电流、电压、电阻、频率、温度、压力、流量、流速和开关量都是生产和生活中常用的主要被控参数。其中，电流、电压、电阻和频率更是越来越重要。这样，做为测量用的万用表的地位就显得举足轻重，特别是高精度的万用表更是发挥着极其重要的作用。 本论文主要研究并且设计一种高精度的数字式万用表。具体测量方法是采用单片机系统对信号进行采集和控制。单片机系统包括MSP430处理器、SPI接口、真有效值转换芯片AD536、模数转换器AD7711、掉电保护和复位以及显示电路等。具体方法是使用模拟电路对各种电信号进行数据采集，经过放大电路和滤波电路之后进行A/D转换，转换后的数字值送进单片机进行数据处理，同时显示出来。其中软件使用IAR编译环境进行C编程，采用模块化的设计方法，从而实现了各种电信号的控制算法模块，数据采集模块、双处理器联机模块和键盘扫描模块。为了测量的准确，在设计时对于频率的测量与其它三路信号分开进行，采用单片机和CPLD结合的方法进行设计，并且将低频和高频部分分开进行测量。 通过对所研制万用表的测试，测量精度达到了5位半。验证了上述研究和设计的可行性。为以后智能仪器的研究提供了一种新的设计思路和方法。

Current, voltage, resistance, frequency, temperature, pressure, flow, flow rate and volume switches are commonly used in the production and life of the main accused of the parameters. Among them, the current, voltage, resistance and frequency is more and more important. In this way, as measured by the multimeter's status has become important, especially in high-precision multimeter is playing an extremely important role. In this paper, the main research and design a high-precision digital multimeter. Specific measurement method is the use of single-chip microcomputer system of collection and control signals. Single-chip microcomputer system includes the MSP430 processor, SPI interface, True RMS converter chip AD536, ADC AD7711, brown-out protection and reduction, as well as show circuit. The specific method is the use of analog circuits on a variety of electrical signals for data collection, through amplifier and filter circuit after the A / D conversion, the digital value after conversion into the single-chip microcomputer for data processing, at the same time displayed. Which software to use IAR compiler for C programming environment, using modular design methods, in order to achieve a variety of signal control algorithm module, data acquisition modules, dual-processor modules and the keyboard scan-line module. To measure the accuracy of the design for frequency measurement and the other three signals separately, the combination of MCU and CPLD design methods, and separated from low-frequency and high frequency measurements. Multimeter developed through the testing, measurement accuracy has reached a half 5 bit. Verification of the feasibility study and design. Intelligent instrument for future research provides a new design ideas and methods.