Laser-based opto-acoustic defectoscopy of construction materials by lyrics321

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									   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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