Switching Assembly for Secure Electrical Load Control
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Solution Overview
Problem
Existing safety relay systems require complex mechanically guided relays or digital microcontrollers to prevent electrical loads from being switched on again after a safety shutdown, which complicates the mechanical and control aspects, and lacks simplicity for higher security levels.
Innovation Solution
A switching arrangement using two changeover relays in series with redundant safety circuits and feedback loops, where the signal path from the restart switch is looped through the changeover relay's quiescent current path, preventing restart by ensuring both relays interrupt the actuator connection, even if one is welded, without requiring microcontrollers or forcibly guided contacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If forcibly guided relays are used to prevent relay contact welding and ensure safety, then reliability is improved, but device complexity increases due to mechanical complexity
Solution Approach 1:
The patent replaces mechanically complex forcibly guided relays with a combination of ordinary changeover relays and electronic control circuits. The control circuit monitors the switching state of the relays and prevents restart operations when welding is detected, thereby achieving the same safety function without mechanical complexity.
Solution Approach 2:
The patent introduces an intermediary control circuit that acts as a mediator between the relays and the restart switch. This control circuit detects the switching state of the relays and conditionally enables or disables the restart function, providing a sophisticated safety mechanism without requiring mechanically complex forcibly guided relays.
2Device complexity
If ordinary changeover relays are used instead of forcibly guided relays, then device complexity is reduced, but reliability decreases due to inability to prevent simultaneous contact closure
Solution Approach 1:
The patent implements feedback control by having the control circuit continuously monitor the switching state of the changeover relays. When welding is detected or when the switching state indicates an unsafe condition, the control circuit prevents the restart switch from operating, thereby ensuring safety despite using simpler ordinary relays.
Solution Approach 2:
The control circuit performs preliminary checks of the relay switching state before allowing restart operations. This preliminary action ensures that the system is in a safe state before permitting restart, compensating for the lack of mechanical interlocking in ordinary changeover relays.
3Extent of automation
If digital microcontrollers are used to control safety switching, then control precision is improved, but device complexity increases due to digital electronics
Solution Approach 1:
The patent uses a simple control circuit with discrete electronic components instead of expensive microcontrollers. This approach achieves the necessary control precision for safety switching while significantly reducing device complexity and cost, making the system more suitable for safety-critical applications where simplicity and reliability are paramount.
4Ease of operation
If restart switch is allowed to operate freely, then ease of operation is improved, but reliability decreases due to risk of accidental restart
Solution Approach 1:
The control circuit provides feedback control for the restart switch by monitoring the relay switching state and conditionally enabling the restart function. This ensures that restart operations are only permitted when the system is in a safe state, preventing accidental restarts while maintaining ease of operation when appropriate.
Solution Approach 2:
The control circuit implements preliminary anti-action by blocking restart operations when unsafe conditions are detected. This prevents potential harmful restart actions before they can occur, while still allowing free restart operation when the system is in a safe state.
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
This configuration achieves reliable and simple redundant switching, preventing accidental restarts and meeting high security levels like PLd of EN ISO 13849 without complex components, ensuring electrical safety and compliance with safety regulations.
Implementation Method 1
a first excitation coil of the first changeover relay is connected to the first connection and to the internal restart switch in such a way that a current flow through the first excitation coil
Data Source
Figure 1
Figure 2
AI summary
A switching arrangement (1) for safely switching an electrical load in accordance with a safety regulation, comprising: a first changeover relay (14), a first terminal (2) for a first safety switch, a second terminal (4) for an external restart switch, a third terminal (6) for an actuator, and a first internal restart switch (22), wherein a first excitation coil of the first changeover relay (14) is connected to the first terminal (2) and to the internal restart switch (22) in such a way that a current flow through the first excitation coil is only caused when the first safety switch is in a predetermined switching state and when the first internal restart switch (22) undergoes a switching operation, is intended to be suitable for higher safety levels and to do without mechanically complex or digital electronic components.For this purpose, a changeover switch of the first changeover relay (14), on which the first excitation coil acts, makes the third terminal (6) for the actuator conductive when the first excitation coil is energized and makes a conductive connection between the second terminal (4) for the external restart switch and the first internal restart switch (22) conductive when the first excitation coil is de-energized.