please only attempt to do the following if youre sure of the answer. include use
ID: 2079958 • Letter: P
Question
please only attempt to do the following if youre sure of the answer.
include useful info related to accelerometer calibration and discuss and conclude on the following:
1-Calibration of measuring system:
2- standard and test accelerometer
3-Relative Sensitivity of Test Accelerometer vs. Frequency graph:
4-Frequency analysis of machine vibration:
5-Frequencies present in the signal and the main vibration frequency:
6- rms lateral acceleration
7- lateral velocity and displacement.
Results Calibration of measuring system: Setting the frequency of the variable frequency oscillator to 150 Hz and increasing the output level to 300 Hz which produce a reading of 1.24 mV on the measuring amplifier. a Standard accelerometer When the output signal is 20 mvig then the measuring amplifier reads: 20 mV. b) Test accelerometer: When the output signal is 20 mVlg then the frequency is 294 Hz. c) Determination of the useful frequency range of the test accelerometer with a sensitivity of 20 mV/g: Measuring Amplifier Charge (mV) Relative Sensitivity (mv) Mounted Resonance Frequency (Hz) 20 14 50 13 100 12 16 200 500 20Explanation / Answer
1) when the frequency of the oscillator is changed from 150 to 300 Hz the output measured by the amplifier is 1.24mV. Which means that the input to the amplifier is frequency and the amplifier measures the change in frequency and displays it as a voltage signal. Now before assuming that this is the actual voltage for the aforementioned change in frequency the measuring accelerometer (test accelerometer) should be calibrated using a standard accelerometer.
2. The standard accelerometer output signal is 20mV/g and this signal is read by the measuring amplifier as 20mV. Whereas the test accelerometer output signal is 20mV/g when the frequency is 294Hz. Which means that the amplifier reads 20mV when the frequency is 294Hz. It means that the oscillator frequency is set to 294Hz after calibration was initiated.
3. The trap shows that the relative sensitivity increases with an increase in oscillator frequency. But the oscillator natural frequency is 5260 Hz at 50mV and so beyond this limit if the frequency is increased then the oscillator cannot be brought back to stability and will keep on resonating even without an input signal. Therefore a stable operating frequency range has to be zeroed in and from the graph it is seen that relative sensitivity between 10 Hz to 100 Hz is a constant and between 100 Hz to 1000 Hz it increases and is maximum at 1000 Hz. At 20 mV relative sensitivity the frequency is 500 Hz and therefore the test accelerometer should be used between a frequency range of 100 Hz to 1000 Hz with a sensitivity of 20mV/g.
4. Frequency analysis of the vibration can be carried out using fourier transform of the signal. It shows the dominant frequencies present in the vibrations.
5. 25 Hz signal is the dominant frequency then in fourier transform that frequency would have the highest magnitude. The 50 Hz signal is not filtered because the high pass filter used may be set to eliminate frequencies less than 50 Hz. These frequencies are obtained because for obtaining a maximum frequency of 500 Hz without aliasing problem. The sampling frequency has to be set to 1000 Hz and thereby extracting all frequencies from 0 to 500 hz and then filtering out the unwanted frequency is the best method to go for.
6. RMS of lateral acceleration gives the rate of change of velocity given by (22mV/(20mV/g))=1.1*9.8=10.79ms^-2.
7. lateral velocity is calculated using Vl=Arms/(2*pi*f) to get the linear velocity due to the acceleration and lateral displacement is calculated using Sl=Arms/((2*pi*f)^2) to get the lateral displacement due to the acceleration
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