MEANS FOR MEASURING MAGNITUDE AND DIRECTION OF A DIRECT CURRENT OR PERMANENT MAGNET, INCLUDING CLIP-ON DIRECT CURRENT SENSING INDUCTOR

• US 3,768,011 A
• Filed: 06/09/1970
• Issued: 10/23/1973
• Est. Priority Date: 06/09/1970
• Status: Expired due to Term

• Current Assignee: William H. Swain
• Original Assignee: William H. Swain
• Inventors: Swain, William H.
• Primary Examiner(s): Rolinec, Rudolph V.
• Assistant Examiner(s): Karlsen, Ernest F.
• Application Number:
  US05/044,761
• Time in Patent Office: 1,232 Days
• Field of Search: 324/117R,127,43R,43G 323/48 328/13,150
• US Class Current: 324/117.00R
• CPC Class Codes: G01R 1/22 Tong testers acting as secondary windings of current transformers
• CPC Class Codes: G01R 19/20 using transductors , i.e. a magnetic core transducer the saturation of which is cyclically reversed by an AC source on the secondary side
• CPC Class Codes: G01R 33/04 using the flux-gate principle

Abstract

A direct current or magnetic intensity input produces an offset in the average magnetic intensity applied to a sense inductor core of non-linear magnetic material. No electrical connection is required, and the measured current need not be interrupted. The core is coupled to an oscillator constructed so that the duty factor modulation and direct current output are linear functions of the input and restore the average magnetic intensity. Clip-on DC milliameter sense inductors which largely cancel magnetic noise are included with the description of embodiments of this invention. They are sensitive, small in size, inexpensive, and will outperform larger and more costly devices. Power consumption is greatly reduced because fewer components are used more effectively.

Claims

1. An instrument for measuring direct current flowing in a conductor comprising, a magnetic core of material having a highly non-linear magnetic characteristic, means enabling the magnetic field of said direct current to operate on said core to produce an offset in average magnetic intensity in said core, a single coupling winding on said core, said winding having two terminals, a power supply having two output terminals, switching means coupling the power supply terminals to the terminals of the coupling winding in a first arrangement so that current flows in the coupling winding in a first direction and alternatively coupling the power supply terminals to the terminals of the coupling winding in a second arrangement so that current flows in the coupling winding in a second direction, means directly responsive to the current in the coupling winding to determine when the current in the coupling winding exceeds a threshold current magnitude to cause the switching means to change the coupling arrangement between the power supply and the coupling winding, and means sensing the algebraic sum of the currents in the coupling winding and providing an output indication of the current flowing in the conductor.

2. An instrument for measuring the intensity and direction of a magnetic field comprising, a magnetic core of material having a highly non-linear magnetic characteristic, said core having lineal form, means enabling the said magnetic field to operate on said core to produce an offset in average magnetic intensity in said core in proportion to the intensity of the magnetic field in the direction of said lineal form core, a coupling winding disposed over at least a part of said core, said winding having two terminals, a power supply having two output terminals, switching means coupling the power supply terminals to the terminals of the coupling winding in a first arrangement so that current flows in the coupling winding in a first direction and alternatively coupling the power supply terminals to the terminals of the coupling winding in a second arrangement so that current flows in the coupling winding in a second direction, means directly responsive to the current in the coupling winding to determine when the current in the coupling winding exceeds a threshold current magnitude to cause the switching means to change the coupling arrangement between the power supply and the coupling winding, and means sensing the algebraic sum of the currents in the coupling winding and providing an output indication of the intensity of the magnetic field in the direction of said lineal form core.

3. An instrument for measuring direct current flowing in a conductor comprising, a magnetic core of material having a highly non-linear magnetic characteristic, means enabling the magnetic field of said direct current to operate on said core to produce an offset in average magnetic intensity in said core, a coupling winding on said core, said winding having two terminals, a power supply having two output terminals, switching means coupling the power supply terminals to the terminals of the coupling winding in a first arrangement so that current flows in the coupling winding in a first direction and alternatively coupling the power supply terminals to the terminals of the coupling winding in a second arrangement so that current Flows in the coupling winding in a second direction, means directly responsive to the current in the coupling winding to determine when the current in the coupling winding exceeds a threshold current magnitude to cause the switching means to change the coupling arrangement between the power supply and the coupling winding means sensing the algebraic sum of the currents in the coupling winding constructed to produce a useful degree of assymetry between the time duration of the said current in the coupling winding in said first direction and the time duration of the said current in the coupling winding in the said second direction, said assymetry being a measure of said offset and thus said direct current flowing in said conductor, means conveying, sensing, and demodulating said assymetry, the output of said demodulating means being suited for driving an output indication of said current flowing in the conductor.

4. An instrument for measuring direct current flowing in a conductor as claimed in claim 1, wherein said core has the shape of a toroid, and said enabling means include means to facilitate passing the said conductor carrying the said direct current through the hole in the said toroid, and said coupling winding comprises a plurality of turns of wire uniformly wound around said core.

5. An instrument for measuring direct current flowing in a conductor as claimed in claim 1, wherein said core has the shape of a toroid split into two equal halves, and said coupling winding is provided by a plurality of turns of wire wound substantially uniformly around each of said equal turns of wire, and said enabling means including means joining the said halves of said core around said conductor to form said core in a shape approaching that of a closed toroid.

6. An instrument for measuring direct current flowing in a conductor as claimed in claim 1, wherein said core is split in at least one location, and said enabling means include means for inserting said conductor in the central sector of said core without the need to interrupt a direct current which may be flowing in said conductor, and means for closing said split in said core so as to minimize the magnetic reluctance of the path around said core including said split, and said coupling winding is provided by a plurality of turns of wire wound around at least one sector of said core.

7. An instrument for measuring direct current flowing in a conductor as claimed in claim 1, wherein said switching means is rectilinear and so constructed that the electrical potential applied to said coupling winding has well defined extremes and makes relatively rapid transition from one of said extremes to the other of said extremes, said transition being initiated when the said current in the coupling winding exceeds said threshold current magnitude.

8. An instrument for measuring direct current flowing in a conductor as claimed in claim 1, wherein said switching means comprises a reversible transistor switch network.

9. An instrument for measuring direct current flowing in a conductor as claimed in claim 1, wherein said means sensing the algebraic sum of the currents in the coupling winding are constructed to produce a useful degree of assymetry between the time duration of the said switching means in the said first arrangement and the time duration of the said switching means in the said second arrangement, said assymetry being a measure of said offset and thus said direct current flowing in said conductor, and means for producing an alternating potential output signal representative of said assymetry in form suited for driving a load.

10. An instrument for measuring direct current flowing in a conductor as claimed in claim 1, wherein said sensing means includes a resistor and a capacitor, said resistor and capacitor being arranged in a parallel connection, the parallel combination being connected in series with the coupling winding so thAt the said current in the coupling winding is caused to flow in said parallel combination, said resistor and capacitor having values selected to produce a useful degree of assymetry between the time duration of the said switching means of said first arrangement and the time duration of the said switching means of the said second arrangement, said assymetry being a measure of the said offset and thus said direct current, and means provided to produce an alternating potential output signal representative of said assymetry in form suited for driving a load.

11. An instrument for measuring direct current flowing in a conductor as claimed in claim 1, wherein said means sensing the algebraic sum of the currents in the coupling winding are constructed to produce a useful degree of assymetry between the time duration of the said switching means in the said first arrangement and the time duration of the said switching means in the said second arrangement, said assymetry being a measure of the said offset and thus said direct current flowing in said conductor, and wherein said means providing an output indication of the current flowing in the conductor are constructed to provide means conveying, sensing, and demodulating said assymetry, the output of said demodulating means being suited for driving an output indication of the said current flowing in the conductor.

12. An instrument for measuring direct current flowing in a conductor as claimed in claim 1, wherein said means sensing the algebraic sum of the currents in the coupling winding are constructed to provide a useful degree of assymetry between the time duration of the said switching means in the said first arrangement and the time duration of the said switching means in the said second arrangement, said assymetry being a measure of said offset and thus said direct current flowing in said conductor, and means are provided to produce an alternating potential output signal representative of said assymetry in form suited for driving a telemetry link constructed to convey said alternating potential output signal to a location remote from said conductor, and means to demodulate said alternating potential output signal conveyed over said telemetry link and produce an electrical signal representative of said direct current in the conductor suited to driving said output indication of the current flowing in the conductor.

13. An instrument for measuring direct currents flowing in a conductor as claimed in claim 9, wherein means are provided for recording said assymetry, and said means to produce an alternating potential output signal are adapted to driving said recording means.

14. An instrument for measuring direct current flowing in a conductor as claimed in claim 1, wherein said means sensing the algebraic sum of the currents in the coupling winding are constructed to produce a useful degree of assymetry between the time duration of the said switching means in the said first arrangement and the time duration of the said switching means in the said second arrangement, said assymetry being a measure of said offset and thus said direct current flowing in said conductor, and means for recording said assymetry, and means to produce and convey an alternating potential output signal representative of said assymetry in form suited for driving said recording means, and means for playing back the record of said recording means, means demodulating said assymetry, said playing back means adapted to drive said demodulating means, said demodulating means constructed to produce an electrical output signal representative of said assymetry and suited to drive said output indication of said direct current flowing in said conductor.

15. An instrument for measuring direct current flowing in a conductor as claimed in claim 1, wherein the said direct current is made up of several independent direct currents, and the said conductor comprises several sepaRate conductors, each one electrically insulated from all others, there being a separate conductor for each of the said independent direct currents, and the said means enabling the magnetic field of said direct current to operate on said core comprises means enabling each of the said independent direct currents flowing in the said several separate conductors to operate on said core to produce an independent offset in average magnetic intensity in said core weighted in proportion to the degree of coupling of each of the said separate conductors to the said core, the total offset in average magnetic intensity in said core being the algebraic sum of the said independent offsets in average magnetic intensity in said core, and said output indicating means provides an output indication of the current flowing in the conductor comprises means providing an output indication of the weighted algebraic sum of the several independent direct currents flowing in the several separate conductors.

16. An instrument for measuring direct current flowing in a conductor as claimed in claim 1, wherein said magnetic core is in lineal form, and said means enabling the magnetic field of said direct current to operate on said core include means for disposing said lineal form core in direction and position relationship to said conductor so as to produce an offset in average magnetic intensity in said lineal form core in proportion to the magnetic field intensity of the said direct current flowing in said conductor at the position and in the direction of said lineal form core, and said coupling winding on said core comprises a plurality of turns of wire disposed around at least part of said core, and the said means providing an output indication of the current flowing in the conductor includes means providing an output indication of the magnetic field intensity due to the said direct current flowing in the conductor at the position and in the direction of said lineal form core.