Design And Realization Of Measurement System On Frequency Automatically

In scientific research or industrial production, it needs to measurement and analysis on the transmission characteristics of a network or circuit. The measurement of frequency response is one of the most basic methods. So the frequency characteristic of the low price and high performance automatic measurement system is very necessary, and it has important practical value and academic significance.Aiming at the shortage of current measurement methods, the automatically measuring system of the frequency characteristics is designed based on DDS technology in this thesis. The system mainly consists of six functional modules, respectively is the signal generator module, signal conditioning module, amplitude detection module, phase detection module, microcontroller control module and the PC processing module. The implementation method of each functional module is respectively investigated and designed in detail. In the signal generator module using parallel communication mode MCU controls AD9850module of the sweep signal source. The frequency range designed is from lOHz to1MHz; the signal conditioning module realizes gain control using operational amplifier OP37, controllable gain amplifier AD8370, resistors and analog switches, it can automatically control the gain of the input and output signal of the circuit being measured, to meet the demand of the amplitude and phase detection circuit, and improve the accuracy of measurement; AD637RMS conversion chip as the core is used for amplitude detection circuit and it can measure the signal amplitude of the output circuit being measured accurately and fast; In the Phase detection module a phase measurement method is proposed, using multiplier MLT04and low-pass filter MAX295. The phase difference being measured can be calculated by DC voltage of MAX295output and the RMS value detected. This method has a good anti-interference performance, and low requirement for the ADC conversion rate. With the high-speed comparator MAX903and D flip-flop it designs a decision circuit of lead and lag phase; It takes AT89S52as the main control circuit, the interface circuits were designed for the DDS module, signal conditioning module, signal detection, dual integral A/D converter, display and keyboard. The main function of MCU is to control the frequency of DDS signal source, implementation automatic gain control, data acquisition, data processing and simple operation, and through the RS232interface communication with PC; PC is as upper computer, using the VB platform, decided to MCU work mode, and the measurement results are graphical display, and have the function of measuring data storage and management. In this thesis, the key is to design hardware circuit of modules and software. It expounds in detail the design of the hardware circuits and the testing software. The circuits designed were tested in actual system. And the hardware and software is alignment. The experiment results show that the effectiveness of design scheme and design method. The frequency characteristics of the automatic measurement system designed has simple structure, stable performance, and the characteristics of the system friendly interface. It reached basically the design purpose.