transducer in the course of tests performance (figure 6). It is also possible to view linear representation of the frequency graph by switching the graph vertical axis into the logarithmic scale (figure 7).
Figure 6. “Signals recorder” program, frequency graph
Figure 7. “Signals recorder” program, linear frequency graph
It is also convenient to use the program “Multichannel recorder” for evaluation of vibration acceleration and frequency non-uniformity in statical mode (i.e. in the case when a constant-frequency sine signal is applied to the input of the vibration exciter (shaker)). Figure 8 shows two different examples acceleration measurements for the vibration transducer. Measurements interval: 1 second.
Figure 8. “Multichannel recorder” program
In the case of periodical calibration, it is allowed to conduct measurements during a time period of 50% from the maximum possible time of shaker system uninterrupted operation.
Acceleration non-uniformity in percentage rate is calculated by the following formula:
where ac and as — stand for the current and the set value of acceleration at the control point.
Frequency non-uniformity in percentage rate is calculated by the following formula:
where fc and fs — stand for the current and the set value of the frequency at the control point.