Time-stamping Protocol for Single-Wire Safety Systems
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Solution Overview
Problem
Industrial safety systems face challenges in accurately time-stamping events without synchronizing devices on the safety circuit, particularly due to the complexity and processing overhead required for precise clock synchronization, especially in systems with dual redundant signal channels.
Innovation Solution
A lightweight time-stamping and synchronization protocol layer that uses autonomous counters and simple mathematics to determine event timing relative to a real-time system clock, eliminating the need for device synchronization by generating time-stamps based on counter values incrementing at a defined frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If clock synchronization is implemented to achieve precise event timing, then measurement precision is improved, but device complexity and processing overhead increase
Solution Approach 1:
Each safety device maintains its own autonomous counter that independently tracks time without requiring synchronization with other devices. The counter increments locally at each device, allowing event timing to be determined self-servingly without external coordination or complex synchronization protocols.
Solution Approach 2:
A lightweight protocol layer is introduced as an intermediary between the counter mechanism and the safety devices. This protocol enables time-stamping functionality by exchanging simple counter values between devices without requiring full clock synchronization, thereby mediating the timing information needs while keeping the system simple.
2Reliability
If dual redundant signal channels are used to enhance safety reliability, then reliability is improved, but device complexity and processing overhead increase
Solution Approach 1:
The single-wire communication channel performs multiple functions: it carries both safety-critical signals and diagnostic communication. By making the communication channel universal, the system achieves the reliability benefits of redundant communication paths while using a single physical wire, thereby reducing complexity without sacrificing safety.
Solution Approach 2:
The patent combines safety signal transmission and diagnostic communication into a single communication channel. This merging of functions allows the system to maintain safety reliability through comprehensive monitoring while avoiding the complexity of implementing separate dual redundant signal channels.
3Measurement precision
If precise clock synchronization is implemented, then time-stamping accuracy is improved, but processing overhead increases
Solution Approach 1:
Each device independently maintains and increments its own counter without requiring synchronization operations with other devices. This self-service approach eliminates the processing overhead associated with clock synchronization while still providing adequate time-stamping accuracy for safety events.
Solution Approach 2:
The system uses a lightweight protocol that exchanges only the essential counter values needed for time-stamping, rather than implementing full clock synchronization. This partial action approach provides sufficient time-stamping accuracy for safety applications without the excessive processing overhead of complete synchronization protocols.
Data Source
AI summary
A time-stamping layer is provided for time-stamping of events detected in an industrial safety system. The technique implemented by the time-stamping layer uses autonomous device counters and simple arithmetic to label detected events (e.g., safety switching events) with accurate time-stamps without the need to synchronize clocks of the individual safety input devices and safety relay on the safety circuit. In some embodiments, the time-stamping technique is implemented in a single-wire safety system architecture that yields reliable safety device monitoring without the need for dual redundant signal channels.