Magnetic Field Sensor Misalignment Compensation for Ground Fault Detection

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Solution Overview

Problem

Conventional ground fault interrupter (GFI) devices are bulky and expensive due to their reliance on differential current transformers, which require costly and complex assembly of phase and neutral wires.

Innovation Solution

A high accuracy differential current sensor using an arrangement of magnetic field sensing elements, such as Hall-effect or magnetoresistive sensors, integrated on a common substrate, which measures current differences and absolute currents, allowing for a compact, low-cost, and programmable solution with misalignment compensation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a differential current transformer is used to detect current imbalance in GFI devices, then the device can reliably detect ground faults, but the device becomes bulky and expensive

Engineering Contradiction:

Improveground fault detection reliabilityVSAvoiddevice size and cost

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent extracts the magnetic field sensing function from the bulky differential current transformer and implements it using integrated magnetic field sensing elements (such as Hall-effect sensors or magnetoresistive sensors) on a single chip. This extraction allows the device to maintain ground fault detection capability while dramatically reducing size and cost by eliminating the need for a large transformer assembly.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent replaces the mechanical/differential transformer-based current sensing system with a magnetic field sensing system using Hall-effect or magnetoresistive sensors. This substitution enables the same ground fault detection function to be achieved with a compact, integrated circuit solution rather than a bulky electromagnetic transformer assembly.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If multiple magnetic field sensing elements are used to compensate for misalignment, then measurement accuracy is improved, but device complexity increases

Engineering Contradiction:

Improvecurrent measurement accuracyVSAvoidsensing element arrangement complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent combines multiple magnetic field sensing elements (at least three elements arranged in a specific geometric pattern) on a single integrated circuit substrate. By merging these elements and their associated circuitry into one compact IC, the device achieves misalignment compensation capability without proportionally increasing overall device complexity or size.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent designs the sensing element arrangement to serve multiple functions: the same set of magnetic field sensing elements is used both for normal current measurement and for detecting misalignment conditions. This multi-functionality allows the device to compensate for misalignment without requiring separate dedicated components, thereby improving measurement accuracy without linearly increasing device complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 sensor provides accurate differential current measurement with reduced component and assembly costs, enabling miniaturization and easier integration into GFI modules, while also offering redundancy and additional sensing capabilities like linear position and angle sensing.

Implementation Method 1

Each of the magnetic field sensing elements can be a selected one of a Hall-effect sensing element and a magnetoresistive sensing element

Methodology Applied

Scientific EffectHall-effect: Hall Effect

Implementation Method 2

Each of the magnetic field sensing elements can be a selected one of a Hall-effect sensing element and a magnetoresistive sensing element

Methodology Applied

Scientific EffectMagnetoresistive sensing: Magnetoresistance

Data Source

PatentUS8896295B2Magnetic field sensor having multiple sensing elements and a programmable misalignment adjustment device for misalignment detection and correction in current sensing and other applications

Publication Date: 2014.11.25 ALLEGRO MICROSYSTEMS LLC

AI summary

A sensor with multiple magnetic field sensing elements for use in current sensing and other applications is presented. The sensor includes an arrangement of two or more magnetic field sensing elements to sense magnetic field associated with a target. The sensor further includes circuitry to generate a sensor output signal based on sensing of at least one of the magnetic field sensing elements of the arrangement. Also included is a programmable misalignment adjustment block to control the circuitry to generate the output signal with compensation for misalignment between the sensor and the target. The programmable misalignment adjustment block can be programmed to select measurement of one of the two or more magnetic field sensing elements, or alternatively, a mathematical combination of measurements of the two or more magnetic field sensing elements, for generating the sensor output signal when a test of the sensor indicates a misalignment.