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排序方式: 共有128条查询结果,搜索用时 15 毫秒
1.
针对瞬时采样方法只适合变频器模拟量比较平滑且采样频率较高的场合和平均值采样法要求采样频率高、运算速度快的问题,设计了一种基于FPGA的Σ-ΔADC转换器,介绍了Σ-ΔADC转换器的结构原理和Sinc3滤波器的设计。该转换器将Σ-Δ调制器和FPGA有效结合,既提高了采样精度,也提高了模拟信号传输的抗干扰能力及检测装置耐压的能力。实验验证了该转换器的正确性。 相似文献
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为了改善传统数据采集系统运算能力差、分辨率低、可靠性低等缺点,结合Δ-Σ技术和FPGA,设计了一种多通道、高分辨率、宽动态范围的新型数据采集系统。提出了一种由Δ-ΣA/D转换芯片、高性能FPGA和DSP组成的数据采集系统方案及其硬件电路实现方法。系统利用A/D器件对信号进行滤波、放大、差分转换和模数转换,利用FPGA设计内部模块和时钟信号进行电路控制及实现数据缓存、数据传递等功能,由高速DSP芯片核心控制,对采样数据进行实时处理。系统能实现24位高分辨率、宽动态范围的信号数据采集与高速实时处理,可用于电压、电流、温度等参量的采集系统中。 相似文献
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从模数转换的基本理论出发,在对一阶Δ-Σ调制器原理深入解析的基础上,得到Δ-ΣADC动态输入范围的计算方法。利用Matlab simulink建立了二阶Δ-Σ调制器系统模型,对调制器电路进行仿真和参数优化,对其性能进行了有效评估。使用轨对轨折叠式共源共栅运算放大器作为调制器的积分器,增大了调制器的动态输入范围;设计的高速比较器将NMOS负载管交叉耦合从放大器输出端引入正反馈,提高了转换速度。设计实现了一款适用于14 bit温度转换芯片的二阶△-∑调制器,信噪比SNR可达87 dB。 相似文献
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《计算机与应用化学》2000,17(1)
Δ3-1,2,4—噻二唑类化合物具有抑制黄瓜霜霉病毒的杀菌活性。本文用半经验PM3方法对25个该类化合物进行了量子化学计算,并依据原子的净电荷、前沿轨道能级、轨道主要成分及原子在前沿轨道中所占比重等计算结果和多重回归分析讨论了该类化合物的活性部位,为该类化合物结构与活性的研究奠定了理论基础。 相似文献
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《International Journal of Hydrogen Energy》2022,47(95):40264-40274
Hydrogen (H2) metabolism in Escherichia coli occurs via reversible membrane-associated hydrogenase enzymes (Hyd). Hyd-3 and Hyd-4 with formate dehydrogenase H (FDH-H) form formate hydrogen lyase complexes. The changes of metabolic pathways and ΔpH (pHin-pHex) regulation during fermentation of glucose, glycerol and formate in non H2-producing hypF (lack of all Hyds) and fdhF (lack of FDH-H) mutants at pH 7.5 were investigated. It was shown that specific growth rate was higher by ~23% in hypF and fdhF, compared to wild type (wt), suggesting the negative effect of H2 on bacterial growth. Moreover, it was shown that H2 generation did not have a vital role in glucose and glycerol utilization rate at 0–72 h. The utilization of external formate was detected in wt (~2.6 mM) and hypF (~0.68 mM), but not in fdhF, due to the absence of enzyme responsible for formate metabolism. Nevertheless, the changes in ΔpH were not evident at 3 h. The ratio of generated end-products and regulation of ΔpH at late log (6 h) and exponential phase (24, 72 h) were various in hypF and fdhF due to formate disproportionation in hypF and proton generation, therewith absence of H2 generation. Taken together it can be concluded that bacteria regulate generation of fermentation end-products via balancing the concentration of acids and ethanol to maintain ΔpH and redox potential values. The results obtained are important for development and regulation of H2 production technology when applying mixed carbon sources. 相似文献
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The aim of the present paper is to show that magnetoelastic sensors can furnish important information about the drying behavior of ceramic materials, and are, therefore, possible alternatives to ultrasonic or cantilever techniques. Sensitive measurements of the resonant frequency of coated amorphous ribbons show characteristic structures at different phases of drying. A model relating the resonant frequency of a magnetoelastic sensor to elastic properties of an applied thin film coating is extended to include the magnetic field dependence of the elastic modulus, the ΔE effect. In this manner, the stress developed during the drying process which contributes to the magnetic anisotropy, can be introduced into the problem. The model is applied to hard clay slurries drying on Metglas 2826MB3 ribbons. The long time value of the sensor resonant frequency is found to be consistent with elastic properties of the clay and the sensor appropriately indicates the appearance of stresses when the meniscus of the drying fluid begins to enter the pores of the solid. 相似文献
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单氟取代苯基二苯乙炔基异硫氰酸酯的合成与液晶性质研究 总被引:1,自引:1,他引:0
为了满足液晶光学器件快速响应的要求,采用有机合成方法获得了6种单氟取代苯基二苯乙炔基异硫氰酸酯类液晶化合物。首先用IR和1HNMR对6种单氟取代液晶化合物的结构进行了表征,其次通过差热分析对其相变温度进行了测试,利用液晶综合参数测试仪对其液晶性能进行了研究。红外和核磁图谱表明合成的化合物即为目标化合物;差热分析获知这些化合物90℃左右进入液晶相,并且氟取代位置在与异硫氰酸酯基相连苯环的2号位置时有相对较低的熔点,最低的熔点可达到83.4℃;液晶综合参数测试结果表明这6种化合物的Δn值为0.432~0.681,同时氟取代位置在与异硫氰酸酯基相连苯环的3号位置时有相对更佳的响应性能。这些化合物在制备快速响应液晶光学器件中可能会有潜在的应用价值。 相似文献
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《Journal of Building Performance Simulation》2013,6(1):53-62
Black-box models such as linear regression have proven to be helpful in ongoing building commissioning in many ways. The aim of this work is to improve linear models with change point for fault detection in buildings. Building simulations revealed poor performance of them (R 2 < 0.7) for some low energy buildings. The regression models (RMs) can be considerably improved by introducing the rate of change of the indoor air temperature (ΔT ind) as an independent variable. Thus, R 2 values were raised by up to 0.5 (e.g. from 0.2 to 0.7, example with the lowest R 2). A new training and application process for the RMs revealed further improvements by using a hierarchical agglomerative clustering algorithm to determine different day-types as additional (categorical) variables in the RM. The application of these improved RMs for outlier detection is demonstrated in three buildings. 相似文献