Laser-based opto-acoustic defectoscopy of construction materials for civil engineering Progress Report Nasir Kenarangui 09/27/07 For this week, the test signal generated by the function generator and the frequency started at 10Hz with the amplitude of 500 mV. The waveform that we observed is shown in Figure1. Figure 1. Test signal #1 without scaling For precise reading of the peak value the “Write to Spreadsheet File “ VI is used. Then a more exact reading of the maximum peak value was recorded to be 323. Scaling factor = 0.5/323= 0.001548 With this scaling factor at hand, the following result was obtained. Figure2. Representation of test signal #1 after scaling. The peak values and their respective frequencies will be recorded in spreadsheet. The result is shown in Table 1 and plotted in Figure 3. This scaling factor is constantly used as the frequency is varied from 10Hz to 20 kHz. The reference voltage value is kept at 500mV peak. Table1. Recorded Measurements Frequency, Hz Scaled Voltage, Volts 10 0.492 20 0.58 40 0.613 60 0.556 80 0.577 100 0.567 200 0.582 400 0.608 600 0.579 800 0.598 1k 0.602 2k 0.587 4k 0.605 6k 0.608 8k 0.656 10k 0.65 20k 0.553 Variations in Voltage Due to Change in Frequiency Scaled Voltage, Volts 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 0 k 10 40 80 1k 4k 8k 20 60 20 Frequency, Hz Figure 3. Variation in Voltage Due to Change in Frequency. The observation that can be made is that the output is changing with the frequency, and the scaling factor may need to change accordingly. Another observation I made with a different test was that the values also change with the sampling rate.
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