METHOD AND APPARATUS FOR THE MEASUREMENT OF ELECTRICAL CURRENT BY MEANS OF A SELF-COMPENSATING CONFIGURATION OF MAGNETIC FIELD SENSORS
First Claim
1. A method of measuring electrical current by computing a function of the output signals of two magnetic field sensors (H1, H2) placed at the two airgaps of a magnetic circuit, both sensors belonging to the type ratiometric with respect to the bias current or both belonging to the type ratiometric with respect to the supply voltage and selected to feature matched temperature coefficients of the respective magnetic field sensitivity;
- wherein a magnetic flux is established in said magnetic circuit by a first winding carrying the current to be measured (IM), and thus resulting, at both magnetic field sensors locations, in a first magnetic field component (BM) proportional to said current;
said method further comprising the step of establishing at said two airgap locations a second magnetic field component (BR) possessing a constant reference value independent from the value of the current to be measured, and in such a way that said second magnetic field component adds to said first component at one of said two locations, while subtracting from it at the other location;
wherein said reference field component can be established by means of at least one permanent magnet or by means of at least one second winding carrying a current of a constant reference value;
said method further comprising the step of processing through and adder circuit and a subtractor circuit the signals generated by said two magnetic field sensors, so as to produce an output sum signal and an output difference signal, and thus resulting in one of said output signals being proportional to the reference field component solely and the other output signal being proportional solely to the magnetic field component established by the current to be measured;
whereby the output signal proportional to the reference field component is then used in a feedback loop arranged to control the common biasing current, in case the magnetic field sensors belong to the type ratiometric with respect to the biasing current, or the common supply voltage, in case the magnetic field sensors belong to the type ratiometric with respect to the supply voltage, of said magnetic field sensors in such a way that said output signal is held at a constant reference voltage value, consequently resulting in an automatic compensation of the impact of temperature drifts of the magnetic sensitivities on the accuracy of the output signal proportional to the current to be measured.
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Abstract
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.
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Citations
4 Claims
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1. A method of measuring electrical current by computing a function of the output signals of two magnetic field sensors (H1, H2) placed at the two airgaps of a magnetic circuit, both sensors belonging to the type ratiometric with respect to the bias current or both belonging to the type ratiometric with respect to the supply voltage and selected to feature matched temperature coefficients of the respective magnetic field sensitivity;
- wherein a magnetic flux is established in said magnetic circuit by a first winding carrying the current to be measured (IM), and thus resulting, at both magnetic field sensors locations, in a first magnetic field component (BM) proportional to said current;
said method further comprising the step of establishing at said two airgap locations a second magnetic field component (BR) possessing a constant reference value independent from the value of the current to be measured, and in such a way that said second magnetic field component adds to said first component at one of said two locations, while subtracting from it at the other location;
wherein said reference field component can be established by means of at least one permanent magnet or by means of at least one second winding carrying a current of a constant reference value;
said method further comprising the step of processing through and adder circuit and a subtractor circuit the signals generated by said two magnetic field sensors, so as to produce an output sum signal and an output difference signal, and thus resulting in one of said output signals being proportional to the reference field component solely and the other output signal being proportional solely to the magnetic field component established by the current to be measured;
whereby the output signal proportional to the reference field component is then used in a feedback loop arranged to control the common biasing current, in case the magnetic field sensors belong to the type ratiometric with respect to the biasing current, or the common supply voltage, in case the magnetic field sensors belong to the type ratiometric with respect to the supply voltage, of said magnetic field sensors in such a way that said output signal is held at a constant reference voltage value, consequently resulting in an automatic compensation of the impact of temperature drifts of the magnetic sensitivities on the accuracy of the output signal proportional to the current to be measured. - View Dependent Claims (2, 3, 4)
- wherein a magnetic flux is established in said magnetic circuit by a first winding carrying the current to be measured (IM), and thus resulting, at both magnetic field sensors locations, in a first magnetic field component (BM) proportional to said current;
Specification