Graphical PLC Algorithm Verification With Automatic Formal Modeling
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Solution Overview
Problem
Existing methods for verifying safety-critical systems, particularly those controlled by Programmable Logic Controllers (PLCs) in safety-related Instrumentation and Control (I&C) systems, are inefficient and costly due to the manual creation of formal models, which can lead to misinterpretation and increased development time and costs.
Innovation Solution
Automated conversion of PLC algorithms from graphical languages like FBD, SFC, and LD into functionally equivalent formal models for model checking, using integrated tools that allow developers to verify algorithms directly within the development environment, reducing the need for expert intervention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If manual creation of formal models is used for verifying PLC algorithms, then verification thoroughness can be maintained, but development time and costs increase significantly
Solution Approach 1:
The patent applies preliminary action by automatically generating formal models from graphical PLC algorithms before verification begins. The system pre-processes the PLC algorithm into a formal representation that can be directly subjected to model checking, eliminating the time-consuming manual model creation step while ensuring the formal model is ready for thorough verification.
Solution Approach 2:
The patent uses copying by creating a formal model that is a faithful representation of the original graphical PLC algorithm. The automatic conversion process generates a formal model that copies the semantics and behavior of the source algorithm, enabling verification without requiring manual reinterpretation or manual model construction.
2Measurement precision
If manual creation of formal models is used for verifying PLC algorithms, then accuracy can be maintained, but expert intervention is required increasing costs
Solution Approach 1:
The patent applies self-service by enabling the PLC algorithm verification process to perform its own formalization automatically. The system converts the graphical PLC algorithm into a formal model without requiring external expert intervention, making the process self-sufficient while maintaining accuracy through automated, consistent transformation rules.
Solution Approach 2:
The patent substitutes the mechanical process of manual expert model creation with an automated computational system. The manual intellectual process of experts creating formal models is replaced by an automatic conversion mechanism that applies formalization rules algorithmically, reducing both complexity and the need for specialized human expertise.
3Productivity
If automated conversion to formal models is implemented, then development time and costs are reduced, but risk of misinterpretation may increase
Solution Approach 1:
The patent implements feedback by incorporating verification steps that check the correctness of the automatically generated formal model against the original PLC algorithm. The system validates that the conversion process has not introduced misinterpretations, providing feedback mechanisms to ensure model accuracy while maintaining automated efficiency.
Data Source
AI summary
A method of model checking a PLC algorithm inscribed in a graphical programming language and a method for automatic test case generation and model-based testing of the PLC implementing these PLC algorithms are provided. The model checking method includes converting the functional block diagram algorithm into a functionally-equivalent formalized functional block diagram algorithm. The method includes model checking the functionally-equivalent formalized functional block diagram algorithm. The verified PLC algorithm is a functional block diagram algorithm including discrete-time deterministic function blocks. The verified PLC algorithm can be then downloaded into a target PLC and periodically executed. The test case generation method includes predefined testable behaviors (unit tests) of each function block and combination of compatible unit tests to valid test cases according the assume-guarantee principle. The resulting test scenarios and test cases are used for model-based grey-box testing in MIL, SIL and HIL testing of the PLC implementing these PLC algorithms.