Leakage Current Clamp With Flux Cancellation and Magnetic Shielding
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Solution Overview
Problem
Existing current measurement clamps struggle to accurately measure low-value AC and DC leakage currents while effectively rejecting external magnetic fields and require complex factory adjustments for sensor balancing.
Innovation Solution
A clamp design featuring magnetic cores shielded by Mu-metal, with flux-cancellation coils and AMR sensors, allows for independent sensor balancing and effective rejection of external magnetic fields, using two opposing magnetic fields to cancel stray flux and incorporate test coils for saturation detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Hall effect sensors are used for DC current measurement, then the clamp can measure DC currents, but the sensors are too noisy to measure very low leakage currents (100 μA) in the presence of large currents (10 A)
Solution Approach 1:
The magnetic shield is divided into two separate half-shields, each surrounding one magnetic core. This segmentation allows independent optimization of each shield-sensor assembly and enables localized flux cancellation without interfering with the other sensor's measurement, thereby reducing noise from external magnetic fields while maintaining the ability to measure low leakage currents.
Solution Approach 2:
A flux-cancellation coil is introduced as an intermediary element between the external magnetic fields and the magnetic sensors. This coil generates opposing magnetic fields that cancel out stray flux from external sources, creating a controlled electromagnetic environment that allows sensitive AMR sensors to measure low currents without being overwhelmed by noise from adjacent conductors.
2Object-affected harmful factors
If flux-cancellation coil is placed inside the magnetic shield, then flux cancellation is effective, but the sensor balancing with regard to external magnetic fields cannot be performed
Solution Approach 1:
The flux-cancellation coil is extracted from the interior of the magnetic shield and repositioned to the exterior, surrounding one or both half-shields. This extraction allows the coil to generate magnetic fields that cancel stray flux from external sources while enabling independent access to each magnetic core for sensor balancing. The coil can be adjusted to compensate for external magnetic fields without constraining the sensor calibration process.
3Object-affected harmful factors
If magnetic sensors are balanced at the factory using Helmholtz coil, then external magnetic field rejection is achieved, but the operator cannot perform balancing alone without sending back to factory
Solution Approach 1:
The clamp is designed with self-balancing capability through the external flux-cancellation coil configuration. The operator can perform sensor balancing independently by adjusting the coil's position or current to compensate for external magnetic fields, eliminating the need for factory calibration. The dual half-shield structure enables the operator to balance each sensor individually using the external coil, making the system self-sufficient for field calibration.
4Object-affected harmful factors
If flux-cancellation coil surrounds both half-shields, then external magnetic field cancellation is maximized, but the complexity of the device increases
Solution Approach 1:
Instead of requiring a complex multi-turn coil system, the invention uses a simple single-turn or few-turn flux-cancellation coil that generates sufficient opposing magnetic fields through high current density. The coil is positioned to surround one or both half-shields, and its effectiveness is achieved through strategic placement rather than excessive complexity. This partial action approach provides adequate flux cancellation while keeping the device structure simple and manufacturable.
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 reliable measurement of low-value AC and DC leakage currents with high rejection of external magnetic fields, allowing operator-adjusted sensor balancing without factory intervention.
Implementation Method 1
the first and second magnetic cores being separated by two diametrically opposite air gaps each receiving a magnetic flux sensor
Implementation Method 2
a flux-cancellation coil surrounding one or the other, or both, of the first and second magnetic shields
Implementation Method 3
the fixed jaw comprises a first magnetic core entirely surrounded by a first magnetic shield and the moving jaw comprises a second magnetic core entirely surrounded by a second magnetic shield
Data Source
AI summary
The invention relates to a measurement clamp comprising a fixed jaw and a moving jaw, the fixed jaw comprising a first magnetic core entirely surrounded by a first magnetic shield and the moving jaw comprising a second magnetic core entirely surrounded by a second magnetic shield, the first and second magnetic cores being separated by two diametrically opposite air gaps each receiving a magnetic flux sensor, and an external flux-cancellation coil surrounds one or the other, or both, of the first and second magnetic shield.