| The measurement uncertainty is critical in application of virtual instrument. The main basis for the evaluation of measurement uncertainty is <Guide to the Expression of Uncertainty in Measurement(GUM)>. However, for dynamic measurement uncertainty evaluation, GUM does not give a clear definition and method. At present, the research on the uncertainty of virtual instrument center on single link of virtual instrument. The uncertainty of virtual instrument, especially the research on the dynamic measurement uncertainty, also is insufficient. Therefore, it is very necessary to put forward an application method of dynamic measurement uncertainty for virtual instrument.In order to try to solve the above problems, the following work has been carried out:1. Based on GUM, the basic principles of measurement uncertainty evaluation are analyzed, and the definition of uncertainty according to type A and type B in GUM is analyzed, then the evaluation process of uncertainty is studied;2. The mathematical model of the sensor is established, and its transfer function is analyzed, then its frequency characteristics are obtained. Then, according to the frequency characteristic curve, its function is fitted. Using the amplitude attenuation and phase lag of dynamic signal described by frequency characteristic, uncertainty in dynamic measurement of the sensor can be evaluated.3.After analysis of discrete systems, a mathematical model of discrete system is established. By using the z-transformation theory, the mathematical model of discrete system is transformed into the form of pulse transfer function. By using the pulse transfer function to analyze the signal transmission of ADC, the uncertainty of ADC is evaluated.4. In the case of a pulse transfer function of ADC cannot be acquired, the dynamic performance parameters of ADC should be analyzed. The noise generated in the A/D conversion process is calculated according to the quantization error. Then taking into account the harmonics in the A/D conversion process, the pulse transfer function of ADC is calculated and analyzed. With the help of mathematical transformation, the pulse transfer function of ADC can be described in the form Fourier transform to calculate the ADC frequency response function. Finally, according to the frequency response function of ADC, the uncertainty of the amplitude and phase of ADC is calculated.5. Based on CA-YD-106 acceleration sensor and NI-PXle-6368 data acquisition card, virtual instrument measurement platform can be established. The dynamic measurement uncertainty of the virtual instrument can be evaluated, and the above method is verified. |
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