US 11,599,090 B2Granted

System and method of network synchronized time in safety applications

AssigneeRockwell Automation Technologies, Inc.

InventorsSteven T. Seidlitz, Mark A. Chaffee

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Abstract

To improve integrity of time synchronization, a node in the safety rated system takes steps to ensure the time to which it is synchronized has not become corrupted. The node receives a synchronize request message from an adjacent network device, which includes the master time, and the node generates an offset value corresponding to a difference between a local time and the master time. The node stores the offset time into a safety memory to ensure that the offset value has data integrity and does not become corrupted. The node performs periodic skew detection between two devices to verify that the clocks remain synchronized. In addition, the node performs a local drift detection to detect if the frequency of the local oscillator on which the local clock value is based begins to change.

Claims17

Dependent claims

A method of generating a safety rated time value for use in a safety rated application, the method comprising the steps of:

receiving a synchronize request message from a first device with a second device,
receiving a first timestamp corresponding to a transmission time of the synchronize request message at the second device, wherein the first timestamp corresponds to a clock in the first device;
generating a second timestamp in the second device upon receipt of the synchronize request message, wherein the second timestamp corresponds to a clock in the second device;
transmitting a delay time request message from the second device to the first device;
generating a third timestamp in the second device corresponding to a transmission time of the delay time request message, wherein the third timestamp corresponds to the clock in the second device;
generating a fourth timestamp in the first device upon receipt of the delay time request message, wherein the fourth timestamp corresponds to the clock in the first device;
transmitting the fourth timestamp from the first device to the second device;
determining an offset time value between the clock in the first device and the clock in the second device as a function of the first timestamp, the second timestamp, the third timestamp, and the fourth timestamp;
storing the offset time value in a standard memory of the second device;
storing a copy of the offset time value in a safety memory of the second device;
transmitting a first diagnostic message from the first device to the second device at a first safety rated time based on the first clock;
transmitting a second diagnostic message from the second device to the first device at the first safety rated time based on the second clock;
generating a first diagnostic timestamp in the first device corresponding to receipt of the second diagnostic message;
generating a second diagnostic timestamp in the second device corresponding to receipt of the first diagnostic message;
and
comparing the first diagnostic timestamp to the second diagnostic timestamp to verify synchronization of the first clock and the second clock.

13 more elements

A node in an industrial control system configured to generate a safety rated time value for use in a safety rated application, the node comprising:

a communication port configured to:
connect to an industrial network,
receive a synchronize request message from a first device via the industrial network,
receive a first timestamp from the first device, wherein the first timestamp corresponds to a time signal in the first device at which the synchronize request message was transmitted,
receive a first diagnostic message at the communication port, the first diagnostic message transmitted from the first device at a first safety rated time based on the time signal in the first device, and
transmit a second diagnostic message from the communication port to the first device at the first safety rated time based on the local time signal;
a clock circuit generating a local time signal;
a processor configured to:
generate a delay time request message for transmission to the first device via the industrial network, and
determine an offset time value between the time signal in the first device and the local time signal as a function of the first timestamp, a second timestamp, a third timestamp, a fourth timestamp, wherein:
the second timestamp is a function of the local time signal and corresponds to the node receiving the synchronize request message,
the third timestamp is a function of the local time signal and corresponds to transmission of the delay time request, and
the fourth timestamp is received from the first device, corresponds to the time signal in the first device, and corresponds to reception of the delay time request at the first device;
generate a diagnostic timestamp corresponding to receipt of the first diagnostic message, and
compare the diagnostic timestamp to another diagnostic timestamp to verify synchronization of the local time signal and the time signal in the first device, wherein the other diagnostic timestamp corresponds to receipt of the second diagnostic message at the first device;
and
a safety memory configured to store a copy of the offset time value.

14 more elements

A method of generating a safety rated time value for use in a safety rated application, the method comprising the steps of:

determining an offset time value between a master clock and a device in the safety rated application;
storing the offset time value in a safety memory of the device;
reading a local time value from a clock circuit in the device;
generating the safety rated time as a function of the local time value and of the offset time stored in the safety memory of the device;
transmitting a first diagnostic message from another device to the device at a first safety rated time based on a clock in the other device;
transmitting a second diagnostic message from the device to the other device at the first safety rated time based on the local time value;
generating a first diagnostic timestamp in the other device corresponding to receipt of the second diagnostic message;
generating a second diagnostic timestamp in the device corresponding to receipt of the first diagnostic message;
and
comparing the first diagnostic timestamp to the second diagnostic timestamp to verify synchronization.

7 more elements

Dependencies are inferred from the claim text.

Facts

Application: 17/037,940Filed 30 Sep 2020
Published: US 2022/0100172 A131 Mar 2022
Granted: 7 Mar 2023
Term ends: Not estimatedThe source records don’t support an estimate.

Classification14 codes

G05B 19/4155
Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to…
G05B 19/0428
Using digital processors: safety, monitoring
H04J 3/0644
Clock or time synchronisation among nodes; Internode synchronisation: external master-clock
H04J 3/0667
Using timestamps: bidirectional timestamps, e.g. NTP or PTP for compensation of clock drift and for compensation of propagation delays