Constant Current Metal Detector Feedback Control
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Solution Overview
Problem
Conventional pulse induction metal detectors face challenges with power efficiency and reduced sensitivity to fast decay metal targets due to delayed signal processing, which contaminates the receive signal with reactive components, and are not optimized for detecting small gold nuggets and fine gold chains effectively.
Innovation Solution
A metal detector design that incorporates negative feedback loops to maintain a constant average current during receive periods, allowing for reduced time constant of critical damping, thereby enabling detection of fast decay targets without signal contamination, and improving power efficiency by minimizing reactive voltage during transmit periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If delayed signal processing is used to avoid reactive component contamination, then receive signal purity is improved, but detection speed and sensitivity to fast decay targets deteriorate
Solution Approach 1:
The patent implements a feedback control system that monitors the transmit coil current and adjusts the reactive voltage compensation in real-time. This allows the system to maintain constant current during the receive period while actively canceling reactive components, enabling immediate signal processing without the traditional delay and thus resolving the contradiction between signal purity and detection speed
Solution Approach 2:
The patent dynamically changes the reactive voltage parameter during operation, switching from a fixed reactive voltage approach to a variable reactive voltage that is actively controlled to maintain constant current. This parameter change enables the system to eliminate reactive contamination while maintaining fast response capability for detecting small gold nuggets and fine gold chains
2Loss of energy
If reactive voltage is minimized during transmit periods, then power efficiency is improved, but transmit field strength may deteriorate
Solution Approach 1:
The feedback control system monitors current and adjusts reactive voltage to maintain optimal operating conditions, ensuring that reactive voltage is minimized only when necessary for power efficiency while maintaining adequate transmit field strength through active current control during the receive period
Solution Approach 2:
The patent employs periodic switching between transmit and receive modes with distinct voltage characteristics. During transmit periods, reactive voltage is applied to build current; during receive periods, reactive voltage is controlled to maintain constant current and minimize power loss, creating an optimized periodic cycle that balances field strength and power efficiency
3Measurement precision
If constant current is maintained during receive periods, then sensitivity to fast decay targets is improved, but device complexity increases
Solution Approach 1:
The patent implements a negative feedback loop that senses transmit coil current and automatically adjusts the reactive voltage to maintain constant current during the receive period. This feedback mechanism achieves constant current control without requiring complex manual intervention or multiple separate control systems, thereby improving sensitivity to fast decay targets while managing device complexity through an integrated control approach
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
The solution enhances the detection of fast decay targets by reducing signal contamination and improving power efficiency, allowing for more accurate detection of small gold nuggets and fine gold chains while maintaining high sensitivity and efficiency.
Implementation Method 1
a transmit coil having an inductance connected to the transmit electronics for receiving the repeating transmit signal cycle and generating a transmitted magnetic field
Implementation Method 2
a receive coil for receiving a received magnetic field during at least one receive period and providing a received signal induced by the received magnetic field
Data Source
AI summary
A metal detector transmitting, through a transmit coil, a repeating transmit signal cycle, which includes at least one receive period and at least one non-zero transmit coil reactive voltage period; and sensing a current in the transmit coil during at least one receive period to control a magnitude and/or duration of the at least one non-zero transmit coil reactive voltage period such that the average value of the current during at least one receive period of every repeating transmit signal cycle is substantially constant from cycle to cycle, and the current during at least one receive period is substantially independent of the inductance of the transmit coil.