Precision, temperature-compensated, shielded current measurement device

Abstract

A current measurement device using a Rogowski coil having a generally toroidal-shaped core with a first winding in one direction and a second winding forming a return loop. The coil is positioned within a two-piece electrostatic shield. A first piece of the electrostatic shield is a partially donut-shaped member having a U-shaped cross-section. The coil is positioned in the donut-shaped member and covered by an encapsulating material. The first piece includes a slit through the cross-section thereof to prevent an electrical loop around the perimeter thereof. The second piece of the electrostatic shield is flat and has a donut-shaped configuration. The second piece is configured with inside and outside peripheral edges such that only one or none of the inside/outside edges contact the first piece. The second piece also has a cross-sectional slit which is in registry with the slit in the first piece.

1 . An electric current measuring device of the type using a coil, comprising;
 a core;   a conductive coil wound about the core, forming a first winding in a first direction and a second winding constituting a return winding; and   an electrostatic shield around the core, outside of the coil, wherein the electrostatic shield comprises a cup portion and a lid portion, each portion being of electrically conductive material.   
   
   
       2 . The electric current measuring device of  claim 1 , wherein the electrostatic shield is configured to prevent the formation of an electrical loop around a perimeter of the coil and around a cross-section of the coil. 
   
   
       3 . The electric current measuring device of  claim 1 , wherein the cup portion and the lid portion have slits through cross-sections thereof, to prevent forming an electrical loop along perimeters thereof. 
   
   
       4 . The electric current measuring device of  claim 3 , wherein the slits in the cup portion and the lid portion are substantially in registry. 
   
   
       5 . The electric current measuring device of  claim 1 , wherein the cup portion and the lid portion are electrically connected to an electrical reference. 
   
   
       6 . The electric current measuring device of  claim 5 , wherein the electrical reference is selected from the group consisting of ground, a driven potential, a shield drain potential and combinations thereof. 
   
   
       7 . The electric current measuring device of  claim 1 , including encapsulating material substantially surrounding the coil between the coil and the electrostatic shield. 
   
   
       8 . The electric current measuring device of  claim 1 , wherein the cup portion and the lid potion are substantially covered by insulating material. 
   
   
       9 . The electric current measuring device of  claim 1 , wherein the cap portion is donut-shaped in configuration, having a U-shaped cross-section and the lid portion is flat, with a donut-shape configuration similar to the cup portion, with inner and outer peripheral edges arranged such that only one or none thereof come into contact with the cup portion. 
   
   
       10 . The electric current measuring device of  claim 1 , wherein the electrically conducting material is non-magnetic. 
   
   
       11 . The electric current measuring device of  claim 1 , wherein the electrically conducting material comprises a woven electrically conducting material. 
   
   
       12 . The electric current measuring device of  claim 1 , wherein the electrically conducting material comprises a mesh. 
   
   
       13 . The electric current measuring device of  claim 1 , wherein the electrostatic shield includes an opening in the cup portion permitting wires from the coil to pass therethrough. 
   
   
       14 . An electrostatic shield for a generally toroidal-shaped coil comprising:
 a partially donut-shaped lower member, the lower member comprising an electrically-conducting, non-magnetic material, the lower member having a slit through a cross-section thereof to prevent an electrical loop along a perimeter thereof; and   a flat upper lid member comprising an electrically-conductive, non-magnetic material configured to fit on top of and to cooperate with the lower member to provide electrostatic shielding for a coil positioned in a volume therebetween, the lid member being donut-shaped with an inner peripheral edge and an outer peripheral edge, only one of which or none of which make physical contact with the lower member, the upper lid member also having a slit through a cross-section thereof, substantially in registry with the slit in the lower member when the upper member is operationally positioned on the lower member.   
   
   
       15 . The electrostatic shield of  claim 14 , wherein the upper and lower members are both substantially covered with electrically insulating material. 
   
   
       16 . The electrostatic shield of  claim 14 , including an opening in the lower member permitting wires from the coil to pass therethrough. 
   
   
       17 . A combination of a coil and an electrostatic shield therefor, for use in on electric current measuring device, comprising:
 a lower electrostatic shield member, generally U-shaped in cross-section, the lower member comprising an electrically-conducting,, non-magnetic material, and configured to receive a coil therein, the lower member having a cross-sectional slit therethrough to prevent an electrical loop around a perimeter thereof;   an upper, flat electrostatic shield lid member comprising an electrically-conducting, non-magnetic material, configured to fit on top of the lower member, wherein the lid member has an inner peripheral edge and an outer peripheral edge, only one of which or none of which make physical contact with the lower member, the upper lid member also having a cross-sectional slit therethrough, substantially in registry with the slit in the lower member when operatively positioned with the lower member;   a coil positioned within the volume defined between the upper and lower members; and   encapsulating material substantially covering the coil within the electrostatic shield.   
   
   
       18 . The combination of  claim 17 , including a connection between the upper and lower members and an electrical reference. 
   
   
       19 . The combination of  claim 18 , wherein the electrical reference is selected from the group consisting of ground, a driven potential, a shield drain potential, and combinations thereof. 
   
   
       20 . The combination of  claim 17 , wherein the coil is in the shape of a toroid and the lower and upper members are correspondingly toroidal-shaped. 
   
   
       21 . The combination of  claim 17 , including an opening in the lower member of the electrostatic shield, permitting wires from the coil to pass therethrough.