Research On The Digital Multimeter Automatic Verification System

Digital multimeter (DMM) is widely used in many fields, such as scientific experiment, metrological calibration, national defense technology, industrial production and agricultural production. Aiming at the problems of time-consuming calibration, tedious data processing, automation control technology is applied to design DMM system automatic calibration system based on 5720A multifunctional standard source.Firstly,this paperillustrates and analyzes the existing DMMS automatic calibration system, based on research status both at home and abroad. This paper presents design proposal for the system which applies two calibration methods, that is, "standard source method" and "direct comparison method". By using computer remote control technology, DMMS are used for information input, metrological verification, data processing and certificate printing and so on. Five major questions, that is, scalability and portability of the system, database management, calibration mode selection, judgment of calibration results and automatic generation of certificate report are discussed in the design proposal.Secondly,5720A multifunction calibrator,1281 DMM, checked DMMS, GPIB bus, GPIB interface card, computer, printer and other auxiliary equipment are applied to composite automatic calibration system. GPIB bus is used to control 5720A multifunction calibrator, 1281 DMM, checked DMMS and to calibrate DMMS AC/DC voltage, AC/DC current and resistance. The concept of modularization is introduced in designing the software. The solutions are provided to solve the major questions, that is, the method to separate calibration and data in designing the system to manage multi-drive code library of the database and dynamically add driver code. Different calibration modes are designed to meet the requirements of program controlled DMMS and non-program controlled DMMS. The calibration results are automatically generated. The module design of certificate can realize automatic generation of the documents. Interface function is studied and demonstrated. The problems aroused in the system operation are solved.Finally, by comparing the results of automatic calibration and human calibration and the investigation of repeatability and stability of the standard device, the automatic calibration system is evaluated. A great many DMM are calibrated through the automatic calibration system, verifying the stable and reliable operations, solving the practical problems effectively, and increasing measurement capacity, which achieves the desired research purpose.