The Design Of Film Thickness Measure System Based On Capacitance Sensor

Uniformity of film thickness is one of the important indicators in evaluating film quality. With the increasing demand for high quality thin films in printing, packaging, insulation materials and other industries, the traditional off-line detection methods can not meet the demand for production testing. This requires developing one on-line detection system, which can not only guarantee film quality, but also meet the production requirements at the same time. On the basis of the above reasons, the measurement system in film thickness was studied in this paper.In this paper, utilizing the characteristics such as high precision, small energy loss, non-contact wear of capacitance sensor, a sensor probe meeting the film thickness measurement requirements was made, and on this basis the capacitance sensor signal detection circuit was designed. In the design of sensor probe, the guard ring technology and driven-cable technology were used to avoid the effect of the fringe field and the generation of parasitic capacitance. In the design of detecting circuit, the measurement program in capacitor capacitance was proposed through the comparison of many popular programs. In addition, signal processing technology, mixed-signal technology, data acquisition, microcontroller programming and digital display technology were used in the capacitor capacitance measurement program.After the system was set up, in this paper the system calibration was carried out to obtain the measurement accuracy firstly, and then through measuring the characteristic of temperature drift, the system was corrected. Finally, the system’s measuring errors were given out, and detailed analysis was produced to the reasons.From the results of thin film measurements, it can be seen that film thickness measurement system using capacitive sensor technology has high accuracy and stability. which lays the foundation for the design of the follow on-line measurement system.