| Sensing elements' automatic test and selecting basing on electric parameter, is significant to improve production efficiency of sensitive elements, to insure products' quality, and to accelerate the industrialization of sensitive elements. The sensing elements' multi-function test and selecting system, which is mainly researched in this paper, can be used for several parameters' test, which only needs a little modification on software, without changing hardware structure. This system can be used for PTC and NTC elements' selecting on resistance, and for ZnO varistors' selecting on voltage.This paper's research content includes hardware design and software development of the sensing elements' multi-function test and selecting system. Hardware design includes I/O section controlled by compuer, data sampling section, selecting mechanism and so on. With the beginning on discussing system's test principle, technics flow and design scheme, the paper discusses in detail on structure of selecting mechanism, components of I/O interface card and peripheral driving circuits, principle and method of data sampling, structure and implementation methods of controlling software, etc.The system's feed and discharge sections are key sections of selecting mechanism. The scheme of step motor-driven dial feed is used in feed section, and elements are carried to test position by selecting plate while it is circling. The scheme of pneumatic blowoff by electric magnetic valve is used in discharge section, and elements are blowed into relevant grade box. Step motor is fully controlled by computer. Compared with common mechanic transmission, this mode has simple mechanic structure, exact localization, and it can run reliably. Data sampling section is implemented by GPIB bus and digital multimeter. When choosing GPIB card, we choose the most advanced IEEE488 interface card, which is based on PCI bus. All function of the GPIB card can be implemented in VC or VB on Windows platform. The selecting grades' controlling is implemented by a piece of parallel 8255A chip and its peripheral driving circuit. In paper, principle, structure and function of both I/O interface card and driving circuit is discussed. The system's software design uses the most popular Object-oriented method and it is based on Windows platform. Every software module's design idea and algorithm flow are showed in paper. Some key technologies on hardware programming control such as GPIB communication technology, 8255A chip's controlling by program, step-motor's driving technology, are also introduced in paper.The software function is much perfect. It can complete quick and exact test and selecting for many sensing chip elements, including PTC resistance, NTC resistance and voltage-sensitive resistance. It can also do analysis and statistic work on selecting result, which is very useful in product quality control and production's management.
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