Current Sensor Stray Field Compensation
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Solution Overview
Problem
Current current measuring systems, particularly those using Hall effect devices, face inaccuracies due to stray magnetic fields from adjacent devices, leading to nuisance tripping of circuit breakers in applications with high in-rush or short circuit currents, as they cannot distinguish between magnetic fields generated by current and stray fields, resulting in false overcurrent indications.
Innovation Solution
A current measuring system employing a first magnetic field sensor and a second sensor with higher sensitivity to stray magnetic fields, coupled with a processor that compares signals from both sensors to determine the presence of stray fields and generate a trip signal only when necessary, thereby preventing false tripping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a Hall effect device is used to measure current, then current measurement capability is provided, but measurement precision deteriorates due to inability to distinguish stray magnetic fields
Solution Approach 1:
The magnetic field sensing function is divided into two separate sensors: a first magnetic field sensor for measuring current and a second magnetic field sensor for detecting stray fields. This segmentation allows each sensor to be optimized for its specific function and enables the system to distinguish between current-generated fields and stray fields through signal processing
Solution Approach 2:
A processor acts as an intermediary between the magnetic field sensors and the trip decision logic. The processor receives signals from both sensors, compares them to determine the presence of stray fields, and generates trip signals only when current exceeds thresholds after compensating for stray field effects. This intermediary processing eliminates false tripping caused by stray fields
2Measurement precision
If magnetic shielding is used to reduce stray field effects, then measurement precision improves, but device complexity and cost increase
Solution Approach 1:
The patent replaces mechanical magnetic shielding structures with an electronic/software-based solution. Instead of using physical barriers to block stray fields, the system uses a processor to detect, measure, and compensate for stray field effects through signal processing algorithms, thereby eliminating the need for complex shielding hardware
3Measurement precision
If distance is increased between sensor and stray field sources, then measurement precision improves, but device size increases
Solution Approach 1:
The processor serves as an intermediary that enables accurate current measurement without requiring physical distance from stray field sources. By detecting stray fields with the second sensor and compensating for their effects in the signal processing stage, the system achieves precision measurement in compact configurations where sensors must be close to current-carrying conductors
4Measurement precision
If multiple sensors are used to detect stray fields, then measurement precision improves, but device complexity increases
Solution Approach 1:
The two magnetic field sensors have different local qualities: the first sensor is optimized for measuring current with appropriate sensitivity, while the second sensor is specifically optimized for detecting stray fields. This differentiation in local quality allows each sensor to perform its specific function effectively, and the processor leverages these complementary characteristics to achieve accurate current measurement with stray field compensation
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 system effectively differentiates between magnetic flux generated by current and stray fields, reducing nuisance tripping and ensuring accurate current measurement, even in applications with close proximity to multiple devices, by using a processor to compare signals from sensors with varying sensitivities and adjust measurements accordingly.
Implementation Method 1
Hall effect devices measure a magnetic flux and output a voltage that corresponds to a level of magnetic flux measured
Implementation Method 2
Hall effect devices measure a magnetic flux and output a voltage that corresponds to a level of magnetic flux measured
Implementation Method 3
The processor is further configured to determine a presence of a stray magnetic field by comparing the first signal and the second signal
Data Source
AI summary
A current measuring system for measuring a current through a conductor is described. The system includes a first sensor configured to measure a first magnetic flux and to generate a first signal proportional to the first magnetic flux. The system also includes a second sensor configured to measure a second magnetic flux and to provide a second signal proportional to the second magnetic flux, the second sensor having a higher sensitivity to stray magnetic fields than the first sensor. The system also includes a processor coupled to the first sensor and the second sensor and configured to receive the first signal and the second signal. The processor is further configured to determine a presence of a stray magnetic field by comparing the first signal and the second signal.