Bistable Relay Safety Circuit with Energy Storage
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Solution Overview
Problem
Bistable electromechanical relays are not suitable for safety technology due to their inability to meet safety integrity level (SIL) requirements, particularly in case of power supply failure, where they may not switch to a safe state, compromising safety functions in automation systems.
Innovation Solution
A switching device comprising a bistable relay, a control device, and a test device with an energy store that allows independent energy supply and cyclic testing, ensuring safe switching and automatic switching to a safe state in case of faults, thereby enhancing safety integrity level (SIL).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If bistable relays are used to reduce power consumption, then energy efficiency is improved, but failsafety cannot be guaranteed because the relay may not switch to a safe state upon power supply failure
Solution Approach 1:
The patent applies preliminary action by pre-charging a capacitor during normal operation before a fault occurs. The capacitor is charged to a voltage level sufficient to drive the relay coil when needed. In the event of power supply failure, this pre-charged capacitor immediately provides the necessary energy to switch the relay to a safe state, eliminating the need for continuous power supply while maintaining failsafety. This resolves the contradiction by preparing the energy storage in advance rather than relying on continuous power consumption.
Solution Approach 2:
The patent introduces a capacitor as an intermediary energy storage element between the power supply and the relay coil. This capacitor acts as a mediator that decouples the continuous power supply requirement from the relay switching operation. During normal operation, the capacitor is charged from the power supply; upon power failure, the capacitor discharges to drive the relay coil, ensuring safe state transition. This intermediary component enables the system to achieve both low power consumption and reliable failsafety.
2Reliability
If unipolar relays operated at rated power are used to ensure safety, then reliability is improved, but power consumption increases significantly
Solution Approach 1:
The patent applies periodic action by using intermittent charging of the capacitor instead of continuous power supply to the relay coil. The capacitor is charged periodically from the power supply during normal operation, maintaining sufficient voltage to drive the relay when needed. This periodic charging approach replaces the continuous rated power operation of traditional unipolar relays, significantly reducing average power consumption while maintaining the ability to switch to a safe state when required.
Solution Approach 2:
The patent extracts the energy storage function from the continuous power supply system and places it in a separate capacitor component. By taking out the energy storage requirement from the main power supply circuit, the system can operate the relay coil only when necessary (upon power failure or intentional switching), rather than requiring continuous rated power. This extraction of the energy storage function enables reduced power consumption while maintaining safety integrity.
3Use of energy by moving object
If bistable relays with auxiliary power supply are used to reduce holding power, then energy efficiency is improved, but device complexity increases due to additional power supply requirements
Solution Approach 1:
The patent applies universality by designing the capacitor to serve multiple functions: it acts as an energy storage element for reducing holding power, provides failsafety capability through immediate discharge upon power failure, and can be charged from the existing power supply without requiring a separate auxiliary power supply device. By making the capacitor multi-functional, the patent achieves energy efficiency and safety improvement without increasing device complexity through additional power supply circuitry.
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 enables bistable relays to be used in safety technology by ensuring they switch to a safe state during power failures, meeting SIL requirements and providing quasi-intrinsically safe properties, with a high diagnostic coverage of 99% as per European standard EN 61508-2.
Implementation Method 1
These bistable relays can, for example, switch from a first mechanically stable switching state to a second stable switching state by means of a time-limited signal pulse at the relay input
Implementation Method 2
EP 2 383 764 A1 shows a bistable relay with a coil arrangement and a movable armature for opening and closing contacts and with a permanent magnet with which the armature can be fixed in its position
Data Source
Figure 1
Figure 2
AI summary
The present invention relates to a switching device for providing safety-relevant functions in automation technology, comprising at least one buffered bistable electromechanical relay, and a test method for monitoring the switching device. The invention proposes a switching device (1) comprising a bistable relay (30), a control unit (10), an energy storage device (40), and a test unit (50). The bistable relay (30) has at least one output signal circuit (35, 36) and can be switched between two states depending on an input voltage signal (UE), with the control unit (10) being configured to control the relay (30). The energy storage device (40) serves to provide energy for at least one state change of the bistable relay (30). The test unit (50) is configured to test the functionality of the energy storage device (40).