Research On Infrared Technology Based Film Thickness Online Measure System

In producing and processing thin films, it is of vital importance to precisely measure the thickness of the films on-line, since it plays a major role in controlling the precision of the products and reducing the cost. In this paper, we provide a tool based on infrared technology to obtain the on-line and real-time measurement of the the thickness of thin films.This paper focuses on the principle of using infrared technology to measure the thickness of thin films, besides, we design the on-line thickness measurement system, which uses DSP as core processor. This system mainly consists of the infrared signal generating circuit, sensitive signal acquisition circuit, analog signal processing circuit, the man-machine interface and TMS320F2812(core processor of digital signals). Using this system, we are now able to realize the functions such as optical signal driving, the photoelectric conversion, analog signal processing, data acquisition, digital signal processing, real-time display of data and human-machine interaction.This system is based on Beer-Lambert Principle, which provides a method to calculate the thickness of thin films out of the differences between the intensity of the emergent light and the intensity of the incident light. In order to avoid disturbances, we add the calibration device to this on-line measuring system. In this paper, we introduce the implementation of on-line measurement of thin films, and we make a thorough analysis and debugging to the hardware and software components of the system.This system is based on the core processor(TMS320F2812), and is made up by four parts: optical signal driving circuit, analog signal acquisition and processing circuit, data sampling and processing circuit and human-machine interaction. We use 555 Timer and LM317 Voltage Regulator to generate the 2.0 KHz square wave signal, which drive the luminous tube to produce 3.4um infrared modulation signal; we use Pbse Infrared photosensitive device to acquire the infrared signal to realize photoelectric conversion, which, after front signal processing and amplifying, goes into the standard band-pass filter designed by filter chip MAC275, and finally we obtain the analog signal with a high signal to noise ratio; we use 16-bit, double-channel AD7606 to realize analog signal sampling, and then we use DSP core processor F2812 and IRR digital filter to realize data filtering, and then we calculate the thickness of the thin films out of the feedback signal using Beer-Lambert Principle,which illustrates the relationship between the thickness of films and the intensity of the optical signal; we use DSP core processor F2182 and LCD touch screen to realize humanmachine interaction based on communication configuration and programming design.This system uses CCS software development platform combined with MATLAB filtering tools as its software development environment, and it meets all functional requirements through programming and debugging.The result of the experiment shows that this system is capable of removing the disturbances and realizing real-time and on-line precise measurement of the thickness of thin films which meets the precision index requirements.