IEEE Transactions on Industrial Informatics

1. "Improving the Real-Time Behavior of Ethernet Networks Using Traffic Smoothing"

Abstract - In modern process control systems, Ethernet is achieving a leading position, proposing itself as a network capable of supporting all communication needs at all levels in the Computer Integrated Manufacturing hierarchy. The main obstacle to using Ethernet at the Field level is the nondeterminism of the Ethernet MAC protocol, which cannot provide real-time traffic with bounded channel access times. This paper focuses on industrial applications featuring soft real-time constraints, such as periodic control or industrial multimedia, which do not require deterministic guarantees on deadline meeting. To cope with this class of applications, Ethernet should be able to guarantee the timely delivery of real-time packets in statistical terms. The paper presents fuzzy traffic smoothing, a technique to perform adaptive traffic smoothing over Ethernet networks at the Field level thus enabling them to provide a statistical bound on packet delivery time. Previous work showed that the fuzzy smoother outperforms other adaptive smoothers proposed in the literature. This paper addresses fuzzy smoother optimization through genetic algorithms. The proposed optimization is applied to tune the inference engine membership functions. The results obtained show the effectiveness of the approach.

2. "FTT-Ethernet: A Flexible Real-Time Communication Protocol That Supports Dynamic QoS Management on Ethernet-Based Systems"

Abstract - Ethernet was not originally developed to meet the requirements of real-time industrial automation systems and it was commonly considered unsuited for applications at the field level. Hence, several techniques were developed to make this protocol exhibit real-time behavior, some of them requiring specialized hardware, others providing soft-real-time guarantees only, or others achieving hard real-time guarantees with different levels of bandwidth efficiency. More recently, there has been an effort to support quality-of-service (QoS) negotiation and enforcement but there is not yet an Ethernet-based data link protocol capable of providing dynamic QoS management to further exploit the variable requirements of dynamic applications. This paper presents the FTT-Ethernet protocol, which efficiently supports hard-real-time operation in a flexible way, seamlessly over shared or switched Ethernet. The FTT-Ethernet protocol employs an efficient master/multislave transmission control technique and combines online scheduling with online admission control, to guarantee continued real-time operation under dynamic communication requirements, together with data structures and mechanisms that are tailored to support dynamic QoS management. The paper includes a sample application, aiming at the management of video streams, which highlights the protocol's ability to support dynamic QoS management with real-time guarantees.

3. "Redundancy Concepts to Increase Transmission Reliability in Wireless Industrial LANs"

Abstract - Wireless LANs are an attractive networking technology for industrial applications. A major obstacle toward the fulfillment of hard real-time requirements is the error-prone behavior of wireless channels. A common approach to increase the probability of a message being transmitted successfully before a prescribed deadline is to use feedback from the receiver and subsequent retransmissions (automatic repeat request-ARQ-protocols). In this paper, three modifications to an ARQ protocol are investigated. As one of these modifications a specific transmit diversity scheme, called antenna redundancy, is introduced. The other modifications are error-correcting codes and the transmission of multiple copies of the same packet. In antenna redundancy the base station/access point has several antennas. The base station transmits on one antenna at a time, but whenever a retransmission is needed, the base station switches to another antenna. The relative benefits of using FEC versus adding antennas versus sending multiple copies are investigated under different error conditions. One important result is that for independent Gilbert-Elliot channels between the base station antennas and the wireless station the antenna redundancy scheme effectively decreases the probability of missing a deadline, in a numerical example approximately an order of magnitude per additional antenna can be observed. As a second benefit, antenna redundancy decreases the number of transmission trials needed to transmit a message successfully, thus saving bandwidth.

4. "QoS-Based Remote Control of Networked Control Systems Via Profibus Token Passing Protocol"

Abstract - This paper focuses on a quality-of-service (QoS)- based remote control scheme for networked control systems via the Profibus token passing protocol. Typically, token passing experiences random network delay due to uncertainties in token circulation, but the protocol has in-built upper and lower bounds of network delay. Thus, to ensure the control performance of networked control systems via the Profibus token passing protocol, the network delay should be maintained below the allowable delay level. As the network delay is affected by protocol parameters, such as target rotation time, we present here an algorithm for selection of target rotation time using a genetic algorithm to ensure QoS of control information. We also discuss the performance of the QoS-based remote control scheme under conditions of controlled network delay. To evaluate its feasibility, a networked control system for a feedback control system using a servo motor was implemented on a Profibus-FMS network.

Abstract - This paper investigates the concept of share-driven scheduling of networks using servers with real-time properties. Share-driven scheduling provides fairness and bandwidth isolation between predictable as well as unpredictable streams of messages on the network.
The need for this kind of scheduled real-time communication network is high in applications that have requirements on flexibility, both during development for assigning communication bandwidth to different applications, and during run-time to facilitate dynamic addition and removal of system components.
We illustrate the share-driven scheduling concept by applying it to the popular controller area network (CAN). We propose a scheduling mechanism that we call simple server-scheduled CAN (S3-CAN), for which we also present an associated timing analysis. Additionally, we present a variant of S3-CAN called periodic server-scheduled CAN (PS2-CAN), which for some network con- figurations gives lower worst-case response-times than S3-CAN. Also for this improvement, a timing analysis is presented. Moreover, we use simulation to evaluate the timing performance of both S3-CAN and PS2-CAN, comparing them with other scheduling mechanisms.

6. "Identification and Fault Diagnosis of a Simulated Model of an Industrial Gas Turbine"

Abstract - In this study, a model-based procedure exploiting analytical redundancy for the detection and isolation of faults of a gas turbine system is presented. The diagnosis scheme is based on the generation of so-called "residuals" that are errors between estimated and measured variables of the process. The work is completed under both noise-free and noisy conditions. Residual analysis and statistical tests are used for fault detection and isolation, respectively. The final section shows how the actual size of each fault can be estimated using a multilayer perceptron neural network used as a nonlinear function approximator. The proposed fault detection and isolation tool has been tested on a single-shaft industrial gas turbine model.

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IEEE Industrial Electronics Society

IEEE Transactions on Industrial Informatics

Volume 1, Number 3, August 2005

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