The Design Of The Extensible Micro Resistance Measure System Based On AC Current Source

With the continuous development of science and technology and the engineering practice, the requirement of measurement and testing accuracy is stricter and stricter in the field of electrical, petrochemical, materials, semiconductor, etc. But there is not a universal measurement and detection scheme. In order to solve this problem, combined with the data collection and analysis functions of actual demand, a set of extensible channel of high-performance general-purpose data acquisition system is designed.The system contains hardware circuit and the development of computer software. The thought of design based on the resistance theory to accomplish the measure of corrosion information. Because of the resistance of the metal sensor is milliohm level, if you want to get a high measuring resolution, the sensitivity of the measure system must reach the level of micro ohm.4-wire method based on AC current source is adopted to realize the resistance monitoring and measurement. The hardware circuit contains the power supply, AC current source, differential circuit, peak-to-peak value detection circuit and the circuit system of STM32 moduIes(ADC, DAC, USART etc.). The labview platform of NI is used to develop the computer software, which contains serial communication, file 10, digital filter and the control software of ART USB2884.To get the ratio of the reference sensor and corrosion sensor is core of the monitoring system. There are 2 method to realize monitor measurement. One is based on the peak-to-peak value detection circuit and the other is based on digital lock in amplifier mechanism. Both methods can get good measurement results, and the results is very close. Both of the resolutions can reach micro ohm level, but the peak-to-peak value detection circuit is more economical than the latter which is based on high precision data acquisition card.After the test and calibration precision, all of the parameters of the acquisition system meet requirements. It can achieve the value of the resistance which is at u? level and will be widely used in power testing, corrosion monitoring, electrical properties testing, metal film measuring and so on.