ELECTRICAL CURRENT DETECTOR

• US 3,882,387 A
• Filed: 03/23/1973
• Issued: 05/06/1975
• Est. Priority Date: 03/23/1973
• Status: Expired due to Term

• Current Assignee: Dennis G. Vikstrom
• Original Assignee: Dennis G. Vikstrom
• Inventors: Vikstrom, Dennis G.
• Primary Examiner(s): Strecker, Gerard R.
• Assistant Examiner(s): Karlsen, Ernest F.
• Application Number:
  US05/344,072
• Time in Patent Office: 774 Days
• Field of Search: 324/117R,117H,127 336/175,176
• US Class Current: 324/117.00R
• CPC Class Codes: G01R 15/185 with compensation or feedback windings or interacting coils, e.g. 0-flux sensors using galvano-magnetic field sensors G01R15/20; conversion of DC into AC using transductors G01R19/20
• CPC Class Codes: G01R 15/186 using current transformers with a core consisting of two or more parts, e.g. clamp-on type G01R15/142 - G01R15/16 take precedence; tong testers G01R1/22
• CPC Class Codes: G01R 19/15 Indicating the presence of current

Abstract

A folded annular core of uniform cross section has an excitation winding and a feedback winding on each core half. A source of unidirectional current pulses periodically energizes the excitation windings to saturate the core. A measuring circuit detects the e.m.f. values induced in each excitation winding after each current pulse terminates, subtracts one value from another and integrates the difference to provide an output signal proportional to the current being measured. A feedback circuit produces a current proportional to the output signals to energize the feedback windings for nulling the core flux due to the current being measured to insure that the device operates in the linear region of the hysteresis loop of the core. A clamp-on current detector uses two folded annular cores to completely encircle a conductor carrying the current to be measured.

Claims

1. Means for measuring a d.c. current in a conductor comprising, a current sensor for placement in the magnetic field of the current including a unitary folded annular core defining two core halves, the core comprising ferromagnetic material of uniform cross section, so that the core halves carry flux proportional to the magnetic field of the current, and an excitation winding and a feedback winding on each core half, and a measuring circuit including, excitation circuit means for delivering to the excitation windings periodic pulses of unidirectional current sufficient to uniformly saturate the core, and a detecting circuit connected with the excitation windings and electrically isolated from the periodic pulses having means for differentially summing e.m.f. pulses generated in the excitation windings by core flux change occurring after the termination of each periodic current pulse, and having integrator means for integrating the differential sum thereby producing a signal proportional to the current in the conductor, and a feedback circuit associated with the detecting circuit and connected to the feedback windings for supplying current for nulling that d.c. flux in the core material which is due to the current being measured.

2. Means for measuring a d.c. current in a conductor comprising, a current sensor for placement in the magnetic field of the current including, a pair of folded annular cores, each core defining two core halves integrally connected at two fold portions, the cores comprising ferromagnetic material of uniform cross section, so that the cores carry flux proportional to the magnetic field of the current, a feedback winding on each core half, and first and second excitation windings on the core halves of one core and third and fourth excitation windings on the core halves of the other core, means for holding the two cores in contact at the fold portions to completely encircle the conductor and for effecting separation of the two cores to permit insertion and removal of the conductor;

and a measuring circuit including, excitation circuit means for delivery to the excitation windings periodic pulses of unidirectional current sufficient to uniformly saturate the core, and a detecting circuit connected with the excitation winding and electrically isolated from the periodic pulses having means for combining e.m.f. pulses generated in first and third excitation windings by core flux change occurring after the termination of each periodic current pulse, means for combining the e.m.f. pulses similarly generated in the second and fourth excitation windings, means for differentially summing the two combined e.m.f. pulses, and having integrator means for integrating the differential sum thereby producing a signal proportional to the current in the conductor, and a feedback circuit associated with the detecting cirCuit and connected to the feedback windings for supplying current for nulling that d.c. flux in the core material which is due to the current being measured.