Design of LXI Digital Multimeter Module
|School||Harbin Institute of Technology|
|Course||Instrument Science and Technology|
|Keywords||Digital Multimeter LXI Σ-ΔA/D convert|
With the development of new generation automatic testing bus—LXIbus, many instrumentation manufacturers have launched their own LXI instrumentations. Meanwhile, LXI researches in China are also being carried out. In order to gain independent technology of LXI and development experience on LXI instruments, advanced researches of LXI key techniques and instruments are carried out in our institute, of which one key instrument is the LXI Digital Multimeter Module demonstrated in this thesis.Based on previous research experience on DMM, combined with design results on LXI interface unit in our institute, considering the design principle of high precision and reliability, the design scheme of DMM is finally proposed after wide survey and sufficient demonstration.Divided into two parts: function and interface, the instrumentation adopts modular design and provides electrical isolation between modular, which could facilitate debugging, upgrade and maintenance as well as reduce interference, ensure precision. Instead of designing multi-power supply, single power supply is used, which not only simplified design, reduced cost but also reduced effect to measurement precision from power supply. The design of each function unit is introduced detailed including design process and some key diagrams. The key techniques applied in the hardware design are emphasized, including amplification and attenuation circuit, ohm current source circuit, serial communication circuit and LXI interface circuit.Trigger system design is described, which supports various trigger sources, including external trigger, LXI wired trigger, LAN trigger and software trigger thus ensures operation flexibility.Measurement precision is improved by using software auto-zero and channel compensation methods in software design. Based onμClinux as the design environment, Client/Server network communication program based on TCP/IP protocol and instrumentation Web interface are developed. The design of IVI-COM driver is also introduced in this paper.Finally, based on the practical tests of the instrumentation, the error of DDM is analyzed. It is proved by results that the functions and technical indexs of the DMM all meet the system requirements.