基于FPGA的PXI高速数据采集系统设计

介绍一种基于FPGA的双通道PXI数据采集系统,系统选用了PXI总线接口芯片PCI9030来实现功能电路与PXI总线间的通讯;采用FPGA芯片对整个硬件系统的工作逻辑时序的控制;同时介绍了数据采集系统的信号调理、AD转换、FIFO等电路;最后介绍了硬件驱动程序设计。仿真及调试结果表明,信号采样实时性和高速数据传输性能均满足要求。     

高精度激光器温度检测系统的设计

设计了一个以AD7793芯片和热敏电阻为核心的高精度温度采集电路,检测结果通过SPI接口实现数据串行同步通信。以TMS320F2812为核心处理器,对采集数据进行快速数字滤波处理并将数据转换为温度值进行液晶显示。实验结果表明:高精度激光器温度检测系统能够实现对环境温度的实时检测,温度检测精度在0.2%以内。     

DSP控制DDS芯片在导向钻井信号传输上的应用

为了提高旋转导向钻井中井下信号传输的抗干扰能力,我们需要对信号进行调制。本文介绍了直接数字频率合成(DDS)的基本原理及DDS芯片AD9837的结构特点,并利用DSP芯片控制AD9837实现了FSK调制,使得井下短程信号传输的抗干扰能力得到增强,同时信号传输效率得到提高。     

基于AD9834的FSK调制信号

用DSPIC和外部任意波形发生器芯片相结合产生正弦波,并根据此波形发生器芯片AD9834对DSPIC产生的基带信号进行数字调制。当基带信号为0时,频率为某一频率。当基带信号为1时,频率为某一频率。这样基带数据就可以用两种不同频率的信号代替。将此方式运用在数字通信方面能在一定程度上提高信号的传输效率。     

USB2.0接口传输的FPGA控制与实现

从系统的总体结构、硬件设计和软件设计3个方面阐述了USB2.0接口传输的FPGA控制与实现的设计方法.FPGA作为硬件设计中的主控芯片,完成了对USB接口芯片FT245R的通信控制、SRAM的读写操作等.通过USB驱动连接应用程序和底层硬件,实现了上位机中数据的发送、显示与存储.测试结果表明,FPGA通过USB接口实现...     

TDLAS甲烷气体检测中驱动信号发生电路的设计

为了满足TDLAS甲烷气体检测要求,以STM32为核心,结合DAC8830、AD9833和OPA188芯片,设计一个驱动信号发生电路。实验数据表明:低频锯齿波信号和正弦波信号噪声小,有效滤除低频噪声干扰;将低频锯齿波信号与10k Hz正弦波叠加,使信号调制到较高频率,通过二倍频正弦波对检测信号进行分析,满足激光器对气体检测驱动信号的要求。     

基于DSP和USB的信号处理系统

本系统在DSP采集处理信号的基础上加入USB主机接口,数字信号处理芯片TMS320VC5402完成信号采集,USB控制芯片SL811HS完成数字信号的存储,直接实现两种设备间的数据传输和存储。     

基于STM32的新型信号发生器设计

给出信号发生器的硬件组成,阐述DDS芯片AD9833的工作原理,SPI通信过程,正弦波、三角波、方波3种信号的软件实现方法。搭建控制平台验证信号发生器的性能,结果表明:该信号发生器信号输出高频噪声少、频率精度高。     

塑料挤出温度模糊控制系统的开发研究

介绍用于控制塑料挤出温度的模糊控制系统的开发，在硬件方面采用AT89C52为主控芯片，用带热电偶冷端补偿的专用芯片AD595进行信号放大，并用V／F变换器AD650与CD4051配合，结合软件算法进行采样。按总结温度模糊控制规则得到的模糊控制表进行控制软件的开发与实现，整个系统具有体积小、成本低、功能强、智能化等特点。     

基于单片机AT89C52的数据采集系统

介绍由AT89C52、RAM、AD574、电源电路、模拟量输入采集处理等模块组成的数据采集系统。应用12位高精度并行A/D转换芯片AD574和八通道故障保护模拟开关实现八路数据采集且利用串行实时时钟芯片记录数据出现时间。该数据采集系统适用各种现场自动化监测及控制,具有性能稳定、可靠性高、响应速度快等优点。     

Thermally Induced Failure of Copper-Bonded Alumina Substrates for Electronic Packaging

Although copper-bonded alumina substrate has been used for some power electronic devices, its use has been rather limited because of lack of information on the thermally induced failure of the substrate. The phenomenology of thermal cracking was experimentally studied in this work. Interface debonding occurred at the side edge of copper chips and grew inwardly along the interface. Subsequently, the interface crack deviated into the alumina after propagating up to approximately 200 μm. The curving of the interface crack was caused by a mixed Mode I and Mode II loading near the edge. The cracking was widespread, whereby small cracks coalesced with one another to form a long, shallow crack along the perimeter of the copper chips. The cracking sensitivity was influenced by such design factors as edge sharpness, nickel plating, and copper backing. Annealing the substrate above 700 K before testing promoted the cracking considerably. The substrate cracking is discussed in terms of stress conditions near the edge.     

Sensory and chemical stability of tortilla chips fried in canola oil,corn oil,and partially hydrogenated soybean oil

The effects of canola, corn, partially hydrogenated soy (PHS), partially hydrogenated canola (PHC), and low-linolenate canola (LLC) oils on sensory and chemical attributes of tortilla chips were determined initially, after Schaal storage for 8 and 16 d (S8 and S16), and after practical storage for 16 and 24 wk (P16 and P24). Fresh chips were similar to each other in characteristic and off-odors/flavors, except that PHC chips had the lowest characteristic and highest off-odor/flavor. All S8 chips had similar lower (P<0.001) characteristic and greater off-odor/flavor scores than hidden reference chips, but PHC chips had a more intense off-odor than did LLC chips. After S16, canola chips had the lowest (P<0.001) characteristic and highest off-odor/flavor; all other chips were similar. At P16, canola, PHC, and LLC chips had slightly higher (P<0.001) characteristic odor/flavor scores than other chips. After P16 and P24, all stored tortilla chips had lower characteristic odor/flavor scores than hidden reference chips. Rancid, painty, buttery odor/flavor, and bitter flavor notes were detected in Schaal and practically stored chips. Stored chips from all oils were similar in color and crispness. The peroxide value and thep-anisidine value for oils extracted from Schaal-stored chips tended to support panelist data; results from similar analyses of practically stored chips did not. Peroxide values andp-anisidine values for stored used frying oils and the corresponding sensory data for stored chips generally did not agree. Results indicate considerable potential for increasing use of canola oil products for frying tortilla chips.     

INFLUENCE OF PROCESS CONDITIONS ON THE DRYING RATE OF CASSAVA CHIPS IN A SOLAR SIMULATOR

Experiments were carried out in a solar simulator to study the influence of air temperature (25-40°C), air relative humidity (40-80%), air velocity (0.95-2.2 m/s), radiation intensity (0-916 W/m²), and loading density (10-30 kg/m²) on the drying rate of a bed of cassava chips (2×2×2 cm). Well-known thin-layer drying equations were fitted to the experimental data, and the empirical constants were used in a statistical analysis of the influence of process conditions on the drying rate. The air temperature, air velocity, radiation intensity, and loading density influenced the drying rate significantly (p=0.05). The effects of the air temperature and the radiation intensity were attributed to the temperature-dependent diffusion of moisture within the chips, while the effect of the air velocity was ascribed to the resistance to mass transfer at the air-chip interface. Equations were presented to express the empirical constants as functions of the process variables.     

INFLUENCE OF PROCESS CONDITIONS ON THE DRYING RATE OF CASSAVA CHIPS IN A SOLAR SIMULATOR

ABSTRACT

Experiments were carried out in a solar simulator to study the influence of air temperature (25-40°C), air relative humidity (40-80%), air velocity (0.95-2.2 m/s), radiation intensity (0-916 W/m²), and loading density (10-30 kg/m²) on the drying rate of a bed of cassava chips (2×2×2 cm). Well-known thin-layer drying equations were fitted to the experimental data, and the empirical constants were used in a statistical analysis of the influence of process conditions on the drying rate. The air temperature, air velocity, radiation intensity, and loading density influenced the drying rate significantly (p=0.05). The effects of the air temperature and the radiation intensity were attributed to the temperature-dependent diffusion of moisture within the chips, while the effect of the air velocity was ascribed to the resistance to mass transfer at the air-chip interface. Equations were presented to express the empirical constants as functions of the process variables.     

聚乳酸/聚酰胺弹性体/聚乙酸乙烯酯共混纤维的制备及性能研究

以聚乙酸乙烯酯(PVAc)为增容剂,采用熔融共混和熔融纺丝的方法制备了聚乳酸(PLA)/聚酰胺弹性体(PAE)/PVAc共混切片和共混纤维,研究了增容剂的加入对共混切片相容性的影响和共混纤维增韧改性效果的影响。结果表明,加入PVAc后,分散相粒子尺寸减小,两相界面模糊,相容性提高。随着PAE弹性体含量增加,初生纤维中PLA的结晶度提高;二级牵伸共混纤维在PAE含量为10%时,综合力学性能最优,断裂强度、模量、断裂伸长率和断裂功分别达412.7 MPa、6345.4 MPa、22.3%和127.4 mJ,共混纤维的可纺性显著提高。     

Mid-Oleic/Ultra Low Linolenic Acid Soybean Oil: A Healthful New Alternative to Hydrogenated Oil for Frying

To determine the frying stability of mid-oleic/ultra low linolenic acid soybean oil (MO/ULLSBO) and the storage stability of food fried in it, tortilla chips were fried in MO/ULLSBO, soybean oil (SBO), hydrogenated SBO (HSBO) and ultra low linolenic SBO (ULLSBO). Intermittent batch frying tests were conducted up to 55 h of frying, and then tortilla chips were aged up to 4 months at 25 °C. Frying oils were analyzed for total polar compounds to determine the frying stability of the oil. Tortilla chips were analyzed for hexanal as an indicator of oxidative deterioration and by sensory analysis using a trained, experienced analytical panel. Results showed no significant differences between the total polar compound levels for MO/ULLSBO and HSBO after 55 h of frying, indicating a similar fry life. However, total polar compound levels for ULLSBO and SBO were significantly higher than for either MO/ULLSBO or HSBO, indicating a lower oil fry life. Hexanal levels in aged tortilla chips fried in SBO were significantly higher than in chips fried in any of the other oils. Tortilla chips fried in MO/ULLSBO and HSBO had significantly lower hexanal levels than in chips fried in ULLSBO. A sensory analysis of rancid flavor intensity showed similar trends to those for hexanal formation. The chips fried in SBO had the highest rancid flavor intensity, with significantly lower hexanal levels in chips fried in HSBO and MO/ULLSBO. Based on these results, MO/ULLSBO not only had a good fry life but also produced oxidatively stable fried food, and therefore would be a healthful alternative to HSBO. Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by the USDA implies no approval of the product to the exclusion of others that may also be suitable.     

Structure and properties of polymer–wood composites based on an aliphatic copolyamide and secondary polyethylenes

Composite materials based on an aliphatic copolyamide and a secondary polyethylene, as thermoplastic matrices, and wood chips as filler were obtained and characterized. The influence of different factors (polymeric matrix type, fractional composition and geometrical characteristics of wood filler, processing parameters and ratio polymer/wood) on the properties of polymer–wood composites (PWCs) was studied. It was demonstrated that the packing factor F has an essential influence on the properties of PWCs: increasing F values determines an improvement in mechanical properties of these materials. Mechanical properties, thermal behaviour, morphological and diffusion characteristics of the analyzed composites were evaluated through specific methods and reported herein. Morphological and DSC data confirmed the presence of strong interface interactions between polymer and wood. The diffusion characteristics of PWCs showed that the diffusion coefficient D essentially depends on filler content in composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1700–1710, 2006     

Near-wall porosity characteristics of fixed beds packed with wood chips

Packed beds of fuel wood chips are commonly found in thermal conversion processes such as combustion or gasification. Wood chips in particular are mostly used as fuel for small-scale domestic heating boilers but also for commercial-scale combustion units. The characterization of spatial voidage distribution inside the wood chip beds is of great importance for flow and reactor modelling. This study focuses on the radial porosity variations of cylindrical beds of three different types of commercially available wood chips including chips classified as G30 size class. The conventional technique of consolidating packed beds with a resin was chosen as the experimental procedure. The radial voidage distribution in different cylindrical beds is determined by image analysis of sections of the solidified packings. Additionally, a packing of monosized spheres was investigated in order to assess the selected procedure in comparison with widely available literature data for spheres. The results are discussed and summarized in a mathematical expression correlating the radial voidage distribution depending on average wood chip size, packing core porosity and dimensionless distance from the tube wall.     

锦纶6切片萃取后产生白点的原因及预防

在锦纶6切片生产过程中,有时会发现萃取后的切片在伍德灯下产生反射白点,这种白点切片的可纺性较差。通过相关的跟踪实验和统计分析,确定了白点是水溶性己内酰胺单体和低分子物,同时找到了产生这种白点切片的根本原因,给聚合装置提供了预防措施。