| With the rapid innovation of measurement technology in modern social science and technology,the requirements for measurement uncertainty are getting higher and higher.Among them,AC voltage measurement is a particularly important technology.Foreign major multimeter manufacturers and research institutions have relatively complete research on AC voltage measurement technology.However,due to a late start in China,there is still a certain gap in measurement uncertainty and measurement range compared to foreign countries.This article aims to propose a measurement scheme to improve the hardware circuit principle,calibration method and component accuracy and other defects.The main research contents of this topic are as follows:Deeply understand the current mainstream AC voltage measurement methods,analyze and compare the advantages and disadvantages of various methods,and propose the overall design of a high-precision AC voltage measurement system,including signal conditioning modules,AC-DC conversion modules,etc.According to the expected measurement uncertainty of the subject,the errors of each module are allocated,the key components are selected from the perspective of error analysis,and methods to suppress the errors caused by key components such as A/D converters are proposed.Research on sampling methods for high-precision measurement of AC voltage,including real-time digital sampling and equivalent digital sampling.Restricted by the Nyquist sampling theorem,the A/D converter is required to have a very high sampling rate and a fast conversion rate,so the real-time digital sampling method is only suitable for low-frequency signals.In order to measure the signal with higher frequency,it is first necessary to accurately measure the signal frequency,propose a frequency measurement scheme,and on this basis realize the use of equivalent digital sampling to complete the effective value measurement.Research on AC voltage measurement and calibration technology.Aiming at the inestimable effects of external noise and electromagnetic interference in the measurement process,as well as errors caused by insufficient accuracy of reference reference,capacitance and resistance,automatic calibration technology is introduced,and the least square method is used to correct The measured data is linearly fitted,and independent calibration parameters are stored for each range,so that the measurement accuracy is greatly improved.Complete the construction of a high-precision AC voltage measurement system.The hardware circuits such as the attenuation circuit,the main amplifier circuit and the AD637 effective value conversion circuit are analyzed and improved methods are proposed.A flatness compensation method is proposed for the problem that the frequency characteristics of the resistance-capacitance divider in the attenuation circuit contains a turning point;the main amplifier circuit adopts a negative feedback closed-loop structure to improve the amplification accuracy,and an external D/A converter is proposed for the problems of uneven frequency characteristics and the existence of DC offset to perform frequency compensation and partial compensation;for the problem of large average error of the AD637 effective value conversion circuit,a post filter method is adopted.Use STM32 to control the entire system.Finally,the CVI/Labwindows software is used to write programs for the upper computer,and the multimeter Agilent 3458 A is used to construct an automatic test system,which saves manpower and reduces the large errors caused by manual measurement.The measurement system is verified experimentally by the automatic test system,and the final experimental data is obtained.The AC voltage measurement system designed in this subject has a measurement effective value range of 10 m V-35 V,a frequency range of10Hz-1MHz,and a maximum uncertainty of 0.05%+0.04%(% measurement value +%range),reaching the level of a six-and-a-half digit multimeter measurement accuracy. |
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