Current measurement

Patent metadata

Field	Value
Publication number	US-9411003-B2
Application number	US-201213684213-A
Country	US
Kind code	B2
Filing date	Nov 22, 2012
Priority date	Nov 23, 2011
Publication date	Aug 9, 2016
Grant date	Aug 9, 2016

Abstract

The present invention relates to current measurement apparatus. The current measurement apparatus comprises first and second measurement devices with each of the first and second measurement devices being operative to measure current in a respective one of a live conductor and a neutral conductor substantially simultaneously. The current measurement apparatus is operative to make plural different determinations in dependence on the substantially simultaneous current measurements.

First claim

The invention claimed is:

1. Current measurement apparatus comprising:
a first electrical component coupled in series with the live conductor to receive a live current in the live conductor;
a second electrical component coupled in series with the neutral conductor to receive a neutral current in the neutral conductor;
at least one acquisition circuit operative to convert a first voltage signal across the first electrical component into a first digital signal that corresponds to the live current signal in the live conductor and a second voltage signal across the second electrical component into a second digital signal that corresponds to the neutral current signal in the neutral conductor; a calibration signal source operative during calibration to provide a known calibration signal that is different from load drawn parts of the live and neutral current signals on the live and neutral conductors;
a correlation detection and correction circuit that is operative during calibration to extract parts of the first digital signal that correspond to the calibration signal parts of the live signal from parts of the first digital signal that correspond to the load drawn parts of the live signal on the basis of their frequency characteristics and that is operative during calibration to extract parts of the second digital signal that correspond to the calibration signal parts of the neutral signal from parts of the second digital signal that correspond to the load drawn parts of the neutral signal on the basis of their frequency characteristics and to determine at least one transfer characteristic for the first and second transfer electrical components;
a storage device to store the determined at least one transfer characteristic;
at least one processing circuit operative during normal operation to determine an absolute current flowing in the live conductor, corresponding to a first digital signal, in dependence upon the at least one transfer characteristic and to determine an absolute current flowing in the neutral conductor, corresponding to a first digital signal, in dependence upon the at least one transfer characteristic.

2. Current measurement apparatus according to claim 1 ,
wherein the calibration signal source includes means for modulating current signal present on the live and neutral conductors.

3. Current measurement apparatus according to claim 1 ,
wherein the calibration signal source includes:
at least one calibration resistor;
a switch to controllably couple the at least one calibration resistor between the live conductor and the neutral conductor; and
a modulating circuit coupled to control the switch to turn t switch on and off to modulate a current signal on the live and neutral conductors.

4. Current measurement apparatus according to claim 3 ,
wherein the first electrical component includes a first transformer operative to measure current flowing in the live conductor; and
wherein the second electrical component includes a resistor.

5. Current measurement apparatus according to claim 1 ,
wherein the first electrical component includes a first transformer operative to measure current flowing in the live conductor;
a calibration conductor that passes through the first transformer and that includes a distal end that is electrically coupled to the neutral conductor at a load side of the second component;
wherein the calibration signal source includes a node electrically coupled to proximal end of the calibration conductor and includes a node electrically coupled to the neutral conductor at a source side of the second component.

6. Current measurement apparatus according to claim 5 further including:
a modulating circuit coupled to control provision of the calibration signal by the calibration signal source.

7. Current measurement apparatus according to claim 1 ,
wherein the first electrical component includes a first transformer operative to measure current flowing in the live conductor;
wherein the second electrical component includes a second transformer operative to measure current flowing in the neutral conductor;
a calibration conductor that passes through the first transformer and that passes through the second transformer;
wherein the calibration signal source is coupled to a node electrically coupled to a proximal portion of the calibration conductor electrically disposed between the calibration signal source and the first transformer and is coupled to a node electrically coupled to a distal portion of the calibration conductor electrically disposed between the calibration signal source and the second transformer.

8. Current measurement apparatus according to claim 7 further including:
a modulating circuit coupled to control provision of the calibration signal by the calibration signal source.

9. Current measurement apparatus according to claim 1 ,
wherein the first electrical component includes a first transformer operative to measure current flowing in the live conductor;
wherein the second electrical component includes a second transformer operative to measure current flowing in the neutral conductor;
a first calibration conductor that passes through the first transformer;
a second calibration conductor that passes through the first transformer; further including:
a switch circuit;
wherein the calibration signal source is coupled to provide the calibration signal to the switch circuit;
wherein a first output of the switch circuit is electrically coupled to a proximal portion of the first calibration conductor electrically disposed between the switch circuit and the first transformer and a second output of the switch circuit is electrically coupled to a proximal portion of the second calibration conductor electrically disposed between the switch circuit and the second transformer; and
wherein distal portions of the first and second calibration conductors are electrically coupled to the neutral conductor.

10. Current measurement apparatus according to claim 9 further including:
a modulating circuit coupled to control provision of the calibration signal by the calibration signal source.

11. Current measurement apparatus according to claim 9 further including:
a differencing circuit operative to determine a difference signal indicative of a difference between the first digital signal and the second digital signal; and
a first arc waveform detector circuit operative to identify first waveform profiles of the first digital signal indicative of an arcing condition.

12. Current measurement apparatus according to claim 1 further including:
a differencing circuit operative to determine a difference signal indicative of a difference between the first digital signal and the second digital signal;
a first arc waveform detector circuit operative to identify first waveform profiles of the first digital signal indicative of an arcing condition; and
a second arc waveform detector circuit operative to identify second waveform profiles of the second digital signal indicative of an arcing condition.

13. Current measurement apparatus according to claim 12 ,
wherein the calibration signal source includes:
at least one calibration resistor;
a switch to controllably couple the at least one calibration resistor between the live conductor and the neutral conductor;
a modulating circuit coupled to control the switch to turn the switch on and off to modulate a current signal on the live and neutral conductors.

14. Current measurement apparatus according to claim 13 ,
a filter circuit that includes a band pass filter operative on the difference signal to filter out higher frequency

Assignees

• Analog Devices Global

Inventors

• Danesh Seyed Amir Ali
• Hurwitz Jonathan Ephraim David

Classifications

• G01R21/06

  by measuring current and voltage (G01R21/08 - G01R21/133 take precedence) · CPC title

• H02H3/006

  Calibration or setting of parameters · CPC title

• G01R19/16547

  voltage or current in AC supplies (switching for protection H02H; circuits for emergency power supply H02J9/00) · CPC title

• H02H3/32

  involving comparison of the voltage or current values at corresponding points in different conductors of a single system, e.g. of currents in go and return conductors · CPC title

• G01R19/2506

  Arrangements for conditioning or analysing measured signals, e.g. for indicating peak values (G01R19/003 takes precedence); Details concerning sampling, digitizing or waveform capturing (displaying waveforms G01R13/00; analog sampling G01R19/0053) · CPC title