Soft-PLC Cold Start Detection via Randomized Safety Time
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Solution Overview
Problem
In safety-oriented control systems, particularly with virtual software control systems (soft-PLC), ensuring a cold start with initial values after a power failure is challenging due to undefined behavior of timers during a 'mains off' state.
Innovation Solution
A method is introduced where a random number is generated and stored during system startup, and added to the safety time in each cycle. This random number is subtracted before calculating time differences, allowing for the detection of a cold start failure by checking tolerance deviations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a virtual software control system (soft-PLC) is used with abstracted hardware, then adaptability and versatility are improved, but reliability deteriorates due to undefined timer behavior during mains off state
Solution Approach 1:
The patent introduces a random number as an intermediary element to distinguish between cold start and warm start scenarios. This random number is added to the safety time during warm starts but not during cold starts, creating a detectable difference that allows the system to reliably identify startup conditions even in virtualized environments with abstracted hardware timers.
Solution Approach 2:
The patent changes the parameter of safety time by adding a random number offset under specific conditions (warm start). This parameter modification creates a distinguishable pattern between cold start (no offset) and warm start (with offset) scenarios, enabling reliable detection of startup conditions despite hardware abstraction.
2Adaptability or versatility
If the system retrieves safety time from an external time source in virtualized environments, then adaptability is improved, but measurement precision deteriorates due to undefined behavior during mains off
Solution Approach 1:
The random number serves as a mediator that encodes startup condition information into the safety time measurement. By adding this random offset only during warm starts, the system creates a measurable distinction between cold and warm starts, compensating for the loss of precision caused by external time sources with undefined behavior.
3Reliability
If two independent timers (standard timer and fail-safe timer) are used to form safety time, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent merges the functionality of two independent timers (standard timer and fail-safe timer) into a unified safety time calculation process. By combining their time differences and comparing against a tolerance threshold, the system maintains reliability while reducing operational complexity compared to managing two completely separate timing mechanisms.
Data Source
AI summary
Method for operating a segment of cycle-oriented control software, wherein to test, in a virtual control system, execution of a cold start mechanism, on a start-up of a runtime environment, a random number is generated, stored in a storage region and added to the storage region upon every further request for a safety time, where at the start of a new cycle, the deviation of the time differences is calculated and, in each cycle, the storage region is accessed and before calculation of the time differences, the random number is re-subtracted from the safety time, when a new start-up of the runtime environment has occurred, this is diagnosable via the tolerance being exceeded, because the second time difference now has an offset that results from the safety time with a new random number of the current cycle and the safety time with the old random number of the previous cycle.