Inductive Metal Detection Sensor Using Frequency Domain Multiplexing
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Solution Overview
Problem
Existing metal detection systems struggle to distinguish a specific metal object from other metal objects and dielectrics in close proximity, particularly in high-pressure waterblasting applications, leading to interference and slow response times.
Innovation Solution
Utilizing inductive sensors with axially aligned transmit and receive coils, operating at lower frequencies below 30 kHz, and employing frequency domain multiplexing to separate signals, allowing for precise detection of metal objects while ignoring dielectrics like water, with each coil set excited at distinct frequencies to minimize cross-talk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If time domain multiplexing with high frequency transmit signals is used, then response time is maintained sufficient, but dielectrics like water are detected which obscures the ability to distinguish metal from other objects
Solution Approach 1:
The patent changes the frequency parameter of the transmit signals from high frequency (used in traditional time domain multiplexing) to lower frequencies below 30 kHz. This parameter change allows the system to avoid detecting dielectrics like water while still maintaining sufficient response time, thereby resolving the contradiction between response speed and detection accuracy
Solution Approach 2:
The patent employs periodic excitation of transmit coils at distinct frequencies, allowing each coil set to be activated in a periodic manner. This periodic action at lower frequencies enables frequency domain multiplexing to separate the signals, achieving both adequate response time and improved metal detection precision by excluding dielectric interference
2Area of stationary object
If multiple coil sets are placed in tight physical proximity, then detection coverage is improved, but cross talk between coil sets occurs
Solution Approach 1:
The patent transitions from time domain multiplexing to frequency domain multiplexing, adding a frequency dimension to the signal separation process. By assigning distinct frequencies to each coil set and processing signals in the frequency domain, the system can place multiple coil sets in tight physical proximity for improved coverage while eliminating cross-talk through frequency-based signal separation
Solution Approach 2:
The patent changes the operating parameter from time-domain sequencing to frequency-domain differentiation. Each transmit coil is excited at a distinct frequency, and the receive coils detect signals that are then separated via frequency domain multiplexing. This parameter change allows multiple coil sets to operate simultaneously in close proximity without mutual interference, improving detection coverage while preventing signal cross-contamination
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 rapid and accurate discrimination of metal objects from other materials and detectors in close proximity, maintaining quick response times and reducing interference from dielectrics.
Implementation Method 1
Each coil set contains a transmit coil and a receive coil, separated by a spacer or wear ring. The transmit coils are electromagnetically excited by electrical current waveforms or signals at different frequencies. The receive coils sense these current waveforms or signals.
Data Source
AI summary
A system for distinguishing target metal objects from each other in close proximity to each other. The method includes transmitting a first sinusoid signal via a first transmit coil to a first receive coil in close proximity to the first transmit coil; transmitting a second sinusoidal signal at a second frequency and amplitude different from the first frequency and amplitude to a second receive coil arranged in close proximity to the second transmit coil and in close proximity to the first receive coil such that received signals in the first and second receive coils include first and second frequency signals from the other of the first and second transmit coils. The received signals are separated via frequency domain multiplexing. The signals are compared to detect a presence of the target having a signal magnitude different from the first received signal and the received second signal and a known reference point.