Antenna-Based Switching State Detection for Safety Relays
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Solution Overview
Problem
Safety switching devices used in industrial systems to protect personnel from electrical machines face challenges in reliably detecting the switching state of switching elements, particularly due to issues like contact welding in relays and semiconductor breakdown, which can lead to incomplete power supply interruption.
Innovation Solution
A safety switching device with an electrical switching element and a monitoring unit using two antennas on different layers of a printed circuit board to determine the switching state through radio transmission of a test signal, allowing for reliable and cost-effective detection of the switching state, including the use of HF or LF signals and resonant frequency changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If forcibly guided relays are used to ensure reliable switching off, then the reliability of switching off is improved, but the device becomes more expensive and larger
Solution Approach 1:
The patent replaces mechanical contact-based switching with a semiconductor switching element (MOSFET or IGBT) that is controlled by gate signals. This substitution eliminates the need for mechanically forced-guided contacts while achieving reliable switching through electronic control and monitoring of the semiconductor device's state.
Solution Approach 2:
The patent introduces an intermediary monitoring circuit that uses capacitive coupling to detect the actual switching state of the semiconductor element. This intermediary system provides reliable state detection without requiring direct mechanical contact or complex forcing mechanisms, thereby maintaining reliability while reducing device complexity.
2Device complexity
If conventional relays are used to reduce cost and size, then device complexity is reduced, but the reliability of switching off deteriorates due to contact welding
Solution Approach 1:
The patent implements a feedback mechanism where the monitoring circuit continuously detects the actual switching state of the semiconductor element and provides this information back to the control system. This feedback allows the system to verify that the switching element has actually opened, preventing undetected contact welding scenarios that plague conventional relays.
Solution Approach 2:
The patent replaces mechanical relay contacts with a semiconductor switching element whose state can be monitored through electrical fields rather than mechanical contact inspection. This substitution eliminates the contact welding problem inherent in mechanical relays while maintaining cost-effectiveness and compact size.
3Device complexity
If semiconductor switching elements are used to reduce size and cost, then device complexity is reduced, but the reliability deteriorates due to semiconductor breakdown
Solution Approach 1:
The patent introduces an intermediary capacitive coupling system between the semiconductor switching element and the monitoring circuit. This intermediary allows the monitoring of the semiconductor's switching state through electrical field changes without requiring direct electrical connection, enabling detection of breakdown conditions while maintaining the benefits of semiconductor technology.
Solution Approach 2:
The monitoring circuit provides continuous feedback on the actual state of the semiconductor switching element by detecting changes in the test signal caused by capacitive coupling. This feedback mechanism enables the system to detect semiconductor breakdown or failure modes that would prevent proper switching off, thereby maintaining reliability despite using compact semiconductor devices.
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
Enables reliable and economical detection of the switching state, preventing errors such as contact welding, while ensuring the power supply can be accurately interrupted, meeting safety standards like SIL3.
Implementation Method 1
a first antenna (24), by means of which a test signal (26) is emitted; a second antenna (28) which receives the test signal (26)
Implementation Method 2
The actual switching state can be determined in particular on the basis of a resonant frequency of the oscillating circuit (38)
Data Source
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AI summary
The invention relates to a safety switching device for switching an electrical load, in particular an electric machine, which can be connected to the switching device, comprising: - an electrical switching element which can have the switching states closed and open in order to selectively close or interrupt a power supply path of the electrical load, - a monitoring unit which determines an actual switching state of the electrical switching element, wherein the monitoring unit comprises a first antenna by means of which a test signal is emitted, - a second antenna which receives the test signal, wherein the second antenna is coupled to the electrical switching element in such a way that the actual switching state of the electrical switching element influences the test signal, wherein the monitoring unit is configured to determine the actual switching state from the influenced test signal.