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.
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19 Nov 2007
TL;DR: Analysis of the factors that affect the synchronization performance in using the precision time protocol provides a theoretical ground for the understanding of simulation results as well as guidelines for choosing both system and control parameters when applying FTP.
Abstract: This paper analyzes the factors that affect the synchronization performance in using the precision time protocol (FTP). We first study the influence of jitter under the assumption of no frequency drifts. Then we study the influence of frequency drift in the absence of jitter. The analytic formulas provide a theoretical ground for the understanding of simulation results as well as guidelines for choosing both system and control parameters when applying FTP.
35 citations
Cites background from "Enhancements to the time synchroniz..."
...(ti -ti-,) (3) Similarly, the change of any slave counter value from time ti,1 to time ti is: S(ti ) = S(ti_l ) + fs * (ti ti-l ) (4)...
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Patent•
29 Jun 2007
TL;DR: In this article, a rod-shaped element is inserted into the channel in such a manner that a free end protrudes from the entry opening, and an orientation of the hidden channel is determined as a function of the first and second distances.
Abstract: In a method for capturing three-dimensional data of an area of space, a plurality of measuring beams (Ls) are sent out to a plurality of measuring points. A detector (50) receives a plurality of reflected beams (Lr) which are reflected by the measuring points (34a). A plurality of distances to the measuring points (34a, 34b) are determined as a function of the reflected beams (Lr). According to one aspect of the invention, at least one object (30) which comprises a hidden channel (66) having a visible entry opening (72) is located in the area of space. A rod-shaped element (32) is inserted into the channel (66) in such a manner that a free end (70) protrudes from the entry opening (72). A first distance to a first measuring point (34a) and a second distance to a second measuring point (34b) are determined. An orientation (74) of the hidden channel (66) is determined as a function of the first and the second distances.
33 citations
Patent•
20 Nov 2014
TL;DR: An articulated arm coordinate measurement machine (AACMM) as discussed by the authors uses a noncontact 3D measurement device, position transducers, a camera, and a processor to project a spot of light to an object point.
Abstract: An articulated arm coordinate measurement machine (AACMM) that includes a noncontact 3D measurement device, position transducers, a camera, and a processor operable to project a spot of light to an object point, to measure first 3D coordinates of the object point based on readings of the noncontact 3D measurement device and the position transducers, to capture the spot of light with the camera in a camera image, and to attribute the first 3D coordinates to the spot of light in the camera image.
31 citations
Patent•
12 Mar 2013
TL;DR: In this paper, a portable articulated arm coordinate measurement machine (AACMM) with a rotary coupler and an optical communication bus was described. But the authors did not specify the position transducers.
Abstract: A portable articulated arm coordinate measurement machine (AACMM) having opposed first and second ends and a plurality of connected arm segments each having at least one position transducer for producing a position signal; an electronic circuit configured to receive the position signals; a first bus for communication with the electronic circuit, wherein at least a portion of the first bus is an optical communication bus configured to transmit light; and a rotary coupler having a first portion and a second portion, the second portion configured to rotate relative to the first portion, the first portion affixed to the first arm segment, the rotary coupler configured to transfer signals on the optical communication bus between the first portion and the second portion.
30 citations
06 Apr 2005
TL;DR: This paper investigates a concept for synchronization in a powerline network and describes an approach which is taking advantage of a special clock synchronization hardware working closely together with a power line physical layer.
Abstract: Although most aspects of clock synchronization are well investigated, most studies focus on high-speed, highly reliable and topologically stable networks. For the synchronization of a distributed system networked using powerline, however, essential modifications are needed in order to cope with the peculiar behaviour of power line as a communication medium. One of these special properties is the non-stable network topology caused by load balancing of the energy suppliers; another is the non-symmetric communication delay, as opposed to the common symmetry assumption in most state-of-the-art synchronization protocols. Finally, it is well understood that high-accuracy clock synchronization needs a very tight coupling of the protocol to the physical layer. This paper investigates a concept for synchronization in a powerline network and describes an approach which is taking advantage of a special clock synchronization hardware working closely together with a powerline physical layer.
30 citations
Cites background from "Enhancements to the time synchroniz..."
...[15] shows in a simulation of cascaded clocks that especially in the power-up phase instable behaviour of the local clocks can occur....
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References
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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....
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...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])....
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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