∑-Δ型24位模数转换器在智能变送器中的应用

小信号处理是现场变送器在信号处理上的一个难点 ,由于现场变送器应用环境比较复杂 ,各种噪声和干扰都非常大 ,介绍了高精度 2 4位模数转换器AD7714在小信号处理方面的应用 ,AD7714与单片机 68HC11的硬件接口 ,模拟滤波和数字滤波 ,小信号采样处理的硬件接线图和软件框图 ,用高级语言编制的采样程序举例以及对小信号处理时绘制印刷线路板方面的注意事项     

Extension of IMC tuning correlations for non-self regulating (integrating) processes

The filter term of a PID with Filter controller reduces the impact of measurement noise on the derivative action of the controller. This impact is quantified by the controller output travel defined as the total movement of the controller output per unit time. Decreasing controller output travel is important to reduce wear in the final control element. Internal Model Control (IMC) tuning correlations are widely published for PI, PID, and PID with Filter controllers for self regulating processes. For non-self regulating (or integrating) processes, IMC tuning correlations are published for PI and PID controllers but not for PID with Filter controllers. The important contribution of this work is that it completes the set of IMC tuning correlations with an extension to the PID with Filter controller for non-self regulating processes. Other published correlations (not based upon the IMC framework) for PID with Filter controllers fix the filter time constant at one-tenth the derivative time regardless of the model of the process. In contrast, the novel IMC correlations presented in this paper calculate a filter time constant based upon the model of the process and the user's choice for the closed-loop time constant. The set point tracking and disturbance rejection performance of the proposed IMC tunings is demonstrated using simulation studies and a bench-scale experimental system. The proposed IMC tunings are shown to perform as well as various PID correlations (with and without a filter term) while requiring considerably less controller action.     

Pulsatile Jet Cleaning of Filter Cloths Contaminated with Yeast Cells

The cleaning of filter cloths is necessary to avoid prolonged system downtime and strong fouling. Reliable cleaning concepts are central to the removal of residues from the complex surface of filter cloths. Particle residues, in particular, play a decisive role in the sufficiency of the cleaning performance. Consequently, enhanced particle‐removal cleaning concepts based on pulsatile jets for filter cloths have been developed. By varying the cleaning parameters, it has been demonstrated that increased pulse numbers and velocities improve the cleaning performance. Furthermore, this promising cleaning concept cleaned more effectively than conventional methods. The reduction in the amount of detergent needed is an ecological and economic advantage of pulsatile cleaning.     

Mitigating adjacent channel interference in vehicular communication systems

In the last few decades, dedicated wireless channels were specifically allocated to enable the development and implementation of vehicular communication systems. The two main protocol stacks, the WAVE standards proposed by the IEEE in the United States and the ETSI ITS-G5 in Europe, reserved 10 MHz wide channels in the 5.9 GHz spectrum band. Despite the exclusive use of these frequencies for vehicular communication purposes, there are still cross channel interference problems that have been widely reported in the literature. In order to mitigate these issues, this paper presents the design of a two-stage FIR low-pass filter, targeting the integration with a digital baseband receiver chain of a custom vehicular communications platform. The filter was tested, evaluated and optimized, with the simulation results proving the effectiveness of the proposed method and the low delay introduced in the overall operation of the receiver chain.     

Several variants of Kalman Filter algorithm for power system harmonic estimation

This paper presents the maiden application of a variant of Kalman Filter algorithm known as Local Ensemble Transform based Kalman Filter (LET-KF) for power system harmonic estimation. The proposed algorithm is applied for estimating the harmonic parameters of a power signal containing harmonics, sub-harmonics, inter-harmonics in presence of white Gaussian noise. These algorithms are applied and tested for both stationary as well as dynamic signals containing harmonics. The LET-KF algorithm reported in this paper is compared with the earlier reported Kalman Filter based algorithms like Kalman Filter (KF) and Ensemble Kalman Filter (EnKF) algorithms for harmonic estimation. The proposed algorithm is found superior than the reported algorithm for its improved efficiency and accuracy in terms of simplicity and computational features, since there are less multiplicative operations, which reduces the rounding errors. It is also less expensive as it reduces the requirement of storing large matrices, such as the Kalman gain matrix used in other KF based methods. Practical validation is carried out with experimentation of the algorithms with the real time data obtained from a large paper industry. Comparison of the results obtained with KF, EnKF and LET-KF algorithms reveals that the proposed LET-KF algorithm is the best in terms of accuracy and computational efficiency for harmonic estimation.     

Improvement of nanoparticle filtration efficiency through synthesis of SiC whisker on graphite felt by the VS CVD mechanism

This study examines the synthesis of SiC whisker on graphite felt through the non-catalytic VS CVD (Vapor Solid Chemical Vaporized Deposition) mechanism in order to investigate its potential as a filter to replace the conventional DPF (Diesel Particulate Filer). Since the CVD process is conducted mostly in high temperature exceeding 1000 °C, many restrictions exist in selecting the substrate. Graphite felt is a filter form of non-woven fabric. The graphite felt was selected as a suitable substrate material for this study based on the VS CVD mechanism due to its relatively low cost, high heat resistance, and high flexibility. The appropriate SiC whisker structure of the nanoscale was grown on the graphite felt that exhibited the fore-mentioned characteristics. This enhanced the filtration performance of the bare graphite felt filter more than two times without compromising the gas permeability. Additionally, thermal oxidation resistance was elevated by at least 200 °C more than the bare graphite felt, thereby indicating the transfer of a part of the desirable chemical properties of the SiC.     

Geosynthetics for waterways and flood protection structures – Controlling the interaction of water and soil

The interaction of water and soil has been both a blessing and a curse in all times within living memory. Water is the origin of life but is also threatening life when appearing unboundedly. Therefore mankind has always worked hard to benefit from water resources on one hand and to deal with the threat of flooding on the other hand. For both, to protect the land and to allow for beneficial uses like irrigation or navigation, often special measures are necessary to keep the water within certain bounds. Structures to achieve a permanently stable situation like irrigation and navigational canals, river training or flood protection measures need suitable material, carefully thought out design and accurate execution. Often a decision has to be made among competitive approaches to optimize such structures. In many cases, geosynthetics can support or improve the functionality and sometimes only with geosynthetics the desired result can be achieved.     

Modeling analyses of radioactive aerosol flow and collection in mesoscopic impactor filters

The concentration of radioactive aerosols in the containment increases rapidly during the serious nuclear accidents. The common aerosol filters use mesh structures or filter papers, which can significantly increase the flow resistance due to the aerosol deposition and retard the containment pressure relief following the nuclear accidents. This paper proposes and studies a MEMS (Micro Electro Mechanical Systems) inertial impactor filters which can filtrate and collect 1 to 3 microns aerosol particles without filter papers. It can significantly reduce the flow resistance in filtering micron-size aerosol particles. The modeling method is given and the simulation results are analyzed.     

Phasor measurement based on IEC 61850-9-2 and Kalman–Filtering

This paper proposes a new technique for estimating phasors during the transient phenomena in the electrical power systems. Unlike traditional Phasor Measurement Units (PMUs) that estimates phasors at process level, the proposed technique estimates phasors at bay level. The estimation technique relies on a robust recursive Kalman–Filtering, which is employed for computing the phasors based on the time-critical IEC 61850-9-2 Sampled Measured Values casted by the substation Merging Units (MUs). Many evolution tests of the proposed technique have been carried out for both stationary and transient phenomena in power systems to determine the accuracy of the measurements obtained at various conditions. The proposed estimator can produce phasors at bay level with reporting rate of 100 frames per second, which is encouraged in IEEE Std C37.118 and can satisfy higher accuracies than provided by the traditional Phasor Measurement Units, which are 0.01 degree and 0.01% for phase and magnitude, respectively.     

Realization of active power filter based on indirect current control algorithm using Xilinx system generator for harmonic elimination

Realization of active power filter with Model Based Design approach is presented in this paper. The approach adopts different modeling platforms as well as selection of proper hardware for step wise verification and testing. The active power filter model is developed using the Matlab/Simulink platform for single phase. The efficiency of the control algorithms such as synchronous detection method and indirect current control for active power filter is analyzed. Efficient control algorithm is developed by Xilinx system generator which is incorporated into Simulink as Xilinx tool box. Xilinx system generator provides a virtual platform for easy and effective design of the required system models in FPGA (field programmable gate array) design environments. Optimized automatic VHDL code is generated for the control algorithm which is simulated using ISE 13.2 for the generation of switching signals for the control of IGBTs of the active power filter. Suitable compensation signal is generated from the active power filter for the better elimination harmonics to improve the power quality. THD is reduced to a considered value which is able to satisfy the limits of the IEEE standard.