US 5,066,904 A · Coaxial current sensors

Abstract

A sensor for measuring large magnitudes of A.C. current utilizes a current divider having parallel conductors and a current comparator coupled to one of the conductors so arranged as to perform first and second stages of scaling of the A.C. current to obtain an output signal from the sensor proportional to the A.C. current. The overall sensor ratio is the product of the ratios of the first and second stages, thereby permitting very large ratios to be obtained. Components of the sensor are arranged so as to cause cancellation of magnetic fields by the sensor and to make the sensor immune from incident magnetic fields.

Claims48

Dependent claims

A coaxial current sensor for providing an output signal proportional to current supplied thereto, comprising:

(a) a coaxial current divider for dividing current supplied thereto, including,
(i) a first conductor, having an aperture extending therethrough between opposite ends thereof, possessing a resistance of a value R.sub.1,
(ii) a second conductor coaxially disposed in the aperture of said first conductor, said second conductor being connected at opposite ends thereof to corresponding opposite ends of said first conductor, and possessing a resistance of a value R.sub.2, whereby an input current, I.sub.in, supplied to one end of said first and second conductors, divides into currents I.sub.1 and I.sub.2 flowing in said first and second conductors respectively, and wherein the current I.sub.2 flowing in said second conductor is given by:
##EQU21## (b) output means coaxially disposed about said second conductor and inductively coupled thereto, for sensing the current I.sub.2 flowing in said second conductor and providing an output signal having a magnitude proportional to the magnitude of the current I.sub.in supplied to said current sensor.

1 more element

A coaxial current divider for dividing current, supplied thereto, in a pre-determined ratio, comprising:

(a) a, cylindrical, first conductor having a cylindrical aperture extending therethrough between first and second ends thereof, including entry means for providing an input current I.sub.in to said first end, said first conductor possessing a resistance of a value R.sub.1, and generating a first magnetic field therearound in response to a current flowing between the first and second ends thereof;
(b) a, cylindrical, second conductor, having first and second ends, coaxially disposed within the aperture of said first conductor, the first and second ends of said second conductor each being connected to a corresponding one of the first and second ends of said first conductor, said second conductor generating a second magnetic field therearound, in response to a current flowing between the first and second ends thereof, said second conductor possessing a resistance of a value R.sub.2, whereby said input current, I.sub.in, divides into currents I.sub.1 and I.sub.2 flowing in said first and second conductors respectively, and wherein I.sub.1 +I.sub.2 =I.sub.in and current I.sub.2 flowing in said second conductor is given by:
##EQU23## (c) a, cylindrical, third conductor, having a cylindrical aperture extending therethrough between first and second ends thereof, and coaxially disposed around said first conductor, said third conductor being connected at the second end thereof to each of the second ends of said first and second conductors, said third conductor generating a third magnetic field therearound in response to a current flowing between the first and second ends thereof, said third conductor including means, at the first end thereof, for exit of the current I.sub.in, the currents I.sub.1, I.sub.2 and I.sub.in flowing through said first, second and third conductors, and producing, respectively the first, second and third magnetic fields in a predetermined interacting relationship, such that, when the currents I.sub.1 and I.sub.2 flow from the first ends to the second ends of each of said first and second conductors, the current, I.sub.in =I.sub.1 +I.sub.2, flows from the second end to the first end of said third conductor, whereby, beyond the outer surface of said third conductor, the sum of the first, second and third magnetic fields is substantially zero.

A current sensor, comprising:

(a) a conductive current divider adapted for series connection to a current component to be sensed, said current divider including,
(i) a first, cup-shaped, member having a first terminal adjacent the bottom end thereof for making a first series connection,
(ii) a shunt resistor, having an aperture extending therethrough between opposite ends thereof, disposed within said first member with one end of said shunt resistor extending beyond the open end of said first member, and the other end of said shunt resistor bonded to the bottom of said first member;
(iii) a second, cup shaped member bonded to that end of said shunt resistor extending beyond the open end of said first member, forming a second terminal for making a second series connection,
(iv) an, elongated, current measuring resistor disposed within said first and second members and being bonded at opposite ends thereof to corresponding bottom ends of said first and second members, whereby an input current applied to the first terminal of said first member is divided into first and second current components with said first current component flowing through said shunt resistor, and the second current component flowing through said current measuring resistor and said second member, and having a magnitude which is a scaled representation of the input current, the first and second current components being combined at the second terminal formed by the bonding of said shunt resistor and said second member;
and
(b) a current comparator, including a magnetic core mounted inside said second member and being inductively coupled to at least a portion of said current carrying element such that said current measuring resistor forms a primary winding of said current comparator, said current comparator further including first and second secondary windings wound on said magnetic core;
(c) amplifier means responsive to an output signal from said first secondary winding and further including an output connected to said second secondary winding for providing a control current thereto for producing a compensating flux in said magnetic core substantially opposing flux induced into said magnetic core by the second current component flowing through said current measuring resistor;
and
(d) means connected to an output of said second secondary winding, and responsive to the current flowing therethrough, for producing an analog output signal representative of the current component to be sensed.

7 more elements

A method of constructing a current sensor and providing an output signal, Iout, therefrom having a magnitude proportional to the magnitude of the current, I.sub.in, supplied to said current sensor, comprising the steps of:

(a) disposing a first conductor having a resistance, R1, coaxially within a second conductor having a resistance, R2;
(b) interconnecting said first and second conductors in a prescribed arrangement, whereby the current, I.sub.in, when supplied to said current sensor, divides into two current components, I1 and I2, in said first and second conductors respectively, wherein I1+I2=I.sub.in, and whereby the current component, I1, flowing in said first conductor provides a first stage of scaling of the current, I.sub.in, as specified by the ratio of R1 and R2 and as given by:
##EQU25## (c) providing a current comparator having a toroidal magnetic core which has wound thereon a secondary sense winding and a secondary compensating winding of N-turns;
(d) disposing said first conductor, coaxially, within the toroidal core of said current comparator to provide a primary winding therefore;
(e) sensing, in the sense winding of said comparator, the magnitude of the current, I1, flowing in said first conductor;
and
(f) in response to the sensing, providing a current compensating signal to the N-turn compensating winding of said current comparator to perform a second stage of scaling of the current, I.sub.in, whereby the magnetizing ampere turns resulting from the current, I1, flowing in said first conductor are made equal to the magnetizing ampere turns resulting from the current compensating signal flowing in the N-turn compensating winding to effect an overall scaling of the current, I.sub.in, and generate an output signal, Iout, from the current compensating winding which has a magnitude equal to the product of two independent scale factors determined by the ratio of R1 and R2 and the number of turns, N, of the current compensating winding as given by:
##EQU26##

5 more elements

In a current sensor, a method of sensing current, comprising the steps of:

(a) applying a current, I.sub.in, to a first terminal of said current sensor, said first terminal generating a magnetic field therearound in response to the flow of the current, I.sub.in, therethrough;
(b) dividing the current, I.sub.in, at said first terminal into two current components, I1 and I2, flowing in first, second and third conductors arranged in a prescribed coaxial relationship and interconnected whereby I1 flows in said first conductor and I2 flows in opposite directions through said second and third conductors, said first, second and third conductors generating corresponding magnetic fields, in response to the passage of current therethrough, which inductively interact to cancel one another and thus prevent the generation of any magnetic field external to said current sensor;
(c) combining the current components, I1 and I2, at a second terminal formed by conjoining said first conductor with a selected one of said second and third conductors to derive a current, I1+I2=I.sub.in, flowing in a direction through said second terminal opposite the direction of the current, I.sub.in, flowing through said first terminal, said second terminal generating a magnetic field therearound in response to the flow of the current, I1+I2=I.sub.in, therethrough;
(d) providing an inductive interaction of the magnetic fields surrounding said first and second terminals whereby the magnetic fields interact to cancel one another and to further cancel incident magnetic fields from sources external to said current sensor to thus render said current sensor substantially immune from the effects of such incident magnetic fields;
and
(e) sensing one of the current components, I1, I2, flowing through a selected one of said first, second and third conductors to generate an output signal from said current sensor which is proportional to the magnitude of the current, I.sub.in, applied to said current sensor.

3 more elements

A coaxial current sensor for providing an output signal proportional to current supplied thereto, comprising:

(a) a coaxial current divider for dividing current supplied thereto, including,
(i) a first conductor, having an aperture extending therethrough between opposite ends thereof, possessing a resistance of a value R1,
(ii) a second conductor coaxially disposed in the aperture of said first conductor, said second conductor being connected at opposite ends thereof to corresponding opposite ends of said first conductor, and possessing a resistance of a value R2, whereby an input current, I.sub.in, supplied to one end of said first and second conductors, divides into currents I.sub.1 and I.sub.2 flowing in said first and second conductors respectively, and wherein the current I.sub.2 flowing in said second conductor is given by:
##EQU27## (b) output means coaxially disposed about said second conductor and inductively coupled thereto, for sensing the current I.sub.2 flowing in said second conductor and providing an output signal having a magnitude proportional to the magnitude of the current I.sub.in supplied to said current sensor;
and
(c) first and second conductive members substantially enclosing said first and second conductors and said output means, said first and second conductors each being connected at opposite ends thereof to a corresponding one of said first and second conductive members, whereby the input current I.sub.in, when supplied to one end of said first and second conductive members, divides into the currents I.sub.1 I.sub.2 flowing in said first and second conductors to thereby be combined, in the other one of said first and second conductive members, as I.sub.1+I.sub.2 equal to I.sub.in.

3 more elements

Dependencies are inferred from the claim text.

Abstract

Claims48

Dependent claims

A coaxial current sensor for providing an output signal proportional to current supplied thereto, comprising:

(a) a coaxial current divider for dividing current supplied thereto, including,
(i) a first conductor, having an aperture extending therethrough between opposite ends thereof, possessing a resistance of a value R.sub.1,
(ii) a second conductor coaxially disposed in the aperture of said first conductor, said second conductor being connected at opposite ends thereof to corresponding opposite ends of said first conductor, and possessing a resistance of a value R.sub.2, whereby an input current, I.sub.in, supplied to one end of said first and second conductors, divides into currents I.sub.1 and I.sub.2 flowing in said first and second conductors respectively, and wherein the current I.sub.2 flowing in said second conductor is given by:
##EQU21## (b) output means coaxially disposed about said second conductor and inductively coupled thereto, for sensing the current I.sub.2 flowing in said second conductor and providing an output signal having a magnitude proportional to the magnitude of the current I.sub.in supplied to said current sensor.

1 more element

A coaxial current divider for dividing current, supplied thereto, in a pre-determined ratio, comprising:

(a) a, cylindrical, first conductor having a cylindrical aperture extending therethrough between first and second ends thereof, including entry means for providing an input current I.sub.in to said first end, said first conductor possessing a resistance of a value R.sub.1, and generating a first magnetic field therearound in response to a current flowing between the first and second ends thereof;
(b) a, cylindrical, second conductor, having first and second ends, coaxially disposed within the aperture of said first conductor, the first and second ends of said second conductor each being connected to a corresponding one of the first and second ends of said first conductor, said second conductor generating a second magnetic field therearound, in response to a current flowing between the first and second ends thereof, said second conductor possessing a resistance of a value R.sub.2, whereby said input current, I.sub.in, divides into currents I.sub.1 and I.sub.2 flowing in said first and second conductors respectively, and wherein I.sub.1 +I.sub.2 =I.sub.in and current I.sub.2 flowing in said second conductor is given by:
##EQU23## (c) a, cylindrical, third conductor, having a cylindrical aperture extending therethrough between first and second ends thereof, and coaxially disposed around said first conductor, said third conductor being connected at the second end thereof to each of the second ends of said first and second conductors, said third conductor generating a third magnetic field therearound in response to a current flowing between the first and second ends thereof, said third conductor including means, at the first end thereof, for exit of the current I.sub.in, the currents I.sub.1, I.sub.2 and I.sub.in flowing through said first, second and third conductors, and producing, respectively the first, second and third magnetic fields in a predetermined interacting relationship, such that, when the currents I.sub.1 and I.sub.2 flow from the first ends to the second ends of each of said first and second conductors, the current, I.sub.in =I.sub.1 +I.sub.2, flows from the second end to the first end of said third conductor, whereby, beyond the outer surface of said third conductor, the sum of the first, second and third magnetic fields is substantially zero.

A current sensor, comprising:

(a) a conductive current divider adapted for series connection to a current component to be sensed, said current divider including,
(i) a first, cup-shaped, member having a first terminal adjacent the bottom end thereof for making a first series connection,
(ii) a shunt resistor, having an aperture extending therethrough between opposite ends thereof, disposed within said first member with one end of said shunt resistor extending beyond the open end of said first member, and the other end of said shunt resistor bonded to the bottom of said first member;
(iii) a second, cup shaped member bonded to that end of said shunt resistor extending beyond the open end of said first member, forming a second terminal for making a second series connection,
(iv) an, elongated, current measuring resistor disposed within said first and second members and being bonded at opposite ends thereof to corresponding bottom ends of said first and second members, whereby an input current applied to the first terminal of said first member is divided into first and second current components with said first current component flowing through said shunt resistor, and the second current component flowing through said current measuring resistor and said second member, and having a magnitude which is a scaled representation of the input current, the first and second current components being combined at the second terminal formed by the bonding of said shunt resistor and said second member;
and
(b) a current comparator, including a magnetic core mounted inside said second member and being inductively coupled to at least a portion of said current carrying element such that said current measuring resistor forms a primary winding of said current comparator, said current comparator further including first and second secondary windings wound on said magnetic core;
(c) amplifier means responsive to an output signal from said first secondary winding and further including an output connected to said second secondary winding for providing a control current thereto for producing a compensating flux in said magnetic core substantially opposing flux induced into said magnetic core by the second current component flowing through said current measuring resistor;
and
(d) means connected to an output of said second secondary winding, and responsive to the current flowing therethrough, for producing an analog output signal representative of the current component to be sensed.

7 more elements

(a) disposing a first conductor having a resistance, R1, coaxially within a second conductor having a resistance, R2;
(b) interconnecting said first and second conductors in a prescribed arrangement, whereby the current, I.sub.in, when supplied to said current sensor, divides into two current components, I1 and I2, in said first and second conductors respectively, wherein I1+I2=I.sub.in, and whereby the current component, I1, flowing in said first conductor provides a first stage of scaling of the current, I.sub.in, as specified by the ratio of R1 and R2 and as given by:
##EQU25## (c) providing a current comparator having a toroidal magnetic core which has wound thereon a secondary sense winding and a secondary compensating winding of N-turns;
(d) disposing said first conductor, coaxially, within the toroidal core of said current comparator to provide a primary winding therefore;
(e) sensing, in the sense winding of said comparator, the magnitude of the current, I1, flowing in said first conductor;
and
(f) in response to the sensing, providing a current compensating signal to the N-turn compensating winding of said current comparator to perform a second stage of scaling of the current, I.sub.in, whereby the magnetizing ampere turns resulting from the current, I1, flowing in said first conductor are made equal to the magnetizing ampere turns resulting from the current compensating signal flowing in the N-turn compensating winding to effect an overall scaling of the current, I.sub.in, and generate an output signal, Iout, from the current compensating winding which has a magnitude equal to the product of two independent scale factors determined by the ratio of R1 and R2 and the number of turns, N, of the current compensating winding as given by:
##EQU26##

5 more elements

In a current sensor, a method of sensing current, comprising the steps of:

(a) applying a current, I.sub.in, to a first terminal of said current sensor, said first terminal generating a magnetic field therearound in response to the flow of the current, I.sub.in, therethrough;
(b) dividing the current, I.sub.in, at said first terminal into two current components, I1 and I2, flowing in first, second and third conductors arranged in a prescribed coaxial relationship and interconnected whereby I1 flows in said first conductor and I2 flows in opposite directions through said second and third conductors, said first, second and third conductors generating corresponding magnetic fields, in response to the passage of current therethrough, which inductively interact to cancel one another and thus prevent the generation of any magnetic field external to said current sensor;
(c) combining the current components, I1 and I2, at a second terminal formed by conjoining said first conductor with a selected one of said second and third conductors to derive a current, I1+I2=I.sub.in, flowing in a direction through said second terminal opposite the direction of the current, I.sub.in, flowing through said first terminal, said second terminal generating a magnetic field therearound in response to the flow of the current, I1+I2=I.sub.in, therethrough;
(d) providing an inductive interaction of the magnetic fields surrounding said first and second terminals whereby the magnetic fields interact to cancel one another and to further cancel incident magnetic fields from sources external to said current sensor to thus render said current sensor substantially immune from the effects of such incident magnetic fields;
and
(e) sensing one of the current components, I1, I2, flowing through a selected one of said first, second and third conductors to generate an output signal from said current sensor which is proportional to the magnitude of the current, I.sub.in, applied to said current sensor.

3 more elements

A coaxial current sensor for providing an output signal proportional to current supplied thereto, comprising:

(a) a coaxial current divider for dividing current supplied thereto, including,
(i) a first conductor, having an aperture extending therethrough between opposite ends thereof, possessing a resistance of a value R1,
(ii) a second conductor coaxially disposed in the aperture of said first conductor, said second conductor being connected at opposite ends thereof to corresponding opposite ends of said first conductor, and possessing a resistance of a value R2, whereby an input current, I.sub.in, supplied to one end of said first and second conductors, divides into currents I.sub.1 and I.sub.2 flowing in said first and second conductors respectively, and wherein the current I.sub.2 flowing in said second conductor is given by:
##EQU27## (b) output means coaxially disposed about said second conductor and inductively coupled thereto, for sensing the current I.sub.2 flowing in said second conductor and providing an output signal having a magnitude proportional to the magnitude of the current I.sub.in supplied to said current sensor;
and
(c) first and second conductive members substantially enclosing said first and second conductors and said output means, said first and second conductors each being connected at opposite ends thereof to a corresponding one of said first and second conductive members, whereby the input current I.sub.in, when supplied to one end of said first and second conductive members, divides into the currents I.sub.1 I.sub.2 flowing in said first and second conductors to thereby be combined, in the other one of said first and second conductive members, as I.sub.1+I.sub.2 equal to I.sub.in.

3 more elements

Dependencies are inferred from the claim text.

Coaxial current sensors

Life of this patent

Abstract

Claims48

Coaxial current sensors

Life of this patent

Abstract

Claims48