Radio Channel Quality in Industrial Wireless Sensor Networks

Emerging Industrial Internet-of-Things systems require wireless solutions to connect sensors, actuators, and controllers as part of high data rate feedback-control loops over real-time flows. A key challenge is to provide predictable performance and agility in response to fluctuations in link quality, variable workloads, and topology changes. We propose WARP to address this challenge. WARP uses programs to specify a network's behavior and includes a synthesis procedure to automatically generate such programs from a high-level specification of the system's workload and topology. WARP has three unique features: (1) WARP uses a domain-specific language to specify stateful programs that include conditional statements to control when a flow's packets are transmitted. The execution paths of programs depend on the pattern of packet losses observed at runtime, thereby enabling WARP to readily adapt to packet losses due to short-term variations in link quality. (2) Our synthesis technique uses heuristics to improve network performance by considering multiple packet loss patterns and associated execution paths when determining the transmissions performed by nodes. Furthermore, the generated programs ensure that the likelihood of a flow delivering its packets by its deadline exceeds a user-specified threshold. (3) WARP can adapt to workload and topology changes without explicitly reconstructing a network's program based on the observation that nodes can independently synthesize the same program when they share the same workload and topology information. Simulations show that WARP improves network throughput for data collection, dissemination, and mixed workloads on two realistic topologies. Testbed experiments show that WARP reduces the time to add new flows by 5 times over a state-of-the-art centralized control plane and guarantees the real-time and reliability of all flows.

Creating a suitable growing environment is necessary to ensure good plant growth in a plant factory, which requires wireless sensor networks (WSNs) to monitor the environment in real time. However, existing WSN clustered routing methods hardly take into account the network unreliability caused by varying link quality among nodes, resulting in reduced stability and accuracy of environmental monitoring. This study proposes a wireless sensor network system strategy for improving network reliability in large-scale reliable wireless sensor networks suitable for plant factory scenarios. Firstly, a hybrid wireless sensor network was designed and built based on Wi-Fi and ZigBee communication protocols. Secondly, a nonlinear link quality prediction model for plant factory scenarios was developed using a function fitting method, taking into account the interference and attenuation caused by the dense concentration of agricultural facilities and plants in plant factories on the wireless signal propagation. Finally, a network coverage optimization scheme was designed by combining a particle swarm optimization (PSO) algorithm and link quality prediction model, and a reliable cluster routing protocol was designed by combining K-means algorithm. The results indicated that the coefficient of determination (R2) for the prediction model was 0.9962. The impact of agricultural facilities and vegetation on link quality was most significant when the node height was 0.7 m. Under the optimal node deployment, the number of nodes was 33, and the network coverage rate (CR) reached 97.512%. Compared with the traditional clustered routing method, the wireless sensor network designed in this study is more applicable to the field of plant factories; it further enhances data transmission effectiveness and link quality, improves the reliability of the network, and realizes the load balancing of the internal transmission of the network, which in turn ensures the accuracy of environmental monitoring and the stability of the system.

Effective communication is crucial for the performance and collaboration within cooperative networked multi-agent systems. However, existing literature lacks comprehensive solutions for dynamically monitoring and adjusting communication topologies to balance connectivity and energy efficiency. This study addresses this gap by proposing a distributed approach for estimating and controlling system connectivity over time. We introduce a modified consensus protocol where agents exchange local assessments of communication link quality, enabling the estimation of a global weighted adjacency matrix without requiring centralized information. The system's connectivity is measured using the second smallest eigenvalue of the communication graph Laplacian, commonly referred to as algebraic connectivity. Additionally, we enhance the consensus protocol with an adaptive mechanism to expedite convergence, irrespective of system size or structure. Furthermore, we present an analytical method for connectivity control based on the Fiedler vector approximation, facilitating the addition or removal of communication links. This method adjusts control parameters to accommodate minor variations in link quality while reconfiguring the network in response to significant changes. Notably, it identifies and eliminates energy-consuming yet non-contributory links, improving long-term connectivity efficiency. Simulation experiments across diverse scenarios and the number of agents validate the efficacy of our proposed algebraic connectivity estimation and tracking strategy. Results demonstrate robust connectivity maintenance against external disturbances and agent failures, underscoring the practical utility of our approach for real-world multi-agent systems.

The paper reports the investigation on the root cause of source-drain leakage in bulk FinFET devices. While the failing device was readily isolated by nanoprobing technique and the electrical analysis pinpointed the potential defect location inside the Fin channel, the identification of physical root cause went through extreme challenges imposed by the tiny-sized device and the unique FinFET 3D architecture. The initial TEM analysis was misled by the projection of a species in the lamella surface and thus could not explain the electrical data. Careful analysis on the device structure was able to identify the origin of the species and led to the discovery of the actual root cause. This paper will provide the analysis details leading to the findings, and highlight the role of electrical understanding in not only providing guidance for physical analysis but also revealing the true root cause of failure in FinFET devices.

A smart factory requires an efficient interaction between a number of physical components on the factory floor with the respective analytical and decision making components from digital domain. The flow of this information has to be continuous in order to reduce the downtime and maintain the productivity target. A smart factory should provide immediate access to the status of processes and device components to the relevant factory operators. With advancement in the concept of internet of things (IoT), many industrial devices on the factory floor now have wireless connectivity. Bluetooth technology is increasingly being used in order to provide operational and productivity status of devices to the factory floor operator. The operator typically has a smart device such as a tablet from where the respective devices can be monitored or controlled. As Bluetooth has a limited range, typically around 5–10 meters, an operator needs to come within this range of the device in order to connect with the respective industrial device and obtain its health and operational status data. Also Bluetooth mainly provides a point-to-point connectivity, thus at a time only one industrial device can be connected. For a factory floor that can have hundreds and thousands of such devices, this task of personally going and obtaining the data from every individual device could be tedious and cumbersome.

Leakage current study and relevant defect localization in integrated circuit failure analysis

To wireless communication, it is easy to be interrupted by all sorts of factors, such as, antenna direction, transmission power, distance, nodes voltage and so on. And the reliable transmission of data is the key problem for Wireless Sensor Networks (WSN) in recent years. In former research, there are many methods which can ensure data reliable transmission, but can not choose the best performance path and reduce the bottleneck link effectively. So, on the basis of analyzing the influence of antenna direction, transmission power, distance and nodes voltage on LQI respectively, the paper proposes a new method—link quality indication based on metric (LQIBM), which can accurately find the link with severe packet loss rate in wireless networks firstly. Second, the model of LQIBM is constructed by Combining the mean and Coefficient of Variation (C.V) of link quality appropriately. Then, the hardware experiment platform is conducted by using wireless communication chip CC2430. Compared with LQIM, the results of simulation and experiment show that LQIBM succeed in finding the best communication path that has much lower packet loss rate, the miscarriage of justice is avoided for LQIM , the path with the bottleneck link is effectively excluded, and the better reliability of the data transmission is achieved for WSN.

The metallurgy and levels of protective elements in the new P91 and P92 martensitic alloys are quite different to older ferrite pearlite and ferrite bainite steels. This is likely to give problems in the positive identification of failure mechanisms and assessment of the life of superheater tubing. Techniques such as spheroidisation and oxide thickness to assess metal temperatures, or hardness testing and cavitation to estimate the level of creep damage cannot be used with these materials, or are likely to give ambiguous results. These issues are discussed in the paper and were explored in depth in part of a project at the University of Surrey to develop “If-Then” rules for an expert system for power plant failure analysis.The main aim of the proposed expert system is to identify the root causes of such failures in superheater tubing and will encapsulate current knowledge about superheater problems in the form of “If-Then” rules. Root causes of creep failures include furnace design and operation, overestimation of alloy creep properties, inadequate heat treatment and a non-optimum content of strengthening elements.A characteristic of these alloys is that oxidation on the steam side of the tubing can induce premature failures due to the insulating effect of the oxide scales raising tube temperatures. In addition, scale spallation could also increase tube temperatures, as spallation debris may collect in the bottom of tubes, blocking steam flow. Attention is drawn to a potential “runaway affect” in which the tube temperature and rate of oxidation increase with time as the oxide builds up. The root cause of this could either be excessive rates of heat transfer or could be due to inadequate oxidation resistance caused by low levels of protective elements. Methods of identifying which of these is the root cause are discussed.

An investigation was conducted to determine the root cause of the premature pavement failure. The premature pavement failure occurred in the form of rutting and alligator cracking. Although the affected portion was repaired by removing and replacing the top 75-mm asphalt concrete (AC), the repaired AC experienced recurring rutting and alligator cracking in a few weeks. Through extensive field and lab testing, it was found that the weak base is the root cause of the premature failure and the brittleness of the AC is secondary. However, both the base and AC were built according to plan and met the current material and field density requirements. It was concluded that density alone for construction quality control is not sufficient, as it was not able to protect against premature failures from occurring. Although there are many different ways to minimize premature failures, an immediate action is to include proof rolling in construction quality control. Proof rolling has been used with success to ensure proper compaction and to locate unstable areas, as the stability is greatly influenced by the degree of densification achieved during compaction.

Sensors deployed in underground tunnels found that radio frequency signals suffer significant signal strength attenuation which can result in considerable variation of link quality on the receiving end. This study analyzes the received signal strength index (RSSI) based on the development of a theoretical wireless sensor model for data collection by enabling sensors to determine the location from which each data packet is obtained. To improve positioning accuracy, the complex radio wave propagation environment requires the use of a voronoi cell to minimize signal attenuation. A relatively simple calculation is used to predict the intensity and perception range of the received wireless signals to measure the extent of signal reduction in the attenuating rock medium. Simulation results show that RSSI-based localization and wireless network lifetime and throughput measurements are more accurate when the node concept is applied to the self-locating rupture zones than the maximum likelihood estimation method. The proposed minimum energy relay routing technique based on beacon node chain deployment is found to help correct localization errors resulting from interference caused by the underground tunnel environment. The extent of localization and power of the sensor nodes are determined based on the beacon node chain deployment of tunnel wireless sensor networks. The algorithm accounts for the distance and the corresponding RSSI between adjacent beacon nodes to calculate the actual path loss parameter in the tunnel. The proposed model can serve as the theoretical basis for locating ruptures in underground wireless sensor network nodes, thus maximizing the monitoring range of large scale tectonic environments while minimizing equipment cost. We recommend that this model can be field tested through a series of experiments by researchers and engineers working in seismology, telecommunication, and information technology.

This case study is to identify and evaluate the root cause for failure of a roller press mill. Cement plant has a heavy crushing operation the roller’s top surface is eroded, which is replaced by hard metal deposition by welding. In manufacturing, most of the steel metals are failing by either fatigue or by hard deposition through welding. In this case, repair welding has been used for several years. But there is no specific welding procedure adapted to repair the large size of the rolling parts as it is very difficult to operate in that situation and constraints of the welding operation. In this connection, the plant was inspected, their log book was verified, and the complete procedure of welding was checked. Further study was done by cutting the small piece of the press roller mill’s material by using diamond abrasive cutter and it was used to prepare the test specimen using wire cut EDM. Further composition of the welding rod and base material were found by SEM study. Subsequently, their hardness values were also measured. From this study, it is concluded that the welding procedure was not followed properly and oxidation took place during the time of weld, because of the large variations of the weldability of the material over the surface of the base metal and also the presence of blue patches in the weld metal during SEM analysis.

Three major cause of failure had been established for bushings with over 20 years of service namely: seals damaged, leaks at expansion gas chamber and corrosion at bushing tap. In the paper, each root cause of failure is illustrated with true faults occurred while in service. Then detailed analysis is presented, and more important, some corrective measures to prevent bushing explosion had been established. Those include inspection procedures that had been applied to identify and remove from service damaged bushings. Furthermore, those bushings had been disassembled and investigated at bushing repair facilities. Internal inspection confirmed suspected damaged and promote corrective maintenance actions. Results demonstrate that paper insulation is largely unaffected by these root causes if treated at early stages. Most important, the dielectric strength of the main insulation is restored after vacuum treatment and impregnation with new oil. Bushing reliability had been evaluated in laboratory condition with impulse, AC overvoltage and partial discharge measurements, demonstrating that it is possible to restore reliability on aged bushings, if the three main cause of failure are corrected on time.

A system approach to solving the tribological problems associated with sealing joints implies comprehensive investigation of all the components. To recognize the root cause of any problem and formulate the required performance for extended reliability we have to evaluate any changes in the system as quantitatively as possible. Any measurable parameters, including geometry, density (porosity), hardness distributions, microstructure and grain size changes observed during routine metallurgical analysis could provide evidence of the root cause of failure. In the head-gasket-block sealing system of the internal combustion engine, the EDS evaluation of the chlorine and sulfur distribution through the head gasket flange fracture in conjunction with analysis of the sludge between the head, block and gasket surfaces pointed to the corrosive nature of the gasket flange cracking.This approach is even more useful for the closed tribological system of telescopic hydraulic cylinders or rotary axle shaft oil seals.

Production processes like continuous annealing and continuous galvanizing/galvannealing rely on welding of two strips across their width, for continuous operation. The operational stability of these lines depends highly on the consistency of the welding process. Any failure of weld joint during processing is detrimental to production as the recovery times are very high (~1–3 days). Two instances of similar weld failures having identical chemical composition and dimensions of the strips were investigated to identify the root cause and establish adequate countermeasures. A systematic approach to evaluate weld performance using metallographic examination was carried out. The examinations revealed that poor nugget formation was the root cause of failure. The nugget formation, its orientation and size were also evaluated after carrying out a series of trials with different welding process parameters, and an optimum condition was arrived at. In summary, the weld failure occurred due to insufficient and unbalanced nugget formation which could be rectified by modifying the welding parameters such as current, pressure and speed.

Root cause analysis of the degradation in a unitized regenerative fuel cell