Estimate of the inaccuracy, caused by individual clocks in a clock synchronization network.

[0001] this invention applies to the field of industrial automation and vehicle technology, more precisely it is intended for communication network works, the exact time or frequency transmitted which, in which a synchronizing signals in a node emits master clock, which by means of intermediate clocks in intermediate node, the the time synchronization minutes respect, be forwarded and Synchronization serve slave clocks in end node, which the use of these exact time, to deliver precisely or scan time details commands to the system controlled by them remotely measuring process data. The application comprises the control of power semiconductors and synchronized drives, the protection of electrical installations, the monitoring of electrical networks nationalre-clamping, the automatic guiding of vehicles, and the implementation of scientific experiments.

[0002] time-critical one systems having a variety of communicating nodes need time details inputs (e.g. measurement values, the to a known, accurate time are scanned) and expenditure (e.g. control commands for the control of semiconductor circuits in achievement static frequency changerstime details ).

[0003] Such systems or applications are based on a precise time synchronization minutes (Precision Time Protocol, PTP), e.g. IEEE 1588, which can provide an accuracy below a microsecond.

[0004] these protocols use a highly exact master clock, which sends messages over a communications network in the specific time. These messages are sent in the right direction over a plurality of intermediate nodes to a plurality of slave clocks. This synchronization messages suffer delays on the connections ( line running time between nodes) in the node (node-internal residence time) and processing.

[0005] The end node in the network depends on the position of the total delay, from the path, the passes through the message, and from the number of intermediate nodes ab.

[0006] To compensate for these delays, the nodes detect the residence time of the messages within itself and the messages to the neighbour nodes line running time the. It a node attaches the Duration for neighbour nodes, or to the neighbour nodes synchronization messages come from the which the, to which the node forwards the synchronization message.

[0007] For example, according to standard IEEE 1588 Precision Time Protocol (IEC 61588:2009), a regularly master clock sends slave clocks with the absolute time to a number a Sync-message over a data network, which contains a number (Transparent watches or federal clocks ) intermediate clocks. Under this Protocol slave clocks Synchronizing the in the end nodes, their inputs and outputs data fro control so that these end node.

[0008] According to IEEE 1588 Transparent watches Calculate with their local clock in the intermediate nodes the residence time. All Nodes Calculate to their neighbour nodes by means of a the Duration echo method, which consists of a question message of the node and a response message of the neighbour node. The banners watches add the residence time and duration for shim field in the Sync-Notification When one shot process, or in the [...]two-step -Method in the message.

[0009] The inaccuracies in the calculation the operating time and residence time are accumulating in the chain of slave clockmaster clock to on. For example, although the accuracy of the indicated with 100 nanoseconds master clock is, on arrival in the intermediate node is the actual accuracy after about 15 slave clock only one microsecond.

[0010] Indeed, each node in the measurement of the dwell time and the delay caused a lack of precision. This inaccuracy depends on the quality of his internal oscillator, by the resolution of the timer, and in the receiver/ transmitter componentstime stamp logictransition effects in the from in the switching logic, etc.. This inaccuracy effected an increased fluctuation and deviation is removed from the the farther the slave clockmaster clock.

[0011] The classical type, the inaccuracy to limit is, to build each intermediate clock so that their maximum inaccuracy is limited and guarantees, e.g. 50 nanoseconds. This [...] is inaccuracy in the measured and recorded. Learning the network planning may be obtained for each node of the network the expected inaccuracy can, knowing the quality of the intermediate node and the topography, and this will be reflected in reconfiguration of the network after failure the master clock or of intermediate nodes, wherein it is guaranteed that the worst, expected inaccuracy still is acceptable for the respective application, e.g.: 1 microsecond. This analysis is statically, assuming that all clocks and compounds behave like guaranteed.

[0012] Some applications require on these static calculation addition, a running estimate, to ensure is maintained, even under abnormal conditions slave clock that the accuracy of the. Knowledge this estimate allows an end node to decide, whether he can still fulfil the task. He can qualify the measured values with this estimate, as the standard IEC 61850-7 - 2 in the form of a code or how this provides the IEEE standard C37-118 provides [...] Time Quality or continuous Time Quality in the form of the. Such current estimate of the inaccuracy is also useful, in order to determine failures or deterioration of the clocks.

[0013] this invention relates to a method for estimating the inaccuracy, which each individual clock on the path between master clockslave clock caused and, with the purpose, the inaccuracy of the time signal slave clock to estimate to each, so that the end node, where these slave clock is incorporated, the accuracy of its measurement values or commands may qualify.

[0014] According to this invention it is proposed a method, by which each Timepiece the inaccuracy, in the correction of the causes which they synchronization message, can estimate.

[0015] the inaccuracy is divided into two components Zum this purpose: the frequency deviation of the local clock and the error in the time stamp logicswitching logicoutput components and in the inlet and in the. While the frequency deviation can be limited by current mood of the oscillator, the error is subject to random variations in the logic, the are estimated as follows.

[0016] In the purposes of calculating the duration with the echo method, e.g. according to IEEE 1588 peer-to-peer, each node to its neighbor nodes the Duration calculated, and in particular for neighbour nodes, where the sync message comes.

[0017] A Timepiece calculated by sending a message to a neighbor the Duration [...], on which of the neighbour [...] responds with a message. Transmits its processing time in the neighbour [...] In step-Method the message, during its processing time in a separate [...]two-step -Methods of neighbour in the report is transmitted.

[0018] A Timepiece calculated from this Echo [...] than half the transit time between sending and receiving of the distortion [...], less the processing time in the neighbour. After several measurements, e.g. via a minute, this value converges to the average of Duration, apart from systematic errors or deviations, the can be corrected, when they are known.

[0019] in wire line running time The, cable or glass fiber is essentially constant, except for small, slow fluctuations due to temperature or other influences. Really a fixed entry no current measurement required and it would be needed would according to calibration, since this value in operation hardly changes, but this can serve as a convenient control of a current measurement configuration and the clock period.

[0020] This measuring the time of flight has fluctuations on, the depend on the quality of the local clock and the logic, both in this nodes as in the neighbour nodes. Since the mean value is constant in principle, this variation is used, the inaccuracy in the time-stamp-and to estimate switching logic.

[0021] a statistical distribution function of measured Duration thus has The, which in a histogram or distribution curve is represented as a mean value μ σ and scattering.

[0022] The scattering σ, which also as variance o², i.e. as a square of the scattering or as a similar mathematical Mass statistics teachings is expressed from the is a measure for the inaccuracy, and from its neighbour is caused by that node.

[0023] Indeed, the same building blocks and by the Sync migrate-messages through the same logic as the [...] messages, so that one can assume that the inaccuracy, which caused the [...] -Replacement, approximately the same as that of the sync message. If the neighbour of the like type as the node itself is is likely that its inaccuracy is almost identical.

[0024] Indeed, this method does not distinguish, from that node or whether the inaccuracy is caused by the neighbor node, it is also not important, since the only on the cumulative inaccuracy in the end node is interested slave clock. On maintenance devices defective can locate at the various ports of the clocks by reading the scattering watches.

[0025] therefore each clock can continuously estimate its contribution to total inaccuracy than approximately two times the scattering the purposes of calculating the duration for neighbour nodes. In practice be somewhat smaller this value is, because scatterers is in addition not arithmetically, as is known from the statistics teachings.

[0026] If other sources of errors are well known, e.g. temperature effects or transient response of the oscillator, this may easily also be involved in this inaccuracy computation.

[0027] The estimate of the contribution of a watch for total inaccuracy can be communicated in various ways an end node or a maintenance equipment. The end node can use this information to be communicated to its measurements to qualify has exceeded, according to the standards IEC 61850-7 - 2 or IEEE C37.118 e.g., or around that its inaccuracy a certain threshold value.

[0028] The same principle can also be applied on federal clocks ( [...] boundary). This on heading no shim field, but they can inform their own accuracy in their records and Specify.

[0029] The same principle applies to mixed intermediate clocks 802,1 AS specified (transparent/boundary) as the IEEE standard.

[0030] wherein measuring the round-trip delay The same principle can also be applied by the end-to-end Method, although only the sum of the travel times is measured.

[0031] The same principle can also be applied at a clock on the variation of its local clock, e.g. by calculating their Allan-scattering. That the clock a plausibility of the inaccuracy can take this into account to notification are derived and inaccuracy.

[0032] This invention will be further explained in the following text and appended drawings illustrates by exemplary reactions: Fig. clock chainmaster clock 1 shows a between a (1) in a first node (11), synchronized e.g. by satellite (10), two Transparent clocks (2,3) in intermediate nodes (12.13) and a slave clock (4) in an end node (14) via input and output (40) is connected with an installation; slave clock is shown wherein only one, although more exist; master clock is shown only one, although other master clocks may exist in readiness; only two ports upon intermediate clock (2) are shown, although such intermediate clocks have a plurality of ports normally, the show to other slave clocks, intermediate clock as in (3) is [...] (30), wherein the node by compounds (21.22,23) are connected.

[0033] 2 shows the time-distance-Fig. according to standard IEEE 1588 divided into sequences message exchange Chart of the:

A) exchanging messages according to the peer-to-peer echo method for determining the propagation time in the direction, where the sync messages (for master clock towards) come

B) exchanging messages according to the peer-to-peer echo method for determining the propagation time in the direction, where the sync messages go ( slave clocks towards to the)

C) transmission of the time-of-flight and residence time of the intermediate node for shim field synchronization message with addition of the sync message.

[0034] 3 shows a histogram of the measurement of the propagation time between two nodes Fig.. It shows the frequency (101) the occurrence of a measurement value in a particular, small interval (102). This frequency has a mean value (103), 97.5 nanoseconds in this example, the has an offset for calibration value (104), in this example 100 nanoseconds,. This frequency σ (105) has a scattering, 4 nanoseconds in this example. A a measure of the inaccuracy of the clock as a multiple of the scattering is determined arbitrarily (106), 24 nanoseconds in this example.

[0035] 2 shows the exchange of messages according to the standard IEEE 1588 Fig., under use of the peer-to-peer time-of-flight, and of a one shot method for transmission of the correction. Enlargement of the concept to a two steps method for transmitting the correction and has been omitted for the sake of simplicity is obvious. Enlarging for 802,1 federal clocks according to the standard IEEE federal clocks or mixed transparent clocks/has been omitted for the sake of simplicity is also self-evident and AS.

[0036] The Minutes operates as follows:

1. (1.2,3 and 4) the duration calculated node Each to a neighbour 0] by sending a message currently t1 [...] [ [...] ], on which of the neighbour [...] responds with a message, which contains the residence time between reception of [...][...] and transmitting (t3-t2 [L [ [...] ], j]), and which arrives at the node [ [...] ] currently t4. Each node to its neighbour the Duration calculated as : [I, j] = A ((t4 [I, j]-t1 [i.j]) - (t3 [i.j]-t2 [I, j]))/ 2, assuming a symmetrical Duration. Although a node on all of its ports the Duration (also on those ports, the are blocked) is calculated here for the sake of simplicity only the Duration in the direction viewed in the direction (2 Fig., A) and master clockslave clock (Fig. 2, B). Although the standard IEEE 1588 master clock provides only a calculation of the duration in the direction, there are other protocols, using the Duration slave clocks in direction. Furthermore a comparison is runtime in the various ports as helpful plausibility monitoring.

2. The master clock (1) a Sync sends message, which contains the specific time U, to which the message has to leave the (2 Fig., carbon) master clock. This Sync-message by the intermediate node migrates (2,3) to for slave clock (4).

According to the standard IEEE 1588 each Transparent Timepiece added the sum of its own and its Duration A p residence time for neighbour master clock for shim field in the direction of the sync message, which he has received from the neighbor. The slave clock (4) and added to the value the Sync gets-message and the Duration for its neighbour t1 the shim field, to set its local clock on the specific time.

3.3 shows a histogram of the travel time measurement in a timepiece Fig., after a number measurements. In this example, a node calculate the mean than 97.5 nanoseconds (while the true, value measured by calibration 100.0 nanoseconds) and the standard 4 nanoseconds as calculated-scattering, the node thereby its inaccuracy on estimates 24 nanoseconds or + / - 12 nanoseconds (6 times the scattering of the propagation time measurement). The average value is close to the real value, the calibration can be announced by the node, to discover an offset. The scattering, the inaccuracy of the measurement on, and, derived thereof, the inaccuracy of the clock. Here a scattering width has been adopted of 3 sigma (Three time standard deviation) arbitrarily, as an expression of the inaccuracy, but others can be defined dispersion widths. Even a symmetrical distribution (Gauss is) not the prerequisite, for example, occurrence can log-normal distributions.

4. In one design, a node detects the histogram by a number counter for each run time interval, according to a known type of statistics. The number counter depends on the expected size of the time-of-flight and the required separation. To old values made in order to, a low-pass filter is applied with a certain window time, e.g. a few minutes,.

5. In another execution of the nodes with known statistical algorithms calculated continuously the scatter, need no further description the. For example, it can identify the Allan-scattering, as the IEEE standard 1588:2008 _AOUNI167AO> 7.6.3 or the ITU-T Recommendation G.810 disclosed, to estimate the inaccuracy of the local clock. A low-pass filter is used, old values window time e.g. a few minutes after a certain, forgetting.

6. this scattering is calculated from inaccuracy The, variance or other measure, the mathematically thereof is derivable, as well as from additional, known inaccuracies, caused e.g. by asymmetry, time automatic controller of the local clock by transient response of the frequency-or, a conventional offset or by temperature effects. The inaccuracy is represented in a short form, e.g. as the standard IEC 1588:2008 _AOUNI167AO> 7.6.3.3 defined, and made available to the other nodes, in particular the maintenance knot (not shown in Figure.

1). This serve various methods, among others:

-A SNMP message is conveyed to a management node according to standard IETF RFC 3410

administrative message according to standard IEEE 1588-A Signalling-or

- [...] -field appended to a PTP message A private, e.g. to Sync or [...], according to IEEE C37.238.

[0037] The principle of measuring the own inaccuracy by measuring the scattering of a measurement value, the actually should change little, can be given increased on federal clocks, protocols with time-of-flight, and in general as the end-to-end and indication measuring assistance that the accuracy of the timepiece is deteriorating or that network elements are present, the disregard the protocol.

[0038] A comparison between ports of a same node can help, to examine the plausibility.

[0039] although the invention has been explained in the drawings and in the text, this should not limit the reaction. Deviations of the execution are specialized persons, which with claims, descriptions and the drawings are familiar, readily known. In "contains" no other elements or closes the floor to claims from steps, and the indefinite shape of the closes Singular-Article no plurality of. The fact that individual elements or steps repeatedly appear in different claims, no combination closes thereof from, the disclosed seems advantageous for the interpretation of the invention and these combinations apply thus as.

[0040] dish words : clock synchronization, [...] time protocol, IEC 61588, IEEE 1588, IEEE C37.118-1, IEEE C37.118-2, IEEE C37.238, PTP, scattering, variance, Allan, deviation, [...], time inaccuracy, clock accuracy, precision, peer-to-peer link delay, end-to-end link delay, propagation time measurement, IEC 61850, [...] measurement unit, The PMU