U.S. patent application number 10/711745 was filed with the patent office on 2005-04-07 for system and method for current sensing using anti-differential, error correcting current sensing.
Invention is credited to Gass, Dale L., Hastings, Jerome K., Solveson, Mark G..
Application Number | 20050073292 10/711745 |
Document ID | / |
Family ID | 34421684 |
Filed Date | 2005-04-07 |
United States Patent
Application |
20050073292 |
Kind Code |
A1 |
Hastings, Jerome K. ; et
al. |
April 7, 2005 |
SYSTEM AND METHOD FOR CURRENT SENSING USING ANTI-DIFFERENTIAL,
ERROR CORRECTING CURRENT SENSING
Abstract
The present invention is directed to system and method for
current sensing using an anti-differential, error correcting,
current sensing system. The invention includes a conductive path
configured to receive a current therethrough. A first current
sensor is positioned on a first side of the conductive path and
configured to monitor a first directional magnetic field induced by
the current. A second current sensor is positioned on a second side
of the conductive path, substantially opposite the first current
sensor, and configured to monitor a second directional magnetic
field induced by the current that is substantially opposite in
direction to the first directional magnetic field. A processing
component is configured to receive feedback from the first current
sensor and the second current sensor and generate an
anti-differential output from the feedback.
Inventors: |
Hastings, Jerome K.;
(Sussex, WI) ; Solveson, Mark G.; (Oconomowoc,
WI) ; Gass, Dale L.; (Brown Deer, WI) |
Correspondence
Address: |
ZIOLKOWSKI PATENT SOLUTIONS GROUP, LLC (EATON)
14135 NORTH CEDARBURG ROAD
MEQUON
WI
53097
US
|
Family ID: |
34421684 |
Appl. No.: |
10/711745 |
Filed: |
October 1, 2004 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60507896 |
Oct 1, 2003 |
|
|
|
Current U.S.
Class: |
324/117H |
Current CPC
Class: |
G01R 15/202 20130101;
G01R 15/207 20130101 |
Class at
Publication: |
324/117.00H |
International
Class: |
G01R 033/02 |
Claims
What is claimed is:
1. A current monitoring system comprising: a conductive path
configured to receive a current therethrough; a first current
sensor positioned on a first side of the conductive path and
configured to monitor a first directional magnetic field induced by
the current; a second current sensor positioned on a second side of
the conductive path, substantially opposite the first current
sensor, and configured to monitor a second directional magnetic
field induced by the current that is substantially opposite in
direction to the first directional magnetic field; and a processing
component configured to receive feedback from the first current
sensor and the second current sensor and generate an
anti-differential output from the feedback.
2. The system of claim 1 wherein the processing component includes
at least one of a summing amplifier and a differential
amplifier.
3. The system of claim 1 wherein the first current sensor includes
a first Hall effect sensor and the second current sensor includes a
second Hall effect sensor.
4. The system of claim 3 wherein the first Hall effect sensor is
configured to generate a first feedback upon detecting the first
directional magnetic field induced by the current through the
conductive path and the second Hall effect sensor is configured to
generate a second feedback upon detecting the second directional
magnetic field induced by the current through the conductive
path.
5. The system of claim 4 wherein the first feedback generated by
the first Hall effect sensor includes an indication of another
current upon detecting a directional magnetic field induced
externally to the conductive path and the second feedback generated
by the second Hall effect sensor includes an indication of another
current upon detecting the directional magnetic field induced
externally to the conductive path.
6. The system of claim 5 further comprising generating the
anti-differential output from the first feedback and the second
feedback to reduce the indication of the another current.
7. The system of claim 3 wherein the anti-differential output is
substantially free of variations due to changes in operating
temperatures of the first Hall effect detector and the second Hall
effect detector and substantially free of variations due to
hysteresis, magnetic core saturation, and eddy currents.
8. The system of claim 3 further comprising a constant current
power supply having at least one of a bias current compensation
circuit and a temperature dependent adjustable gain configured to
compensate for Hall gain drift and wherein the processing component
includes a temperature dependant op-amp gain loop configured to
compensate for temperature dependent electronic drift.
9. The system of claim 1 wherein the first current sensor and the
second current sensor are substantially free of ferromagnetic field
concentrating materials.
10. The system of claim 1 further comprising an adjacent conductive
path positioned proximate to the conductive path and having a
current flow therethrough.
11. The system of claim 10 wherein the first current sensor, the
second sensor, and the processing component are configured to
perform common mode error correcting to substantially eliminate
feedback attributable to the adjacent conductive path from the
anti-differential output.
12. A current sensor comprising: a first Hall effect sensor
positioned proximate to a conductor and configured to provide a
first feedback indicative of a current flow through the conductor;
a second Hall effect sensor positioned proximate to the conductor
and configured to provide a second feedback indicative of the
current flow through the conductor; and a processing device
configured to generate a summed difference of the first feedback
and the second feedback to reduce feedback corresponding to
magnetic fields induced externally from the conductor.
13. The current sensor of claim 12 wherein the first Hall effect
sensor is positioned on a first side of the conductor and the
second Hall effect sensor is positioned on a second side of the
conductor, wherein the first side of the conductor is substantially
opposite the second side of the conductor.
14. The current sensor of claim 12 wherein the first Hall effect
sensor is configured to provide feedback having a first polarity
upon detecting magnetic fields induced by current flow through the
conductor and the second Hall effect sensor is configured to
provide feedback having a second polarity upon detecting magnetic
fields induced by current flow through the conductor.
15. The current sensor of claim 14 wherein the first Hall effect
sensor and the second Hall effect sensor are configured to provide
feedback having the first polarity upon detecting magnetic fields
induced externally from the conductor.
16. The current sensor of claim 15 wherein the processing component
includes a differential amplifier configured to sum the difference
of the feedback having the first polarity and the feedback having
the second polarity to substantially remove feedback generated upon
detecting magnetic fields induced externally from the
conductor.
17. The current sensor of claim 12 wherein the processing component
includes an amplifier configured to calculate at least one of a sum
and a difference of the first feedback and the second feedback to
generate the summed difference.
18. The current sensor of claim 12 further comprising a constant
current power supply having at least one of a bias current
compensation circuit and a temperature dependent adjustable gain
configured to compensate for Hall gain drift.
19. The current sensor of claim 12 wherein the summed difference is
substantially free of variations due to changes in operating
temperatures of the first Hall effect detector and the second Hall
effect detector.
20. The current sensor of claim 12 wherein the current sensor is
substantially free of ferromagnetic core materials.
21. The current sensor of claim 12 wherein the summed difference is
substantially free of variations due to hysteresis, magnetic core
saturation, and eddy currents.
22. The current sensor of claim 12 wherein the summed difference is
zero when no current flow is present through the conductor.
23. A method of determining current flow through an electrical path
comprising the steps of: generating a first feedback represented by
a first vector having a first direction and a first magnitude upon
detecting a first direction of magnetic flux induced by a current
flow through an electrical path and a second vector having the
first direction and a second magnitude upon detecting a second
direction of magnetic flux induced externally from the electrical
path; generating a second feedback represented by a third vector
having the first direction and the first magnitude upon detecting a
third direction of magnetic flux induced by the current flow
through the electrical path and a fourth vector having a second
direction and the second magnitude upon detecting the second
direction of magnetic flux induced externally from the electrical
path; and summing the first feedback and the second feedback to
create an anti-differential sum thereby substantially canceling the
effects of the first feedback and the second feedback represented
by the second vector and the fourth vector.
24. The method of claim 23 further comprising the step of
correcting for Lorentz force drifts associated with temperature
variations by providing a temperature dependent supply of power to
a sensor system configured to generate the first feedback and the
second feedback.
25. The method of claim 23 further comprising the step of
correcting for electronic drift associated with temperature
variations.
26. The method of claim 23 wherein the first direction of magnetic
flux and the third direction of magnetic flux are substantially
opposite.
27. The method of claim 23 wherein the steps of generating the
first feedback and generating the second feedback include
monitoring the electrical path includes monitoring at least one of
a conductive wire, a bus bar, and an integrated circuit (IC) board
etching to determine the first, second and third directions of
magnetic flux.
28. The method of claim 23 wherein the steps of generating the
first feedback and generating the second feedback further comprises
receiving feedback from at least two Hall sensors configured to
detect oppositely directed magnetic flux induced by current flow
through the electrical path to generate the first feedback and the
second feedback.
29. The method of claim 28 further comprising compensating for a
Hall voltage zero flux offset by matching the at least two Hall
sensors.
30. The method of claim 28 further comprising removing phase shifts
such that the anti-differential sum is in phase with current flow
through the electrical path.
31. An anti-differential current sensing system comprising: an
electrically conductive path; a first Hall effect sensor disposed
proximate to a first side of the electrically conductive path and
configured to generate a first measure of a current flow through
the electrically conductive path by monitoring magnetic fields; a
second Hall effect sensor disposed proximate to a second side of
the electrically conductive path, substantially opposite the first
side of the electrically conductive path, and configured to
generate a second measure of the current flow through the
electrically conductive path by monitoring magnetic fields; and a
processing device configured to receive the first measure of the
current flow and the second measure of the current flow and
generate an output from the first measure of the current flow and
the second measure of the current flow substantially free of errors
due to magnetic fields generated externally from the conductive
path.
32. The system of claim 31 wherein the processing device includes
at least one of a summing amplifier and a differential amplifier
configured to reduce the first measure of the current and the
second measure of the current by an amount attributable to magnetic
fields induced externally to the electrically conductive path.
33. The system of claim 32 wherein the processing device includes
an op-amp.
34. The system of claim 31 wherein the first Hall effect sensor and
the second Hall effect sensor are positioned about a periphery of
the electrically conductive path.
35. The system of claim 31 wherein the current flow through the
electrically conductive path includes at least one of a direct
current (DC) and an alternating current (AC).
36. The system of claim 35 wherein the current flow includes a
frequency of greater than 30 kHz.
37. The system of claim 31 further comprising a second electrically
conductive path proximate the electrically conductive path.
38. The system of claim 37 wherein the electrically conductive path
and the second electrically conductive path include a wire having a
first radius and a second radius, respectively.
39. The system of claim 38 wherein the electrically conductive path
and the second electrically conductive path are disposed at a
distance separating the electrically conductive path and the second
electrically conductive path by approximately three times a greater
of the first radius and the second radius to provide a buffer for
common mode error correcting.
40. The system of claim 39 wherein the buffer is configured such
that a summed difference of the first measure of the current flow
through the electrically conductive path and the second measure of
the current flow through the electrically conductive path includes
an error of not greater than 1%.
41. The system of claim 37 wherein the electrically conductive path
and the second electrically conductive path each include a bus bar
and wherein the bus bars are disposed at a distance of
approximately one-and-one half times a width of the bus bars.
42. The system of claim 41 wherein the buffer is configured such
that a summed difference of the first measure of the current flow
through the electrically conductive path and the second measure of
the current flow through the electrically conductive path includes
an error of not greater than 1%.
43. The system of claim 31 wherein a summed difference of the first
measure of the current flow and the second measure of the current
flow is substantially free of variations due to hysteresis,
magnetic core saturation, and eddy currents.
44. The system of claim 31 wherein the first current sensor and the
second current sensor are matched to provide feedback such that a
summed difference of the first measure of the current flow and the
second measure of the current flow is zero when no current flow is
present through the electrically conductive path.
45. A current sensor system comprising: means for carrying current;
means for generating a first feedback upon detecting magnetic flux
in a first direction induced from the means for carrying current;
means for generating a second feedback upon detecting magnetic flux
in a second direction induced from the means for carrying current,
wherein the first direction is substantially opposite the
direction; and means for generating an anti-differential sum from
the first feedback and the second feedback to reduce feedback
generated upon detecting stray magnetic flux.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of prior U.S.
Provisional Application Ser. No. 60/507,896 filed Oct. 1, 2003 and
entitled INTEGRATED, COMMUNICATING, NON-CONTACT CURRENT SENSOR AND
ARC FAULT DETECTOR FOR BUS, CABLE AND FEED THROUGH
INSTALLATIONS.
BACKGROUND OF THE INVENTION
[0002] The present invention relates generally to current measuring
and monitoring, more particularly, to a system and method for
measuring current by sensing magnetic flux associated with current
flow through a conductor. A dual Hall sensor configuration is
utilized to sense magnetic flux and provide feedback to a
processing component. The processing component is arranged to
generate an anti-differential output from the feedback received to
remove feedback attributable to magnetic fields induced externally
from the conductor.
[0003] Measuring and monitoring of current flow through a conductor
is an important analysis that is performed in a wide variety of
applications and circumstances. Current sensing designs often fall
into one of two categories: contact topologies and non-contact
topologies.
[0004] Contact sensors are common in many circumstances but include
many inherent limitations. For example, while shunt-type sensors
are readily applicable to direct current (DC) applications,
shunt-type sensors are not suited to alternating current (AC)
applications due to errors caused by induced loop voltages. On the
other hand, while current transformers (CT) are suited for AC
applications, such are inapplicable to DC applications due to the
fundamental nature of transformers.
[0005] In any case, these contact-based sensor systems are
typically large and may be difficult to employ, especially in areas
where tight size constraints are necessary. Specifically, in order
to deploy a contact-based sensor, such as a resistive shunt, it is
necessary to remove the conductor from service. Additionally, shunt
based sensors require lugs to form an electrical connection and a
mounting means to secure the device in position. Similarly,
CT-based sensors necessarily require adequate accommodations for a
transformer.
[0006] Non-contact current sensing designs are often preferred in
many applications because they reduce common mode noise typically
experienced with direct contact designs, such as shunts.
Non-contact designs also reduce heat buildups often associated with
resistive shunts and the need to use burdened current transformers.
Additionally, non-contact designs provide scalable outputs that are
desirable for use with digital controllers.
[0007] A variety of designs and approaches have been developed for
non-contact current monitoring systems. One common and desirable
form of non-contact sensing and monitoring of current flow includes
indirectly determining current flow through a conductor by
detecting a magnetic field or flux induced as a result of the
current flow through the conductor.
[0008] For example, metal core based systems are often used to
measure the current flow through a conductor by detecting the
magnetic flux induced by the current flow. The metal core is
utilized to magnify the magnetic flux concentration and, thereby,
provide increased accuracy in detecting the magnetic flux and the
extrapolated current readings. Various topologies including
"open-loop," "closed-loop," "flux gate," and "dithering" designs
may be utilized, although all include limitations.
[0009] Open-loop sensors use the magnetic properties of the metal
core material to magnify the magnetic flux induced by the current
flow through the conductor. However, to extrapolate the current
measurements from the detected magnetic flux, these sensors rely on
the "near linear" operational range of the metal core. A
ferromagnetic core that enters a "saturation" operational range can
distort the reported current compared to the actual current
profile. Specifically, as saturation is reached, a current level
that changes with time produces a time changing magnetizing force
that produces a time changing magnetic flux density within the
core. That is, as the core material approaches magnetic saturation,
the "magnetic gain" declines and approaches the "magnetic gain" of
air. As such, the magnetic field within the metal core is distorted
in proportion to the difference in permeability at various points
along a hysteresis loop of the metal core. Therefore, should the
operating conditions lead to the saturation of the metal core,
inaccurate current measurements may be gathered. Accordingly,
sensing ranges of metal core sensors are typically hard-limited to
the "near-linear" operational range.
[0010] Additionally, sensors relying on metal cores can experience
hysteresis in the metal core that may produce a zero current offset
error. Specifically, when at low or zero current levels, the metal
core may act as a weak permanent magnet and report a persistent
flux though little or no current is actually present. As such, zero
offsets are particularly troublesome when monitoring DC power
systems. As all permeable ferromagnetic materials exhibit some
level of hysteresis, which produces an error at zero current, metal
core sensors are susceptible to erroneous current measurements at
low or no current levels. Furthermore, increased inductance can
produce phase shifts between the actual current profile and the
reported current profile.
[0011] Furthermore, while electronic-based sensors are typically
limited by the voltage rails used in the sensor output stages,
current sensors employing metal cores have an additional limitation
imposed by the saturation point of the material. For example, a
sensor with a scale factor of 1 volt per amp with a 5 volt rail
will be limited to 5 amps regardless of the range of the detector.
In metal core based sensors it is well known that the dynamic range
is typically limited to 10:1. Therefore, it is known that metal
core current sensors include range, accuracy, and repeatability
limits in proportion to the propensity for hysteresis, saturation,
and non-linearity of the material used in the core.
[0012] "Closed-loop" sensors, flux gate approaches, and dithering
approaches utilize a combination of electronic circuits and bucking
coils to compensate for these material related errors and/or
average-out errors. However, these systems merely diminish the
effects of the errors, and do not entirely eliminate the potential
for errors and incorrect current readings.
[0013] Accordingly, in order to eliminate the potential for
inaccurate current measurements due to metal core saturation,
hysteresis, or eddy currents, air-core sensors may be used to
measure and monitor current. However, while the removal of the
metal core eliminates the potential for inaccurate current
measurements due to metal core saturation, hysteresis, or eddy
currents, the air core does not have the magnetic flux magnifying
or concentrating effect of metal cores. Therefore, air-core current
sensors are readily susceptible to influence by external magnetic
fields and may provide inaccurate current measurements. As such,
air-core sensors are typically unsuitable for applications where
multiple high external magnetic fields are present. As an
overwhelming percentage of current sensors are required to be
deployed in areas where numerous conductors and corresponding
magnetic fields are in close proximity, air-core sensors are often
undesirable.
[0014] It would therefore be desirable to design a system and
method for non-contact current sensing that does not rely on
ferromagnetic materials and is not susceptible to magnetic fields
induced externally from the monitored conductor. That is, it would
be desirable to have a system and method for non-contact current
sensing that does not include the inherent limitations of
metal-core based current sensors while providing accurate current
feedback in the presence of external magnetic fields. Furthermore,
it would be desirable to have a system and method for concentrating
magnetic flux associated with a particular conduction to increase
monitoring accuracy.
BRIEF DESCRIPTION OF THE INVENTION
[0015] The present invention is directed to a system and method
that overcomes the aforementioned drawbacks. Specifically, an
anti-differential, error correcting, sensor topology is utilized
that eliminates the need for ferromagnetic concentrators. As such,
the sensor eliminates the limitations associated with metal-core
based current sensors and is capable of providing accurate current
monitoring in the presence of external magnetic fields.
[0016] In accordance with one aspect of the invention, a current
monitoring system is disclosed that includes a conductive path
configured to receive a current therethrough, a first current
sensor positioned on a first side of the conductive path and
configured to monitor a first directional magnetic field induced by
the current, and a second current sensor positioned on a second
side of the conductive path, substantially opposite the first
current sensor, and configured to monitor a second directional
magnetic field induced by the current that is substantially
opposite in direction to the first directional magnetic field. A
processing component is configured to receive feedback from the
first current sensor and the second current sensor and generate an
anti-differential output from the feedback.
[0017] According to another aspect of the invention, a current
sensor is disclosed that includes a first Hall effect sensor
positioned proximate to a conductor and configured to provide a
first feedback indicative of a current flow through the conductor
and a second Hall effect sensor positioned proximate to the
conductor and configured to provide a second feedback indicative of
the current flow through the conductor. A processing device is
configured to generate a summed difference of the first feedback
and the second feedback to reduce feedback corresponding to
magnetic fields induced externally from the conductor.
[0018] In accordance with another aspect, the invention includes a
method of determining current flow through an electrical path. The
method includes generating a first feedback represented by a first
vector having a first direction and a first magnitude upon
detecting a first direction of magnetic flux induced by a current
flow through an electrical path and a second vector having the
first direction and a second magnitude upon detecting a second
direction of magnetic flux induced externally from the electrical
path. The method also includes generating a second feedback
represented by a third vector having the first direction and the
first magnitude upon detecting a third direction of magnetic flux
induced by the current flow through the electrical path and a
fourth vector having a second direction and the second magnitude
upon detecting the second direction of magnetic flux induced
externally from the electrical path. The method then includes
summing the first feedback and the second feedback to create an
anti-differential sum thereby substantially canceling the effects
of the first feedback and the second feedback represented by the
second vector and the fourth vector.
[0019] In accordance with yet another aspect of the invention, an
anti-differential current sensing system is disclosed that includes
an electrically conductive path. A first Hall effect sensor is
disposed proximate to a first side of the electrically conductive
path and configured to generate a first measure of a current flow
through the electrically conductive path by monitoring magnetic
fields and a second Hall effect sensor is disposed proximate to a
second side of the electrically conductive path, substantially
opposite the first side of the electrically conductive path, and
configured to generate a second measure of the current flow through
the electrically conductive path by monitoring magnetic fields. A
processing device is configured to receive the first measure of the
current flow and the second measure of the current flow and
generate an output from the first measure of the current flow and
the second measure of the current flow substantially free of errors
due to magnetic fields generated externally from the conductive
path.
[0020] According to another aspect of the invention, a current
sensor system is disclosed that includes means for carrying current
and means for generating a first feedback upon detecting magnetic
flux in a first direction induced from the means for carrying
current. The current sensor system also includes means for
generating a second feedback upon detecting magnetic flux in a
second direction induced from the means for carrying current,
wherein the first direction is substantially opposite the direction
and means for generating an anti-differential sum from the first
feedback and the second feedback to reduce feedback generated upon
detecting stray magnetic flux.
[0021] Various other features and advantages of the present
invention will be made apparent from the following detailed
description and the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The drawings illustrate one preferred embodiment presently
contemplated for carrying out the invention.
[0023] In the drawings:
[0024] FIG. 1 is a perspective diagram of an anti-differential
current sensor configuration in accordance with the present
invention.
[0025] FIG. 2 is a schematic of one embodiment of the
anti-differential current sensor configuration of FIG. 1 in
accordance with the present invention.
[0026] FIG. 3 is a schematic of another embodiment of the
anti-differential current sensor configuration of FIG. 1 in
accordance with the present invention.
[0027] FIG. 4 is a graph illustrating the relationship between the
influence of external magnetic fields and conductor position in
accordance with the present invention.
[0028] FIG. 5 is an illustration of the influence of magnetic field
strength upon parallel conductors at a first distance.
[0029] FIG. 6 is an illustration of the influence of magnetic field
strength upon parallel conductors at a second distance.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0030] The present invention is related to a system and method for
non-contact based, anti-differential, error-correcting current
sensing. A plurality of magnetic flux sensors is arranged about a
conductor and provides feedback to a processing component or device
configured to generate an output with reduced feedback induced by
magnetic fields external to the conductor. The plurality of
magnetic flux sensors may be disposed in geometrically designed
recesses configured to amplify the magnetic flux received by the
plurality of magnetic flux sensors. The system may be disposed in a
variety of configurations designed for optimal disposition of the
plurality of magnetic flux sensors about a given conductor type.
Some examples of possible configurations include etched spiral path
topologies for low current and printed circuit board current
sensing, dual-spiral and spiral-helix topologies for contact based
current sensing, and wire and bus bar mount topologies for wire and
bus bar conductors. Furthermore, the system may be integrated with
additional systems that utilize current sensing as well as
communication interfaces.
[0031] Referring to FIG. 1, a perspective view is shown of an
anti-differential current sensor configuration 10 arranged about a
conductor 12 in accordance with the present invention. The
conductor 12 is illustrated as a round wire for exemplary purposes
only but, as will be described, may include any form of current
conductor including bus bars, integrated circuits, printed circuit
boards, circuit breakers, and the like. The conductor includes a
current flow therethrough, as illustrated by an arrow 14 and
labeled "I." As is well known, the current flow 14 through the
conductor 12 induces a magnetic field, as illustrated by arrows 16,
labeled "B.sub.1." Two magnetic flux sensors H.sub.1, H.sub.2,
preferably Hall effect sensors, are disposed on substantially
opposite sides of the conductor 12. The positioning of the Hall
effect sensors H.sub.1, H.sub.2 on substantially opposite sides of
the conductor 12 aids in reducing the effects of externally induced
magnetic fields, labeled "B.sub.2" and illustrated by arrows 17,
that can otherwise cause inaccurate readings of the current 14
through the conductor 12. That is, the two current sensors H.sub.1,
H.sub.2 are used in a configuration that reports the current inside
the conductor 12 to a processing component 18 that is configured to
calculate a sum or summed difference of the feedback from the two
current sensors H.sub.1, H.sub.2 to generate an anti-differential
output having reduced influences from externally induced magnetic
fields B.sub.2 17. Specifically, the anti-differential current
sensor configuration 10 provides an anti-differential output 19
that is a highly accurate indication of the current flow 14 through
the conductor 12 and is substantially free of influence from
externally induced magnetic fields B.sub.2 17.
[0032] The anti-differential current sensor configuration 10 may
include various architectures or configurations of the current
sensors H.sub.1, H.sub.2 and processing component 18. Referring now
to FIG. 2, a first configuration of the anti-differential current
sensor configuration 10a is shown. The conductor 12 is again shown
with opposing Hall effect sensors H.sub.1, H.sub.2 disposed about a
periphery of the conductor 12. FIG. 2 illustrates the conductor 12
in the form of a wire. However, it is contemplated that the
conductor may be of various forms. Therefore, FIG. 2 shows the
conductor 12 as a wire conductor while FIG. 3 shows a conductor 12a
in the form of a bus bar. Additionally, it is contemplated that the
Hall effect sensors H.sub.1, H.sub.2 may not only be disposed about
the periphery of the conductor 12 but may be disposed within flux
concentrating recesses within the conductor 12 to improve the
magnetic flux detected by the Hall effect sensors H.sub.1,
H.sub.2.
[0033] The current flow 14 through the conductor 12 is again
represented as "I" and the associated magnetic field, which circles
the conductor, is represented as "B.sub.1," 1 6. According to the
first configuration of the anti-differential current sensor 10a,
the Hall effect sensors H.sub.1, H.sub.2 are not only disposed on
opposite sides of the conductor 12 but are also configured to
provide feedback of positively designated current flow upon
detecting oppositely directed magnetic flux. That is, Hall effect
sensor H.sub.1 provides feedback indicating that a positive current
value of magnitude "I" has been determined upon detecting a
directional magnetic flux in a first direction 20. Therefore, the
feedback generated by Hall effect sensor H.sub.1 upon detecting
directional magnetic flux B.sub.1 16 in the first direction 20 is
represented as "+I.sub.B1," 21.
[0034] On the other hand, according to the first configuration of
the anti-differential current sensor 10a, Hall effect sensor
H.sub.2 is configured to provide feedback indicating that a
positively designated current flow has been determined upon
detecting a directional magnetic flux in a second direction 22.
Therefore, the feedback generated by Hall effect sensor H.sub.2
upon detecting directional magnetic flux B.sub.1 16 in the second
direction 22 is also represented as ".sup.+I.sub.B1," 24.
Accordingly, even though the directions 20, 22 of the magnetic flux
B.sub.1 16 are substantially opposite in direction when detected by
Hall effect sensor H.sub.1 as opposed to Hall effect sensor
H.sub.2, both Hall effect sensors H.sub.1, H.sub.2 provide positive
feedback ".sup.+I.sub.B1," 21, 24.
[0035] Following this convention, upon detecting a stray or foreign
magnetic field B.sub.2 17 that is induced or generated externally
to the conductor 12 and generally impinges upon each Hall effect
sensor H.sub.1, H.sub.2 substantially equally, the Hall effect
sensors H.sub.1, H.sub.2 provide substantially equal and opposite
feedback. Specifically, unlike the magnetic field B.sub.1 16
induced by the current flow 14 through the conductor 12, which
uniformly encircles the conductor 12, the externally induced
magnetic field B.sub.2 17 is generally directionally uniform with
respect to impinging upon the Hall effect sensors H.sub.1, H.sub.2.
Accordingly, due to the directional configuration of the Hall
effect sensors H.sub.1, H.sub.2, Hall effect sensor H.sub.1 will
provide feedback indicating a positive current flow upon detecting
the magnetic field B.sub.2, while Hall effect sensor H.sub.2 will
provide feedback indicating a negative current flow upon detecting
the magnetic field B.sub.2 17. That is, Hall effect sensor H.sub.1
will provide positive feedback ".sup.+I.sub.B2," 26 while Hall
effect sensor H.sub.2 will provide negative feedback
".sup.-I.sup.B2," 28.
[0036] All feedback, .sup.+I.sub.B1, .sup.+I.sub.B2,
.sup.+I.sub.B1, and .sup.-I.sub.B2, is then passed to a processing
component 18a. According to the first configuration of the
anti-differential current sensor 10a, the processing component 18a
is a summing amplifier, such as a summing operational amplifier (op
amp), and is configured to provide an algebraically summed
anti-differential output. However, while the processing component
18a is illustrated as a summing op amp, it is contemplated that a
wide variety of processing components may be utilized.
Specifically, any processing component, whether analog or digital,
that is capable of generating an anti-differential sum of feedback
received may be utilized within the anti-differential current
sensor configuration 10a. Therefore, the term "processing
component" as utilized herein is defined to include any analog,
digital, or discrete components that may be configured to generate
an algebraic sum of its inputs.
[0037] Therefore, the processing component 18a receives all
feedback from the Hall sensors H.sub.1, H.sub.2 and provides a sum
of .sup.+I.sub.B1+.sup.+I.sub.B1+.sup.+I.sub.B2+.sup.-I.sub.B2. As
such, the feedback generated in response to the externally induced
magnetic flux B.sub.2 17 (.sup.+I.sub.B2, .sup.-I.sub.B2) cancels
and the anti-differential output 30 of the processing component 18a
is generally twice the current flow 14 through the conductor 12, as
determined from the magnetic field B.sub.1. Therefore, regardless
of the strength, direction, or concentration of extraneous magnetic
fields B.sub.2 17, the output 30 of the processing component 18a is
.sup.+2I.sub.B1. The first configuration of the anti-differential
current sensor configuration 10a thereby yields accurate current
measurements by reducing, if not essentially removing, feedback
associated with stray magnetic fields B.sub.2 17 induced or
generated externally to the conductor 12 from which current
feedback is desired.
[0038] Referring now to FIG. 3, a second configuration of the
anti-differential current sensor 10b is shown. For exemplary
purposes, FIG. 3 illustrates a conductor 12a, this time in the form
of a bus bar. Again, it is contemplated that the Hall effect
sensors H.sub.1, H.sub.2 may not only be disposed about the
periphery of the conductor 12a but may be disposed within flux
concentrating recesses within the conductor 12a to improve the
magnetic flux detected by the Hall effect sensors H.sub.1,
H.sub.2.
[0039] As will be described in detail below, the second
configuration of the anti-differential current sensor 10b differs
from the first configuration of the anti-differential current
sensor 10b shown in FIG. 2 by the architecture or configuration of
the Hall effect sensors H.sub.1, H.sub.2 and the configuration of
the processing component 18b. Specifically, due to the
configuration of the Hall effect sensors H.sub.1, H.sub.2 about the
conductor 12a, the processing component 18b is configured as a
differential or "differencing" amplifier.
[0040] In accordance with one embodiment, the differential
amplifier is a differential op amp, configured to calculate an
algebraically summed difference of the feedback received to
generate an anti-differential output. However, while the processing
component 18b is illustrated as a differential op amp, it is
equally contemplated that a wide variety of processing components
may be utilized. Specifically, any processing component, whether
analog or digital, that is capable of calculating a summed
difference of feedback received to generate the desired
anti-differential output may be utilized within the
anti-differential current sensor configuration 10b. Therefore, the
term "processing component" as utilized herein is again defined to
include any analog, digital, or discrete components that may be
configured to generate an algebraic sum of feedback received.
[0041] According to the second configuration of the
anti-differential current sensor 10b, the Hall effect sensors
H.sub.1, H.sub.2 are disposed on opposite sides of the conductor
12a and are configured to provide equal and oppositely designated
feedback of the current flow 14 through the conductor 12a upon
detecting oppositely directed magnetic flux 20, 22. That is, Hall
effect sensor H.sub.1 provides feedback indicating that a positive
current value of magnitude "I" has been determined upon detecting a
directional magnetic flux in a first direction 20. Therefore, the
feedback generated by Hall effect sensor H.sub.1 upon detecting
directional magnetic flux B.sub.1 16 in the first direction 20 is
represented as ".sup.+I.sub.B1," 21.
[0042] On the other hand, according to the second configuration of
the anti-differential current sensor 10b, Hall effect sensor
H.sub.2 is configured to provide feedback indicating that a
negatively designated current flow has been determined upon
detecting a directional magnetic flux in a second direction 22.
Therefore, the feedback generated by Hall effect sensor H.sub.2
upon detecting directional magnetic flux B.sub.1 16 in the second
direction 22 is represented as ".sup.-I.sub.B1," 24a. Accordingly,
since the directions 20, 22 of the magnetic flux B.sub.1 16 are
substantially opposite when detected by Hall effect sensor H.sub.1
as opposed to Hall effect sensor H.sub.2, Hall effect sensors
H.sub.1, H.sub.2 provide substantially equal feedback that is
directionally opposite, ".sup.+I.sub.B1" 21 and ".sup.-I.sub.B1"
24a respectively. That is, the feedbacks 21, 24a are substantially
equal in magnitude but each has opposite polarity.
[0043] Following this convention, upon detecting another magnetic
field B.sub.2 17 that is induced or generated externally to the
conductor 12a and generally impinges upon each Hall effect sensor
H.sub.1, H.sub.2 substantially equally, the Hall effect sensors
H.sub.1, H.sub.2 provide substantially equal feedback.
Specifically, due to the directional configuration of the Hall
effect sensors H.sub.1, H.sub.2, Hall effect sensors H.sub.1,
H.sub.2 will both provide positive feedback 26, 28a, represented as
".sup.+I.sub.B2," upon detecting the magnetic field B.sub.2. Even
slight variations in the strength of the stray magnetic fields
result in little error inducement because of the relative strength
of the stray fields as compared to that of the sensed
conductor.
[0044] All feedback, .sup.+I.sub.B1, .sup.-I.sub.B1,
.sup.+I.sub.B2, and .sup.+I.sub.B2 is then passed to the processing
component 18b. As previously described, according to the second
configuration of the anti-differential current sensor 10b, the
processing component 18b is configured in a differential
configuration to generate the desired anti-differential output
eliminating feedback generated upon detecting the externally
induced magnetic field B.sub.2. That is, the processing component
receives the feedback .sup.+I.sub.B1, .sup.-I.sub.B1,
.sup.+I.sub.B2, and .sup.+I.sub.B2 and algebraically calculates a
summed difference. Specifically, a summed difference is generated
as (.sup.+I.sub.B1+.sup.+I.sub.B2)-(.sup.-I.sub.B1+.sup.+I.sub.B2)
yielding .sup.+2I.sub.B1, 30.
[0045] Therefore, through the second configuration of the
anti-differential current sensor 10b includes a different
configuration of the Hall effect sensors H.sub.1, H.sub.2 and the
differential amplifier 18b rather than the summing amplifier 18a of
FIG. 2, both the first configuration of the anti-differential
current sensor 10a and the second configuration of the
anti-differential current sensor 10b yield the same
anti-differential output 30 that effectively excludes influence
from externally induced magnetic fields 17. As such, both the first
configuration of the anti-differential current sensor 10a and the
second configuration of the anti-differential current sensor 10b
provide highly accurate current measurements by reducing, if not
essentially removing, feedback associated with stray magnetic
fields induced or generated externally to the conductor 12a from
which current feedback is desired.
[0046] These highly accurate non-contact based current measurements
of the above-described current sensor configurations allow the
current sensor configuration to operate in environments having
various external magnetic fields without degrading current
measurements from a specific conductor. However, the accuracy of
the current sensor in detecting a particular magnetic field
associated with a particular conductor can be improved if the
current sensor is configured, for example, for the particular
conductor configuration and current level being monitored.
Additionally, by disposing the sensors in close proximity to the
monitored conductor or within current concentrating recesses,
accuracy can be improved.
[0047] By matching the Hall effect sensors, the system is
substantially free of errors due to zero flux offsets and Hall
effect gain differences. Furthermore, matching the Hall effect
sensors substantially corrects zero flux offset drift associated
with temperature fluctuations. However, for configuration utilizing
a single Hall effect sensor, it is contemplated that active
electronic correction may be utilized to offset zero flux offset
drift associated with temperature fluctuations.
[0048] Referring to FIG. 4, the strength of magnetic fields induced
by current flow through a plurality of conductors and the strength
of such at various distances are shown. FIG. 4 shows that the
magnetic field detected by current sensors associated with three
different conductor sizes, at three current levels, exponentially
decreases as the distance from the center of the conductor
increases. For example, the external magnetic field 32 detected by
a current sensor disposed 0.4 inches from a 1/0 wire carrying 45
amps is substantially proportionate to the magnetic field 34
detected at only 0.1 inches from a No. 6 AWG wire carrying 13.3
amps. Accordingly, to overcome interference from a magnetic field
induced by an adjacent 1/0 wire carrying 45 amps, a current sensor
configured to monitor the No. 6 AWG wire carrying 13.3 amps should
have a common mode field correction capacity of at least 16% of the
rating of the No. 6 AWG wire.
[0049] This point is illustrated in FIGS. 5 and 6, which show the
magnetic flux interactions due to adjacent parallel conductors 36,
38 carrying approximately 100 amps of current in opposite
directions. FIG. 5 shows the interaction of magnetic fields induced
by adjacent conductors 36, 38 in close proximity. Concentric
circular shadings 40 represent the strength of the magnetic fields
induced by the current flow through the conductors 36, 38. The
magnetic fields induced by each conductor 36, 38 interact to form a
combined oval magnetic field 40 rather than two independent
magnetic fields. In this case, a current sensor disposed to monitor
one of the conductors 36, 38 will detect a relatively large
externally induced magnetic field. As such, the monitor must have a
relatively high common mode field correction capacity forming a
tolerance or "buffer" for the influence of magnetic fields induced
externally from the conductor being monitored. While significantly
high common mode field correction capacities are readily
attainable, it is often desirable to limit the common mode field
correction capacities so as to control costs. For example, the
common mode field correction capacity of a sensor may be configured
to be 25% of the conductor rating. In this case, a separation of
adjacent conductors is desirable to assure that the common mode
field correction capacity of the sensor is not exceeded.
[0050] Referring to FIG. 6, the adjacent, parallel conductors 36,
38 are separated so that the induced magnetic fields 42, 44 are
sufficiently isolated so as to remain below the common mode field
correction capacity of a given sensor. Specifically, the conductor
gage and corresponding amperage rating must be considered against
the common mode field correction capacity of a sensor to determine
the preferable separation of the conductors 36, 38. For example,
should a sensor be configured to have a common mode field
correction capacity of 25%, a separation of approximately three
times the radius of the conductor 36, 38 would be a preferred
minimum separation. Accordingly, a sufficient buffer is formed to
tolerate the influence of magnetic fields induced externally from
the conductor being monitored without affecting the summed
difference calculated from the feedback generated by the
sensor.
[0051] This principle can be extended to multiple adjacent
conductors in various forms arranged in an array. That is, FIGS. 5
and 6 illustrate wire conductors 36, 38 for exemplary purposes
only. Other conductor forms such as bus bars and the like may be
preferable in some configuration and are also contemplated.
Specifically, when using wires in an array formation the separation
requirements are compounded as additional conductors are added
and/or wire gages increased. As such, it is often desirable to
utilize bus bar configurations whereby conductor "radius" is
reduced, thereby reducing adjacent conductor separation
requirements.
[0052] The present invention yields error correcting for externally
induced magnetic fields for current sensing and monitoring of both
AC and DC power sources. The anti-differential output generated is
high fidelity due to the absence of magnetic core materials. Low
inductance, achieved as a function of an air core configuration,
allows the current sensor configuration to be highly responsive to
change as well as provides in-phase, real-time, current feedback
vectors. The sensor configuration includes wide and dynamic range
abilities due to the absence of permeable materials and the absence
of a saturation point.
[0053] Additionally, the absence of non-linear saturating or
ferromagnetic core materials eliminates DC error offsets associated
with hysteresis of ferromagnetic materials and allows the current
sensor configuration to be utilized to monitor AC and DC circuits.
Therefore, the system generates an anti-differential output that is
substantially free of variations due to hysteresis, magnetic core
saturation, and eddy currents because the system is substantially
free of ferromagnetic field concentrating materials. Furthermore,
the elimination of metallic core materials reduces the overall size
of the current sensor configuration and lowers consumed power. The
sensor configuration is flexibly deployable to conductors including
current flows from a few milli-amps to a few thousand amps.
[0054] By matching the Hall effect sensors, the system is
substantially free of errors due to zero flux offsets and Hall
effect gain differences. Furthermore, matching the Hall effect
sensors substantially corrects any zero flux offset drift
associated with temperature fluctuations. Furthermore, a constant
current power supply may be utilized having a bias current
compensation circuit or a temperature dependent adjustable gain to
compensate for Hall gain drift. Additionally or alternatively, the
processing component includes a temperature dependant op-amp gain
loop configured to compensate for temperature dependent electronic
drift. Also, Lorentz force drifts associated with temperature
variations can be corrected using by the temperature dependent
supply to power the anti-differential current sensor.
[0055] Additionally, while the above-described system is described
with respect to utilizing a pair of Hall effect sensors within the
anti-differential topology, it is contemplated that alternative
magnetic flux sensors may be equivalently utilized. Specifically,
magnetoresistive structures (MRS), giant magnetoresistive
structures (GMRS), and the like may be equivalently utilized within
the anti-differential topology.
[0056] While the above-described technique has been described with
respect to current monitoring systems, it is equivalently
applicable for voltage and/or power monitoring systems. That is, it
is contemplated that additional systems and subsystems may be
utilized with the above described techniques and topologies to
equivalently generate highly accurate voltage and/or power
measurements.
[0057] Therefore, the present invention includes a current
monitoring system having a conductive path configured to receive a
current therethrough, a first current sensor positioned on a first
side of the conductive path and configured to monitor a first
directional magnetic field induced by the current, and a second
current sensor positioned on a second side of the conductive path,
substantially opposite the first current sensor, and configured to
monitor a second directional magnetic field induced by the current
that is substantially opposite in direction to the first
directional magnetic field. A processing component is configured to
receive feedback from the first current sensor and the second
current sensor and generate an anti-differential output from the
feedback.
[0058] According to another embodiment of the invention, a current
sensor includes a first Hall effect sensor positioned proximate to
a conductor and configured to provide a first feedback indicative
of a current flow through the conductor and a second Hall effect
sensor positioned proximate to the conductor and configured to
provide a second feedback indicative of the current flow through
the conductor. A processing device is configured to generate a
summed difference of the first feedback and the second feedback to
reduce feedback corresponding to magnetic fields induced externally
from the conductor.
[0059] Another embodiment of the present invention includes a
method of determining current flow through an electrical path. The
method includes generating a first feedback represented by a first
vector having a first direction and a first magnitude upon
detecting a first direction of magnetic flux induced by a current
flow through an electrical path and a second vector having the
first direction and a second magnitude upon detecting a second
direction of magnetic flux induced externally from the electrical
path. The method also includes generating a second feedback
represented by a third vector having the first direction and the
first magnitude upon detecting a third direction of magnetic flux
induced by the current flow through the electrical path and a
fourth vector having a second direction and the second magnitude
upon detecting the second direction of magnetic flux induced
externally from the electrical path. The method then includes
summing the first feedback and the second feedback to create an
anti-differential sum thereby substantially canceling the effects
of the first feedback and the second feedback represented by the
second vector and the fourth vector.
[0060] A further embodiment of the present invention has an
anti-differential current sensing system that includes an
electrically conductive path. A first Hall effect sensor is
disposed proximate to a first side of the electrically conductive
path and configured to generate a first measure of a current flow
through the electrically conductive path by monitoring magnetic
fields and a second Hall effect sensor is disposed proximate to a
second side of the electrically conductive path, substantially
opposite the first side of the electrically conductive path, and
configured to generate a second measure of the current flow through
the electrically conductive path by monitoring magnetic fields. A
processing device is configured to receive the first measure of the
current flow and the second measure of the current flow and
generate an output from the first measure of the current flow and
the second measure of the current flow substantially free of errors
due to magnetic fields generated externally from the conductive
path.
[0061] According to another embodiment of the invention, a current
sensor system includes means for carrying current and means for
generating a first feedback upon detecting magnetic flux in a first
direction induced from the means for carrying current. The current
sensor system also includes means for generating a second feedback
upon detecting magnetic flux in a second direction induced from the
means for carrying current, wherein the first direction is
substantially opposite the direction and means for generating an
anti-differential sum from the first feedback and the second
feedback to reduce feedback generated upon detecting stray magnetic
flux.
[0062] The present invention has been described in terms of the
preferred embodiment, and it is recognized that equivalents,
alternatives, and modifications, aside from those expressly stated,
are possible and within the scope of the appending claims.
* * * * *