System and method of network synchronized time in safety applications

Patent metadata

Field	Value
Publication number	US-11599090-B2
Application number	US-202017037940-A
Country	US
Kind code	B2
Filing date	Sep 30, 2020
Priority date	Sep 30, 2020
Publication date	Mar 7, 2023
Grant date	Mar 7, 2023

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.

First claim

We claim:

1. 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.

2. The method of claim 1 further comprising the step of:
determining a safety rated time value in the second device by:
reading a time value from the second clock,
reading the copy of the offset time value from the safety memory, and
adding the copy of the offset time value from the safety memory to the time value from the second clock.

3. The method of claim 1 wherein:
the synchronize request message is received periodically at the second device,
each of the first, second, third, and fourth timestamps are generated or received in the second device responsive to each synchronize request message,
the offset time value is determined in response to each synchronize request message, and
at least one of the first diagnostic message and at least one of the second diagnostic message are transmitted between each synchronize request message.

4. The method of claim 1 further comprising the steps of:
transmitting at least one additional first diagnostic message from the first device to the second device at prescheduled safety rated times based on the first clock;
transmitting at least one additional second diagnostic message from the second device to the first device at the prescheduled safety rated times based on the second clock;
generating at least one additional first diagnostic timestamp in the first device corresponding to receipt of the at least one additional second diagnostic message;
generating at least one additional second diagnostic timestamp in the second device corresponding to receipt of the at least one first diagnostic message; and
comparing the first diagnostic timestamp to the second diagnostic timestamp and comparing each of the at least one additional first diagnostic timestamps to the at least one additional second diagnostic timestamps to verify synchronization of the first clock and the second clock.

5. The method of claim 4 wherein:
the at least one additional first diagnostic message includes either the first diagnostic timestamp or the at least one additional first diagnostic timestamp corresponding to the prior received second diagnostic message,
the at least one additional second diagnostic message includes either the second diagnostic timestamp or the at least one additional second diagnostic timestamp corresponding to the prior received first diagnostic message, and
comparing the first diagnostic timestamp to the second diagnostic timestamp and comparing each of the at least one additional first diagnostic timestamps to the at least one additional second diagnostic timestamps occurs after each first and second diagnostic message is transmitted.

6. The method of claim 1 further comprising the steps of:
generating a first local clock signal with a first oscillator in the clock circuit of the second device, wherein the first local clock signal is used to generate the second timestamp and the third timestamp;
generating a second local clock signal with a second oscillator in the clock circuit of the second device; and
comparing the second local clock signal to the first local clock signal to detect drift of the first local clock signal after determining the offset time value.

7. The method of claim 1 wherein the first device includes a hardware circuit in a communication port configured to generate the first timestamp when the synchronize request message is transmitted and configured to generate the fourth timestamp when the delay time request message is received and wherein the second device includes a hardware circuit in a communication port configured to generate the second timestamp when the synchronize request message is received and configured to generate the third timestamp when the delay time request message is transmitted.

8. The method of claim 1 further comprising an initial step of scheduling communication times between the first device and the second device to minimize other network traffic when the synchronize request message and the delay time request message are being transmitted.

9. 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 i

Assignees

• Rockwell Automation Tech Inc

Inventors

• Seidlitz Steven T
• Chaffee Mark A

Classifications

• Y02P90/02

  Total factory control, e.g. smart factories, flexible manufacturing systems [FMS] or integrated manufacturing systems [IMS] · CPC title

• H04J3/0667 Primary

  Bidirectional timestamps, e.g. NTP or PTP for compensation of clock drift and for compensation of propagation delays (arrangements for monitoring round trip delays in packet switching networks H04L43/0864) · CPC title

• G05B2219/33097

  Variable ticks, align clocks, to synchronise cycles with other machine, robot · CPC title

• H04J3/0644

  External master-clock · CPC title

• G05B19/4186

  by protocol, e.g. MAP, TOP · CPC title