A compact and low-cost light-emitting diode (LED) with center wavelength of 295 nm and high light density was used measure the concentration of sulfur dioxide, which has a strong structured absorption band in the ultraviolet region 300 nm. Differential optical absorption spectroscopy (DOAS) was used to determine the concentration of sulfur dioxide using reference absorption spectrum due to 1000 ppm SO2. A sensitivity of about 1.5 ppm was achieved with a gas cell in 1-s integration time, enabling real-time monitoring of sulfur dioxide.
Tobacco is one of the most important economic crops in the world, assessment of its quality has a very important business significance. A compact, low-cost, and maneuverable optical sensor system for classification evaluation of different tobaccos was described in this paper using light-emitting-diodes (LEDs)-induced fluorescence. The principal components analysis (PCA) method is used to extract the dominant features of the tobaccos for identifying the classification of tobaccos. The technique is suitable for practical identification due to the use of a straightforward data evaluation method and compact system.
KEYWORDS: Signal processing, Signal to noise ratio, Sensors, Signal detection, Interference (communication), Time metrology, Lanthanum, Digital electronics, Analog electronics, Niobium
A new signal processing circuit for position sensitive detector (PSD) is proposed in this paper. Using this circuit, the photocurrents of PSD can be directly transformed into digital signals, and the signal-to-noise ratio can be greatly improved, but the measurement time is extended. The measurement results show that the agreement between theory and experiment is quite good.
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