In the field of electronic measurement, frequency is an important parameter. It is often used as the basic parameter and reference value of computation. With the continuous development of computer network and Electronic Science and technology, the measurement of frequency is getting higher and higher. At this time, a high-precision frequency meter is particularly important.

With the development of frequency measurement technology, the measurement methods are mainly divided into measuring frequency method, time interval, fragrance conversion frequency measurement method, digital recruitment method, interpolation frequency measurement method and frequency mixing frequency measurement method. In the digital frequency measurement method, two improvements have been made in the frequency measurement method of equal precision. On the one hand, the measurement accuracy is improved without increasing the working frequency of the system and prolonging the measuring threshold time. By using the adaptive frequency division of the measured signals, the shortcomings of the preset threshold time are eliminated, and the synchronous logic circuit is simplified, and the system reliability is improved.

The SYN5636 type general counter has the "multiple parallel counting method": Based on multi-channel parallel processing capability, fast computation speed, low cost and high integration FPGA, it uses multiplex different frequency reference signals to count; absolute error can only be 1, and the highest accuracy count result is selected. When implemented, a high-speed comparator module is built by using a wideband amplifier and a high-speed comparator. The FPGA is used as the frequency measuring module. The control module is composed of single chip microcomputer, LCD display screen and keyboard, and the Verilog parallel programming is used to realize the "multi channel parallel counting method". It is expected to achieve high precision measurement of the frequency of 1 Hz to 199M Hz sinusoidal signal, and realize the time interval measurement of the other signal and the duty cycle measurement of the pulse signal.

The frequency meter takes FPGA and MCU as the core, and adopts the method of "multiple parallel counting". High precision measurement of signal frequency. The input signal is converted to square wave signal input through high frequency amplification and comparison module. The FPGA unit is counted in parallel after multiplying the frequency of different multiplier. Finally, a single output value with high output precision is selected by the single chip microcomputer, and the final measurement result is obtained by conversion relation. After testing, the digital frequency meter can realize the frequency measurement of 1Hz ~ 199mhz and 10mvrms ~ 1Vrms sinusoidal signals, the absolute error of relative error is not more than 0.0001%; the time interval between 100Hz to 1MHz and 50mV to 1V square wave of the same frequency is measured, the measurement range is 0.1us ~ 100ms, the absolute error of relative error is not more than 1%; the absolute value of relative error is not greater than 1% for the measurement of duty ratio of 50mV to 100ms and pulse signal. Therefore, it has the characteristics of high accuracy, wide frequency range and wide range of measurement.

In the field of science and technology, frequency is one of the most basic and most common physical parameters. As a basic measuring instrument, digital frequency meter is widely used for its high accuracy, fast speed, simple operation and digital display. Many physical quantities, such as temperature, pressure, flow, liquid level, pH, vibration, displacement, velocity, etc., can be converted into signal frequency through transducers, and can be measured with a frequency meter. All kinds of measuring instruments, control equipment and real-time monitoring system based on frequency meter have been applied to all aspects of the international people's livelihood.

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