The Automatic Measuring System Of PTC Thermistor On AC Characteristics

Alternating current characteristics, which reflect PTC thermistors'I-t property and aging property, are one of the most important characteristics of PTC thermistor. The PTC thermistor ac characteristics automatic measuring system, which was mainly researched in this paper, can be used to measure PTC thermistor's I-t property and aging property automatically. The system has 48 measuring channels and it can measure 48 PTC thermistors at one time. With advanced structure, high measuring efficiency, steady work and some other advantages, the system provides a modern analysis and measuring method for PTC thermistors'development and application.The main content of this paper is made up of measuring principle, hardware design and software development of the PTC thermistor ac characteristics automatic measuring system. The hardware design includes electrical source design, measuring controlled circuit design, data acquisition section design, checking-at-zero circuit design and so on. On the basis of measuring principle and users'requirement, this paper designs the main frame of the system and explains detailed both the principle and the method for hardware circuit design. Also the system's software design and its function are expanded. The measuring controlled circuit, which is used for measuring channels'selectioncontrol and acquiring channels'selection control, is mainly made up of 96 programmable channel switches, including 48 for channels'selection control, 47 for acquisition control and one for main switch control. To make sure the measuring results being accordant and exact, a section for checking whether the current is approaching to zero is designed, named checking-at-zero circuit. Data acquisition section is implemented by digital oscilloscope TDS2012 controlled by GPIB bus. 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. I/O control section is made up of two industry I/O card: PCI-1752 and PCI-1756, both of which are also based on PCI bus. There are 96 output signals for control and 1 input signal for checkout. 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 is showed in this paper. Some key technologies on hardware programming control such as GPIB communication technology are also introduced in this paper.The software function of the system is also perfect. By executing the software, the oscilloscope can be controlled remotely and the measuring process will be totally revealed when you start your test. Also, the software can draw curves of every test. It can do some analysis and statistic work on selecting result and it can input the selecting result into a printer, a Excel file and a Word file, which is very useful in product quality control and production's management.