Time synchronization system for industrial control network using global reference pulses
First Claim
1. A method of synchronizing local clocks among industrial control devices communicating on a network, the synchronizable being to a time value of a master clock in a first industrial control device, the method comprising the steps of:
- (a) detecting at the first industrial control device a global reference pulse;
(b) storing at the first industrial control device, a first time value of the master clock at the time of detection of the global reference pulse by the first industrial control device;
(c) transmitting from the first industrial control device a time message on the network containing the stored first time value of the master clock;
(d) detecting at a second industrial control device the global reference pulse;
(e) storing at the second industrial control device, a second time value of a local clock in the second industrial control device at a time of detection of the global reference pulse at the second industrial control device;
(f) receiving at the second industrial control device the time message and comparing the first time value to the second time value to produce an error value; and
(g) correcting the local clock of the second industrial control device according to the error value.
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Abstract
Local clocks used for coordinating events in an industrial control system may be synchronized using time messages transmitted on standard communication networks. A master industrial controller incorporates a time values in a time messages transmitted to the other controllers, the time value indicating the tie of occurrence of an independent global synchronizing pulse. All controllers also capture the local time of the global synchronizing pulse and these times may be compared to the time message from the master industrial controller to deduce a time error value independent of network messaging delays. The error value is used to correct the local clocks.
171 Citations
14 Claims
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1. A method of synchronizing local clocks among industrial control devices communicating on a network, the synchronizable being to a time value of a master clock in a first industrial control device, the method comprising the steps of:
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(a) detecting at the first industrial control device a global reference pulse;
(b) storing at the first industrial control device, a first time value of the master clock at the time of detection of the global reference pulse by the first industrial control device;
(c) transmitting from the first industrial control device a time message on the network containing the stored first time value of the master clock;
(d) detecting at a second industrial control device the global reference pulse;
(e) storing at the second industrial control device, a second time value of a local clock in the second industrial control device at a time of detection of the global reference pulse at the second industrial control device;
(f) receiving at the second industrial control device the time message and comparing the first time value to the second time value to produce an error value; and
(g) correcting the local clock of the second industrial control device according to the error value. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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Specification