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 the value of an electric current (IM) by computing a function of the output signals of two magnetic field sensors (H1, H2) each inserted in a respective one of two airgaps of a magnetic circuit, both sensors belonging to the type ratiometric with respect to the supply current or both belonging to the type ratiometric with respect to the supply voltage and featuring matched temperature coefficients of the respective magnetic field sensitivity;
- wherein a magnetic flux is established in said magnetic circuit by a first winding being configured to carry the current being measured (IM), and thus resulting, at both magnetic field sensors locations, in a first magnetic field component (BM, B(IM)) proportional to said current being measured;
said method further comprising the step of establishing at said two magnetic field sensors locations a second magnetic field component (BR, B(IR)) possessing a constant reference magnetic field value, independent from the value of the current being measured, adding to said first magnetic field component at one of said two magnetic field sensors locations, while subtracting from it at the other location;
wherein said second magnetic field component is established by means of at least one permanent magnet or by means of at least one second winding configured to carry a current of a constant reference value;
said method further comprising the step of processing through and adder circuit and a subtractor circuit the output 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 sum and difference signals being proportional to said second magnetic field component solely and the other one of said output sum and difference signals being proportional solely to the first magnetic field component established by the current being measured;
whereby the output signal proportional to said second magnetic field component is then used in a feedback loop configured to control the supply current feeding the two series supplied magnetic field sensors, in case the magnetic field sensors belong to the type ratiometric with respect to the supply current, or the supply voltage of the two parallel supplied magnetic field sensors, in case the magnetic field sensors belong to the type ratiometric with respect to the supply voltage, in order to hold at a constant reference voltage value said output signal proportional to said second magnetic field component, 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 said first magnetic field component established by 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 the value of an electric current (IM) by computing a function of the output signals of two magnetic field sensors (H1, H2) each inserted in a respective one of two airgaps of a magnetic circuit, both sensors belonging to the type ratiometric with respect to the supply current or both belonging to the type ratiometric with respect to the supply voltage and featuring matched temperature coefficients of the respective magnetic field sensitivity;
- wherein a magnetic flux is established in said magnetic circuit by a first winding being configured to carry the current being measured (IM), and thus resulting, at both magnetic field sensors locations, in a first magnetic field component (BM, B(IM)) proportional to said current being measured;
said method further comprising the step of establishing at said two magnetic field sensors locations a second magnetic field component (BR, B(IR)) possessing a constant reference magnetic field value, independent from the value of the current being measured, adding to said first magnetic field component at one of said two magnetic field sensors locations, while subtracting from it at the other location;
wherein said second magnetic field component is established by means of at least one permanent magnet or by means of at least one second winding configured to carry a current of a constant reference value;
said method further comprising the step of processing through and adder circuit and a subtractor circuit the output 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 sum and difference signals being proportional to said second magnetic field component solely and the other one of said output sum and difference signals being proportional solely to the first magnetic field component established by the current being measured;
whereby the output signal proportional to said second magnetic field component is then used in a feedback loop configured to control the supply current feeding the two series supplied magnetic field sensors, in case the magnetic field sensors belong to the type ratiometric with respect to the supply current, or the supply voltage of the two parallel supplied magnetic field sensors, in case the magnetic field sensors belong to the type ratiometric with respect to the supply voltage, in order to hold at a constant reference voltage value said output signal proportional to said second magnetic field component, 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 said first magnetic field component established by 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 being configured to carry the current being measured (IM), and thus resulting, at both magnetic field sensors locations, in a first magnetic field component (BM, B(IM)) proportional to said current being measured;
Specification