PLC Unit Distributed Comparison for SIL3 Response Performance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In programmable logic controllers, dualizing SIL2-compliant units to achieve SIL3 compliance results in decreased response performance due to the CPU unit needing to compare input/output signals, limiting application and increasing costs when using SIL3-compliant units, which have excessive reliability and redundancy.
Innovation Solution
A PLC unit with a system bus interface for direct data exchange between units, a dualization setting retention unit, and an information comparing unit to ensure consistency and perform error processing, allowing compliance with both SIL2 and SIL3 without overloading the CPU unit or increasing redundancy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two SIL2-compliant units are dualized to achieve SIL3 compliance, then the safety level is improved, but the response performance deteriorates due to the CPU unit needing to compare all input/output signals
Solution Approach 1:
The patent divides the comparison function into two parts: the input unit compares input signals with its counterpart directly, and the output unit compares output signals with its counterpart directly. This segmentation removes the comparison burden from the CPU unit, allowing it to focus on control operations while maintaining SIL3 compliance through distributed comparison functionality.
Solution Approach 2:
The patent introduces a new communication dimension between input/output units and their counterparts through the system bus, enabling direct comparison operations without CPU intervention. This dimensional change in data flow allows parallel comparison operations to occur independently alongside the main control logic execution.
2Reliability
If SIL3-compliant units with higher grade components are used, then the safety level is improved, but the manufacturing cost increases
Solution Approach 1:
The patent designs a universal PLC unit structure that can operate at either SIL2 or SIL3 compliance levels. The same hardware platform supports both safety levels by enabling or disabling the dualization and comparison functions, eliminating the need for separate high-grade component configurations and reducing manufacturing costs while maintaining flexibility.
Solution Approach 2:
The patent changes the operational parameters of the PLC unit (specifically the safety integrity level configuration) rather than changing the physical components. By adjusting software settings and enabling/disabling comparison functions, the system achieves SIL3 compliance using standard components, avoiding the cost increase associated with higher-grade hardware.
3Reliability
If the CPU unit performs all comparison operations in dualized configuration, then the safety level is improved, but the device complexity increases
Solution Approach 1:
The patent segments the comparison functionality from the CPU unit and distributes it to the input and output units. Each input unit compares its input signals with its counterpart, and each output unit compares its output signals with its counterpart. This segmentation reduces the CPU's operational complexity while maintaining the safety benefits of dualized comparison.
Solution Approach 2:
The input and output units perform self-comparison operations with their counterparts directly, without requiring CPU intervention for each comparison. This self-service capability reduces the computational burden on the CPU and simplifies the overall system architecture by distributing intelligence to the edge units.
Data Source
AI summary
A programmable logic controller system has: an input unit system section in which plural input units are combined; a CPU unit system section in which plural CPU units are combined; and an output unit system section in which plural output units are combined. Each system section has: a setting retaining unit to retain a setting indicating whether to use any of the plural units alone or use the plural units in a multiplexed manner; and a comparing unit to make a comparison of processed data between the plural units when the setting indicates using the plural units in a multiplexed manner, to send the processed data if the comparison result indicates consistency, and to perform an error process if the comparison result indicates inconsistency. In the setting retaining unit, whether to use alone or in a multiplexed manner is set based on an externally-input setting instruction.