Portable inspection system design for grouting quality evaluation of post-tensioned prestressed ducts

A portable inspection system based on coplanar capacitive sensor for grouting quality is presented. With the derived semi-analytical equation for capacitive proximity sensor, the optimal parameters of sensor are determined. Based on the principle of capacitive proximity sensor, data acquisition unit and data conversion unit are designed. To promote the system, system control unit and data display unit are designed. According to the approximation theory, the system verification test is designed by measuring capacitance of different thickness of liquid on the glass surface and comparing the measurement results with the COMSOL simulation results, data processing and system error evaluation are done. Experiments show that the average relative error of the system is less than 9.5%, and the resolution is 0.1mm. In addition, the inspection system volume (except the coplanar capacitive sensor) is 100mm×80mm×30mm. The experimental results illustrate that the system can effectively distinguish the stratification of grouting in the ducts, and the test results are reliable and accurate.