Title of Invention

CURRENT DETECTOR AND CURRENT MEASUREMENT APPARATUS INCLUDING SUCH DETECTOR

Abstract

ABSTRACT A CURRENT SENSOR AND A CURRENT MEASUREMENT APPARATUS The invention relates to a current sensor comprising a metallic link member having two end portions of conductive material and an intermediate portion interconnecting the end portions, said intermediate portion being formed of a resistive material and an integrated circuit analog to digital converter mounted on said link member, said converter having analog input terminals commented to respective ones of said two end portions and a digital output for connection to a processing apparatus.

Full Text

This invention relates to a current sensor intended for use in an electrical apparatus such as a residual current detection device, a current meter or a power meter. It is an object of the present invention to provide a current sensor in an economical form In accordance with the invention there is provided a current sensor comprising a metallic link member having two end portions of conductive material and an intermediate portion interconnecting the end portions, said intermediate portion being formed of a resistive material, and an integrated circuit analog to digital converter mounted on said link member, said converter having analog input terminals connected to respective ones of said two end portions and digital output terminals for connection to a processing apparatus. Conveniently, the converter is attached to the intermediate portion by a layer of electrically insulative adhesive material and the analog input terminals of the converter are connected to the end portions by wire bonds. The converter preferably includes a delta-sigma modulator which provides a high frequency one-bit digital data. One or more decimation filtering stages may be included in the converter. The converter may also have a voltage reference terminal for connection to a reference voltage source, the converter operating to provide digital output signals respectively representing the current flowing through said intermediate portion and digital output signals representing the voltage on one of said end portions. The present invention relates to an analog to digital converter mounted on the intermediate resistive portion of a shunt, whereas EP 0445048 relates to a measuring sensor comprising a hollow cylindrical shunt. EP 0445048 does not disclose a current sensor with a resistive intermediate portion. The shunt resistor R5 in EP 0445048 is formed from a cylindrical element o made from copper with a typical resistance of 1.8 x 10" ohms/metre. In addition, all of the current carrying components of the same material. The present invention, in comparison, defines a current sensor comprising a metallic link member having two end portions and a resistive intermediate portion. In a preferred embodiment the intermediate portion is made of Manganin, which has a much larger resistance of 0.29 X 10'‘ ohms/metre. In addition, the EP0445048 converter is not mounted on the link member. Instead, it is mounted on the support 29 which is connected to the rectangular flexible part 28 by a strip 30. Furthermore, the converter embodying the invention is an analog to digital converter, but this is not disclosed in EP0445408. The present invention requires that the analog to digital converter is mounted on the shunt with its terminals connected to respective end portions. This is not disclosed in US 6,034,521. The US patent No. 6,034,521 is concerned with much higher voltage applications than the subject invention, which mentions large scale power converters having voltages of5kV and tending towards 10or20kV. The subject application 3 concerned with an apparatus such as RCD, a current meter or power meter, for example as used in domestic power supplies. Due to the high voltage involved, US 6,034,521 describes a current sensor with an optical light guide connector. The detection electronics are placed inside a cavity formed between two parts of the shunt to provide mechanical and electromagnetic shielding. Such shielding is not really an issue for embodiments of the claimed current sensor, as it is not intended for use in specialized high voltage applications. In contrast, embodiments of the subject invention are directed to a current sensor of an economical form. The shunt is manufactured in a much more economical way by slicing up a sandwich into strips, The US 6,034, 521 shunt in comparison must be fabricated in two parts and then assembled with the electronics inside the cavity. Embodiments of the present invention require mounting an analog to digital integrated circuit on the shunt itself, for the purpose of producing a digital output indicative of current flowing through the shunt. US 5, 701,253 does not disclose this. US 5,701,253 is concerned with power measurement and teaches a way from the claimed structure by suggesting that an isolation barrier be provided between the shunt and the processing circuit. Accordingly, the present invention provides a current sensor comprising a metallic link member having two end portions of conductive material and an intermediate portion interconnecting the end portions, said intermediate portion being formed of a resistive material, and an integrated circuit analog to digital converter mounted on said link member, said converter having analog input terminals connected to respective ones of said two end portions and a digital output for connection to a processing apparatus. With reference to the accompanying drawings in which : Figure 1 is a perspective view of one example of a current detector In accordance with the invention, Figure 2 is a sectional view of the detector, Figure 3 is an elevation of the detector, Figure 4 is a block diagram of a simple form of an electronic circuit for the detector, and Figures 5 and 6 are block diagrams of more complex forms of electronic circuits. The detector shown in Figures 1 to 3 includes a rigid composite conductor strip having two end portions 13 of copper and an Intenmediate portion 14 of a resistive material such as manganin. The strips are fonned by slicing up a sandwich formed by electron beam welding of the copper bars to opposite sides of a manganin bar. The shunts formed by the resistive portions 14 manufactured by this method mav have a nominal rp<:i> of 0.2mQ, to a tolerance of less than 5%. The resistance of adjacent slices from the sandwich may differ by as little as 2%. A signal pre-processing ASIC 15 is mounted on the manganin portion 14 by means of a layer of electrically insulating adhesive 16. Wire leads 17 connect two analog input terminals of the ASIC to respective ones of the copper end portions 13. Further leads connect terminals on the ASIC to conductors of a lead frame 18 parts of which are shown. As shoVvn in Figure 3 the ASIC, the manganin portion, the wire leads and the lead frame conductors are all enclosed within a block 19 of electrically insulating encapsulation material for the protection thereof. Opposite ends of the copper end portions 13 project from the encapsulation block 19. Turning now to Figure 4, it will be seen that the main block within the ASIC 15 consists of a single delta-sigma modulator 20. There is also an analog input circuit which has its input terminals connected to the copper end portions 13. The output of the ASIC 15 in this case consists of a high frequency one-bit data signal train. In use, the ASIC output is connected via a transformer or other isolation barrier 22 to a processor 23. The processor in this arrangement is configured to carry out one or more decimation filtering operations to convert the one-bit signal stream into a multi-bit digital valve at a lower frequency. The processor 23 may typically be configured to receive signals from a plurality of the detectors and to sum these signals to ascertain whether the current flows through the detectors are balanced. Such an arrangement 6 can be used for residual current correction allowing an actuator to trip a switch if an unbalanced condition is found to exist. The processor 23 may alternatively or additionally compare the instantaneous current level with a trip level so that overcurrent tripping can be controlled. In the alternative embodiment shown in Figure 5, the ASIC is nibre complex and includes one or more of the decimation filtration stages 24 and a serial output driver 25 to transmit the bits of the multi-bit digital signal produced by the filtration stage 24 serially to the processor. With this arrangement, the configuration of the processor can be simplified as part or all of the decimation filtration operation is carried out in the ASIC. In the arrangement shown in Figure 6 the ASIC has a further analog input which can be connected to a reference voltage source. Two analog input stages 21a and 21b are present and these feed signals to two independent delta-sigma modulators 20a,20b. As shown, there are two independent decimation filtration stages 22a,22b for the two one-bit digital signal streams. The outputs of the stages 22a,22b may, as shown, be connected to a common serial output stage or (not shown) separate serial output stages may be provided. It will be appreciated that the arrangement of Figure 6 may be modified by the omission of the two filtration stages 22a,22b where all filtration is to be carried out by the processor. where voltage as well as current Is monitored by the processor, precise calibration of the shunts can be achieved. This allows more accurate determination of the current balance in RCD applications. Moreover, as voltage and current are both being monitored to a high level of precision, accurate power consumption metering can be obtained. Where the devices of the invention are used in RCD and overcurrent trip systems, the processor can be programmed to recognise the transients which may occur when loads are switched in and out of circuit to avoid false tripping. Many other convenient functions can be programmed into the processor, made possible by the high precision of the current measurements capable of being carried out. WE CLAIM : 1. A current sensor comprising a metallic link member having two end portions of conductive material and an intermediate portion interconnecting the end portions said intermediate portion being formed of a resistive material, and an integrated circuit analog to digital converter mounted on said link member, said converter having analog input terminals connected to respective ones of said two end portions and a digital output for connection to a processing apparatus. 2. The current sensor as claimed in claim 1, in which the converter is attached to the link member by a layer of electrically insulating adhesive. 3. The current sensor as claimed in claim 2, wherein the converter is attached to the intermediate portion. 4. The current sensor as claimed in claim 3, in which the analog input terminals of the converter are connected to the end portions by means of wire bonds. 5. The current sensor as claimed in any one of the preceding claims, wherein the converter has a voltage reference terminal for connection to a reference voltage source and said converter operates to provide digital output signals representing the current through said intermediate portion and digital output signals representing the voltage on one of the end portions. 6. The current sensor as claimed in any one of the preceding claims, wherein said converter has a delta-sigma modulator, which provides a high frequency one-bit digital data stream. 7. The current sensor as claimed in claim 6, wherein the converter also has at least one decimation filter stage. 8. The current sensor as claimed in any one of the preceding claims, comprising a processor circuit connected to receive and process digital signals received from the digital output. 9. The current sensor as claimed in claim 8, wherein the processor circuit is configured to carry out one or more decimation filtering operations on the received digital signals. 10. A current measurement apparatus comprising at least one current sensor as claimed in any one of the preceding claims. 11. A current sensor, substantially as herein described with reference to figures 1 to 3, 5 and 6 of the accompanying drawings.

Documents:

in-pct-2000-0860-che abstract.pdf

in-pct-2000-0860-che claims-duplicate.pdf

in-pct-2000-0860-che claims.pdf

in-pct-2000-0860-che correspondence-others.pdf

in-pct-2000-0860-che correspondence-po.pdf

in-pct-2000-0860-che description (complete)-duplicate.pdf

in-pct-2000-0860-che description (complete).pdf

in-pct-2000-0860-che drawings-duplicate.pdf

in-pct-2000-0860-che drawings.pdf

in-pct-2000-0860-che form-1.pdf

in-pct-2000-0860-che form-13.pdf

in-pct-2000-0860-che form-19.pdf

in-pct-2000-0860-che form-26.pdf

in-pct-2000-0860-che form-3.pdf

in-pct-2000-0860-che form-5.pdf

in-pct-2000-0860-che form-6.pdf

in-pct-2000-0860-che pct.pdf

in-pct-2000-0860-che petition.pdf