Research On Infrared Technology Based Film Thickness Online Measure System

The measurement of film thickness has significant importance in the processof film production. This paper introduces a project used to realize the onlinemeasurement for film thickness by the application of the infrared technology.This project can be used to measure the film thickness during the process of filmproduction.The principle of measurement for film thickness by the application of theinfrared technology has been studied. Based on the principle, an onlinemeasurement system with DSP as the core has been designed. This system iscomposed mainly of five parts. They are temperature control circuit, filmthickness sensing circuit, preprocessing circuit, man-machine interface, and thecore processing chip TMS320F2812. The system accomplishes photoelectricconversion, signal processing, timely sampling, data processing, timely datadisplaying, and man-machine interface function.Film thickness measure system is based on the principle of Lamber-Beer.When film is illuminated by light, there exists an intensity difference between theinput light and the output light. The difference complies with the formula ofLamber-Beer. To avoid the environment light and the common mode interference,modulation light and reference group have been adopted on the foundation of themeasure principle. The design method and the measure process have beenanalyzed. The hardware and the software of the system have been designed anddebugged.With DSP as the core, the system is composed of analog signal obtain andprocess, digital signal obtain and process, and man-machine interaction. Theanalog signal obtain module works with2.9um and3.4um infrared LEDs as thetwo light sources. The555timer has been designed to drive the two LEDs togenerate modulation infrared rays. The difference of the phase the twomodulation driving signals is180°. These two driving signals drive the two LEDsrespectively. Infrared photoconductive resistance which can be cooled byrefrigeration circuit transfers the infrared signal to electric signal. The filter chipMAX275has been applied to design the bandpass circuit to filter the analogsignal. The16bit AD chip, AD976(A), has been used for signal acquisition. DSPchip TMS320F2812functions as the core processing chip, realizing digital signal processing, FIR digital filter, communicating with LCD touch screen JCR56HDto accomplish man-machine interaction.This system combines the software MATLAB and the DSP softwaredevelopment platform CCS to realize the simulation, programming anddebugging of software part.The results of the experiment show that this system functions well inmeasuring the film thickness with high accuracy.