Soft-PLC Safety Program Checksum Verification at Startup
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Solution Overview
Problem
Existing safety-related programmable logic controllers (PLCs) require dedicated hardware and lack a mechanism to ensure the execution of the correct safety program after power off/on transitions, posing risks in critical processes.
Innovation Solution
A method involving checksum verification of safety programs across a communication network ensures the correct safety program is executed by generating and comparing load memory checksums with stored checksums, stopping execution if discrepancies are detected, and utilizing redundant storage for increased reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If checksum verification across communication network is implemented, then reliability of safety program execution is improved, but device complexity increases
Solution Approach 1:
A utility program acts as an intermediary between the control software and the network participant. This intermediary manages the checksum verification process by automatically querying the stored checksum from the network participant and comparing it with the load memory checksum, thereby improving reliability without requiring complex direct integration between the control software and network infrastructure.
Solution Approach 2:
The checksum of the safety program is pre-stored on a network participant before the control software executes. This preliminary action enables verification at startup without requiring complex runtime checks, as the expected checksum value is already available in the network for comparison.
2Adaptability or versatility
If virtual controllers are used instead of dedicated hardware, then adaptability is improved, but reliability of safety program execution deteriorates
Solution Approach 1:
The system implements feedback by comparing the load memory checksum (generated from the actual safety program in memory) with the stored checksum (retrieved from the network participant). This feedback mechanism detects any discrepancies between the intended safety program and what is actually loaded, ensuring integrity even in virtualized environments where direct hardware access is abstracted away.
Solution Approach 2:
The patent replaces the mechanical/hardware-based safety verification mechanism (direct hardware access and firmware testing) with a software-based checksum verification system that operates over a communication network. This substitution maintains reliability while enabling adaptability to virtual controllers and different hardware platforms.
3Productivity
If multiple instances of control software are operated, then productivity is improved, but difficulty of detecting and measuring increases
Solution Approach 1:
Each instance of control software performs self-verification by generating its own load memory checksum and comparing it with the corresponding stored checksum retrieved via the utility program. This self-service approach enables multiple instances to operate independently with automatic verification, improving productivity without proportionally increasing the difficulty of detecting and measuring program integrity across instances.
Data Source
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Figure 3~4
AI summary
The invention relates to a method for operating a control software (Soft-PLC) for controlling a process, wherein the control software (Soft-PLC) is run within a runtime environment (FW) on a computer system (1), and a safety program (F-Prog) for running in the control software (Soft-PLC) is loaded into a load memory (10), wherein a checksum (FCC-con) of the program code of the safety program (F-Prog) is stored in a network participant (3) connected to the computer system (1) via a communication network (2), wherein when the control software (Soft-PLC) starts up in the runtime environment (FW) over the program code of the safety program (F-Prog) stored in the load memory (10), a load memory checksum (FCC-act) is generated, furthermore, the previously stored checksum (FCC-con) is queried from the network participant (3) and compared with the load memory checksum (FCC-act),In case of a discrepancy, the processing of the safety program (F-Prog) in the control software (Soft-PLC) is stopped.