José Carlos Campelo

Distributed industrial control systems: a fault-tolerant architecture

Abstract Nowadays, distributed architectures are the base of many manufacturing systems. Some aspects like fault-tolerance, system validation and design process are very important in the development of these systems. In this paper we study the dependability of three different architectures of a distributed system, and we show the development of both physical and logical fault injectors and the implementation of local performance monitors. We also study the impact of checkpointing mechanisms on the system performance in a control system based on a CAN network. Finally we propose a distributed system design methodology based on codesign.

Application of Wireless Sensor Network to Direct Load Control in Residential Areas

This paper describes the application of wireless sensor network to monitor and control electrical loads in residential areas, mainly heating and cooling loads, which accounts for around 50% of the residential electricity consumption. In this way, a control algorithm has also been implemented in order to select the optimum load control strategy according to a target demand profile and a set of prefixed constraints, allowing the customers to modify their power demand with minimum comfort levels. Therefore, this application offers the residential customers a flexible, powerful and low-cost tool to manage their electrical loads, avoiding any additional wiring and extending the wireless sensor network technology to small customers, with around 30% share of the global electricity consumption. This system has been implemented in a university environment, and the results are also included in this paper.

Development and Assessment of a Wireless Sensor and Actuator Network for Heating and Cooling Loads

This paper describes a wireless sensor-actuator network to monitor and manage thermostatically controlled loads, mainly heating and cooling loads, which accounts for around 50% of the residential electricity consumption. A decentralized system is proposed to modify the electrical power demand according to a target demand profile and a set of prefixed constraints, maintaining minimum comfort levels and minimizing the infrastructure requirements. This solution offers the residential customers a flexible, powerful and low-cost tool to modify their power demand profile, avoiding any additional wiring and extending the wireless sensor-actuator networks technology towards small customers, with around 30% share of the global electricity consumption. The proposed system has been implemented and assessed in a university environment, where heating and cooling loads have been monitored and controlled. Acquired data are also included in this paper as well as an example of the forced switching-off time periods applied on the controlled loads, leading to approximately 15% reduction of the peak power demand.

A Reference Model for Monitoring IoT WSN-Based Applications

The Internet of Things (IoT) is, at this moment, one of the most promising technologies that has arisen for decades. Wireless Sensor Networks (WSNs) are one of the main pillars for many IoT applications, insofar as they require to obtain context-awareness information. The bibliography shows many difficulties in their real implementation that have prevented its massive deployment. Additionally, in IoT environments where data producers and data consumers are not directly related, compatibility and certification issues become fundamental. Both problems would profit from accurate knowledge of the internal behavior of WSNs that must be obtained by the utilization of appropriate tools. There are many ad-hoc proposals with no common structure or methodology, and intended to monitor a particular WSN. To overcome this problem, this paper proposes a structured three-layer reference model for WSN Monitoring Platforms (WSN-MP), which offers a standard environment for the design of new monitoring platforms to debug, verify and certify a WSN’s behavior and performance, and applicable to every WSN. This model also allows the comparative analysis of the current proposals for monitoring the operation of WSNs. Following this methodology, it is possible to achieve a standardization of WSN-MP, promoting new research areas in order to solve the problems of each layer.

DICOS: a real-time distributed industrial control system for embedded applications

Abstract The Fault-tolerant Systems Research Group of the Technical University of Valencia has developed the distributed industrial control system (DICOS) system. This paper describes DICOS nodes. The architecture of DICOS nodes and the error detection mechanisms used are presented. These mechanisms are based on the internal capabilities of the 16-bit microcontroller used and control flow checking and deadlines control with the aid of a second 8-bit microcontroller. Experimental results about the effectiveness of those mechanisms are shown in this paper.

On-chip debugging-based fault emulation for robustness evaluation of embedded software components

As manufacturers integrate more off-the-shelf components in embedded products, their robustness evaluation becomes more necessary. This requirement is however difficult to meet using non-intrusive evaluation methods, especially in the case of systems-on-a-chip (SoCs). Research presented in this paper investigates the use of on-chip-debugging (OCD) mechanisms to evaluate the ability of SoC-embedded software components to withstand the occurrence of external faults. These faults are emulated by corrupting the information that components are able to receive through their public interfaces. Once a fault has been injected, reaction of targeted components is studied using OCD monitoring capabilities. The ability of these capabilities to run in parallel with the rest of the SoC internal mechanisms is exploited in order to carry out previous tasks without requiring the source code of the component under study and without interfering (neither spatially nor temporally) with the system nominal execution. Results show potentials and limitations of the approach and let us define directions for future investigation.

Hierarchical Reliability and Safety Models of Fault Tolerant Distributed Industrial Control Systems

In order to study different configurations of distributed systems hierarchical models are needed. Hierarchical models are suitable to friendly and easily study the influence of different parameters in distributed systems. In this paper a hierarchical modelling approach of a distributed industrial control system is presented. In this sense, different fault tolerant techniques to be used are evaluated and different possible system configurations are studied. Two fault tolerant architectures for the distributed system nodes are explained and their influence in the whole system is evaluated. Also the benefits of using checkpointing techniques are presented. In order to do the hierarchical models we use stochastic activity networks and the UltraSAN tool.

GTSO: Global Trace Synchronization and Ordering Mechanism for Wireless Sensor Network Monitoring Platforms

Monitoring is one of the best ways to evaluate the behavior of computer systems. When the monitored system is a distributed system—such as a wireless sensor network (WSN)—the monitoring operation must also be distributed, providing a distributed trace for further analysis. The temporal sequence of occurrence of the events registered by the distributed monitoring platform (DMP) must be correctly established to provide cause-effect relationships between them, so the logs obtained in different monitor nodes must be synchronized. Many of synchronization mechanisms applied to DMPs consist in adjusting the internal clocks of the nodes to the same value as a reference time. However, these mechanisms can create an incoherent event sequence. This article presents a new method to achieve global synchronization of the traces obtained in a DMP. It is based on periodic synchronization signals that are received by the monitor nodes and logged along with the recorded events. This mechanism processes all traces and generates a global post-synchronized trace by scaling all times registered proportionally according with the synchronization signals. It is intended to be a simple but efficient offline mechanism. Its application in a WSN-DMP demonstrates that it guarantees a correct ordering of the events, avoiding the aforementioned issues.

Suitability Evaluation of Multipoint Simultaneous CO2 Sampling Wireless Sensors for Livestock Buildings

The environment in livestock buildings must be controlled to ensure the health and welfare of both workers and animals, as well as to restrict the emission of pollutants to the atmosphere. Among the pollutants generated inside these premises, carbon dioxide (CO2) is of great interest in terms of animal welfare and ventilation control. The use of inexpensive sensors means that complete systems can be designed with a number of sensors located around the building. This paper describes a study of the suitability of multipoint simultaneous CO2 sensors operating in a wireless sensor network, which was found to operate satisfactorily under laboratory conditions and was found to be the best alternative for these applications. The sensors showed a highly linear response to CO2 concentrations, ranging from 500 to 5000 ppm. However, individual sensor response was found to differ, which made it necessary to calibrate each one separately. Sensor precision ranged between 80 and 110 ppm CO2, and sensor response to register a 95% change in concentration was estimated at around 5 min. These features mean this type of sensor network can be used to monitor animal welfare and also for environmental control in poorly ventilated livestock premises. According to the tests conducted in this study, a temporal drift may occur and therefore a regular calibration of sensors would be needed.

A Decentralized Wireless Solution to Monitor and Diagnose PV Solar Module Performance Based on Symmetrized-Shifted Gompertz Functions

This paper proposes and assesses an integrated solution to monitor and diagnose photovoltaic (PV) solar modules based on a decentralized wireless sensor acquisition system. Both DC electrical variables and environmental data are collected at PV module level using low-cost and high-energy efficiency node sensors. Data is real-time processed locally and compared with expected PV module performances obtained by a PV module model based on symmetrized-shifted Gompertz functions (as previously developed and assessed by the authors). Sensor nodes send data to a centralized sink-computing module using a multi-hop wireless sensor network architecture. Such integration thus provides extensive analysis of PV installations, and avoids off-line tests or post-processing processes. In comparison with previous approaches, this solution is enhanced with a low-cost system and non-critical performance constraints, and it is suitable for extensive deployment in PV power plants. Moreover, it is easily implemented in existing PV installations, since no additional wiring is required. The system has been implemented and assessed in a Spanish PV power plant connected to the grid. Results and estimations of PV module performances are also included in the paper.