Alessandra Flammini

IEEE 1588-based Synchronization System for a Displacement Sensor Network

This paper deals with a displacement sensor network that is built over Ethernet and synchronized according to IEEE1588. Actually, distribution of precise time reference in an Ethernet network allows implementations of distributed measurement systems, overcoming limitations of complex architecture. The application of the well known IEEE1588 lets sensors to share the same time reference and, in the case of displacement measures, enables accurate calculation of cross-derived quantities (multidimensional speed and acceleration). In this work a description of the sensor architecture is given and the attention is focused on the IEEE1588 implementation. In particular the proposed low-cost system does not use any dedicated synchronization hardware but it can reduce the deviation from time reference down to 20 mus

Design and Implementation of a Wireless Fieldbus for Plastic Machineries

Fieldbus systems are well known in the industrial automation world. Due to the increasing demand for scalability and capability of working in harsh environment, the use of wireless communication is gaining in importance. In the past, some efforts were pursued to encapsulate wired standards over wireless link, but their diffusion is limited by reliability and predictability requirements. In addition, event-driven protocols borrowed from the consumer world (as IEEE802.11 or IEEE802.15.4) are not well suited for some industrial applications. In this paper, authors present the design and the experimental evaluation of a wireless real-time communication protocol that tries to overcome these limits. It exploits standard hardware to lower cost and implements a hybrid medium access strategy. Time Division Multiple Access scheduling is used to ensure time deadlines respect, while Carrier Sense Multiple Access with Collision Avoidance is used for acyclic communications, as those involved in network management. It has been successfully adopted for temperature monitoring in plastic machineries. The prototype network adopts star topology and can manage up to 16 nodes with a refresh time of 128 ms.

IEEE802.11 sensor networking

This paper deals with a smart-transducer wireless network for industrial applications. Thanks to its high popularity, a solution based on IEEE802.11 (also known as wireless fidelity or Wi-Fi) is experimentally investigated. A master-slave network organization is proposed to allow several sensors to be connected with generic Wi-Fi devices like PCs; a proprietary protocol over Internet Protocol (IP)/User Datagram Protocol (UDP) has also been developed. Last, some low-cost prototypes have been built to test the network behavior performances in terms of timing characteristics and power dissipation. Experimental results prove the applicability in a soft real-time (nontime-critical) industrial context.

On the Use of IEEE 1588 in Existing IEC 61850-Based SASs: Current Behavior and Future Challenges

The International Electrotechnical Commission (IEC) 61850 standard describes the communication inside the substation automation system (SAS) setting the base for new interoperating devices that share information using the Ethernet network infrastructure. More recently, the request of time synchronization among SAS components for the timestamping of critical events or synchrophasor measurement has generated a very high interest in the IEC 61850 working group for distributed synchronization protocols like IEEE 1588. This paper analyzes the current situation, matching different implementations of the IEEE 1588, and their respective accuracy, with the requirements of typical SAS applications: from the millisecond synchronization accuracy required by fault recorder application to the microsecond required by the sampled values (SV). The main focus of this paper is on the integration of IEEE 1588 with real already existing systems, and the goal is the performance comparison of different architectures. For these reasons, experimental tests have been carried out using a real SAS network infrastructure [redundant gigabit optical fiber Ethernet network managed using rapid spanning tree protocol (RSTP)]. The results show that, under ideal conditions, the IEEE 1588 protocol can achieve synchronization accuracy slightly worse (80 ns) than legacy IRIG-B systems (15 ns). However, IEEE 1588 makes possible a great cabling reduction and a simplified maintenance when synchronization is directly transferred on the SAS system bus. On the other hand, experiments highlight that nodes connected through a legacy RSTP infrastructure, which does not support IEEE 1588 messages, can lose the time synchronization in the case of network traffic or reconfiguration of the network. Therefore, the integration of IEEE 1588 over existing IEC 61850 station bus is basically a tradeoff between installation costs and performance since it requires the replacement of already installed Ethernet infrastructure. In the last part, this paper analyses the challenges for the next SAS generation that has to combine on the same plants the high accuracy IEEE 1588 implementation with high-availability protocols based on IEC 62439. Since the lifetime of an SAS is more than ten years and the adoption of these technologies takes several years, some solutions that introduce synchronization and high-availability protocols guaranteeing compatibility with existing technologies have been analyzed, too. For instance, an adaptation block that (when attached to a high-availability network) reconstructs the interface signals (e.g., synchronization signals) required by traditional bay has been proposed.

Automation of Distribution Grids With IEC 61850: A First Approach Using Broadband Power Line Communication

The IEC 61850 standard allows for a structured grid automation system where critical tasks like grid protections, renewable energy sources management, synchronized measurements, and monitoring applications share the communication network. So far, the use of IEC 61850 has been mainly limited to the primary substations, but more interesting could be the coordinated actions between primary and secondary substations in order to quickly react to faults and to reduce service downtimes for final customers. Unfortunately, the communication networks between primary and secondary substations are today only partially deployed. Considering this context, the broadband power line over medium voltage grid (MV-BPL) could be a suitable solution for closing the communication gaps between substations that use IEC 61850. The main objective of this paper is to present the outcomes of the first phase of a project whose final goal is the implementation in real grids of distribution grid automation based on IEC 61850. A new and comprehensive set of experiments on a real (and in service) medium voltage grid in Italy has been designed and carried out. The practicability of IEC 61850 communication over the distribution grid is assessed comparing the time characteristics of the MV-BPL against the transfer time classes of the IEC 61850, determining which IEC 61850 services may be transported over MV-BPL. The experimental long-term analysis highlights that more than 90% of the service requests are transferred on the network with a round-trip time lower than 40 ms even in the case of four hops, a time which is compatible with the IEC 61850 fast automatic interactions on MV grid.

Model and Experimental Characterization of the Dynamic Behavior of Low-Power Carbon Monoxide MOX Sensors Operated With Pulsed Temperature Profiles

Wireless sensor networks for home automation or environment monitoring require low-cost low-power sensors. Carbon monoxide (CO) metal-oxide (MOX) sensors could be suitable in terms of device cost, but they show some severe limits, such as the need to be heated, which means large power consumption and the need for complex and frequent calibration procedures, which increases the overall cost. This paper investigates the possibility to partially overcome these limits by a low-cost detection system based on a suitable commercial sensor (TGS 2442, Figaro, Inc.) and an ad hoc measurement technique exploiting specifically tailored temperature profiles. To this aim, the authors study the dynamic behavior of low-power CO MOX sensors operated with pulsed temperature profiles by means of two approaches: 1) sensor modeling and 2) experimental evaluation. To analyze how the sensor dynamic response changes as a function of the CO concentration, the authors individuate a temperature profile, which ensures satisfactory sensitivity to the target gas and very low power consumption. Moreover, some parameters describing the sensor response shape are selected, which prove to be significant in terms of both robustness to environmental conditions and calibration simplicity.

A CMOS Integrable Oscillator-Based Front End for High-Dynamic-Range Resistive Sensors

A new oscillating circuit is proposed to estimate the resistance and parallel parasitic capacitance of resistive chemical sensors. The circuit is able to reveal the resistance in a wide range (from tens of kiloohms to more than 100 GOmega) due to the adopted resistance-to-time technique. In addition, the parallel capacitance (up to 50 pF) can be estimated. The circuit, which does not need any initial calibration, is very simple and compact and is suitable to be integrated with a standard CMOS technology to obtain a low-cost and low-power device for a sensor array interface. Different kinds of post layout simulations concerning the CMOS integrated implementation have been conducted. Experimental results obtained using a discrete prototype board, both on passive components and on real sensors (metal-oxide sensors), have shown good linearity and reduced percentage error with respect to the theoretical expectations.

Application of an ANFIS Algorithm to Sensor Data Processing

Smart sensors are becoming very popular; one of their main advantages is the capability to perform some extra processing on raw data. In this way it is possible to overcome intrinsic limitations due to transducing technique; for example, it is possible to use low very simple sensors and apply linearization techniques to improve performances without increasing the cost. Obviously, the adopted algorithm should be as simple as possible. In this paper, a new calibration technique is presented; it is based on adaptive neuro-fuzzy networks and it has shown superior performances with respect to traditional algorithms, despite its easiness of implementation. Feasibility has been demonstrated with a pyroelectric biaxial positioning system, reaching the limit of the adopted test bench, in the order of 20mum

Application of an optimal look-up table to sensor data processing

This paper presents a new method for calculating a look-up table to evaluate the measurand when a sensor pair is considered. A least mean squares technique has been used to calculate look-up table entries directly from sparse calibration data. The algorithm has been implemented by using the eight-bit MC68HC11 microcontroller; it reduces to a half the maximum value of the approximation error referred to the full scale if compared with the classical methods. A resistive network with end point linearity referred to the full scale of 15% has been used to emulate a sensor pair and the two input signals have been sampled with an 8-bit A/D converter.

Performance analysis of PROFINET networks

Nowadays, Ethernet networks may be profitably employed also at the lowest levels of factory automation systems. Indeed, suitable application layer protocols for Ethernet have been recently developed in order to cope with the critical requirements imposed by the industrial applications. In this paper we focus on the protocols used by PROFINET, an emerging standard for industrial communications based on Ethernet, which is now available in two different versions, named CBA and IO. After a description of the protocols, we show the results of some tests aimed at evaluating the performances of such a network. In particular, we concentrate the attention on the times necessary to transfer limited amounts of data among stations. With regard to PROFINET CBA, the outcomes of an experimental set-up comprising several components, show, for the transfer times, highly variable values, dependent on the network load. Conversely, for PROFINET IO, the results of a set of numerical simulations we performed, allow to expect constant transfer times of some milliseconds, or even less, provided that an accurate time synchronization between stations is maintained.