CA1253570A

CA1253570A - Current measurement shunt

Info

Publication number: CA1253570A
Application number: CA000461662A
Authority: CA
Inventors: Gilles Roy; Guy Olivier; Georges-Emile April
Original assignee: Individual
Current assignee: APRIL GEORGES EMILE
Priority date: 1984-08-23
Filing date: 1984-08-23
Publication date: 1989-05-02

Abstract

ABSTRACT OF THE DISCLOSURE
A current measurement shunt which is immune to the effects of strong stray magnetic fields is composed of conductive strips laid down by printed circuit techniques on alternate sides of a printed circuit board. The circuit is folded back upon itself to form a return path of alternated connected strips.

Description

i7~

l CW-lO95 ~ CURRENT MEASUREMENT SHUNT
; The invention described herein relates to electric instruments and particularly to a current measuring shunt.
Shunts are used in connection with electrical instruments for measuring the flow of electrical current in circuits, particularly circuits carrying heavy current. The shunt carries most of the current to be measured through a resistance calibrated in relation to the instrument with which it is used so that there is a predetermined relationship between the current through the shunt and the vbltage drop across the shunt. The electrical measuring instrument is usually a sensitive milli~olt meter connected across the shunt to measure the voltage drop, the instrument itself carrying only a small fraction of the total curren~
being measured, most of which bypasses the instrument and flows through the shunt. In this case, it is difficult to maintain its resistance constant because of the heat generated in the measuring device.
Most shunts currently in use comprise two massive solid terminal blocks usually formed of copper or brass castings or extrusions. Extending between the terminal blocks are a plurality of spaced strips of conducting material, the ends of which are soldered or welded in slots machined in the opposing faces of the terminal blocks. These shunts are costly to build because skilled labour is required to machine the slots in the terminal blocks accurately and patO02/ll ~

'~ 2~ 357 ~

2 CW-1095 because scrap losses are high due to the large amount of metal in any terminal blocks that must be scrapped because of machining errors. Furthermore, assembly is difficult because of the weight of the massive terminal blocks which makes them difficult to handle.
Also it is necessary to maintain the temperature of the shunt constant and the device therefore is cooled by air, but since variation in current flow produces different levels of heating, a uniform flow of air thereover cannot possibly maintain a constant temperature. Sînce the resistance of the copper and pieces varies about 0.4% per degree centigrade and since the resistance of the welded joints and copper is an appreciable percentage of the total resistance, the accuracy of the device is limited to about 1%.
Moreover, known current measuring shunts are not compensated, that is, the device i8 not protectecl against the influence of stray magnetic fields. In those cases, the current is estimated by measuring the voltage drop across at least a portion of the shunt, and it will be apparent that the voltage developed will not be a true indication of the current because of the effect that the induced voltage will have on the reading. Such stray magnetic fields also distort the current distribution in the shunt so that it may be greater in one part than in another. Regardless of where the sensing or voltage measuring elements are positioned in the shunt, they will not be capable of sensing an average flow of current under all conditions of operation Other known current measuring devices determine the current values by measuring the flux density surrounding a current carrying conductor. They consist of a plurality of L-shaped magnetic yoke sections assembled to form a square surrounding the bus bar but spaced from each other at their ends to form air gaps therebetween. The sensing elements located within the gaps respond to the flux flow thereacross and thereby provide a reading of the current flowing in the bus bar assembly. The primary disadvantage of this kind of construction is the iron of the yoke must be operated at a patO02/11 ~L~535q~3

3 CW-1095 flu~ density less than that which will cause saturation of the iron. In the event a large number of ampere turns are involved, such as 500,000, in order to prevent the iron from saturation, it is necessary to provide Large air gaps which result in inaccuracy in the reading taken.
The above-cited disadvantages indicate the need for an improved current measuring shunt capable of both eliminating the problems connected with known devices and extending the range to measure current of high magnitude.
The primary object of my invention, therefore, is to provide a relatively small device capable of measuring current values up to about 1,000 amperes of frequencies, up to 40-50 kilohertz and within an accuracy range of about 1%.
Another object of my invention is to provide current measuring shunt wlth substantial immunity to electromagnetic effects from adjacent stray field generators.
Yet, another object of my invention is to provide a shunt which is simple in construction, for~ed o~ relatively lightweight component parts, and hence is less costly and easier to manufacture.

SUMMARY OF THE INVENTION
The present invention amply satisfies all of the foregoing requirements of current measuring shunts simultaneously and does it, moreover, with a minimum of expense and complexity.
Broadly, the invention permits the measurement of current without the influence of stray magnetic fields by forming two bus bars made from conductive material and formed by standard etching method on the opposite surfaces of printed circuit ~p.c.) board. Bus bars are compris~d of a plurality of conductive portions and portions located on one surface of printed board are connected with conductive portions on the opposite surface of the board through holes in the p.c. board. The particular way of connecting the conductive portions divides the current into two parallel branches such that the current flows in a transposed patO02/11 - i ~ ~5 3~7 ~

4 CW-1095 configuration. Bus bars are provided with a pair o~
conductive bars that are produced on both surfaces of printed board to provide a voltage signal proportional to the current passing through said bus bars.
While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which we regard as our invention, it is believed the invention will be better understood from the following description taken in connection with the accompanying drawings in which:
Figure 1 shows a current measuring shunt.
Referring to the drawing, there is illustrated in Figure 1 a typical installation of shunt comprising two bus bars 1 and 2 that are divided in a plurality of conductive portions. Bus bars 1 and 2 made from a conductive material such as copper and are formed by standard etchi.ng method on printed circuit board 3. The conductlve portions of bar 1 belonging to one of the surfaces of printed board 3 are connected with conductive portions of bus bar 2 belonging to the opposite surface of printed circuit board 3 through holes, made in printed board 3.
Current measurement bars 4 and 5 are accordingly connected by fastening suitable leads to the ends of bus bars 1 and 2 and also are produced on the surfaces of the printed circuit board 3.
The current is divided into two parallel branches both of which provide for current flow in a transposed configuration (shown by arrows on Fig. 1) so as to eliminate the effect of stray magnetic fields.
The connections of conductive portions through holes in printed circuit board is performed either by conducting pins soldered on both sides of the printed circuit board or by plating the inside walls of the holes by standard plating techni~ues.
Numerous and varied other arrangements may be utilized by those skilled in the art without departlng from the spirit and scope of the invention.
patO02/11

Claims

CLAIMS:

1. A current measurement shunt comprising a serially connected chain of electrically conductive, strips laid down on a relatively thin flat insulating medium in a predetermined pattern such that current flow in a first section of the chain alternates from one side of said insulating medium to the other as the current passes from strip to strip, said chain being folded back upon itself so that a second section of the chain comprises a second set of serially connected conductive strips interspersed between the strips of said first section and being insulated therefrom and being connected serially in such a manner that the total length of the strips of said first section and the total length of the strips of the second section are substantially equal, and each section of said chain carries current substantially equidistantly on both sides of said insulating medium.

2. A current measurement shunt as claimed in claim 1 wherein the shunt comprises two serially connected chains connected in parallel and laid down in close proximity, in a side by side spaced insulated relationship and connected in such a manner that adjacent strips of each chain carry current in opposite directions.

3. A current measurement shunt for use on a printed circuit board comprising a serially connected chain of strips of a preselected conductive material of substantially the same width and thickness laid down in a predetermined manner on said printed circuit board, such that current flow in a first section of said chain alternates from one side of said printed circuit board to the other as the current passes from strip to strip, said chain being folded back upon itself so that a second section of the chain comprises a second set of serially connected strips inter-spersed between the strips of the first section and being insulated therefrom, the total length of the strips in the first and second sections being substantially equal.

4. A shunt as claimed in claim 3 comprising a pair of chains of serially connected strips connected in parallel and laid down on said printed circuit board in a close, but spaced insulating relationship such that adjacent strips of both chains carry current in opposite directions.

5. A current measuring shunt comprising at least a pair of conducting paths formed by elongated flat conductive segments of a suitable preselected conductive material, the conductive segments for each path extending substantially in registry along both sides of opposing surfaces of a relatively thin flat insulating medium, the conductive segments being connected together in a predetermined manner such that each of the conducting paths of said pair extend substantially parallel to each other, and the conducting paths so formed alternately pass from one surface to the other of said insulating medium in an evenly transposed manner such that the current flow in any two segments in registration on opposing sides of said insulating medium is in opposite directions.

6. A current measuring shunt comprising two bus bars made from electrically conductive material and formed on the opposite surfaces of an insulative board, said bus bars are comprised of a plurality of conductive portions where said conductive portions belonging to one surface of said insulative board are connected with conductive portions of opposite surfaces of said board through holes made in said board so that current applied to said bus bars is divided into two parallel branches and flows in a transposed configuration;
said bus bars are connected with current measurement terminals that are formed on both surfaces of said insul-ative board by means of fastening suitable leads by said bus bars.

7. A current measuring shunt according to claim 6 wherein bus bars are made from copper.

8. A current measuring shunt according to claim 6 wherein connections of conductive portions formed on both sides of non-electrically conductive board are performed by using a conductive plating material deposited on the side-walls of the holes or by conductive pins soldered on both sides of the insulative board or by using fusible material such as solder to fill said holes.