Safety-Rated Network Time Synchronization With Offset Integrity Checks
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Solution Overview
Problem
Current safety-rated industrial control systems face challenges in detecting failures within the control network, particularly in time-synchronous operations, where timestamp errors can occur due to corruption or synchronization issues, limiting the reliability of time synchronization in safety-critical applications.
Innovation Solution
A method and system for generating a safety-rated time value by determining an offset time value between clocks in adjacent devices through synchronized request and delay time messages, ensuring accurate time synchronization by storing this offset in a safety memory, and using it to generate timestamps for events, thereby maintaining data integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If standard time synchronization methods are used in control networks, then time coordination between devices is achieved, but timestamp errors can occur due to corruption or synchronization issues, reducing reliability in safety-critical applications
Solution Approach 1:
The patent divides the time synchronization function into separate safety-rated and non-safety-rated components. The offset time value determination is performed in a safety-rated manner with dedicated safety memory, while allowing standard time synchronization protocols to operate in non-safety portions of the system. This segmentation allows timestamp accuracy to be maintained through proper synchronization while ensuring reliability through safety-rated validation and storage of critical time data.
2Reliability
If safety integrity levels are increased to detect more failures, then safety detection capability is improved, but system complexity and diagnostic coverage requirements increase
Solution Approach 1:
The patent introduces an intermediary approach by using offset time value determination as a mediator between safety-critical timestamp requirements and standard time synchronization protocols. The offset calculation serves as a safety-rated validation layer that checks synchronization accuracy without requiring complete redesign of the time synchronization infrastructure. This intermediary mechanism provides safety detection capability while avoiding the full complexity of implementing safety-rated protocols throughout the entire time synchronization system.
Data Source
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AI summary
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.