Open-Loop Current Sensor with Dual Detectors for Fast Response
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Solution Overview
Problem
Conventional open-loop current sensors suffer from slow signal response times due to eddy currents in magnetic circuits and electronic components, limiting their frequency range and requiring costly redesigns for optimal performance in applications like motor control systems.
Innovation Solution
An open-loop current sensor design featuring a magnetic circuit with an air-gap and dual magnetic field detectors, including a Hall effect sensor integrated in an ASIC and a conductive coil on a printed circuit board, allowing for adaptable configuration and enhanced sensitivity through interconnected coil portions on different layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional open-loop current sensors use a magnetic circuit made of ferromagnetic materials (iron silicon, iron nickel) to concentrate magnetic flux, then the magnetic induction in the air-gap is proportional to the primary current, but eddy currents in these materials cause delay in the signal response time
Solution Approach 1:
The patent extracts the magnetic field detection function from the conventional integrated ASIC and implements it using discrete magnetic field sensors positioned in the air-gap. This separation allows the magnetic circuit to be optimized for rapid response using non-conductive materials while maintaining accurate magnetic flux concentration, thereby reducing eddy current delays while preserving measurement precision
Solution Approach 2:
The patent changes the electrical conductivity parameter of the magnetic circuit material by using non-conductive or low-conductivity materials (such as ferrite or composite materials) instead of conventional high-conductivity ferromagnetic materials. This parameter change reduces eddy current formation and associated signal delays while maintaining sufficient magnetic flux concentration through the air-gap
2Loss of time
If ferrite materials are used to reduce eddy currents in the magnetic circuit, then the response time delay is reduced, but the materials saturate rapidly and have high remanence
Solution Approach 1:
The patent segments the magnetic circuit into distinct functional zones: a magnetic flux concentration path using ferrite or composite materials for rapid response, and discrete magnetic field sensors positioned in the air-gap for accurate detection. This segmentation allows each component to be optimized independently, mitigating the saturation and remanence issues of ferrite materials through proper design of the magnetic path and air-gap geometry
3Productivity
If multiple magnetic field detectors operating over different frequency ranges are used to increase operational bandwidth, then the frequency range is extended, but the device complexity increases and requires costly redesign
Solution Approach 1:
The patent implements a universal magnetic field sensing platform using discrete sensors that can detect magnetic fields across a broad frequency range. The modular architecture with sensors positioned in the air-gap allows the same basic configuration to serve multiple frequency ranges and application requirements, eliminating the need for costly redesigns while maintaining extended operational bandwidth
4Loss of time
If discrete magnetic field sensors are used instead of integrated ASIC to reduce signal processing delay, then the response time is improved, but the device complexity and manufacturing cost increase
Solution Approach 1:
The patent uses discrete magnetic field sensors that can be positioned and configured to replicate the magnetic field detection function of integrated ASIC sensors. This approach allows for easier manufacturing and adaptation while maintaining the rapid response characteristics, as discrete sensors can be independently selected and positioned without requiring complex integrated circuit fabrication processes
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 design achieves rapid response times, improved sensitivity, and cost-effective adaptability for various applications, with signal processing that maintains low power consumption and compactness, suitable for high-frequency applications like motor control systems.
Implementation Method 1
A commonly used magnetic field detector is a Hall effect sensor provided in an ASIC. The magnetic flux created by the primary current is concentrated in the magnetic circuit, whereby a magnetic induction B in the air-gap is proportional to the primary current. The Hall cell furnishes a voltage proportional to the magnetic induction in the air-gap
Implementation Method 2
a second magnetic field detector, which comprises a conductive coil formed on the circuit board
Implementation Method 3
Eddy currents oppose the variation of magnetic flux thus causing a delay in the magnetic induction appearing in the air-gap. The ferromagnetic materials (iron silicon, iron nickel) often used for magnetic circuits built of stacked laminations, are relatively good electrical conductors thus providing little resistance to eddy currents
Data Source
Figure 1
Figure 2a~3c
Figure 4~5
AI summary
Open-loop electrical current sensor (1) for measuring the electrical current flowing in a primary conductor, comprising a magnetic circuit (3) with an air-gap (4), and a magnetic field sensing device (5) positioned at least partially in said air-gap. The magnetic field sensing device comprises a circuit board (7), a first magnetic field detector (8) mounted on the circuit board, and a second magnetic field detector (11). The second magnetic field detector comprises a conductive coil formed on the circuit board, the output signals of the first magnetic field detector and the second magnetic field detector being adapted for connection to a signal processing circuit (6) generating an output signal representative of the primary electrical current.