Multi-Frequency Metal Detector Drive Control With Reduced Harmonics
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Solution Overview
Problem
Current multi-frequency metal detectors face challenges in efficiently detecting metal contaminants due to the generation of high energy harmonics and the need for complex filtering circuitry, which increases costs and reduces sensitivity.
Innovation Solution
A method and apparatus for generating a multi-frequency drive signal with selectable frequency components using a converter with drive switches controlled by a drive controller, producing a pulse sequence signal that maximizes coil current while minimizing transmitter currents, and utilizing an admittance unit with resonant circuits to enhance sensitivity and reduce noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a multi-frequency drive signal is generated using conventional filtering circuitry to remove harmonics, then the sensitivity for metal contaminant detection is improved, but the device complexity and cost increase
Solution Approach 1:
The patent extracts only the necessary frequency components (fundamental frequency and selected harmonics) using a frequency selector that chooses specific switching periods, rather than attempting to filter out all unwanted harmonics. This selective extraction approach eliminates the need for complex filtering circuitry while maintaining detection sensitivity.
Solution Approach 2:
The patent performs preliminary selection of frequency components by configuring the drive circuit to generate specific harmonics in advance through controlled switching periods. The frequency selector pre-determines which frequency components to include before detection, avoiding the need for post-generation filtering.
2Measurement precision
If the drive coil is driven at high current to improve detection sensitivity, then the sensitivity for metal contaminant detection is improved, but the transmitter power consumption increases
Solution Approach 1:
The patent employs periodic switching action with variable switching periods to generate the desired multi-frequency signal. By controlling the switching period, the system can generate specific frequency components including harmonics without requiring continuous high-power transmission, thus reducing overall power consumption while maintaining detection sensitivity.
Solution Approach 2:
The patent dynamically adjusts the switching period to generate different frequency components as needed. This dynamic control allows the system to optimize power consumption by generating only the necessary frequency components at the required moments, rather than continuously transmitting at high power.
3Adaptability or versatility
If multiple frequency components are used to detect different types of metal contaminants, then the adaptability for detecting various contaminants is improved, but the device complexity increases
Solution Approach 1:
The patent makes the drive circuit universal by enabling it to generate multiple frequency components including fundamental frequency and various harmonics through a single configurable switching mechanism. The frequency selector allows one circuit to perform multiple functions by selecting different switching periods, eliminating the need for separate circuits for each frequency.
Solution Approach 2:
The patent uses dynamic control of the switching period to generate different frequency components on demand. This dynamic capability allows a single circuit to adapt to different detection requirements for various metal contaminants without requiring multiple fixed-frequency circuits, thus maintaining simplicity while achieving versatility.
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 allows for flexible operation across a wide range of products and contaminants, reducing costs and improving sensitivity by maximizing coil currents while minimizing transmitter power and complexity.
Implementation Method 1
a drive coil (L61) connected to an output of the transmitter unit (10) and designed for producing an electromagnetic field in a product
Implementation Method 2
at least one detection coil arranged for detecting fluctuations in the magnetic field caused by metallic particles present in the product
Implementation Method 3
an admittance unit (5) connected between the converter (4) and the drive coil (L61), comprising resonant circuits which are individually tuneable to frequency components of the drive signal
Data Source
Figure 1a
Figure 1b
Figure 2
AI summary
Method for operating a metal detector (1), which comprises a drive coil (L61) for producing an electromagnetic field in a product, and at least one detection coil (L62, L63) arranged to detect fluctuations in the magnetic field caused by metallic particles present in the product, and a multifrequency transmitter unit (10) comprising a converter (4) with a plurality of drive switches (S41, S42; S43, S44) driven by a drive controller (2) according to operating instructions such, that the drive switches (S41, S42; S43, S44) alternately conduct a drive current (iD) through the drive coil (L61) so that the generated electromagnetic field exhibits two or more different frequency components (fD1, fD2); comprising the steps of: - determining a waveform of the drive current (iD) for the at least two different frequency components (fD1, fD2); - determining at least one pulse-width modulated or pulse-density modulated PXM-signal (SPXM) corresponding to the determined waveform of the drive current (iD); - PXM-signalPXM according to the operating instructions provided selecting the at least one determined PXM-signal (SPXM) which is determined online or stored in a memory module (231; 232) ; and - generating and applying the determined PXM-signal (SPXM) to control the drive switches (S41, S42; S43, S44). The inventive metal detector (1) therefore allows selecting at least one stored PXM-signal (SPXM) stored in the drive controller (2) with which a drive current (iD) can be generated with at least two different frequency components (fD1, fD2), which drive current (iD) is applied directly or via an admittance unit (5) to the drive coil (L61).