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 accurately utilizing time synchronization due to potential errors in timestamp corruption along the network, particularly in black channel methods, which can limit the ability to detect failures and ensure safety integrity levels (SIL) in time-synchronous operations.
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 timestamp messages, ensuring data integrity and accurate time synchronization, involving a synchronize request, delay time request, and storing the offset value in safety memory to correct for clock discrepancies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If black channel method is used for time synchronization, then device complexity is reduced, but measurement precision of timestamps deteriorates due to potential corruption
Solution Approach 1:
The patent introduces an intermediary verification mechanism where the receiving device acts as a mediator to detect timestamp corruption. The receiving device compares the timestamp against the actual reception time and generates an error indication when discrepancies are detected, thereby maintaining timestamp accuracy without requiring complex preemptive protection systems in all devices.
2Reliability
If redundant safety mechanisms are implemented throughout the network, then reliability improves, but device complexity increases
Solution Approach 1:
The patent segments the safety mechanisms into two distinct groups: white devices (safety-rated) and black devices (non-safety-rated). This segmentation allows critical safety functions to be concentrated in specific devices that require full safety certification, while other devices can operate with simpler, less complex configurations, thereby maintaining overall system reliability without universally increasing device complexity.
Solution Approach 2:
The receiving device serves as an intermediary safety mechanism that compensates for the lack of redundant safety features in black channel devices. By implementing verification and error detection at the receiving end, the system achieves reliable timestamp synchronization without requiring every network device to possess complex safety-rated components.
3Measurement precision
If timestamp verification is performed at every device, then measurement precision is maintained, but loss of time increases due to verification overhead
Solution Approach 1:
The patent extracts the complex timestamp verification and corruption detection functions from all devices and concentrates them specifically in the receiving device. This extraction allows transmitting devices to operate with simpler, faster timestamp generation without verification overhead, while the receiving device performs the necessary verification only when receiving timestamps, thereby maintaining accuracy without universal time loss.
Data Source
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.