涂层、钢筋混凝土电化学阻抗现场测试仪的研制

Development of a Device for Field Measurement of Electro- chemical Impedance Spectra of Coatings and Reinforced Concrete

当今,实际工程中缺乏现场快速简便测量涂层、钢筋混凝土状态的仪器。利用高速单片机、数字信号发生器、双通道同步高速AD和高输入阻抗模拟电路,设计了一套电池供电、适于现场应用的便携式电化学阻抗(EIS)测试仪。考虑到涂层或钢筋混凝土的高阻抗以及现场测试过程易受外部噪声干扰的特点,仪器电路设计中采取了双通道8阶低通滤波器和前置放大器来提高电流分辨率;采用相关积分算法,借助具有电磁屏蔽特性的护环电极探头减小了外部耦合噪声对微弱信号的干扰,实现了高精度阻抗测试。仪器通过频率扫描测量涂层/金属界面的阻抗谱,计算出涂层电阻、电荷传递电阻和界面电容,进而监测金属构件的腐蚀状态。对室内涂层钢板的测试表明,该仪器测量的阻抗谱与PAR 273电化学测试系统的测量结果有良好的一致性。

A portable device with cell power supply for field measurement of the electrochemical impedance spectra of coatings and reinforced concrete was designed and developed. This device consisted of a high-speed microcontroller, a direct digital signal synthesizer, a simultaneous dual-channel alternating/direct sampling module and a high-speed analog circuit. To avoid the disturbance of external noise to sampled signals in the presence of high impedance of coating and reinforced concrete system, bi-channel 8-order low-pass filters and pre-amplifiers were integrated in the electric circuit to improve the current resolution. With the help of a fast correlation algorithm and a dedicated design of electromagnetic interference-proof probe,as-developed device was capable of monitoring the quality of coatings and corrosion of reinforced concrete. Based on calculation of the coating resistance, charge transfer resistance and interfacial capacitance, the corrosion status of metals under coating or concrete could be in-situ evaluated. Indoor tests with coated steel sheets showed that the impedance spectra measured with the present device agreed well with those obtained with PAR 273 electrochemical test system.