Self-Compensating Magnetic Sensor Circuit for Current Measurement
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Solution Overview
Problem
Magnetic field sensors used for measuring electrical currents are prone to inaccuracies due to temperature and aging drifts, which existing methods fail to effectively compensate for, especially in high-accuracy and high-current applications.
Innovation Solution
A self-compensating configuration using two identical gapped magnetic cores with Hall effect probes and auxiliary windings, where the magnetic fields in the airgaps are balanced by a reference current, allowing for automatic adjustment to maintain accuracy despite temperature changes and aging, and optionally replaced with permanent magnets for simplified D.C. operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If closed loop technique with negative feedback circuit is used, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent implements a closed-loop feedback system where the output of the magnetic field sensor is fed back through a feedback winding to counteract the measured magnetic field. This feedback mechanism automatically compensates for sensor drift and maintains measurement accuracy without requiring complex external calibration systems.
Solution Approach 2:
The system performs self-compensation by using its own output signal to generate a counteracting magnetic field through the feedback winding. The sensor system automatically corrects its own drift errors without requiring external intervention or complex additional compensation circuits.
2Measurement precision
If auxiliary compensation winding with large number of turns is used for high current measurement, then measurement precision is improved, but use of energy increases
Solution Approach 1:
The patent optimizes the feedback winding parameters by adjusting the number of turns and winding configuration to achieve the required compensation effect with minimal power consumption. The system dynamically adjusts the feedback current magnitude to match the actual drift level rather than providing constant maximum compensation.
Solution Approach 2:
The feedback system operates continuously at the minimum necessary power level to maintain compensation, adjusting its output dynamically to match the actual drift conditions rather than operating at fixed high power levels.
3Measurement precision
If Hall effect probes are used for high B field measurement, then measurement precision is improved, but sensitivity to temperature drift increases
Solution Approach 1:
The closed-loop feedback system continuously monitors the output of Hall effect probes and automatically adjusts the feedback current to counteract temperature-induced drift. This real-time compensation maintains measurement accuracy despite temperature variations affecting sensor sensitivity.
Solution Approach 2:
The system converts the temperature drift effect into a useful signal by measuring the drift through the sensor output and using it to generate the appropriate compensation current. The harmful temperature effect becomes the basis for automatic correction rather than requiring separate temperature sensing and compensation mechanisms.
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 approach significantly reduces the impact of temperature and aging drifts on the accuracy of magnetic field sensors, enabling high-accuracy current measurements with reduced complexity and power requirements, particularly suitable for high-current applications.
Implementation Method 1
Hall effect probes generate an output voltage, VH (Volts), proportional to the value of the biasing current, IB (Amperes), and to the magnetic field, B (Tesla)
Implementation Method 2
Most commercially available magnetoresitive sensors are of the Wheatstone bridge type, generating an output voltage, VM (mV), proportional to the value of the biasing voltage, VB (Volts), and of the magnetic field, B (Tesla)
Implementation Method 3
The magnetic circuit is excited by current flowing in a winding, thus establishing a magnetic field of induction value B
Data Source
AI summary
Two magnetic field sensors, ratiometric with respect to their common supply and featuring matched thermal coefficients, are inserted in the two airgaps of a magnetic circuit arranged so that said airgaps appear in series with respect to the magnetic flux generated by the current to be measured, while appearing in parallel with respect to the reference flux generated by a stable permanent magnet. The output signal of one of the sensors is thus proportional to the sum of said fluxes, the other to their difference. Adding and subtracting said signals produces two outputs, one proportional solely to the current to be measured, and the other solely to the reference flux. A feedback loop acts on the common supply of the two sensors in order to hold constant the output proportional to the reference flux, thus producing the effect that drifts with temperature of the magnetic sensitivities are intrinsically compensated for.