Design and implementation of an integrated safety management system for compressed natural gas stations using ubiquitous sensor network

To increase awareness of safety in facilities where hazards may exist, operators, managers, and executive officers on the site should be able to monitor such facilities. However, most compressed natural gas (CNG) service stations in Korea use only local-mode monitoring, with only on-site operators to monitor the facility. To complement this local-mode monitoring, an online safety management system called Ubiquitous-gas safety management system (U-GSMS) was developed. The U-GSMS consists largely of software and hardware. The software consists of systems that can manage safety and operations, while the hardware consists of sensors installed in the gas facility and wireless communication systems using a ubiquitous sensor network (USN) technology that facilitates communication between sensors as well as between sensors and other devices. As these systems are web-based, on-site operators as well as managers and executive officers at the headquarters can more effectively and efficiently perform monitoring and safety management.     

化工过程监测系统的传感器网络设置问题研究

化工过程监测系统的性能与其传感器网络的设置方式有直接联系。通过建立化工过程有向图模型,结合故障传播模式分析和传感器网络搜索算法,从过程监测的角度研究了传感器设置问题。给出了考虑故障可观性与分辨率下的传感器设置方法。并以CSTR-heat exchanger过程为例,说明了统计过程监测方法与传感器网络设置问题相结合的重要性。     

Developmental studies of an adaptive on-line softsensor for biological wastewater treatments

Efficient monitoring and automatic control systems for biological wastewater treatment processes, especially those dealing with bioinhibitory pollutants, such as phenol, are urgently required in order to meet increasingly stringent environmental regulations. Practical on-line sensors of variables that describe water quality, such as BOD or individual toxic pollutants such as phenol, are not commercially available; e.g. phenol is generally monitored off-line by spectrofluorometry. Inference software sensors could be an attractive alternative for on-line monitoring of these variables. As a first step towards the development of inferential sensors for biological wastewater treatment processes, we consider in this study, a simplistic version of such a process which consists of a continuous culture of Pseudomonas putida Q5 degrading phenol. In this work, we propose a neural network based inferential sensor for phenol monitoring using on-line biomass concentration measurements by spectrophotometry. The network was built with wavelets as the basis functions and the adaptive algorithm for the weights was based on a Lyapunov stability analysis. Predicted phenol output of the network showed good agreement with experimental data, over fairly broad ranges of inlet phenol concentration and dilution rate step changes. Simulations were conducted to find convergence conditions and to investigate possible sources for errors in phenol estimates.     

Multi‐point monitoring of cross‐linking reactions

The feasibility of deploying optical fiber sensors to obtain qualitative and quantitative information on the cross‐linking characteristics of thermosetting resin systems has been demonstrated by a number of researchers. This article is concerned with the demonstration of a low‐cost fiber‐optic Fresnel sensor system for monitoring the cross‐linking reactions at multiple locations. Cross‐linking reactions can be influenced by a number of parameters including the stoichiometry of the resin and hardener, and the heat‐transfer rates in and out of the preform as a function of the cross‐section of the preform. In situations where there is a variation in the thickness of the preform or when large components are processed, a facility to monitor the cross‐linking reactions at multiple locations will be valuable because the rate and extent of the cross‐linking can be inferred. In this article, six Fresnel sensors were immersed in individual vials containing an epoxy/amine resin system and processed (cross‐linked) in an air‐circulating oven. One additional vial with a Fresnel sensor immersed in the neat epoxy resin (no hardener) was co‐located in the oven to enable the effect of temperature to be monitored. The feasibility of using the multiplexed Fresnel sensors for cure monitoring was demonstrated successfully. The sensors in the post‐cross‐linked samples were used to study the effects of heating and cooling cycles. The feasibility of detecting the glass transition temperature using the Fresnel sensor is discussed along with the factors that give rise to variability in the output Fresnel signals. © 2014 The Authors. Journal of Applied Polymer Science Published by Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41088.     

Water networks security: A two-stage mixed-integer stochastic program for sensor placement under uncertainty

This work describes a stochastic approach for the optimal placement of sensors in municipal water networks to detect maliciously injected contaminants. The model minimizes the expected fraction of the population at risk and the cost of the sensors. Our work explicitly includes uncertainties in the attack risk and population density, so that the resulting problem involves optimization under uncertainty. In our formulation, we include the location of a number of sensors as first stage decision variables of a two-stage mixed-integer stochastic linear problem; the second stage evaluates the population at risk for the scenario obtained in the first stage and that information is then used to modify the first stage decisions for the next iteration. Since the model is integer in the first stage, a generalized framework based on the stochastic decomposition algorithm allows us to solve the problem in a reasonable computational time. The paper describes the mixed-integer stochastic model and the algorithmic framework, and compares the deterministic and stochastic optimal solutions. The network used as our case study has been derived through the water network simulator EPANET 1.0; four acyclic water flow patterns are considered. Results show a significant effect of uncertainty in sensor placement and total cost.     

Embedded NMR sensors to monitor evaporable water loss caused by hydration and drying in Portland cement mortar

Providing adequate moisture content in cement-based materials is important during hydration of the cement paste to ensure proper development of their mechanical and durability properties. Subsequently, water is involved in the deterioration of concrete either as a pure liquid or by carrying aggressive species. This paper explores the use of small embedded NMR sensors to monitor evaporable water loss in Portland cement mortars. Results indicate that these sensors are effective in detecting loss of evaporable water due to hydration and drying. During drying, the mass loss is linearly proportional to the NMR signal loss. In addition, the amount of evaporable water detected with the sensor has a good correlation with the amount of evaporable water in a companion specimen tested in a traditional low field magnet by NMR and by gravimetric measurements.     

常州市老镇区典型河道水体面源污染的模拟计算

随着点源污染逐渐得到有效控制,面源污染逐渐成为引发城市河流水环境问题的主要原因。以常州市新北区老镇区水域面积71000m~2的某典型河道为研究对象,通过模拟计算的方法对不同的面源污染物负荷进行了研究。结果表明,通过模拟可计算出面源污染中地表径流及干湿沉降带来的污染负荷,老镇区典型河流污染物中地表径流带来的污染高于干湿沉降带来的污染。     

Optimal sensor placement for agro-hydrological systems

The estimation of soil moisture is essential for developing advanced closed-loop irrigation schemes. One associated problem is how to place the sensors appropriately in the soil to provide good measurements for state estimation. In this work, we address the problem of optimal sensor placement for state estimation of agro-hydrological systems. A systematic approach is proposed to find the minimum number of sensors that ensures the observability of the entire system and then to find the best locations of the sensors in terms of degree of observability. The Richards equation that is used to describe the dynamics of the agro-hydrological system is discretized into a large-scale nonlinear state-space model. In the proposed procedure, the key steps include order reduction of the large-scale system model, exploration of the minimum number of sensors needed for state estimation and optimal placement of the sensors in the soil. Three different scenarios are considered and optimal sensor placement is addressed for all the scenarios using the proposed procedure. Simulation results show the effectiveness of the proposed procedure and methods.     

流化床反应器结块故障的声纹特征提取及监测技术

流化床反应器的物料结块故障不仅影响产品质量,严重的还会影响生产。为了监测流化床反应器的物料结块故障,提出了一种基于压电声波传感器和声纹特征提取的故障监测方法。在流化床外壁粘贴压电陶瓷声波传感器,采用长屏蔽电缆电荷传输和音频采样方式,监测流化床内物料撞击床壁的声波信号。分析了正常颗粒物料和物料结块情况下声波信号的时域波形、功率谱和声纹特征,重点比较了正常信号和故障信号声纹特征的稳定性和可区分度。通过提取声纹特征,运用神经网络模型实现了对物料结块故障的准确监测。用不同位置声波传感器的感测信号验证故障监测模型的结果验证了这种方法具有较高的时空域鲁棒性。用不同信号抽取率对原始信号进行了重采样,对重采样数据分别进行了声纹特征提取、监测模型的训练和检验,结果表明适当降低信号采样率不影响流化床物料结块的监测结果。为流化床物料结块故障监测问题提供了一种新的系统结构和实现方法。     

Performance characteristics of the low-cost Plantower PMS optical sensor

Abstract

Low-cost sensors have become very popular in recent years for monitoring air pollutants. Commonly, they are calibrated by correlating their signals with reference instrument measurements and using a machine learning model to account for the influence of air properties. As particle properties vary over location, such calibration models are only relevant to measurements made at the calibration location during a limited time period. For a more general operation of these sensors it is critical that their measurement performance is established using the calibration approaches commonly for research grade instruments. Without loss the generality, here we conducted an experimental study with size-classified, composition and concentration varied particles to determine the response function of a popular low-cost sensor, Plantower PMS5003. The sensor response in all the size channels is analyzed using Tikhonov regularization and quadratic programing method with the constraints of nonnegative and monotonic response with particle size. We show that the shape of the response function is closely related to the light scattering response, consistent with what might be expected for an optical sensor. The response function shows that signals in all size channels have a complex dependence on particle material and size distribution. Accurate determination of particle mass and number distributions from the sensor signals in different channels is, thus, not straightforward. The response function calculation is validated by comparing sensor measured and predicted signals using polydispersed particles. The obtained response functions provide critical insight into the operation of a popular low-cost sensor and guidance on interpretation of its results.

Copyright © 2019 American Association for Aerosol Research     

线性系统非冗余测量网络的优化设计

研究了线性系统非冗余测量网络设计的问题 ,采用混合整数线性规划方法与图论方法相结合建立了考虑可靠性以及精度的要求下建设费用最小的模型 .此模型适用于采用多块测量仪表测量同一物流的问题 ,求解此模型可以确保得到全局最优解 .对文献中例题的计算结果说明了本文方法的正确性     

砾间接触氧化技术在流域治理中的应用

随着中国城市化进程的高速发展,来自区域内分散点源和非点源的污染对水环境造成了严重影响,给流域环境治理带来了重大挑战。排水系统的不完善导致污染加剧,大量老旧城区基础设施给雨污分流带来更大的困难,因此,迫切需要寻找能适用于原位治理的技术措施来消减污染。与传统的人工湿地技术相比,砾间接触氧化技术具有工艺效果稳定、占地小、不易堵塞、操作维护简便等优点,对CODCr、NH3-N、SS等有良好的去除效果,可以用于河道水的处理及污水处理厂尾水的深度处理。更重要的是,由于其可以全地下建造,能够充分利用河滩地、景观、公共绿地等不同性质的地块,从而具有生态和土地多重利用的特点,可以通过系统性的规划和景观设计,打造出为公众提供休闲、游憩、环境教育及体验自然水环境的公共服务设施,因此是一种具有良好前景的生态工法,可以作为流域治理中一种重要的原位治理措施。     

Synthesis of water networks considering the sustainability of the surrounding watershed

This paper presents a new mathematical programming model for the optimal synthesis of recycle and reuse networks considering simultaneously the integration of the water network system and the surrounding watershed to satisfy process and environmental constraints. The model considers the optimal location of the new industrial facility to integrate its wastewater discharge to the environment with the surrounding watershed through a disjunctive formulation. The pollutants discharged for the new plant are tracked simultaneously with the other discharges to the watershed (i.e., residential, sanitary, industrial and extractions), and the natural phenomena that affect the composition of the watershed (i.e., evaporation, filtration, etc.), in addition to the chemical reactions that are carried out in the rivers. The objective function consists in minimizing the total annual cost that is constituted by the installation of the new plant cost (including the transportation for raw materials, products and services, as well as the land cost), the wastewater treatment costs (including the piping cost) and the fresh sources cost. Two example problems were used to show the applicability of the proposed methodology.     

New sensor network design and retrofit method based on value of information

Traditionally, the sensor network design procedure was based on positioning sensors so that certain network monitoring capabilities (e.g., observability, redundancy, and error detectability) of key variables are assured at minimum sensors cost. We present a new approach that is based on maximizing economic value of information minus cost instead of the traditional approach that requires the satisfaction of performance targets. This article presents the conceptual aspect and computation issues of this new approach: the connection between the new approach and the traditional minimum‐cost approaches is explored and the computational methods to solve the proposed problem are presented. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

On the robustness of the soft sensors used to monitor a vial freeze-drying process

Process monitoring is a key issue in pharmaceutical freeze-drying to evaluate if the limit product temperature is approached, to identify the ending point of the main drying stage, and to estimate the value of some parameters of a mathematical model of the process so that it can be used for cycle optimization. Soft sensors can be used for this purpose: three algorithms, based on the extended Kalman filter and on product temperature measurement, have been compared in this study; they differ on the number of estimated parameters and on the way used to set their initial estimates. Results evidence that the accuracy of estimates is strongly dependent on the initial values of model parameters, and soft sensors #1 and #2 require a preliminary investigation to get accurate initial estimates of the heat and mass transfer coefficients. Soft sensor #2 should be preferred as it just requires an initial estimate of the heat transfer coefficient. Significant advantages are obtained with soft sensor #3: accurate estimates are obtained whichever values of the parameters are used to start the calculations (provided that reasonable values are used) and, thus, it can be effectively used to monitor the freeze-drying cycle without any preliminary investigation. Soft sensor #3 should thus be preferred to the other tools for freeze-drying monitoring.     

Process monitoring with disposable chemical sensors fit in the framework of process analysis technology (PAT) for innovative pharmaceutical development and quality assurance

The innovative principle of enzymatic sensors applied to monitor the feeding process in disposable bioreactors is described. Innovative is the type of enzyme immobilized within the 'paste' to monitor L-glutamate. Innovative is the application of the miniaturized disposable sensor developed at C-CIT AG for continuous monitoring. The sensor allows the amount of the digested nutrient to be estimated from the amperometric signal. Innovative is the wireless signal transduction between the sensor mounted to the bioreactor and the signal receiver. An example of a process control run is given and, also, the biocompatibility and the specifications of the biosensors. The comparison of results evaluated by different analytical methods is discussed.     

Development of a novel self-validating soft sensor

A self-validating soft sensor is proposed that not only can perform self-diagnostics and self-reconstruction, but also generate a variety of output data types, including the prediction values, input sensors status of soft sensor and the uncertainty values which represent the credibility of soft sensor??s output. The input sensors are validated before performing a prediction by principal components analysis (PCA) model. These validated data are then employed for subsequent recursive partial least square (RPLS) prediction. Other than input sensor validation and modeling for prediction, a t-statistic confidence interval is created and the status of input sensors is offered. By using this self-validating soft sensor, we can determine the work condition of the soft sensor and take proper actions in real time. The usefulness of the proposed method is demonstrated through a case study of a wastewater treatment process.     

Practical aspects of batch sedimentation control based on fractional density changes

In this paper, a method of monitoring a batch sedimentation process and of controlling the removal of clarified liquid from the batch settler is presented. The proposed method is based only on pressure measurement, and thus an optic sensor is not required. It is shown, that it is possible to monitor the progress of batch sedimentation by measuring hydrostatic pressure at a certain distance from the bottom of the settler. This approach ensures a relatively low-cost control and monitoring of this process. A mathematical model of the phenomenon being used is presented and validated using an experimental batch sedimentation pilot plant. Guidelines for the location of pressure sensor are presented based on simulation investigations. Experimental results also show that it is possible to distinguish between temporary surface disturbances and failure of the sedimentation process.     

Carbon nanotube/polymer nanocomposites: Sensing the thermal aging conditions of electrical insulation components

Carbon nanotube (CNT)/polymer composites with filler loading close to percolation threshold are demonstrated as sensor materials to monitor the thermal aging of insulation components. In order to represent the real aging conditions of the monitored component, the sensor is made of the same polymer material as the one used in the monitored component and placed in close proximity to the component. During thermal aging, the polymer matrix shrinks, leading to a slight increase of volume percentage of CNTs and a substantial decrease in resistivity of the sensors. The sensors are aged at different temperatures and the resistivity change at each temperature is fitted into the modified Arrhenius equation to yield the activation energy of the aging reactions. The activation energy obtained from the sensor signals is similar to those obtained by conventional elongation measurements and the thermal evaluation of the insulation component according to IEEE standard 275. Therefore, the resistivity value of the sensor can be used to accurately predict the remaining life of the monitored parts. These sensors provide many advantages over conventional conditioning monitoring methods, including no damage to the insulation system, real-time monitoring, facile operation, low cost, and much higher sensitivity.     

Monitoring tensile fatigue crack growth and fiber failure around a notch in laminate SIC/SIC composites utilizing acoustic emission,electrical resistance,and digital image correlation

Acoustic emission, electrical resistance, and surface optical techniques were used to monitor matrix cracking and fiber-breakage during fatigue in tension for [0/90]2s SiC-based laminate composite single-notch specimens. Acoustic emission sensors were positioned in several locations including on the edge of the specimen which enabled location of events through the width and the location of internal tunnel-type cracks. Surface optical techniques, including digital image correlation, enabled the extent of surface crack growth. From these two sets of data a simple circuit could be constructed of the different damaged and undamaged regions in the region of the notch that was in good agreement with the change in electrical resistance, thus establishing a correlation with change in ER and damage development. The unique placement of AE sensors on the edge of the specimen also enabled the capture and location of what are believed to be fiber failure events prior to ultimate failure.