Frequency Measurement Based On Labview Virtual Instrument System And Application

As digital technology and other electronic technologies develop rapidly, there's higher and higher demand for frequency stability and accuracy in signal source. The most convenient way to evaluate the performance of signal source is to measure it's frequency in high precision. At the same time, as one of modern technique in experiment, virtual instruments are widely used in the fields of test in engineering, long-distance control and teaching. In this thesis, several frequency measuring methods and techniques had been compared and analyzed. A virtual instrument system in frequency measuring and analyzing has been developed on the platform of LabVIEW and the synchronously multi-periods frequency measurement method based on phase-coincide detection technique has been used in its hardware system. This system can be used to measure and analyze the crystal oscillator's warm up property, frequency stability within a day, short term stability, ageing rate, frequency retrace and accuracy. Afterwards, this system has been used in measuring and analyzing some crystal oscillators of high stability in common use and it has been proved by these experiments to be a easy-operating, steady-running system with friendly-interface.The synchronously multi-periods frequency measurement method is one of the most advanced methods among all the frequency measuring methods. However, when it was used in this virtual instrument system to measure signal's frequencies in high precision or super-precision, we had found that the measuring precision in the synchronously multi-periods frequency measurement method depends both on the value of referenced and measured frequency and their differences. In the latter part of the thesis, these factors were studied in detai' through mathematical analyses and computer simulation. Furthermore, a method has been proposed to improve the measurement system and increase the measuring precision, which is to make the referenced frequency close to the measured frequency using phase-lock in technique.