Metal Detector Phase Shift Circuit Sampling Ferrite Detection
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Solution Overview
Problem
Existing metal detectors using inductively coupled sensors face challenges with calibration stability and high processing demands, requiring expensive DSP processors and user calibration before each use.
Innovation Solution
A metal detector with a phase shift circuit and electronic storage for calibration information, allowing for synchronized sampling of the amplitude of the phase-shifted output signal, enabling a conventional microprocessor to determine object presence and distance without pre-use calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the whole waveform is recorded and changes are calculated at every point on the waveform, then the detection accuracy is improved, but the processing overhead increases considerably requiring expensive DSP processors
Solution Approach 1:
The patent extracts only the essential information needed for detection by using synchronized sampling at specific phases rather than processing the entire waveform. The sampling switch samples the receiver coil signal at predetermined phases synchronized with the transmitter coil excitation, extracting only the relevant amplitude information while discarding unnecessary waveform data, thereby reducing processing requirements.
Solution Approach 2:
Instead of processing the complete waveform, the patent applies partial action by sampling only at specific critical phases of the waveform that contain the necessary detection information. The sampling switch operates at predetermined phases synchronized with the excitation signal, performing partial sampling that is sufficient for detection purposes without the excessive processing of the entire waveform.
2Reliability
If user calibration or automatic calibration is performed immediately prior to each use, then calibration stability is improved, but the device complexity and calibration delay increase
Solution Approach 1:
The patent applies preliminary action by performing calibration once during manufacturing rather than requiring calibration before each use. The calibration information is stored in memory during the manufacturing process, and this pre-stored calibration data is then used during normal operation without requiring additional calibration steps, thereby eliminating calibration delay and reducing device complexity.
3Measurement precision
If the whole waveform is recorded for analysis, then the detection precision is improved, but the calibration delay increases
Solution Approach 1:
The patent extracts only the essential detection information by sampling the waveform at specific synchronized phases rather than recording and analyzing the entire waveform. This extraction approach maintains detection precision by focusing on the critical phases where object presence information is encoded, while significantly reducing the time required for calibration and analysis.
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 reduces processing overhead, eliminates the need for expensive DSP chips, and allows for accurate detection of ferrite and non-ferrite objects without user calibration, enhancing usability and reducing manufacturing complexity.
Implementation Method 1
The transmitter coil is excited with a periodically varying excitation signal which produces and alternating magnetic field
Implementation Method 2
The magnetic field induces a sensor signal in the receiver coil
Data Source
AI summary
A metal detector for detecting the presence of a ferrite object in the proximity of inductively coupled sensor having overlapping D shaped transmitter and receiver coils. The metal detector has a phase shift circuit to phase shifting a sensor output signal by a known amount and a switch operating in synchronization with an excitation signal of the sensor for sampling the amplitude of the phase shifted output signal.