Optical Coupler Input Module for Fault Detection in Safety Circuits
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Solution Overview
Problem
Existing fault-tolerant systems in safety control systems face limitations in diagnostic fault coverage due to the analogue nature of input circuits, particularly in defending against latent faults, and require improved isolation and redundancy to maintain operational reliability.
Innovation Solution
An input module utilizing optical couplers with light emitting diodes, feedback photodiodes, and Zener diodes for electrical isolation and fault tolerance, ensuring that latent faults do not disrupt normal operation by using a series connection of LED drive sub-circuits and parallel Zener diodes to mitigate short and open circuit faults, and maintaining functionality across a wide power supply voltage range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If optical couplers are used for electrical isolation in fault-tolerant systems, then fault tolerance and isolation are improved, but device complexity increases
Solution Approach 1:
The input circuit is divided into multiple independent channels, each with its own optical coupler and processing circuitry. This segmentation allows faults in one channel to be isolated without affecting other channels, achieving fault tolerance while managing complexity through modular design
Solution Approach 2:
Optical couplers are introduced as intermediary devices between the input signal and the processing circuits. These optical couplers provide electrical isolation while transmitting signal information, enabling fault containment without direct electrical connection between stages
2Measurement precision
If analogue input circuits are used for sensor signal processing, then signal processing capability is maintained, but diagnostic fault coverage is limited
Solution Approach 1:
Multiple copies of the input circuit are implemented in parallel, each processing the same analogue signal independently. This allows the system to maintain analogue signal processing capability while providing redundant paths for fault detection and diagnosis
Solution Approach 2:
Feedback mechanisms are incorporated to monitor the operational status of each circuit channel and detect faults. The feedback information enables the system to identify latent faults and maintain diagnostic coverage while preserving analogue signal processing functionality
3Reliability
If redundant circuits are implemented for fault tolerance, then system reliability is improved, but power consumption increases
Solution Approach 1:
The system implements partial redundancy by providing multiple circuit channels that can operate independently. Not all channels need to be active simultaneously, allowing the system to achieve fault tolerance with reduced power consumption by activating only necessary channels
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides a high degree of fault tolerance, low power consumption, and accuracy in fault detection and isolation, ensuring continuous operation even with latent faults, and maintaining system reliability by preventing fault propagation and minimizing disruption.
Implementation Method 1
each optical coupler/controller comprises a light emitting diode drive sub-circuit driving a light emitting diode
Implementation Method 2
The light emitting diode is coupled to a feedback photodiode and to an output photodiode
Data Source
AI summary
This invention relates to fault detection in electrical circuits. The invention provides an input module for electrically isolating an input signal received via a field sensor to be transmitted to a plurality of processors, in which the input module comprises a plurality of optical coupler/controller circuits; and each optical coupler/controller comprises a light emitting diode drive sub-circuit driving a light emitting diode; and an input sub-circuit; and in which a sensor voltage representing said input signal and a supply voltage are connected to each input sub-circuit; and each of said light emitting diode drive sub-circuits are connected in series between the supply voltage and ground.