Design Of Photoelectric Sensor Module Of Near-infrared Spectrometer

With the continuous development and mature of modern spectroscopy techniques, the application of spectrology is becoming more and more prevalent, it is applied in the domain of military, pharmacy, agriculture, food and mineral measurement. Near-infrared spectroscopy develops most rapidly since the nineties of twentieth century. Near-infrared optical sensors is the basic element and decisive part of near-infrared spectroscopy, therefore, the development of sensors technology of NIR is a very important factor in driving the spectroscopy techniques toward deeper and broader application.In near-infrared spectroscopy instruments, optical sensors used in them determine the wavelength range, resolution, and wavelength accuracy of the instrument largely. At the present time, lattice sensors of near infrared spectrophotometer in the market are mainly made of silicide, PbS and InGaAs. While the type of linear array CCD sensors are more various. We need to select different sensors for defferent design requirements. From the practical point of view, this paper chose the refrigeration-type PbS lattice infrared sensor P2682-01, which is producted by Hamamatsu Photonics Co., Ltd. And selected the line array CCD sensor TCD1200D, which is producted by Toshiba Corporation. The following designs are based on these two kinds of sensors.For the refrigeration-type PbS lattice infrared sensor P2682-01, this paper introduces the principle of its cooling-Semiconductor refrigeration technology, and then describes the characteristics of the application of the sensor, and after that, the paper designs the schems of the sensor. In the circuits designing, a constant current source is contrived by the use of three-terminal adjustable regulator LM317 to provide a stable cooling current for the optical sensor. In the photoelectric conversion part, the ultralow offset voltage operational amplifier OP07 is used to design the circuits of weak signal extraction and amplification, and a bandpass filter is devised to select the right-frequent signal in order to suppress the noise outside of the passband. The very wide-used micro controller AT89S52 is used to designe the section of cooling condition monitoring circuit. In addition, a 16-bit AD7715 ADC chip is configured in data sampling, while the LCD module of LCD1602 is used to display the state of refrigeration.For the linear array CCD sensor TCD1200D, the paper introduces the working principle of CCD, and describeds the element of TCD1200D's characteristics and driving methods. This paper also analyzes the scheduling in driving the optical sensor. EPM7128AETC100-10 which is producted by the corporation of Altera has been selected to create the scheduling that is required by TCD1200D. The macrocell, I / O pins and other resources available of the chip is its advantage in leaving room for future extensions. Before the designing the driving circuit, it is necessary to employ the software of Quartusâ…¡to design the procedures of tim ing generation. The design uses the idea of top-down to do logic designing. The top-level file is of schematic form, while the underlying files are of VHDL language. A waveform simulation is employed to ensure the designs are right for the requirements of TCD1200D. In the aspect of hardware designing, the output signals of EPM7128AETC100-10 must be converted by HD74HC04 to improve the ability of driving. The signals bear more driving ability are transferred to TCD1200D in order to drive CCD for charge storage, transfer and detection. The output signal of TCD1200D is processed by the dual 160MHz rail-to-rail amplifier AD8042, a differential amplifier is designed to adjust the output signal of the sensor. And then the final output signal of the linear array CCD sensor is obtained.After the completion of the basic design, the paper describes the results of debugging of the circuits that had been designed before, and the actual data and waveforms were tested and saved. The results are analyzed comparatively in the paper and necessary conclusion are given. The signal to noise ratio and stability of the refrigeration-type PbS lattice infrared sensor P2682-01 under cooling condition are better than normal temperature. But the signal to noise ratio is not obvious as expected before. The results is consistent with the product of P4638 which was bought from Hamamatsu Photonics Co., Ltd. Linear CCD detection rate is far higher than the lattice PbS sensor, and in theory, more than ten times can be detected in one minute.Finally, the overall work of the paper are summarized, and some aspects of the system still need to be improved are put forward.