What Is the Swept Harmonic X Measurement Type In the NIDSA Read Measurement Function?Primary Software: Driver Software>>NI-DSAPrimary Software Version: 1.0 Primary Software Fixed Version: N/A Secondary Software:
Problem: What is the Swept Harmonic X measurement type in the NIDSA Read Measurement function? Solution: The NI-DSA driver is the software used to program National Instruments NI 4551 and NI 4552 Dynamic Signal Analyzer (DSA) boards. The function in the NIDSA instrument driver used to obtain data from the DSA board into your programming environment (e.g. LabVIEW, LabWindows/CVI, Visual Basic, etc...) is called NIDSA Read Measurement. The NIDSA Read Measurement function has 53 different measurement types which you can obtain. There is a group of 5 measurements which you can read from your DSA board called 'Swept Harmonic 1', 'Swept Harmonic 2', 'Swept Harmonic 3', 'Swept Harmonic 4', and 'Swept Harmonic 5'. These measurements are only available when using your DSA board in Swept Sine Mode. When using your DSA board in Swept Sine Mode (1 of 3 possible modes - others are FFT Analyzer Mode and Octave Analysis Mode), there are several different types of information which you can obtain. The most intuitive of these is the Swept Frequency Response which plots a transfer function of the system in question. When using the Swept Sine Mode of the DSA board, a sine wave is output from the DSA board. This sine wave is input to both channel 0 of the DSA board and the system whose frequency response we are interested in. The output of this system is then input to channel 1 of the DSA board. The DSA board compares the signal levels of channels 0 and 1 (system input and output) at different frequencies to generate a transfer function. This is the what the Swept Frequency Response measurement type returns to us when we read this information. When we read Swept Harmonic X, we obtain similar information, but fundamentally different. When we read Swept Harmonic 1, we obtain the transfer function of the system in question with the 2nd harmonic of the system's output signal compared to the fundamental frequency of the system's input signal. So if we are outputting a swept sine and are currently outputting at 1 kHz (system input), the DSA board will compare the system output signal's signal strength at 2 kHz with the system input's signal strength at 1 kHz. We end up with something similar to the following: Swept Harmonic 1 System Input Frequency (Hz) - 10 20 30 40 50 60 70 80 90 100 etc... System Output Frequency (Hz) - 20 40 60 80 100 120 140 160 180 200 etc... So, with Swept Harmonic 1, we are obtaining a transfer function of the system's 2nd harmonic response vs. first harmonic (fundamental) input. The other measurement types work the same way, except for different harmonics. Swept Harmonic 2 compares 3rd harmonic response against fundamental input. Swept Harmonic 3 compares 4th harmonic response against fundamental input, and so forth. Related Links: Attachments:
Report Date: 12/21/2000 Last Updated: 05/31/2003 Document ID: 24KE5QY5 |
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