Magnetron Anode Current Monitoring for Microwave Overheat Detection
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Solution Overview
Problem
Existing high-frequency heating apparatuses, such as microwave ovens, face challenges in accurately detecting the operating state, particularly in empty or overheating conditions, leading to potential thermal breakdown of components like the magnetron and high-voltage diodes, due to inadequate temperature detection accuracy and sensitivity.
Innovation Solution
A state detection device that monitors the anode current of the magnetron, using a combination of threshold value control and changing value detection control based on multiple readings over a predetermined time period to determine the operating state, thereby preventing abnormal operating conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a thermistor is placed near the magnetron to detect temperature, then the temperature detection capability is improved, but the detection accuracy and sensitivity remain insufficient to prevent thermal breakdown
Solution Approach 1:
The patent replaces the mechanical/physical temperature sensing method (thermistor placement) with an electrical parameter detection method. By monitoring the anode current of the magnetron, the system indirectly detects temperature conditions and abnormal operating states. This substitution provides more accurate and sensitive detection of overheating conditions compared to physical thermistor placement.
Solution Approach 2:
The patent introduces an intermediary detection approach where the anode current serves as a mediator to indicate the thermal state of the magnetron. Instead of directly measuring temperature with a thermistor, the system uses the anode current as an intermediary parameter that correlates with temperature and provides earlier, more accurate warning of thermal breakdown conditions.
2Reliability
If multiple detection methods are implemented to improve detection accuracy, then the reliability of abnormal state detection is improved, but the device complexity increases
Solution Approach 1:
The patent makes the existing anode current detection circuit perform multiple functions. The same current detection mechanism is used both for normal operating control and for detecting abnormal states such as empty heating and overheating. This multi-functionality improves detection reliability without requiring separate dedicated detection systems, thereby avoiding increased device complexity.
Solution Approach 2:
The patent combines the abnormal state detection function with the existing current detection and control system. By merging the temperature monitoring function into the anode current detection circuitry, the system achieves reliable abnormal state detection without adding separate complex detection hardware, thus maintaining simplicity while improving reliability.
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 approach enhances the accuracy of detecting abnormal states like empty heating or overheating, reducing the risk of component damage and ensuring safe operation by continuously monitoring the anode current and adjusting the apparatus's output accordingly.
Implementation Method 1
a magnetron 12... generating microwaves
Implementation Method 2
the AC power from a commercial power supply 11 is rectified into a DC current by a rectifying circuit 13
Implementation Method 3
The DC current is converted into a current of a desired high-frequency (20 to 40kHz) by the on/off operation of the semiconductor switching elements within the inverter 16
Implementation Method 4
a primary winding 181 is applied with a high-frequency voltage outputted from the inverter 16 and a secondary winding 182 is applied with a high voltage in accordance with a winding ratio
Implementation Method 5
The secondary winding 182 of the boosting transformer 18 is provided with a voltage doubler rectifying circuit 19 for rectifying the output of the secondary winding
Implementation Method 6
high-frequency heating apparatus... a magnetron 12 for generating microwaves
Data Source
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AI summary
An operating state detection technique is provided which makes it possible to accurately detect an abnormality of a high-frequency heating apparatus. An anode current detected by the anode current detection resistor 40 of a magnetron is inputted into the A/D converter terminal of a microcomputer 27 on a control panel circuit board side. The current is subjected to an analog-to-digital conversion to thereby obtain an anode voltage IaDC value. The microcomputer 27 determines an operating state based on a plurality of the anode voltage IaDC values thus read. Further, the microcomputer 27 obtains a summed value of the IaDC values corresponding to one period of the revolution of rotary antennas 68, 69 to thereby determines the operating state of the high-frequency heating apparatus 100 based on the summed value. According to the aforesaid IaDC value reading method, it makes it possible to accurately detect an abnormality without an erroneous operation also in correspondence to the change of the feeding distribution. Further, the microcomputer 27 changes, in accordance with the set output of the high-frequency heating apparatus, a threshold value used for determining the abnormality and a changing value (increasing amount) from the start of the operation with respect to the change of the output of the apparatus and the operating state of a heated subject etc., whereby it makes it possible to accurately detect an abnormality without an erroneous operation.