Safety Switching Device Overvoltage Protection Self-Test
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Solution Overview
Problem
Existing safety switching devices are not effectively protected against overvoltages, and their protective mechanisms cannot be checked during operation, posing risks to safety and compliance with safety standards.
Innovation Solution
A safety switching device with a clamping circuit-based overvoltage protection system, featuring two series-connected switching elements and a reference point for voltage monitoring, allows for continuous functionality checking without disrupting the system, ensuring safe disconnection in case of overvoltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If clamping circuits with fuses are used for overvoltage protection, then the power supply is reliably interrupted, but the functionality can only be checked by actually shorting the input and blowing the fuse
Solution Approach 1:
The system includes a self-test capability where the control unit periodically activates the protection circuit through the monitoring circuit without requiring external intervention. The system tests its own protection functionality by simulating overvoltage conditions and verifying the tripping mechanism, enabling continuous self-verification without fuse replacement or external shorting
Solution Approach 2:
The monitoring circuit provides continuous feedback about the protection circuit's functionality to the control unit. The control unit receives status information and can trigger test sequences that verify the clamping circuit responds correctly to overvoltage conditions, allowing functionality checking during normal operation without disrupting the power supply
2Reliability
If safety switching devices are designed to meet high safety standards like PL e or SIL 3, then safety and reliability are improved, but the complexity and cost of the device increase
Solution Approach 1:
The monitoring circuit serves multiple functions: it monitors output voltage for overvoltage detection, tests protection circuit functionality, and provides feedback to the control unit. This multi-functionality reduces the need for separate dedicated circuits for each function, maintaining high safety standards while limiting complexity growth
Solution Approach 2:
The invention combines the overvoltage protection circuit, monitoring circuit, and test circuit into a single integrated power pack unit. By merging these functions into one cohesive system with shared components where possible, the design achieves the functional requirements for PL e or SIL 3 certification without the complexity of completely separate systems
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 effective protection against overvoltages, enables continuous safety function checking during operation, and meets high safety standards like PL e or SIL 3, ensuring the system's safety and reliability while being cost-effective.
Implementation Method 1
a first and a second switching element (54, 56) connected in series connecting an input (58) of the power supply unit (50) to a ground connection (60)
Implementation Method 2
an interrupter element (62) in the supply line (52), which trips when the first and the second switching element (54, 56) is in the low-impedance state
Implementation Method 3
a reference point (64) being arranged between the first and the second switching element (54, 56), which has a voltage value which, when the first switching element (54) is in the closed, low-impedance state and the second switching element (56) is in the open state, has a first defined expected value
Data Source
Figure 1
Figure 2~2a
Figure 3
AI summary
A safety switching device (10) for failsafe switching on and off of a technical installation (11) has an input (24) for picking up an input signal and a failsafe control/evaluation unit (28) which processes the input signal and generates as a function thereof an output signal for switching the technical installation (11) on and off. The safety switching device also has a power supply unit (50) having an earth terminal (60) for making available at least one operating voltage for the control/evaluation unit (28), wherein the power supply unit (50) picks up an input voltage via a feed line (52) and makes available a defined output voltage on the output side. The power supply to the power supply unit (50) is interrupted if the instantaneous output voltage is higher than the defined output voltage. The interruption takes place in that a first and a second switching element (54, 56) which are connected in series connect the input (58) of the power supply unit to ground (60), and by means of an interrupter element (62) in the feed line (52), which interrupter element (62) triggers when the first and second switching elements (54, 56) are in the closed, low-impedance state. Arranged between the first and the second switching elements (54, 56) is a reference point (64) which has a voltage value which is a first anticipated value (66) when the first switching element (54) is in the closed, low-impedance state and the second switching element (56) is in the open state, and a second anticipated value (68) when the first switching element (54) is in the open state and the second switching element (56) is in the closed, low-impedance state.