The Development And Application Of Seven-electrode Conductivity Instrument Based On Embedded System

Aluminum and its alloys surface passivation process in aluminum factory is an important pre-treatment process. Passivation process in every process has strict standards, especially the washing process, generally based on the level of the solution conductivity value to reflect the extent of the work of cleaning in the concentration of the bathin the industrial field, and then the real-time status monitoring process. Passivation solution in the passivation process is mainly composed of hydrofluoric acid. Hydrofluoric acid will corrode ordinary measuring electrode, and the presence of a weak anti-interference ability and ease of scaling and other issues. Passivation process metrics for each industrial washing process varies, desired measurement range, and low bath conductivity value of the last pure water washing step, the higher conductivity meter for measurement accuracy, the existing conductivity meter in accuracy difficult to achieve measurement requirements, and the price of the required measuring instruments is very high.In this paper, a set of seven electrode conductivity meter has been designed, based on embedded system, which is designed for aluminum plant passivation process. The entire instrument is composed of seven-electrode conductivity sensor and conductivity display controller. Seven-electrode conductivity sensor use the structure of seven-electrode conductivity cell, combined with the detection principle of constant current excitation source and select a new electrode material according to the nature of the industrial field. Conductivity display controller based on the ARM Cortex-M4 core microprocessor chip STM32F429 and chip C8051F060 with high AD conversion precision system as Dual-CPU. According to different functions, the whole system is divided as the core controller module, conductivity and temperature measurement module, communication module, human-computer interaction module and system power supply module. When measured by the automatic shift range after excitation by a constant current source excitation seven-electrode conductivity cell, conductivity cell measuring electrodes produce a certain AC voltage analog signal, an analog voltage signal after amplification processing, AC/DC conversion process and optical isolation, and finally through after feeding ADC data conversion from the slave CPU to the host CPU, the host CPU utilization within the integrated advantages of LCD-TFT controller using emWin graphics library design window interface, the measurement data is displayed on the 7-inch LCD screen and more enrich and improve the system in real time.After the system hardware and software, and delivers the interface display, automatic range downshift four conductance calibration and temperature compensation functions properly. In the whole test system, we make the measurement accuracy test and measurement results reproducible experiments, and test results were analyzed. The results show a higher detection accuracy of the system, good reproducibility, well to meet the testing requirements.