Bus Subscriber Monitoring Circuit for Safe Fault Isolation
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Solution Overview
Problem
In safety-related systems with distributed security modules via a communication bus, central processing units lack direct access to bus-coupled output modules, making it difficult to switch off outputs independently of logic units in case of common cause faults, such as voltage drifts outside the permitted range.
Innovation Solution
A bus subscriber device with two bidirectionally coupled logic units, a monitoring circuit, and a transmission unit that can block communication upon detecting a fault, ensuring the system enters a safe state by controlling bus signals and preventing faulty communication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a monitoring circuit is implemented in the central processing unit to detect faults, then fault detection capability is improved, but the ability to directly switch off bus-coupled output modules is lost due to lack of direct access
Solution Approach 1:
The patent introduces a monitoring circuit as an intermediary component that receives monitoring signals from the central processing unit and has direct access to the bus-coupled output modules. This intermediary bridges the gap between the CPU's fault detection capability and the need for direct control over output modules, allowing the monitoring circuit to independently switch off outputs when faults are detected without requiring direct CPU access to the modules.
2Reliability
If redundant structure with two logic units is implemented, then fault tolerance is improved, but common cause faults such as voltage drift affect both channels simultaneously
Solution Approach 1:
The monitoring circuit serves as an intermediary that is independent of the redundant logic units. It monitors the supply voltage separately and can switch off output modules based on voltage conditions without being affected by common cause faults that simultaneously impact both logic units. This independence ensures that voltage drift does not prevent the system from entering a safe state.
Data Source
AI summary
A device, having a safe state, is coupleable to a communication bus. The device includes a first logic unit; a second logic unit; a monitoring circuit; a transmission unit; and a first test line. The device is adapted such that the first logic unit communicates with a bus via the transmission unit in a communication phase and the monitoring circuit emits a monitoring signal to the transmission unit upon a fault so that the transmission unit blocks the communication. The first and/or the second logic unit is coupled to the monitoring circuit via the first test line so as to emit a first test signal to the monitoring circuit.