Enhancements to the time synchronization standard IEEE-1588 for a system of cascaded bridges
22 Sep 2004-pp 239-244
TL;DR: In this paper, a bypass clock instead of the boundary clock is proposed as an enhancement of the IEEE-1588 standard for bridged networks, where the local clock adjustment can be modeled by a corresponding control loop.
Abstract: The IEEE-1588 standard for a high precision time synchronization now exists since 2002. For using this standard in bridged networks a so-called boundary clock is defined, where the local clock adjustment can be modeled by a corresponding control loop. At the field level of industrial automation systems, the line topology is very important. By using Ethernet at the field level, the resulting chain of bridges leads to a cascade of control loops and may lead to instabilities and deviations of the distributed clocks, which are not acceptable. For this application a bypass clock instead of the boundary clock is proposed as an enhancement of the IEEE-1588 standard. The effectiveness of this extension to be evaluated by simulation technique.
Citations
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20 Jun 2005
TL;DR: This paper addresses PROFINET, an industrial communication standard based on Ethernet, designed to be employed at different levels of factory automation systems, and presents the results of a set of tests carried out on the two application layer protocols specified by the standard.
Abstract: In this paper we address PROFINET, an industrial communication standard based on Ethernet, designed to be employed at different levels of factory automation systems. After a general description, we focus on the two application layer protocols specified by the standard, namely PROFINET CBA and PROFINET IO. In detail, we first illustrate the major protocols features and then present the results of a set of tests we carried out. Regarding PROFINET CBA, the tests have been executed on an experimental set-up, whereas for PROFINET IO we show the outcomes of some numerical simulations. In both cases, the results are in accord with the performance figures envisaged by the PROFINET technical documentation.
7 citations
Cites background from "Enhancements to the time synchroniz..."
...Such a goal will be achieved by means of some improvements to the IEEE1588 standard which have been recently proposed [25]....
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TL;DR: This paper develops an algorithm to improve the PTP protocol, which is verified by simulation and highlights the influence of frequency drift on the synchronization performance.
7 citations
Cites background or methods from "Enhancements to the time synchroniz..."
...Authors of [Jasperneite et al. 2004a] introduced the transparent clock concept to replace the socalled boundary clock....
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...978-1-1234-7890-2/08/$20.00 © 2008 IFAC 8333 10.3182/20080706-5-KR-1001....
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...The transparent clock synchronization protocol ([Jasperneite et al. 2004a]) is depicted in Figure 2....
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Patent•
14 Jan 2011
TL;DR: In this paper, a portable articulated arm coordinate measuring machine (AACMM) is described, which includes a manually positionable articulated arm portion having opposed first and second ends, the arm portion including a plurality of connected arm segments, each arm segment including at least one position transducer for producing a position signal, a measurement device attached to a first end of the AACMM, and an electronic circuit which receives the position signals from the transducers and provides data corresponding to a position of the measurement device.
Abstract: Implementing a portable articulated arm coordinate measuring machine includes receiving a first request to perform a function. The portable AACMM includes a manually positionable articulated arm portion having opposed first and second ends, the arm portion including a plurality of connected arm segments, each arm segment including at least one position transducer for producing a position signal, a measurement device attached to a first end of the AACMM, and an electronic circuit which receives the position signals from the transducers and provides data corresponding to a position of the measurement device. Implementing the portable articulated arm coordinate measuring machine also includes identifying a source device from which the first request is received, implementing the function pursuant to the first request, selecting a destination device as the source device of the first request by identifying from which of a first and second port the first request is received, and transmitting information derived from implementing the function to the destination device.
6 citations
24 Oct 2008
TL;DR: This paper quantifies the ldquo1 mus-conformrdquo line-length of the Transparent Clock Mechanism of peer-to-peer Precision Time Protocol (PTP Version 2), i.e. the number of elements that stay within the plusmn1 mus sync error tolerance for crystal oscillator output frequencies.
Abstract: This paper quantifies the ldquo1 mus-conformrdquo line-length of the Transparent Clock Mechanism of peer-to-peer Precision Time Protocol (PTP Version 2), i.e. the number of elements that stay within the plusmn1 mus sync error tolerance, for crystal oscillator output frequencies of 100 MHz, 250 MHz, 500 MHz and 1 GHz, i.e. for time quantization errors of 10 ns, 4 ns, 2 ns and 1 ns.
6 citations
Cites background from "Enhancements to the time synchroniz..."
...It was enhanced by the transparent clock (TC) concept, introduced in [2], which has been adopted in the new version of IEEE 1588 published in 2007 (IEEE 1588 version 2 was approved by the IEEE on March 27, 2008)....
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20 Mar 2012
TL;DR: In this paper, the authors present the state of the art regarding power system evolution, IEEE 61850 (Communication Networks and Systems in Substations) standard on synchrophasor measurements and synchronization system is presented.
Abstract: Modern electric power systems can be considered as the consequence of the continuous technological evolution, often pushed by economical, political and social requirements. As an example, the main transformations in electric distribution systems arise from the diffusion of
“Distributed Generation” (DG), i.e. small production plants, often supplied through renewable energy sources, whose presence has significant implications on both energy management (since “active networks” are needed to take into account bidirectional energy flows by means of innovative devices) and protection systems (since adaptive protections can be used to automatically reconfigure the network in the case of fault occurrence). In general, in both transmission and distribution networks, monitoring, control and protection tasks are usually performed by Intelligent Electronic Devices (IEDs), which can be, by their nature,
connected to each other by suitable communication links. A famous example of this approach is represented by the series of Standard IEC 61850 (Communication Networks and Systems in Substations). These standards are related to networks and communication systems within the substation, but are used as a reference in all those circumstances in which an electrical system is managed through the use of IEDs communicating with each other (as in the case of active
distribution networks). In this way, control and protection schemes practically become algorithms, whose correct
behavior is determined firstly by the availability of data measured in strategic points of the network. The critical role of the above mentioned applications, which clearly emerges from their implications on safety, as well as from economical considerations, makes it of fundamental importance the evaluation of correctness and trustworthiness of the information on which such actions are based. Many of these applications implemented for control and protection purposes in electric power
networks require the acquisition of information by Wide Area Monitoring System (WAMS) from strategic points of the system and need that the acquired data have an extremely accurate common time reference. Generally, amplitudes and phases of the positive sequence voltages are the
quantities to be estimated in the network nodes. Because of the extension of power networks, suitable measurement devices should be used to ensure proper synchronization between the collected data. Thus, the key components of WAMSs are represented by Phasor Measurement Units
(PMUs) designed to measure synchronized phasors (synchrophasors). Typical synchronization specifications for synchrophasors measurement are in the order of
few microseconds. Such a tight synchronization requirements lead to the need of highly accurate clock settings, such as the ones bases on satellite systems. Currently, the Global Positioning System (GPS) is the only system to provide a time reference with sufficient availability and accuracy for
most distributed monitoring and control applications in power systems. As an alternative, in situations where many devices are located in a geographically limited sub-area (e.g. a substation) of the system and are connected to each other by suitable communication networks (as described by the series of standard IEC 61850), it could be advantageous to distribute the time reference of a high accuracy clock to the devices through suitable network synchronization protocols. Between them, the PTP (Precision Time Protocol)
defined in the Standard IEEE 1588 offers the best accuracy performance. It is worth mentioning that the Standard IEC 61850-9-2 practically indicates Ethernet as a preferred communication solution, thus offering an optimal support to implement 1588 synchronization in electric power plants. In this context, it should be recalled that the IEEE 1588
profile for power system applications (project PC37.238) is being developed under IEEE Power System Relaying Committee (PSRC) and Power System Substation Committee (PSSC). The scope covers all power system applications, including Synchrophasors. The group works in close coordination with TC57 WG10, which plans to adopt the PTP profile in the next revision of IEC 61850. In the first part of this thesis, the state of the art regarding power system evolution, IEEE
Standard on synchrophasor measurements and synchronization system is presented. In particular, the problems related to the evolution of the power system along with some possible advantages due to the implementation of Phasor Measurement Units in Wide Area Monitoring Systems are introduced. After a general description of the architecture of a distributed measurement system based on PMUs, the new synchrophasors standard is analysed, highlighting the differences with
previous versions, the requirements for the measurement of synchrophasors and the definition of synchrophasor under steady-state and dynamic conditions. Moreover, a summary of the possible synchronization solutions is introduced. For each solution, advantages and disadvantages are highlighted. In particular, satellite system and network based protocol are analysed in detail. In the second part of the thesis, a synchronization solution able to exploit the worldwide availability of the GPS and the possibility to disseminate the synchronization signal with high
accuracy by means of the network synchronization protocol IEEE 1588 is proposed. This solution is used for the synchronization of PMUs. The objective of this work is to analyse the possibility to synchronize PMUs via PTP and to study the impact that such a synchronization solution has on the performance of measurement systems under both steady-state and anomalous operating conditions,
as well as its effects on the applications that make use of their data. Two different versions of the PTP are used: the first one uses hardware-assisted time-stamp mechanism whereas the second one uses software-only time-stamp mechanism. Two experimental systems are characterized in detail with an accurate description of all the used hardware and software components, and their synchronization performances under different operative conditions are analysed. Finally, among all the sources which may contribute to the uncertainty introduced by PMUs, the last part of this thesis analyses the impact of the phasor estimation models on the accuracy of these devices, with particular attention to algorithms proposed in literature for the estimation of dynamic phasors and studies their performances under several different conditions.
6 citations
References
More filters
01 Jan 2003
TL;DR: OMNeT++ is fully programmable and modular, and it was designed from the ground up to support modeling very large networks built from reusable model components.
Abstract: The paper introduces OMNeT++, a C++-based discrete event simulation package primarily targeted at simulating computer networks and other distributed systems. OMNeT++ is fully programmable and modular, and it was designed from the ground up to support modeling very large networks built from reusable model components. Large emphasis was placed also on easy traceability and debuggability of simulation models: one can execute the simulation under a powerful graphical user interface, which makes the internals of a simulation model fully visible to the person running the simulation: it displays the network graphics, animates the message flow and lets the user peek into objects and variables within the model. These features make OMNeT++ a good candidate for both research and educational purposes. The OMNeT++ simulation engine can be easily embedded into larger applications. OMNeT++ is opensource, free for non-profit use, and it has a fairly large user
2,316 citations
TL;DR: The NTP synchronization system is described, along with performance data which show that timekeeping accuracy throughout most portions of the Internet can be ordinarily maintained to within a few milliseconds, even in cases of failure or disruption of clocks, time servers, or networks.
Abstract: The network time protocol (NTP), which is designed to distribute time information in a large, diverse system, is described. It uses a symmetric architecture in which a distributed subnet of time servers operating in a self-organizing, hierarchical configuration synchronizes local clocks within the subnet and to national time standards via wire, radio, or calibrated atomic clock. The servers can also redistribute time information within a network via local routing algorithms and time daemons. The NTP synchronization system, which has been in regular operation in the Internet for the last several years, is described, along with performance data which show that timekeeping accuracy throughout most portions of the Internet can be ordinarily maintained to within a few milliseconds, even in cases of failure or disruption of clocks, time servers, or networks. >
2,114 citations
"Enhancements to the time synchroniz..." refers background or methods in this paper
...The effectiveness of this extension will be evaluated by simulation technique....
[...]
...This due to a decrease in price provoked by the office Ethernet market, high bandwidth, switching technology [3], priority features [4], full duplex operation [2], availability of Ethernet bridges as well as Ethernet-enabled products fulfilling industrial environmental requirements (e.g. [15])....
[...]
27 Sep 2004
TL;DR: A protocol is provided in this standard that enables precise synchronization of clocks in measurement and control systems implemented with technologies such as network communication, local computing, and distributed objects.
Abstract: A protocol is provided in this standard that enables precise synchronization of clocks in measurement and control systems implemented with technologies such as network communication, local computing, and distributed objects. The protocol is applicable to systems communicating via packet networks. Heterogeneous systems are enabled that include clocks of various inherent precision, resolution, and stability to synchronize. System-wide synchronization accuracy and precision in the sub-microsecond range are supported with minimal network and local clock computing resources. Simple systems are installed and operated without requiring the management attention of users because the default behavior of the protocol allows for it.
1,428 citations
05 Dec 2002
TL;DR: This paper discusses the major features and design objectives of the IEEE-1588 standard, designed to serve the clock synchronization needs of industrial systems, and recent performance results of prototype implementations of this standard in an Ethernet environment are presented.
Abstract: This paper discusses the major features and design objectives of the IEEE-1588 standard. Recent performance results of prototype implementations of this standard in an Ethernet environment are presented. Potential areas of application of this standard are outlined.
1,112 citations
01 Apr 1994
TL;DR: In this article, the authors describe a series of incremental improvements in system hardware and software which result in significantly better accuracy and stability, especially in primary time servers directly synchronized to radio or satellite time services.
Abstract: This paper builds on previous work involving the Network Time Protocol, which is used to synchronize computer clocks in the Internet. It describes a series of incremental improvements in system hardware and software which result in significantly better accuracy and stability, especially in primary time servers directly synchronized to radio or satellite time services. These improvements include novel interfacing techniques and operating system features. The goal in this effort is to improve the synchronization accuracy for fast computers and networks from the tens of milliseconds regime of the present technology to the submillisecond regime of the future.In order to assess how well these improvements work, a series of experiments is described in which the error contributions of various modern Unix system hardware and software components are calibrated. These experiments define the accuracy and stability expectations of the computer clock and establish its design parameters with respect to time and frequency error tolerances. The paper concludes that submillisecond accuracies are indeed practical, but that further improvements will be possible only through the use of temperature-compensated local clock oscillators.
227 citations