The Design Of Portable Frequency Selecting Vector Meter Based On FPGA

The technology of vector measurement has been applied widely in the field of scientific research, engineering application and so on. For instance, vector measurement is irreplaceable in railway transporting frequency track measurement, the hot communication field, modern medical field and millitary field. In engineering, measurand signal is not a single frequency in time and frequency domain, so we should choose a particular frequency signal from mixed frequency signals. In addition, the instrument hope to brin g into field operation, it puts forward higher requirement for volume, power consumption, operation flexibility, etc. The vector measurement instrument today for vector measurement is difficult to satisfy all these needs.We use differential frequency pulse converting technology and the principle of switch multiplication to design a portable frequency selecting vector meter which can accurately measure the phase difference, amplitude and frequency of a signal. The design not only come over the disadvantages of the traditional single-function frequency meter or phase meter, but increase four working modes to satisfy the different measuring needs which are appointing frequency mode, selecting frequency mode,scanning frequency mode and transplanting frequency mode. For the reason that the meter will do fieldwork in many circumstances, we design a instrument that is portable,low power consuming, operating-interface friendly and network-connecting. We select easy-operating touch screen TFT as our human and machine interface which will reduce the requirement of the operating people. There are two communicating methods of our design: wired communication based on the module of USB and wireless communication based on the module of WIFI. The function can transport the measuring results real-timely to the host computer which needs the results. By this method, it is convenient to dynamically monitor and analyze the measuring results.In the process of measuring the phase, we use two-stage differential frequency converting to optimize the process of phase measuring which is to increase the accuracy of the measurement. According to frequency range of the measured signal, we usesoftware to control the analog switch. Meanwhile, we measure phase by straightly measure phase, one-stage differential frequency converting to measure the phase or two-stage differential frequency converting to measure the phase. In the process of actualize the differential frequency converting, we need pulse signal and measured signal to make a frequency mixing. We use pulse converting technology principle to come up with a signal source design plan based on FPGA. We use arithmetic analysis and Matlab simulation to compute the error range of the pulse signal of different frequency which will provide important reference value of the design of signal generator. When we convert the differential frequency, we use the switch multiplication principle based on high-speed analog switch which is to optimize the design of our circuit and decrease the cost a lot.Our portable frequency selecting vector meter takes the EP4CE15F17C8 N of Cyclone chip series as the main controller, by designing the core Nios II to control the outer circuit. By programming, we flexibly change the working mode in the four working modes according to the measuring requirement. The human and machine interface transplants u COS II and uc GUI in Nios II to show the measuring results and input control instructions. The technological indicators of the instrument are as follows:the frequency measuring range is 10Hz~10MHz, the resolution of frequency is 0.1Hz;the amplitude measuring range is 10 m V ~100V, the accuracy is 1%; the phase measuring range is 0.0°~359.9°, the resolution is 0.1°.