Virtual Instrument For PTCR Integrated Characteristic Parameters Test

Determination of the properties of PTCR materials is very important for their theoretical study and application. The thesis discussed several common parameters' testing theory and methods of PTCR based on PTCR testing principle and the national standards. Combining the new technology of virtual instrument, this thesis put forward a new solution for PTCR characteristic parameters testing, and probed into the application and development prospect of virtual instrument in the field of PTCR parameters testing.Considered of the characteristics of virtual instrument and characteristic parameters testing, three basic principles are determined at the beginning of this design: Universal interface accorded with PnP (Plug and Play). Unitized and standardized circuit module. The guiding theory of that software is hardware.This thesis uses the parallel port of PC as the communication interface to reduce the development and production cost. The bus should be extended because insufficient of the control signals offered by parallel port. 1'wire technology is adopted to realize standard bus interface. The application of this technology enhances the system anti-disturbing ability, simplifies the circuit structure, and expands the control bus greatly. Some interfaces are kept for expanding system function in advance.As a try for circuit standardization, the system realizes the standard protection circuit unit and recovering-time circuit unit, which are connected to system through standard 44 pins' bus interface. Universal switch network and signal modulate circuit are designed. The switch network is shared by different instrument. 12-bit data-acquisition MAX186 is used to offer 1mV resolution ratio for the signal modulate circuit. Program-controlled power supply and program-controlled current limit resistance are realized based on the theory of binary code. Power voltage(0～1154V) and resistance(0～121Ω) can be altered optionally.With the guiding theory that software is hardware, the hardware has been simplified as it could be. The software system adopts C++ as program language and Visual C++ as the developing platform. By utilizing C++ programming method of OOP, perfect application program frame and strong class libraries of Visual C++, the relations of different objects are clear and the system is extendible easily. This system not only offer friendly operation interface, accurate data process and the function of figure plotting, but also probe into the systematic test error and try to dispel it by software method.This thesis analyses the application of this system on the PTCR parameters testing emphatically in V-I characteristics, operating time, and recovering-time etc. The result proved that this system has reached the anticipated goal and been greatly improved than relative traditional instrument. Undoubtedly, the virtual instrument system for PTCR characteristic parameters testing will offer a powerful tool to the parameter testing of PTC material.