Design And Realization Of PTCR R-T Measuring System Based On Micro Controller Unit

The main performance characteristics of PTC(Positive Temperature Coefficient)thermal resistance (PTCR) contain R-T, V-I and thermal characteristic. Among these characteristics, R-T characteristic is the basic one. The determination of the properties of PTC materials is very important for their theoretical study and application. This dissertation gives a detailed discussion on the measuring principles and methods of R-T characteristic of PTCR. On the base of conventional R-T characteristic testing system which is based on the computer, FLUKE45 multimeter, and to meet the intelligence device's requirement of miniaturization and low cost, PTCR R-T characteristic testing system has been designed which is based on the micro controller unit (MCU) and liquid crystal display.Composite signal microcontroller C8051F020 MCU has been used as main controller in this testing system, extending data storage device and liquid crystal display to save and display data. Testing system uses a cost-effective dual digital multimeter (DMM) chip and designs an external circuit to precisely measure resistance which is between 1 ohm and 600 megohm. Different parts of the system are discussed in modules including the serial communication interface between MCU and DMM, the I/O interface between MCU and LCD, MCU and keyboard, means of improving the ability of the system's anti-interference. Based on 1-wire control bus technology, the system uses PCA of MCU creating PWM (Pulse Width Modulated) to simulate code signal serialing into the decoder chip, gates testing sample channels.Besides,the dissertation gives individual discussing on the software part of the system such as the code of serial communication, the temperature control code, the code of the initiation of LCD and keyboards, automatic shift measure code, data process code and so on. All the codes are programmed under the C51 platform.In this paper, the designed system and the conventional system which is based on PC have both been used to do R-T test on PTCR samples. According to the testing result, we find that the R-T characteristic curve and R-T characteristic parameters obtained by the two testing method agree well, indicating that the system designed in this dissertation is feasible.