Magnetic Intrusion Detection in Switch Mode Power Supply Meters
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Solution Overview
Problem
Consumption meters, such as electric, gas, heat, and water meters, are vulnerable to strong external magnetic fields, which can cause malfunction and erroneous readings, and existing magnetic field detection methods often fail to accurately detect intrusions due to the physical separation of detectors from the inductive components, leading to potential meter failure.
Innovation Solution
A consumption meter equipped with a magnetic field detector that senses the magnetic field related to the switching operation of the switch mode power supply, specifically positioned near inductive elements like transformers, allowing for precise detection of critical magnetic intrusions by monitoring frequency components characteristic of the switching operation, and includes a control circuit to initiate actions such as power reduction or alarm signals in response to detected intrusions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Hall sensor or reed relay is used to detect magnetic fields, then the meter can detect magnetic intrusion, but the detector is physically separated from the inductive component causing false detection
Solution Approach 1:
The detector coil is integrated with the transformer core, forming a single unified structure where the detector coil is wound around the same core as the transformer. This merging eliminates the physical separation problem, ensuring that the detector measures the exact magnetic field affecting the inductive component while maintaining high detection reliability.
2Reliability
If a strong external magnetic field is applied to the meter, then the transformer and coil effects are destroyed causing power supply failure, but the meter should maintain magnetic immunity
Solution Approach 1:
The detector coil continuously monitors the magnetic field around the transformer core and provides feedback to the control circuit. When magnetic intrusion is detected, the control circuit responds by switching to an alternative power supply mode or activating protection mechanisms, thereby maintaining meter reliability despite the presence of strong external magnetic fields.
Solution Approach 2:
The detector coil is positioned to detect magnetic field changes before they reach critical levels that would destroy the transformer and coil effects. By detecting the magnetic intrusion early, the system can take preliminary protective actions to prevent power supply failure and maintain magnetic immunity.
3Device complexity
If the detector coil is positioned far from the transformer, then the device complexity is reduced, but the detection accuracy decreases
Solution Approach 1:
The detector coil is integrated with the transformer core structure, wound around the same core in close proximity. This merging achieves the optimal detection precision by placing the detector exactly where the magnetic field is most intense, while the integration into the core structure actually simplifies the overall device assembly rather than increasing complexity.
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 solution provides a high degree of security in detecting magnetic intrusions, ensuring the vital meter functions are maintained by reducing power consumption and enabling accurate measurement of consumed quantities, while allowing for remote monitoring and provider intervention.
Implementation Method 1
A detector coil of electrically inductive material is arranged in relation to the switch mode power supply so as to sense a magnetic field related to the switching operation of the switch mode power supply
Data Source
Figure 1~2
Figure 3
AI summary
A consumption meter having a magnet detector to be able to detect magnetic intrusion. The meter includes a measurement circuit (MC) and a calculator circuit (CA) which are both powered by a switch mode power supply (PS) operating according to an electric switching scheme typically characterized by certain switching frequency components. A detector coil (C), preferably an air coil, is arranged in relation to the switch mode power supply (PS) so as to sense a magnetic field (M) related to the switching operation of the switch mode power supply, e.g. a magnetic field (M) in a frequency range including at least some of the characteristic switching frequency components. The detector coil (C) is preferably positioned near an inductive element, e.g. a transformer (T), of the power supply (PS) to catch an increase in the magnetic field (M) from the transformer (T) caused by magnetic intrusion. A detector circuit (DC) detects a change in the electric signal from the detector coil (C). With this approach, a magnetic intrusion effect on the power supply (PS) is detected rather than detecting a magnetic field from an unknown intruding magnet. Hereby it is possible to catch every attempt to magnetically destroy the function of power supply (PS) and thereby destroy the vital meter function. Based on an output from the detector circuit (DC) an appropriate action can be initiated by the meter, e.g. by means of a control circuit (CC) serving to switch off power supply to non-vital circuits in the meter, such as a radio transmitter (RFT), when magnetic intrusion is detected. The detector circuit (DC) can be implemented by means of simple comparator circuits serving to compare the electric output of the detector coil (C) with a threshold value.