US 4,947,107 A · Magneto-optic current sensor

Abstract

A sensor (10) for sensing the magnitude of current flowing in a conductor (12) based upon the Faraday effect is disclosed. The invention utilizes a magneto-optic material having one or more layers (32) in which alignment with an optical fiber is not critical in achieving accurate current measurements. A magneto-optic material (28) in accordance with the invention includes one or more layers (32) each having a substrate having opposed surfaces coated with a material exhibiting the Faraday effect in which light from a light source is transmitted through the magneto-optic element without substantial internal reflection and is incident upon a surface area of the coating which is greater than the surface area of the beam of light. Furthermore, the invention measures the magnitude of current flowing in the conductor accurately by utilizing null detection for a first range of current values from zero to a first magnitude having either of two possible polarities and measures a second range of current values extending from the first magnitude to a second magnitude having either of the two possible polarities in which null detection is not utilized. By not utilizing null detection for the second range of current values, circuit response time is enhanced by allowing the inductance of the nulling coil to be reduced. Transient response is thus improved.

Claims28

Dependent claims

In a magneto-optical current sensor for measuring the magnitude of current flowing in a conductor with a magneto-optic material, through which a plane polarized light beam is transmitted that is oriented in parallel with a component of a magnetic field produced by the current which causes rotation of the plane polarized light beam by an amount proportional to the current, a nulling circuit for producing a current which is to be applied to a coil magnetically coupled with the magneto-optic material to cause the plane of polarization of the light beam to be rotated in opposition to the rotation caused by the sensed current comprising:

(a) means for providing a signal proportional to the angle of rotation in the magneto-optic material;
(b) a comparator producing an output of a first level when the signal is greater than a predetermined value and producing an output of a second level when the signal is less than the predetermined value wherein;
(c) means, coupled to the comparator, for producing current which is applied to the coil and a signal proportional to the current flowing in the coil;
(d) an amplifier, coupled to the means for providing a signal proportional to the angle of rotation, for providing an amplified output signal of the signal proportional to the angle of rotation;
and
(e) means, for summing the output signal from the amplifier and the signal proportional to the current flowing in the coil, to produce an output signal proportional to the current flowing in the conductor.

3 more elements

A magneto-optical current sensor for measuring the magnitude of current flowing in a conductor with a magneto-optic material through which a plane polarized light beam is transmitted that is oriented in parallel with a component of a magnetic field produced by the current which causes rotation of the plane polarized light beam by an amount proportional to the current, comprising:

(a) first means, responsive to a sensed angle rotation of the plane of polarization, for producing a current which is applied to a coil magnetically linked with the magneto-optic material to cause the plane of polarization of the light beam to be rotated by an amount equal in magnitude and opposite in direction to the rotation caused by the sensed current when the sensed current is in a first range of current values;
(b) second means, responsive to a sensed angle of rotation of the plane of polarization, for producing a signal which is proportional to the sensed current in a second range of current values larger in magnitude than the first range of current values;
and
(c) output means, responsive to the first means for producing a current and the second means for producing a signal, for producing an output signal proportional to the current flowing in the conductor in the first and second ranges.

1 more element

A magneto-optic current sensor for measuring the magnitude of current flowing in a conductor comprising:

(a) a light source for emitting light to be transmitted;
(b) means, optically coupled to the light source, for collimating the light emitted from the light source into a substantially parallel beam having a cross-sectional area;
(c) a polarizer, optically coupled to the beam, for polarizing the light beam into a first plane of polarization;
(d) a magneto-optic element, optically coupled to the polarizer, which receives the light beam on an input side with the light beam passing through the element without substantial internal reflection and outputs the light on a discharge side, the element rotating the plane of polarizing of the input beam in proportion to a magnetic field coupled in parallel to an optical axis of the beam passing through the element and comprising at least one layer with each layer having a substrate coated with a material exhibiting the Faraday effect with each layer having a cross-sectional area of coating intercepted by the light beam which is equal to or greater in surface area than the cross-sectional area of the light beam intercepting the layer;
(e) means, optically coupled to the light beam outputted from the output of the magneto-optic element, for producing an output proportional to the magnitude of the rotation of the plane of polarization in the element;
(f) first means, responsive to the output proportional to the magnitude of the rotation of the plane of polarization, for producing a current which is applied to a coil magnetically coupled with the magneto-optic element to cause the plane of polarization to be rotated by an amount equal in magnitude and opposite in direction to the rotation caused by the sensed current when the sensed current is in a first range of current values;
(g) second means, responsive to the output proportional to the magnitude of the rotation of the plane of polarization, for producing a signal which is proportional to the sensed current when the sensed current is in a second range of current values;
and
(h) output means, responsive to the first means for producing a current and the second means for producing a signal for producing an output signal proportional to the current flowing in the conductor in the first and second ranges.

6 more elements

In magneto-optical current sensor for measuring the magnitude of current flowing in a conductor with a magneto-optic material, through which a plane polarized light beam is transmitted that is oriented in parallel with a component of a magnetic field produced by the current which causes rotation of the plane polarized light beam by an amount proportional to the current, a nulling circuit for producing a current which is to be applied to a coil magnetically coupled to the magneto-optic material to cause the plane of polarization of the light beam to be rotated in opposition to the rotation caused by the sensed current comprising:

(a) means for providing a first signal proportional to the angle of rotation in the magneto-optic material;
(b) means, responsive to the first signal, for producing an output signal having a first level when the first signal is greater than a predetermined value and a second level when the first signal is less than the predetermined value;
(c) means, responsive to the first signal, for producing a signal proportional to the current flowing in the coil and the current which is applied to the coil;
(d) an amplifier, coupled to the means for providing a first signal proportional to the sensed angle of rotation, for providing an amplified output signal of the first signal proportional to the angle of rotation;
and
(e) means, for summing a signal which is a function of the output signal and the amplified output signal, to produce an output signal proportional to the current flowing in the conductor.

3 more elements

Dependencies are inferred from the claim text.

Magneto-optic current sensor

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Magneto-optic current sensor

Life of this patent

Abstract

Claims28