Research Of The High Precision Digital Phase Meter

This subject is based on the horizontal topic of "The Digital Phase Meter with High Precision and Broadband", which is cooperated with Tianjin Zhonghuan Electronic Instrument Company. In view of the domestic present digital meter with single function, low automation and accuracy, this paper is studied deeply with the high precision digital phase meter. Based on the in-depth analysis of many phase measurement systems:numerical sampling, digital correlation method, phase-voltage conversion method, phase-time conversion method and the phase discrimination with zero-crossing, this paper is designed a high precision digital, which is used the FFT algorithm based on FPGA. The most outstanding characteristic of this phase meter is to realize the high precision, range automatic switching and versatility. Compared with the traditional phase meter, the precision of the phase difference measurement is advanced from0.1°to0.05°. The mean work of this paper is the design of the hardware circuit and software.Part1:The hardware design of high precision digital phase meter:(?) The design of the auto-range system based on counting. It includes attenuator, amplifier, amplitude detection circuit and the auto-range circuit. To a certain extent, this design shorts the development cycle of instrument because of its high precision and strong portability.(?) The design of shaping circuit. It is based on the Schmitt trigger and it is used to convert the sine wave to square wave.(?) The design of A/D sampling and conversion circuit. This design based on the high precision16bit A/D chip ADS1605is used the typical coupling differential circuit,which is supplied by TI company. Its advantage is slightly low bandwidth, small AC signal distortion and low noise. Because it is a differential input circuit, and the shaping circuit output is a single-ended signal, it needs to use the differential amplifier AD8138chip to convert single-ended signal to differential signal.(?) The front panel design. It is designed by ICM7216, because it contains decoding circuit, drive circuit and it will automatically create the decimal point shift to reduce lots of programmes. The frequency meter design realizes the function of the phase meter diversification.(?) The power design. In order to improve the accuracy of power, it chooses the voltage regulator (LM317, LM337and LM323) to complete the design of power.Part2:The software design of high precision digital phase meter:This paper studies the FFT algorithm which is a high efficient algorithm of Discrete Fourier Transform (DFT) deeply. It uses the EP2C15AF256C8chip of Cyclone II series based on FPGA and the FFT IP Core is used to measure the phase difference. The Matlab simulation proves the correctness of result. Compared to traditional phase meter, it is proved by many examples that this method improves the phase difference from0.1°to0.05°.