Safety PLC Soft Error Aggregation for SIS Risk Detection
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Solution Overview
Problem
Safety instrumented systems (SIS) face challenges in differentiating between soft and hard errors, leading to potential incorrect hardware failure interpretations and unwanted actions, due to the lack of effective methods for managing soft errors in safety programmable logic controllers (PLCs).
Innovation Solution
A method is introduced to manage soft errors by receiving expected soft error rates, aggregating and predicting actual soft error rates for I/O modules, and taking actions based on threshold deviations, including visual displays and identifying specific causes within the SIS to reduce soft errors and prevent false hardware failure triggers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If soft errors are not differentiated from hard errors, then the SIS can incorrectly interpret them as hardware failure, but implementing differentiation requires complex error management systems
Solution Approach 1:
The patent segments error management by creating separate tracking mechanisms for soft errors and hard errors. Soft error counters are maintained separately from hard error detection, allowing the system to distinguish between transient soft errors and permanent hardware failures without requiring complete system redesign.
Solution Approach 2:
The patent introduces an intermediary error analysis layer that sits between the I/O modules and the safety PLC decision-making logic. This intermediary layer aggregates soft error data, compares it against expected rates, and only presents differentiated error information to the safety system, reducing complexity while maintaining reliability.
2Reliability
If the SIS takes action on every detected error, then safety response is immediate, but soft errors cause unwanted actions
Solution Approach 1:
The patent implements preliminary action by pre-establishing expected soft error rates for different I/O module types and configuring threshold deviation criteria before errors occur. When soft errors are detected, the system immediately compares them against pre-set expectations and only triggers safety actions when deviations exceed thresholds, preventing unwanted responses to normal soft errors while maintaining rapid response to actual hazards.
3Measurement precision
If soft error rates are monitored and compared against expected rates, then deviations can be detected, but this requires additional data collection and processing
Solution Approach 1:
The patent applies universality by designing the error aggregation and analysis functionality to be integrated within the existing safety PLC architecture. The same processor and memory resources that handle safety logic also perform soft error rate monitoring and comparison, eliminating the need for separate dedicated hardware and reducing overall system complexity while maintaining measurement precision.
Data Source
AI summary
A method for managing soft errors associated with one or more safety programmable logic controllers (PLCs) is provided. The method includes receiving an expected soft error rate for type(s) of input/output (I/O) modules over time, receiving respective soft error data that was aggregated by the respective safety PLCs based on soft errors detected by I/O modules coupled to the respective safety PLCs. Actual soft error rates are determined per I/O module type based on the received soft error data, and soft error rates are predicted for the safety PLC(s) per I/O module type. The actual and/or predicted soft error rates are compared to the expected soft error rate per I/O module type. The method further includes taking one or more actions in response to a threshold deviation between the actual and/or predicted soft error rates relative to the expected soft error rate for the corresponding I/O module type.