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The paper presents a framework to evaluate dependability of PROFIBUS-DP networks. An hierarchical modeling approach is proposed, which considers both the effects of permanent and transient faults. Stochastic Petri Nets are used as the modelling technique to obtain dependability models with emphasis in the use of analytical/numerical methods to provide model's solutions. In scenarios where its difficult to apply this approach, compact simulation models are derived.

Distributed control systems operation strongly depends on the communication system performance. Therefore, their analysis becomes an important aspect to be considered, particularly in situations where communications have real-time constrains and the network operates on faulty environments. In this paper the behavior of PROFIBUS network in the presence of faults is analyzed. This analysis is performed in an experimental base supported by a real network. The network operation is disturbed through a set of fault injection experiments from which performance metrics related with PROFIBUS outage times are evaluated.

The paper proposes a dependability model which enables the evaluation of Profibus-DP networks in scenarios of transient faults which affect data communications. The full behavior of Profibus-DP communication stack is modeled, including: cyclic process data exchange between master and slave stations; configuration, parameterization and diagnostics of slave stations. The model is based on a high level stochastic Petri net formalism referred as stochastic activity networks (SAN), supported by the Mobius tool. High modeling power, state-of-the-art analytical and simulation solutions, and a flexible and integrated environment are their main features. Dependability measures are established from the fulfillment of the real-time constraints (deadlines) defined on process data messages exchanged between master and slave stations. The reward concept is used to define the measures, which are obtained by means of a simulation approach. A case study is proposed to assess the model performance

The paper proposes a dependability model to evaluate the behavior of a CANnetwork in scenarios of transient faults which affect data communications. Fault occurrenceis modeled by a Markov Modulated Poisson Process (MMPP) which is capable todescribe the typical behavior of electromagnetic interferences (EMI) that occur in industrialenvironments. An accurate and efficient representation of the network behavior isachieved by adopting a set of assumptions that reduce the pessimism level and which arecloser to the real operating conditions. The model is based on Stochastic Petri Nets, whichare a high-level modeling formalism able to produce very compact and efficient models,supporting both analytical and simulation solutions. Dependability measures are establishedfrom the fulfillment of the real-time constraints (deadlines) defined on messagesexchanged between network nodes. Analytical and simulation solutions are both investigated.A case study is proposed to asses both model performance and network dependability.

Fieldbus networks have been assuming a high acceptance in the industrial environment, replacing the old centralized control architectures. Due to time critical nature of the tasks involved in these environments, the fulfillment of dependability attributes is usually required. Therefore, the dependability is an important parameter on system design, which should be evaluated. Several factors can affect system dependability. The environmental ones are the most common and due to the particularity of the industrial environment this susceptibility is increased. In this paper, we propose a framework based on fault injection techniques, supported by a hardware platform, which emulates a fault set, representative of industrial environment scenarios, intending to disturb data communications on a PROFIBUS network. From these fault injection experiments, relevant data is gathered and a further analysis is carried out in order to evaluate dependability attributes.

The paper presents a framework to evaluate dependability of PROFIBUS-DP networks. An hierarchical modeling approach is proposed, which considers both the effects of different kinds of faults - permanent, transient and common-cause square and the interaction between hardware and software components. Stochastic Petri Nets are used as the modeling technique to obtain dependability models, with emphasis in the use of analytical/numerical methods to provide model's solutions. In scenarios where its difficult to apply this approach, compact simulation models are derived.

The work presented in this paper consisted on the integration of several areas within a factory by using different communication standards. The described implementation satisfies several types of requirements, which include not only the functional requirements, but also the preservation of previous investments. The fulfilment of the latter imposed the use of heterogeneous technologies, both in terms of vendors and generations. This resulted in additional difficulties for the integration that were overcome. The use of OSI based technologies, such as those developed in the scope of CCE-CNMA, contributed to the success of this work.

The objective of this work was to evaluate the NPK influence on yield and oil, proteins and phytochemical contents in sunflower grain and to explore the potential of mathematical model of marginal contributions of fertilization effects. The field experiment was conducted in 3 3 incomplete factorial model, in two randomized blocks, with 15 parcels for block. The treatments were zero, 30 and 60 kg ha -1 of N, P and K. The achene yield increased with fertilizer doses until 55 kg of N ha -1 , 41 kg ha -1 of K 2 O and 46 kg ha -1 of P 2 O 5 . The achene oil content answered positively to increased K 2 O and P 2 O 5 . Proteins content decreases as K 2 O rate increases. No influence of the fertilization was observed in concentrations of chlorogenic acid, total sterols and total phosphorus on achene.

International audience; Simultaneous failures of multiple devices make the dominant contribution to the unreliability of wireless sensor networks. They can hamper communications over long periods of time and consequently disturb, or even disable, the management algorithms of the network. In this preliminary work, we consider two types of common cause failures: hardware, and the temporary disruption of links. We propose an evaluation methodology based on the fault tree formalism for analyzing the reliability and availability of any wireless sensor network when common cause failures are considered.

View references (14)In this paper, a new traffic separation mechanism is proposed for IEEE 802.11e networks. Such Traffic Separation Mechanism (TSm) allows the coexistence of CSMA standard stations with modified (real-time) stations in the same network domain. A station implementing the proposed TSm scheme has the same operating behavior as a standard IEEE 802.11e network station, except in what concerns the evaluation of the backoff delay. For the case of stations implementing the TSm scheme, whenever they have traffic to transfer, they eventually impose its transfer prior to the transfer of any other message with lower priority. This behavior guarantees the highest transmitting probability to the TSm stations in an open communication environment, where multiple IEEE 802.11e standard stations may coexist with a subset of TSm-enabled real-time stations.

Dependability has become an essential parameter on system design. The fulfillment of the system function, either in mission oriented or in continuous operation, requires knowledge about all possible failure modes. If a fault occurrence causes a mis-operation it should be approached a design for a dependable system. Some issues should be performed both at system design and development stages, in order to build a robust system, by evaluating correctly failure conditions and guaranteeing the fulfillment of the system function. The main one is the validation process as well as it conditions the modelling methods associated to and the techniques to be adopted. This paper presents an approach for analysis of validation techniques for electronic systems. The analysis points out two directions, verification techniques needed to support the design at different phases and fault forecasting techniques to assess systems behavior for modelling faults activation and occurrence.

This paper presents a framework to evaluate fieldbus; dependability in presence of transient faults. Several fault models, which copes most situations found in an industrial environment, are proposed. Fault impact on fieldbus communications is evaluated taking into account different communication protocols and specific operating modes. Bus redundancy and common-cause faults are also considered. Analytical models are proposed and closed-form expressions derived, enabling the identification of the most relevant parameters from a dependability viewpoint. Copyright (C) 2001 IFAC.

Within industrial environments a multitude of different working practices, manufacturing technologies and information systems are continually appearing. Significant benefits can be achieved through integration of the information allowing key decisions to be made based on timely and accurate data. This communication presents the work carried out at an industrial site consisting on the integration of several areas and based on the use of different communication standards. The implementation satisfies several types of requirements, which include not only the functional requirements, but also the preservation of previous investments. The use of OSI (Open Systems Interconnection) based technologies, such as those developed in the aim of CCE-CNMA (CIME Computer Environment by integrating a Communication Network for Manufacturing Applications), contributed to the success of this work.

The paper presents a framework to evaluate dependability of fieldbus networks. An hierarchical modeling approach is proposed, which considers both the effects of different kinds of faults - permanent, transient and common-cause - and the interaction between hardware and software components. Stochastic Petri Nets are used as the modeling technique to obtain dependability models, with emphasis in the use of analytical/numerical methods to provide model's solutions.

The operation of networked control systems strongly depends on the performance of its communication infrastructure. Therefore, their evaluation becomes an important aspect to be considered, particularly in situations where network traffic has real-time constraints and the network operates in faulty environments. In this paper a set of fault injection experiments were performed on a Profibus-DP network in order to assess the impact of faults in the network operation. The experiments reproduce typical conditions found in industrial applications, considering different traffic loads and fault scenarios. Several performance metrics were evaluated, such as the bus cycle time, messages response times and worst case response times. Copyright © 2007 IFAC.