Fast Detection Key Technology Research For AOTF Infrared Spectrometer

In recent years, AOTF(acousto-optic turnable filter)infrared spectrometer has advantages such as lightweight, flexibility, good reliability and it is easy to do on-line analysis. It has been more and more widely used in the areas of food security, agriculture, animal husbandry, chemical industry, tobacco and other areas. The spectroscopic data needs to have higher spectral resolution with the further development of the spectral analysis technology. But the amount of a different wavelength spectrum acquisition is achieved by time sequential scan. The speed of obtaining spectrum curve depends on not only the number of spectral sampling point, but also the spectral sampling rate, and AOTF Spectrum sampling speed is related to light and electricity transmission speed of response(microsecond), but the existing technology is mainly limited in photoelectric detection sampling speed, especially signal sampling rate.Lock-in amplified circuit has been usually used in AOTF infrared spectrometer circuit design, as this method has high signal-to-noise ratio, stable performance, mature technology and sampling rate of 100 milliseconds per point. The principle of lock-in circuit: a signal is modulated to generate a certain frequency ac signal, then the multilevel filter circuit will be used to filter out noise, after that, it is turned into dc signal. The low pass filter has limited the sampling rate of the whole system, so it is difficult to be further improved.This paper describes another circuit design system, in which a programmable precision low noise integrator is used. The integrator which has a controllable switch could be built-in integration capacitors, and the integration time of the integrator is determined by programming. It is very convenient to control. A system has been developed according to the above-described method and used to do these experiments: At first, acquire data at different light intensity and fixed integration time. Secondly, acquire data at fixed light intensity and different integration time. Data analysis has showed that this circuit design approach could achieve very high sampling rate, and its high signal to noise ratio can be guaranteed. This method has the potential application value.