U.S. patent application number 15/251082 was filed with the patent office on 2017-06-29 for sensing apparatus for sensing current through a conductor and methods therefor.
The applicant listed for this patent is Everspin Technologies, Inc.. Invention is credited to David Hayner, Markus Schwickert, Angelo Ugge.
Application Number | 20170184635 15/251082 |
Document ID | / |
Family ID | 59087165 |
Filed Date | 2017-06-29 |
United States Patent
Application |
20170184635 |
Kind Code |
A1 |
Ugge; Angelo ; et
al. |
June 29, 2017 |
SENSING APPARATUS FOR SENSING CURRENT THROUGH A CONDUCTOR AND
METHODS THEREFOR
Abstract
A sensing apparatus for characterizing current flow through a
conductor includes a plurality of magnetic sensors. In some
embodiments, the sensors are grouped in pairs to achieve common
mode rejection of signals generated in response to magnetic fields
not resulting from current flow through the conductor. Sensors
having different levels of sensitivity are used to collect
information regarding the magnetic field generated by the current
flowing through the conductor, where such information is processed
in order to characterize the magnetic field. In some cases the
sensors are included on or in flexible material that can be wrapped
around the conductor.
Inventors: |
Ugge; Angelo; (Chandler,
AZ) ; Schwickert; Markus; (Scottsdale, AZ) ;
Hayner; David; (Waco, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Everspin Technologies, Inc. |
Chandler |
AZ |
US |
|
|
Family ID: |
59087165 |
Appl. No.: |
15/251082 |
Filed: |
August 30, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62271833 |
Dec 28, 2015 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01R 15/207 20130101;
G01R 15/20 20130101; G01R 33/0005 20130101 |
International
Class: |
G01R 15/20 20060101
G01R015/20 |
Claims
1. A sensing apparatus for sensing current through a conductor, the
sensing apparatus comprising: a first pair of magnetic sensors,
wherein each magnetic sensor of the first pair of magnetic sensors
has a first level of sensitivity with respect to a magnetic field
generated by the current through the conductor; and a second pair
of magnetic sensors, wherein each magnetic sensor of the second
pair of magnetic sensors has a second level of sensitivity with
respect to the magnetic field generated by the current through the
conductor, wherein the second level of sensitivity is less than the
first level of sensitivity.
2. The sensing apparatus of claim 1, wherein the sensing apparatus
is disposed on a common substrate with the conductor.
3. The apparatus of claim 1, wherein: each magnetic sensor of the
first pair of magnetic sensors is positioned a first distance from
a spatial axis corresponding to the conductor, wherein the spatial
axis corresponds to a direction of current flow within the
conductor; and each magnetic sensor of the second pair of magnetic
sensors is positioned a second distance from the spatial axis for
the conductor, wherein the second distance is greater than the
first distance.
4. The apparatus of claim 3, further comprising a third pair of
magnetic sensors, wherein each magnetic sensor of the third pair of
magnetic sensors is positioned a third distance from the spatial
axis for the conductor, wherein the third distance is greater than
the second distance and a third level of sensitivity of magnetic
sensors in the third pair of magnetic sensors is less than the
second level of sensitivity.
5. The apparatus of claim 3, wherein the first pair of magnetic
sensors includes: a first magnetic sensor positioned at a first
point on a first virtual circle having a radius equal to the first
distance, wherein a center of the first virtual circle corresponds
to the spatial axis for the conductor; and a second magnetic sensor
positioned at a second point on the first virtual circle.
6. The apparatus of claim 5, wherein the first and second points
are about 180 degrees apart on the first virtual circle.
7. The apparatus of claim 5, wherein the second pair of magnetic
sensors includes: a third magnetic sensor positioned at a first
point on a second virtual circle having a radius equal to the
second distance, wherein a center of the second virtual circle
corresponds to the spatial axis for the conductor; and a fourth
magnetic sensor positioned at a second point on the second virtual
circle.
8. The apparatus of claim 7, wherein the first virtual circle and
the second virtual circle are concentric virtual circles lying in a
common plane perpendicular to the spatial axis for the
conductor.
9. The apparatus of claim 7, wherein the center of the first
virtual circle is positioned at a different point on the spatial
axis for the conductor than the center of the second virtual
circle.
10. The apparatus of claim 1, wherein each magnetic sensor of the
first pair of magnetic sensors has a different composition than
each magnetic sensor of the second pair of sensors.
11. The apparatus of claim 1, wherein each magnetic sensor of the
first pair of magnetic sensors has a same composition as each
magnetic sensor of the second pair of sensors, and wherein the
sensing apparatus further comprises buffering material positioned
with respect to the second pair of magnetic sensors such that the
buffering material reduces sensitivity of each of the magnetic
sensors in the second pair of magnetic sensors such that each
magnetic sensor of the second pair of magnetic sensors has the
second level of sensitivity.
12. The apparatus of claim 1, wherein each magnetic sensor in the
first pair of magnetic sensors and the second pair of magnetic
sensors senses magnetic field in a first direction, wherein the
first direction is perpendicular to the spatial axis corresponding
to the conductor.
13. The apparatus of claim 12, wherein each magnetic sensor in the
first pair of magnetic sensors and the second pair of magnetic
sensors also senses magnetic field in a second direction, wherein
the second direction is i) perpendicular to the spatial axis
corresponding to the conductor and ii) perpendicular to the first
direction.
14. The apparatus of claim 1, wherein each magnetic sensor of the
first pair of magnetic sensors has a first angular orientation with
respect to a spatial axis corresponding to the conductor, wherein
the spatial axis corresponds to a direction of current flow within
the conductor, and wherein each magnetic sensor of the second pair
of magnetic sensors has a second angular orientation with respect
to the spatial axis corresponding to the conductor.
15. The apparatus of claim 1 further comprising: a plurality of
additional pairs of magnetic sensors, wherein, within each pair of
additional magnetic sensors, a first magnetic sensor of the pair
has a sensitivity with respect to the magnetic field generated by
the current through the conductor that is about equal to a
sensitivity of a second magnetic sensor of the pair.
16. The apparatus of claim 15, wherein at least one of the
plurality of additional pairs of magnetic sensors includes magnetic
sensors having the first level of sensitivity with respect to the
magnetic field generated by the current through the conductor.
17. A sensing apparatus for sensing current, the sensing apparatus
comprising: a first pair of magnetic sensors, wherein each magnetic
sensor of the first pair of magnetic sensors is positioned a first
radial distance from a spatial axis corresponding to a conductor,
wherein the spatial axis corresponds to a direction of current flow
within the conductor; a second pair of magnetic sensors, wherein
each magnetic sensor of the second pair of magnetic sensors is
positioned a second radial distance from the spatial axis
corresponding to the conductor, wherein the second radial distance
is greater than the first radial distance; a third pair of magnetic
sensors, wherein each magnetic sensor of the third pair of magnetic
sensors is positioned a third radial distance from the spatial axis
corresponding to the conductor, wherein the third radial distance
is greater than the second radial distance; and processing
circuitry coupled to the first, second, and third pairs of magnetic
sensors, wherein the processing circuitry is configured to select
information received from at least one of the first, second, and
third pairs of magnetic sensors as representative information
regarding the current flow within the conductor.
18. The sensing apparatus of claim 17, wherein the processing
circuitry is further configured to: select the representative
information such that it includes information received from a
plurality of pairs of magnetic sensors; and process the
representative information to determine a magnitude of current flow
within the conductor.
19. A sensing apparatus for sensing current, the sensing apparatus
comprising: a first pair of magnetic sensors, wherein each magnetic
sensor of the first pair of magnetic sensors is positioned a first
radial distance from a spatial axis corresponding to a conductor,
wherein the spatial axis corresponds to a direction of current flow
within the conductor; a second pair of magnetic sensors, wherein
each magnetic sensor of the second pair of magnetic sensors is
positioned the first radial distance from the spatial axis
corresponding to the conductor; processing circuitry coupled to the
first and second pairs of magnetic sensors, wherein the processing
circuitry is configured to process information received from the
first and second pairs of magnetic sensors to determine a magnitude
of current flow within the conductor.
20. The sensing apparatus of claim 19, wherein the processing
circuitry is disposed on a common substrate with the first and
second pairs of magnetic sensors.
Description
RELATED APPLICATIONS
[0001] This application claims priority to and the benefit of U.S.
Provisional Application No. 62/271,833, filed Dec. 28, 2015. The
content of application 62/271,833 is incorporated by reference
herein in its entirety.
TECHNICAL FIELD
[0002] The disclosure herein relates generally to magnetic sensors,
and, more particularly, to using magnetic sensors to characterize
current flowing through a conductor.
BACKGROUND
[0003] There are various ways to measure an electrical current,
including, but not limited to, use of a shunt resistor, a current
transformer, or a magnetic sensor. Shunt resistors provide a
voltage proportional to a current flowing through the shunt
resistor, which is in series with a load. In some cases, a shunt
resistor provides an accurate reading with a low offset. However,
shunt resistors are not electrically isolated from the load, and
current sensors using shunt resistors can be damaged when exposed
to large currents.
[0004] A current transformer includes primary and secondary coils.
The primary coil carries a primary current to be measured, and the
primary coil, via the primary current, induces a magnetic field in
the secondary coil. A current is generated in the secondary coil
that is proportional to the primary current scaled by a turns
ratio, which relates to the number of loops of the primary and
secondary coils. While a current transformer offers electrical
isolation, a current transformer is generally large and bulky.
[0005] Magnetic sensors measure current based on the principles of
Maxwell's equations, which provide that the magnitude of a magnetic
field generated by the flow of current through, e.g., a conductor
is (a) inversely proportional to a distance from the center of the
conductor to the point of measurement, and (b) proportional to the
current flowing in the conductor. When used to measure current,
magnetic sensors provide electrical isolation and relatively
accurate current readings. In addition, magnetic sensors have
relatively low power consumption, good reliability characteristics,
and suffer little degradation over time in comparison to the other
types of current sensors.
[0006] While magnetic sensors provide good reliability and
generally accurate current readings, their dynamic range is
limited. Magnetic sensors designed to sense small currents are
typically overwhelmed by much larger currents and unable to provide
any useful information regarding such larger currents other than
the current is greater than a maximum level of current the sensor
is capable of measuring. Similarly, sensors designed to measure
larger currents may be unable to provide useful information
regarding very small currents.
[0007] Thus, it is desirable to provide a magnetic sensor-based
sensing apparatus for characterizing current flow through a
conductor that is less susceptible to external magnetic fields
unrelated to the current flow, where the sensing apparatus has a
wide dynamic range useful for varying levels of current.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a block diagram of a current sensing apparatus in
accordance with an exemplary embodiment;
[0009] FIG. 2 is a block diagram providing a perspective view of a
portion of the current sensing apparatus of FIG. 1 in accordance
with an exemplary embodiment;
[0010] FIG. 3 is a block diagram of a current sensing apparatus in
accordance with an exemplary embodiment;
[0011] FIGS. 4-6 are block diagrams showing magnetic sensor arrays
in accordance with exemplary embodiments;
[0012] FIG. 7 is a block diagram showing a sensing apparatus
mounted to a circuit that includes a current-carrying trace in
accordance with an exemplary embodiment;
[0013] FIG. 8 is a block diagram of a current sensing apparatus in
accordance with an exemplary embodiment;
[0014] FIG. 9 is a flow chart illustrating a method for
characterizing current flowing through a conductor in accordance
with an exemplary embodiment;
[0015] FIG. 10 is a flow chart illustrating a method for
calibrating a sensing apparatus in accordance with an exemplary
embodiment;
[0016] FIG. 11 is a block diagram of a sensor array included in a
length of flexible material in accordance with an exemplary
embodiment;
[0017] FIG. 12 is a block diagram of the sensor array of FIG. 11
wrapped around a conductor in accordance with an exemplary
embodiment;
[0018] FIG. 13 is a block diagram of a sensor array included in a
length of flexible material in accordance with an exemplary
embodiment;
[0019] FIG. 14 is a block diagram of a sensing apparatus in
accordance with an exemplary embodiment; and
[0020] FIG. 15 is a block diagram of a sensor apparatus included in
an example application in accordance with an exemplary
embodiment.
DETAILED DESCRIPTION
[0021] The following detailed description is merely illustrative in
nature and is not intended to limit the embodiments of the subject
matter or the application and uses of such embodiments. Any
implementation described herein as exemplary is not necessarily to
be construed as preferred or advantageous over other
implementations.
[0022] For simplicity and clarity of illustration, the figures
depict the general structure and/or manner of construction of the
various embodiments. Descriptions and details of well-known
features and techniques may be omitted to avoid unnecessarily
obscuring other features. Elements in the figures are not
necessarily drawn to scale: the dimensions of some features may be
exaggerated relative to other elements to assist improve
understanding of the example embodiments.
[0023] The terms "comprise," "include," "have" and any variations
thereof are used synonymously to denote non-exclusive inclusion.
The term "exemplary" is used in the sense of "example," rather than
"ideal."
[0024] In the interest of conciseness, conventional techniques,
structures, and principles known by those skilled in the art may
not be described herein, including, for example, the physical
composition of magnetic sensors, production of such sensors,
fundamental principles of magnetism, basic operational principles
of magnetic sensor devices, and basic electronics.
[0025] During the course of this description, like numbers may be
used to identify like elements according to the different figures
that illustrate the various exemplary embodiments.
[0026] For the sake of brevity, the functional aspects of certain
systems and subsystems (and the individual operating components
thereof) may not be described in detail herein. Furthermore, the
connecting lines shown in the various figures contained herein are
intended to represent exemplary functional relationships and/or
physical couplings between the various elements. It should be noted
that many alternative or additional functional relationships or
physical connections may be present in an embodiment of the subject
matter.
[0027] Techniques and technologies may be described herein in terms
of functional and/or logical block components, and with reference
to symbolic representations of operations, processing tasks, and
functions that may be performed by various computing components or
devices. Such operations, tasks, and functions are sometimes
referred to as being computer-executed, computerized,
software-implemented, or computer-implemented. In practice, one or
more processor devices can carry out the described operations,
tasks, and functions by manipulating electrical signals
representing data bits at memory locations in the system memory, as
well as other processing of signals. The memory locations where
data bits are maintained are physical locations that have
particular electrical, magnetic, optical, resistive, or organic
properties corresponding to the data bits. It should be appreciated
that the various clock, signal, logic, and functional components
shown in the figures may be realized by any number of hardware,
software, and/or firmware components configured to perform the
specified functions. For example, an embodiment of a system or a
component may employ various integrated circuit components, e.g.,
memory elements, digital signal processing elements, logic
elements, look-up tables, or the like, which may carry out a
variety of functions under the control of one or more
microprocessors or other control devices.
[0028] Magnetic sensors sense magnetic field in one or more
directions. Such magnetic sensors typically have a dynamic range in
which they are operable to provide meaningful information regarding
a magnetic field to which they are exposed. For example, if the
magnetic field is so small that it is outside the dynamic range of
the magnetic sensor, the sensor does not generate any output
information regarding such a field that is below its sensing
threshold. Similarly, if the magnetic field is so great that it
saturates the magnetic sensor, the magnetic sensor outputs
information indicating that it is sensing a magnetic field having a
magnitude that is equal to or greater than the high end of the
dynamic range of the magnetic sensor. When the magnetic field is
within the dynamic range of the sensor, the magnetic sensor
generates output information that is based on the magnetic field.
For example, the magnetic sensor may provide an analog output where
the magnitude of the output is proportional to the magnitude of the
magnetic field as detected by the sensor and the sign of the output
indicates a positive or negative direction of the magnetic field
with respect to the directional axis to which the magnetic field is
referenced.
[0029] As described in more detail below, embodiments are disclosed
herein that employ a plurality of magnetic sensors arranged in an
array. In some embodiments, the sensors are arranged in pairs,
where each pair of magnetic sensors allows for common mode
rejection of external magnetic fields that are unrelated to the
current being measured. In some embodiments, the array of magnetic
sensors includes a plurality of pairs of magnetic sensors, where
different pairs of sensors have different levels of sensitivity to
the magnetic field corresponding to the current to be measured. For
example, in some embodiments, the magnetic sensors of a first pair
of sensors are spaced a first distance from the conductor, while
the sensors in a second pair are spaced a second, greater distance
from the conductor such that the sensitivity of the second pair to
the magnetic field generated by current through the conductor is
reduced by the added distance. In other embodiments, the
orientation of the magnetic sensors in a second pair of sensors may
be adjusted such that the magnetic field is perceived differently
than a first pair of sensors such that the second pair of sensors
is less sensitive to the magnetic field.
[0030] In other embodiments, the composition of the sensors in each
pair of sensors is different such that, even if spaced an equal
distance from the conductor, sensitivity to the magnetic field for
each pair of sensors in the sensor array is varied. For example,
sensors in a second pair of sensors may be sized or constructed to
include materials that make those sensors less sensitive to the
magnetic field of the conductor such that those sensors have a
different dynamic range than a first pair of sensors. In yet other
embodiments, buffering materials are included in the sensor array
to adjust the sensitivity of certain sensors in order to shift
their dynamic range with respect to the magnetic field generated by
the current through the conductor. Notably, these different
techniques for adjusting the sensitivity of the sensors to the
magnetic field (different distance, different orientation,
different composition, supplemental buffering materials, etc.) can
be combined in various combinations to achieve the desired
variation in sensitivity for the sensors in the array. Having
sensors with different levels of sensitivity to the magnetic field
generated by the current provides for an expanded dynamic range for
the overall sensor array. Small currents that generate small fields
can be characterized by sensors having high levels of sensitivity,
whereas larger currents whose fields saturate the sensors with high
sensitivity can be characterized by sensors having lower levels of
sensitivity that are not overwhelmed by the higher-magnitude
magnetic fields generated by the larger currents.
[0031] Also disclosed herein is processing circuitry used to
combine the information provided by the plurality of sensors in the
sensor array to produce the desired characterization information
regarding the current flow through the conductor. Such processing
circuitry, which can be implemented as discrete hardware, software
executing on a processor, or a combination thereof, determines
which sensors are providing useful input and combines the input
from multiple sensors to generate characterization data regarding
the current flow. Such characterization data can include, for
example, the presence/absence of current, magnitude of the current,
and direction of the current flow. As discussed in more detail
below, in some embodiments, the processing circuitry is included on
the same substrate as the sensor array, whereas in other
embodiments the processing circuitry is implemented on a separate
substrate from the array. In yet other embodiments, such processing
circuitry can be included on more complex integrated circuits or
circuit boards along with additional processors or related
circuitry. For example, the processing circuitry can be designed as
an application specific integrated circuit (ASIC) that is included
on a printed circuit board or a standard cell that can be dropped
into an integrated circuit design that includes other circuit
elements. The processing may also be realized with the use of
software on a processor connected to the sensor array.
[0032] Other example embodiments are presented in which the sensor
array is disposed in or on a length of flexible material that can
be wrapped around or otherwise mounted to a conductor. Tie-wraps
and tapes with embedded or mounted sensors are described below in
which the relative placement of the sensors with respect to the
conductor is varied based on the positioning of the sensors in/on
the flexible material and the manner in which the flexible material
is attached to the conductor. In some embodiments, the flexible
material includes an output port or other circuitry to provide the
sensor information to processing circuitry apart from the flexible
material, whereas in other embodiments, the processing circuitry is
included on the flexible material. Embodiments with the sensor
array in or on the flexible material provide adaptive current
sensors that can easily be applied to a variety of different sized
conductors.
[0033] FIG. 1 illustrates a sensor array 20 coupled to a processing
circuit 30. The sensor array 20, which includes magnetic sensors
21-24, is placed on or near conductor 10 in order to detect and
characterize current flow in conductor 10. In some embodiments, the
sensor array 20 and the conductor 10 are included on the same
substrate, whereas in other embodiments, conductor 10 is on a
different substrate or is a stand-alone conductor such as a wire.
In some embodiments, the sensor array is included in a structure
designed to receive the conductor 10 in a manner that ensures the
conductor 10 is properly positioned with respect to the sensors
21-24 in order to enable the sensors 21-24 to provide useful
information regarding the magnetic field generated by current
flowing through the conductor 10. For example, the structure on
which the sensor array 20 is included may include a trench or hole
for insertion of a wire. In other examples, mounting points
included on the sensor array structure help position the sensor
array 20 relative to the conductor 10. In yet other embodiments,
each of the sensors 21-24 is a separate structure that has been
positioned relative to the other sensors in order to form the
array.
[0034] Each of the magnetic sensors 21-24 senses magnetic field in
at least one direction. For example, in one embodiment, each of the
magnetic sensors 21-24 is a uniaxial sensor that senses magnetic
field in a direction perpendicular to the conductor. For example,
each sensor may sense magnetic field having flux lines that extend
directly into and out of the page, which is shown to correspond to
the Z-axis in FIG. 1. In other embodiments, each of magnetic
sensors 21-24 is a multi-axial magnetic sensor that is capable of
detecting magnetic fields in multiple directions. For example,
while a uniaxial magnetic sensor may detect magnetic field going
into and coming out of the page (Z-axis), a multi-axial magnetic
sensor may also detect magnetic fields in a right-to-left direction
corresponding to the X-axis, and/or in the up-and-down direction
corresponding to the Y-axis. Such multiaxial magnetic sensors can
be formed using sets of uniaxial sensors positioned in different
orientations. In other embodiments, such multi-axial magnetic
sensors may be formed together in a single plane where flux guides
are used to redirect magnetic field relative to the plane in which
the sensors are formed to enable sensing of magnetic fields that
normally would not be perceptible within the plane the magnetic
sensors are formed. Such flux guides and multi axis magnetic
sensors are discussed in U.S. Pat. No. 8,390,283, issued Mar. 5,
2013, and entitled "Three Axis Magnetic Field Sensor," which is
incorporated by reference herein. Further details regarding example
magnetic sensors are discussed in U.S. Patent Application
Publication No. 2014/0138346, published May 22, 2014, and entitled
"Process Integration of a Single Chip Three Axis Magnetic Field
Sensor," which is also incorporated by reference herein. In some
embodiments, each magnetic sensor 21-24 is formed using unshielded
magnetoresistive sensing elements that are electrically coupled
together in a Wheatstone bridge configuration. Such a configuration
is also discussed in detail in U.S. Pat. No. 8,390,283. In some
embodiments, a single die having sensors corresponding to multiple
axes is used where the sensors corresponding to some of the axes
are ignored in characterizing the current through the conductor.
For example, a three-axis magnetic field sensor such as those
described in U.S. Pat. No. 8,390,283 can be used where the X- and
Y-axis sensors are disregarded and only information from the Z-axis
sensors are used.
[0035] As shown in FIG. 1, magnetic sensors 21 and 22 are
positioned closer to conductor 10 then magnetic sensors 23 and 24.
If a spatial axis is defined as running through the center of the
conductor 10 (or the position where conductor 10 is expected to be
inserted) and in the direction of the current flow through
conductor 10, each magnetic sensor in the first pair of magnetic
sensors 21, 22 is positioned a first distance from the spatial axis
corresponding to the conductor and each magnetic sensor in the
second pair of magnetic sensors 23, 24 is positioned a second
distance from the spatial axis, where the second distance is
greater than the first distance. As such, any magnetic field
generated by current flowing through conductor 10 will have a
greater impact on magnetic sensors 21 and 22 then it will on
magnetic sensors 23 and 24 as the strength of the magnetic field is
inversely proportional to the distance from the point of origin of
the magnetic field to the point where the field is sensed. As such,
while each of the magnetic sensors 21-24 may be substantially
similar in construction, magnetic sensors 23 and 24 are described
as "less sensitive" to the magnetic field generated by current
flowing through the conductor 10 based on their positioning further
away from the conductor 10. As such, the sensor array 20 depicted
in FIG. 1 includes a first pair of sensors 21 and 22 that have a
first level of sensitivity with respect to the magnetic field
generated by current through the conductor 10 and a second pair of
sensors 23 and 24 that have a second level of sensitivity with
respect to the magnetic field generated by current through the
conductor 10, where the second level of sensitivity is less than
the first level of sensitivity.
[0036] In operation, when a current flows through conductor 10,
thereby resulting in a magnetic field being generated, each of the
sensors 21-24 may or may not generate relevant information based on
the magnetic field. For example, if a small current is flowing
through conductor 10 such that a small magnetic field is generated,
the perception of that magnetic field by sensors 21 and 22 may be
sufficient to result in those sensors generating information
regarding the strength and direction of the magnetic field, whereas
sensors 23 and 24 may be too far from the conductor 10 to perceive
the magnetic field to a degree that results in the generation of
useful information. Conversely, a strong magnetic field resulting
from a much larger current in conductor 10 can saturate magnetic
sensors 21 and 22, whereas magnetic sensors 23 and 24, having
reduced sensitivity to the magnetic field based on their more
distant positioning with respect to conductor 10, are able to
generate relevant output information regarding that magnetic field
as they are not saturated. In yet another example, the current
through the conductor 10 may be such that the resulting magnetic
field is perceived by all of magnetic sensors 21-24 and is within
the dynamic range of each of those sensors 21-24 such that all four
sensors are able to provide output information regarding the
magnetic field. In such an example, the magnetic field does not
result in any of the magnetic sensors 21-24 being saturated, yet
the field is of sufficient magnitude to be perceived and evaluated
by each of the sensors 21-24.
[0037] The processing circuit 30 included in FIG. 1 receives the
information generated by each of the magnetic sensors 21-24 and
evaluates that information in order to provide characterization
data regarding the magnetic field being generated by the current
flowing through conductor 10, and thus, characterization data
regarding the current itself. The processing circuit 30 determines
whether each of the sensors 21-24 is providing relevant information
regarding the magnetic field, and, once the relevant information
has been selected for further processing, the processing circuit 30
is configured to process that information to generate the
characterization data regarding the current flow through the
conductor 10. For example, the processing circuit 30 can determine
that the first pair of magnetic sensors 21 and 22 are saturated,
thereby indicating that the magnitude of the magnetic field is
beyond the dynamic range of sensors 21 and 22. As such, the
processing circuit will omit or give no weight to the information
provided by the first pair of magnetic sensors from the relevant
information that it selects for further processing to characterize
the current flow through the conductor 10. In such an example, the
processing circuit 30 may also determine that the sensors 23 and 24
are not saturated, and in fact are providing relevant information
regarding the magnetic field being generated by the current through
the conductor 10. As such, the processing circuit can analyze the
information provided by sensors 23 and 24, while omitting the
information provided by sensors 21 and 22, to characterize the
current flowing through conductor 10.
[0038] In another example, the processing circuit 30 determines
that both the first pair of magnetic sensors 21 and 22 and the
second pair of magnetic sensors 23 and 24 are operating within
their respective dynamic ranges and are not saturated by the
magnetic field being generated by the current flowing through
conductor 10. As a result, the processing circuit 30 can use the
information being provided by all of the magnetic sensors 21-24 in
characterizing the current flow through the conductor 10. For
example, the processing circuit 30 may perform a weighted average
with respect to the information received from the sensors 21-24 in
order to arrive at the characterization data for the current
flowing through conductor 10. Such a weighted average may take into
account the different levels of sensitivity of the magnetic sensors
21-24.
[0039] In some embodiments, a calibration procedure is used to
refine the characterization data generated by the processing
circuit 30. For example, a known current can be sent through the
conductor 10, where the processing circuit 30 generates
characterization data corresponding to that known current based on
initial parameter settings within the processing circuit 30.
Calibration methods can then be used to adjust those parameter
settings in order to provide characterization data aligned with the
known current flowing through the conductor 10. For example, a 1
Amp current may be sent through conductor 10, where the initial
characterization data produced by the processing circuit 30
indicates that the sensing apparatus is detecting a current of 0.9
Amps flowing through the conductor 10. As a result, parameters
included in or referenced by the processing circuit 30 can be
adjusted such that the characterization data produced by the
processing circuit 30 more accurately reflects the actual current
flowing through the conductor 10. It should be appreciated that in
some embodiments, such calibration may not be necessary based on
the tolerances with respect to the current characterization that
are acceptable for the particular application. In other
embodiments, calibration at many different levels of current
through the conductor 10 is performed in order to ensure that the
sensing apparatus is properly calibrated throughout a wide dynamic
range and can therefore characterize currents of both low and high
magnitude.
[0040] FIG. 1 shows the sensor array 20 including a plurality of
pairs of magnetic sensors. The magnetic sensors 21-24 are grouped
in pairs in order to provide common mode rejection with respect to
external magnetic fields perceived by the magnetic sensors 21-24
that are not generated as a result of current flow through the
conductor 10. FIG. 2 provides a different perspective view of the
conductor 10 and magnetic sensors 21-24. The view presented in FIG.
2 corresponds to the perspective view indicated by the arrow
labeled "A" in FIG. 1. In the example illustrated, the sensors
21-24 are positioned in the same plane with conductor 10. The
magnetic field generated by the current through conductor 10 is
represented by concentric circles around conductor 10. Assuming the
current is along the X-axis and coming out of the page in FIG. 2,
the right-hand rule indicates the magnetic field corresponding to
that current is oriented in a counterclockwise direction such that
sensors 21 and 23 perceive magnetic field in a downward (-Y)
direction, whereas magnetic sensors 22 and 24 perceive magnetic
field in an upward (+Y) direction. Assuming the magnetic sensors 21
and 22 are placed the same distance away from conductor 10, are
composed of the same materials, and have the same structure, those
matched sensors 21 and 22 should perceive the same amount of
magnetic field, but with opposite polarity, resulting from the
current through the conductor 10. FIG. 2 also shows an external
magnetic field 50 directed in a downward direction, where the
magnetic field 50 is unrelated to the current flowing through the
conductor 10. In order to prevent magnetic field 50 from adversely
influencing the characterization of the current flow through
conductor 10 by the sensing apparatus, the magnetic sensors 21-24
are grouped in differential pairs, such that the influence of the
magnetic field 50 on one of the sensors within each differential
pair cancels out the influence of the magnetic field 50 on the
other sensor within the differential pair. Thus, while magnetic
sensors 21 and 22 perceive the magnetic field associated with the
current flowing through conductor 10 as having opposite polarity,
both magnetic sensors 21 and 22 perceive magnetic field 50 in the
same manner (i.e. as having the same magnitude and direction). As
such, by providing the output information from magnetic sensors 21
and 22 to a differential amplifier 60 as shown in FIG. 3, the
contributions to the output information generated by sensors 21 and
22 in response to external magnetic field 50 cancel out.
[0041] In order to provide optimal common mode rejection of signals
resulting from the detection of an external magnetic field such as
field 50, the magnetic sensors 21 and 22 are preferably
symmetrically aligned to the field 50, relative to the conductor
10. In the case illustrated in FIG. 2, this would correspond to
points that are about 180.degree. apart on a virtual circle having
a center corresponding to the conductor 10. In other words, the
sensors are placed on opposite sides of the conductor. However, in
other embodiments, the positioning of magnetic sensors 21 and 22
need not be as precise, as a lower level of rejection of such
common mode signals resulting from external magnetic fields may be
acceptable. Similarly, sensors 23 and 24 can be placed 180.degree.
apart on a larger virtual circle having a center corresponding to
the conductor 10. In some embodiments, the first virtual circle
corresponding to magnetic sensors 21 and 22 and the second virtual
circle corresponding to magnetic sensors 23 and 24 are concentric
virtual circles line lying in a common plane that is perpendicular
to the spatial axis for the conductor. In other embodiments, the
virtual circles may be offset such that the center of the first
virtual circle is positioned at a first point on the spatial axis
for the conductor, whereas the center of the second virtual circle
is positioned at a second, different point on the spatial axis.
[0042] Notably, while FIGS. 1 and 2 show the magnetic sensors 21-24
grouped in pairs, other embodiments do not require such matched
sets of magnetic sensors. For example, if external magnetic fields
are not a significant concern, a simpler embodiment can include
only magnetic sensors 21 and 23, where each of magnetic sensors 21
and 23 provides a different level of sensitivity with respect to
the magnetic field generated by current flowing through the
conductor 10. Thus, while such an embodiment would lack the common
mode rejection of undue influences from external magnetic fields,
it would still provide a sensor array with a wider dynamic range
than is supported by a single magnetic sensor. As discussed below,
the sensor array can include a large number of sensors, thereby
providing a very wide dynamic range with respect to sensing
currents of different amplitudes. In such embodiments that do not
fully support common mode rejection of external magnetic fields,
the processing circuit 30 can still analyze the information
provided by the plurality of sensors in the array to determine
which sensors are providing relevant information regarding the
magnetic field resulting from the current flow through the
conductor 10 and process that information accordingly in order to
characterize the current through conductor 10.
[0043] FIG. 4 illustrates a sensor array 120 that includes a
plurality of magnetic sensors 121-128. A horizontal line represents
the expected positioning of a conductor 110 through which current
flows that results in a magnetic field. As shown, current flow is
along the X-axis. As discussed above, the conductor 110 may be
disposed on the same substrate as the sensor array, or it may be a
separate wire or trace to which the sensor array is affixed or
otherwise relatively positioned. As illustrated in FIG. 4, the
first pair of magnetic sensors 121 and 122 includes magnetic
sensors that are each positioned a first radial distance from a
spatial axis corresponding to the conductor 110. Similarly,
magnetic sensors 123 and 124 constitute a second pair of magnetic
sensors positioned a second radial distance from the spatial axis
corresponding to the conductor 110, where the second radial
distance is greater than the first radial distance. Magnetic
sensors 125 and 126 form a third pair of magnetic sensors
positioned at a third radial distance from the spatial axis, and
magnetic sensors 127 128 form a fourth pair of magnetic sensors
positioned at a fourth radial distance from the spatial axis. As
shown, the fourth radial distance is greater than the third radial
distance, and the third radial distance is greater than the second
radial distance. While the sensor array 120 depicted in FIG. 4
includes four pairs of magnetic sensors where each pair includes
magnetic sensors positioned at successively greater distances from
the conductor 110, it should be appreciated that the sensor array
120 can include any number of pairs of magnetic sensors.
Embodiments with greater numbers of sensors can be used to provide
a wider dynamic range and better resolution within that dynamic
range.
[0044] As discussed above with respect to FIG. 1, processing
circuitry can be coupled to the pairs of magnetic sensors 121-128
included in the sensor array 120, where the processing circuitry is
configured to select information received from a least one of the
pairs of magnetic sensors as representative information that can be
used to characterize the current flow within the conductor. The
processing circuitry receives the information from each of the
magnetic sensors 121-128 and determines which of the sensors
121-128 are providing relevant information for characterizing the
current flow through the conductor 110. Magnetic sensors that are
saturated can be ignored or given no weight, whereas the
information from magnetic sensors operating within their dynamic
range is used to characterize the current flow through the
conductor 110. In some embodiments, the processing circuitry only
relies on information received from a single pair of magnetic
sensors, whereas in other embodiments, the processing circuitry can
combine the information provided by two or more pairs of magnetic
sensors in order to arrive characterization data for the current
through the conductor 110.
[0045] FIG. 5 illustrates another example of a sensor array 220,
where sensor array 220 includes a plurality of magnetic sensors
221-228. Magnetic sensors 221-228 are positioned relative to
conductor 210 in order to detect a magnetic field generated by
current flowing through conductor 210 along the X-axis. As shown in
FIG. 5, the sensor array 220 includes multiple pairs of magnetic
sensors, and some of the pairs of magnetic sensors are positioned a
same radial distance along the Y-axis from the spatial axis
corresponding to the conductor 210, which, as shown in FIG. 5, is
the X-axis. In some embodiments all of the sensors 221-226 are
positioned in a common plane with respect to the Z-axis. For
example, magnetic sensors 221 and 222 are positioned a first radial
distance from the conductor 210, and magnetic sensors 225 and 226
are positioned the same first radial distance away from the
conductor 210. Similarly, magnetic sensors 223 and 224 are
positioned the same distance away from the conductor 210 as sensors
227 and 228.
[0046] The embodiment depicted in FIG. 5 provides multiple magnetic
sensors having the same or similar sensitivity with respect to the
magnetic field flowing through the conductor 210. Thus, magnetic
sensors 221 and 225 should perceive about the same magnetic field
and generate about the same output information in response to
current flowing through the conductor 210. However, imperfections
in the sensors or materials surrounding the sensors can lead to
detection errors that can impact the ability of the sensor array
220 to be used to accurately characterize the current flow through
the conductor 210. As such, providing additional magnetic sensors
within the sensor array 220 having the same sensitivity as other
sensors in the sensor array 220 allows the corresponding processing
circuitry to average the input from sensors having the same or
similar levels of sensitivity in order to reduce or minimize
detection errors. FIG. 5 illustrates multiple pairs of magnetic
sensors in which some of the pairs have different spacing from the
conductor 210, and therefore different degrees of sensitivity with
respect to the magnetic field generated by current flowing through
the conductor 210. In other embodiments, the sensor array may only
include a plurality of pairs of magnetic sensors in which all of
the magnetic sensors have the same sensitivity. For example, all of
the sensors can be spaced equally distant from the spatial axis
corresponding to the conductor 210. In such an embodiment, the
dynamic range of the overall sensor array may not be expanded
beyond the dynamic range for each individual sensors, however, the
presence of redundant pairs of sensors allows corresponding
processing circuitry to average the information received from those
sensors to arrive at a more accurate characterization of the
current flow through the conductor 210.
[0047] FIG. 6 illustrates a sensor array 320 that includes magnetic
sensors 321-326. The sensor array 320 includes pairs of magnetic
sensors that are equally spaced with respect to the conductor 310.
Instead of varying the sensitivity of the sensors 321-326 by
varying their positions with respect to the conductor 310, in some
embodiments, the sensitivity of the magnetic sensors 321-326 is
varied by varying the composition of magnetic sensors 321-326. In
other embodiments, buffering material can be selectively added to
the sensor array 320 in order to reduce the sensitivity of certain
magnetic sensors within the sensor array.
[0048] For example, in some embodiments, sensors 323 and 324 may be
different in composition then sensors 321 and 322 such that sensors
323 and 324 are less sensitive to the magnetic field generated by
the current flowing through conductor 310. Thus, although sensors
323 and 324 are positioned just as close to conductor 310, their
reduced sensitivity provides the same advantages as having magnetic
sensors 323 and 324 positioned further away from conductor 310 as
the dynamic range of sensors 323 and 324 is different from that of
sensors 321 and 322. As such, while a larger current may cause
sensors 321 and 322 to saturate, the reduced sensitivity of sensors
323 and 324 may allow them to continue to operate within their
dynamic range, thereby providing relevant information to allow the
current through conductor 310 to be characterized. Providing
sensors with different composition can include providing sensors
having a different size, a different shape, or sensors that include
different materials.
[0049] In other embodiments, each of the sensors 321-326 has the
same composition, however additional buffering material 333-336 is
added to certain sensors within the sensor array 320 in order to
reduce their sensitivity with respect to the magnetic field
generated by the current flowing through the conductor 310. For
example, sensors 323 and 324 may be positioned near buffering
materials 333 and 334 that reduce the sensitivity of magnetic
sensors 323 and 324 to the magnetic field, thereby giving them a
different dynamic range than sensors 321 and 322. For sensors 325
and 326, a thicker layer of such buffering material may be
employed, or a different type of buffering material may be used
that is more effective in reducing sensitivity of the magnetic
sensors 325 and 326. As a result, magnetic sensors 325 and 326 are
even less sensitive to the magnetic field than sensors 323 and
324.
[0050] In yet other embodiments, the sensitivity of sensors in the
array can be adjusted by changing the orientation of the sensors
with respect to the direction of the magnetic field to be sensed.
For example, a sensor placed perpendicular to the direction of
magnetic field to be sensed may have the maximum level of
sensitivity to that field, whereas when the sensor is angled
slightly away from perpendicular, the sensitivity is reduced. As
such, having pairs of sensors oriented slightly differently can
provide an array of sensors with different levels of sensitivity to
a particular magnetic field.
[0051] As described above, the sensitivity of sensors within the
sensor array can be controlled using a variety of techniques in
order to provide sensors having different dynamic ranges with
respect to detection of the magnetic field generated by current
flowing through a conductor. Such techniques include spacing the
sensors at different distances from conductor, changing the
orientation of the sensor with respect to the direction of magnetic
field to be sensed, changing the composition (e.g. size, shape,
materials) of the sensor, and adding additional buffering materials
that reduce the sensitivity of the sensors. While these techniques
have been generally presented as being used separately in the
different embodiments discussed above, one of ordinary skill in the
art appreciates that such sensitivity control techniques can be
combined in various ways in order to produce a sensor array having
a wide variety of sensors with different levels of sensitivity.
[0052] FIG. 7 illustrates an example embodiment that includes a
sensor array 420 mounted to a substrate 405, which, in some
embodiments is a printed circuit board or integrated circuit.
Substrate 405 is shown to include a conductor 410. In some
embodiments, the conductor 410 is a trace on the surface of the
substrate 405, whereas in other embodiments, the conductor 410 is
embedded within the substrate 405. In the example embodiment shown
in FIG. 7, the sensor array 420 includes a plurality of sensors
421-426 that are included on a separate substrate from the
substrate 405. For example, the structure shown in FIG. 7 may be a
multichip module that includes one integrated circuit that includes
the sensor array 420 is mounted to a second integrated circuit 405
that includes the conductor 410. Such mounting can be facilitated
by mounting points 435, which, in some embodiments are solder pins
on a package corresponding to one of the integrated circuits.
[0053] The sensor array 420 can be used to characterize current
flow through the conductor 410. As depicted, current is flowing
through the conductor 410 in a direction coming out of the page,
which, for the sake of illustration is assumed to correspond to the
Z-axis. As such, the flux lines corresponding to the magnetic field
generated by that current are shown to be counterclockwise in
direction. In the example shown in FIG. 7, the close placement of
the sensor array 420 to the conductor 410 can result in the
magnetic field generated by the current through the conductor 410
having different directional components corresponding to different
axial directions as perceived by each of the sensors 421 through
426. Assuming the vertical direction corresponds to the Y-axis,
sensors 425 and 426 perceive magnetic field resulting from the
current through conductor 410 that is generally in the Y direction.
In contrast, sensors 421 and 422 perceive magnetic field with a
main component that is horizontal and parallel to the X-axis.
[0054] In such an embodiment, sensors capable of sensing magnetic
field in different directions can be included within the sensor
array 420. In one example, sensors 421 and 422 are uni-axial
sensors that only sense magnetic field in the X direction, whereas
sensors 425 and 426 sense magnetic field in only the Y direction.
In other embodiments, each of the magnetic sensors 421-426 is a
multi-axial sensor capable of sensing magnetic field in both the X
and Y directions. In yet other embodiments, each of the magnetic
sensors 421-426 is a three-way multi-axial sensor capable of
sensing magnetic field in each of the X, Y, and Z directions.
[0055] While not shown in FIG. 7, a processing circuit, which may
be included on substrate 420 or substrate 405, can be configured to
receive the information generated by the sensor array 420 and
process that information in order to characterize the current flow
through the conductor 410. By including magnetic sensors having
sensing capabilities in multiple directions, scenarios, such as
that illustrated in FIG. 7, in which there is a need to sense the
different directional components of the magnetic field are
addressed.
[0056] FIG. 8 illustrates a block diagram corresponding to a
sensing apparatus that includes a sensor array 520 coupled to
circuitry 530, where circuitry 530 is used to characterize current
flow through a conductor 510. As discussed above, conductor 510 can
be included on the same substrate as sensor array 520, or, in other
embodiments, can be separate from the sensor array 510. The sensor
array 520 is positioned relative to the conductor 510 in order to
allow the sensors included in the sensor array 520 to detect and
measure the magnetic field generated by current flowing through the
conductor 510. Similarly, the circuitry 530 can be included on the
same substrate is the sensor array 520, or may be disposed on a
separate substrate.
[0057] Sensor array 520 includes a plurality of sensors arranged in
an array such as those discussed above with respect to FIGS. 1-7.
Thus, the sensors included in the sensor array 520 can include
pairs of sensors position at different distances from the conductor
510, sensors having different sensitivity based on their
composition, etc. The sensors included in sensor array 520 can be
discreet devices, devices all formed on an integrated circuit, or
devices arranged on a printed circuit board.
[0058] Circuit 530, which is used for characterizing current flow
through the conductor 510, includes input circuitry 550, processing
circuitry 540, and output circuitry 560. Input circuitry 550 is
configured to receive information from the magnetic sensors in the
sensor array 520. The processing circuitry 540 is coupled to the
input circuitry 550 and is configured to select relevant
information from the information received from the magnetic sensors
in the sensor array 520 and process that relevant information to
generate characterization data regarding the current flow through
the conductor 510. As noted above, selecting relevant information
from the information received can include determining which
magnetic sensors in the sensor array 520 are saturated and omitting
information from those sensors. Such selection can also include
determining that magnetic sensors are not saturated and are
detecting magnetic field within their dynamic range. Information
from such magnetic sensors can be included in the relevant
information processed to characterize the current flow. Selection
of the relevant information can be accomplished using the
multiplexer 544 that is controlled by a range select circuit 542. A
combining circuit 543 can be used to combine multiple sets of
information corresponding to multiple sensors in the sensor array
520. The range select circuit 542 controls the multiplexer 541 and
selects which sets of information from which sensors are passed
through to the combining circuit 543. The range select circuit 542
receives the output of the combining circuit 543. As such, the
range select circuit can select and evaluate the information
received from individual sensors or sets of sensors in order to
determine which sensors are providing information to be included in
the relevant information used to characterize the current flow
through the conductor 510.
[0059] After the range select circuit 542 has determined which
sensors are providing useful relevant information that will be used
to characterize the current flow through the conductor 510, the
output from the combining circuit 543 outputs the characterization
data corresponding to the current flowing through the conductor
510. In some embodiments, the output produced by the circuit 530 is
an analog indication of the current flow through the conductor 510,
whereas in other embodiments, the output is digital in format.
[0060] In some embodiments, the circuit 530 is composed of discrete
components implemented on printed circuit board. In other
embodiments, the circuit 530 is included on a single integrated
circuit, where that integrated circuit may also include other
processing circuitry such as a microcontroller or processor that
manages current flow through conductors in a system. For example,
in an automotive system, sensor arrays such as sensor array 520 can
be used to monitor the flow of current through various conductors
in the control and power systems for the automobile, where a
processor includes the circuitry for managing the numerous systems
within the automobile. Such a processor can also include the
circuit 530 that is used to monitor current flow in different
portions of the automobile using one or more sensor arrays. In some
embodiments, portions of the circuit 530 may be shared with other
components in the system. For example, the range selection circuit
542 may correspond to a microprocessor executing code that examines
the output of the combining circuit 543 and controls the
multiplexer 544.
[0061] FIGS. 9 and 10 are flow charts that illustrate exemplary
embodiments of methods relating to characterization of current flow
through a conductor using an array of magnetic sensors. The
operations included in the flow charts may represent only a portion
of the overall process used in characterizing current flow. For
illustrative purposes, the following description of the methods in
FIGS. 9 and 10 may refer to elements mentioned above in connection
with FIGS. 1-8. It should be appreciated that the methods may
include any number of additional or alternative tasks, the tasks
shown in FIGS. 9 and 10 need not be performed in the illustrated
order unless specified otherwise, and the methods may be
incorporated into a more comprehensive procedure or process having
additional functionality not described in detail herein. Moreover,
one or more of the tasks shown in FIGS. 9 and 10 can be omitted
from an embodiment as long as the intended overall functionality
remains intact.
[0062] FIG. 9 illustrates a flow chart of a method for
characterizing current flow through a conductor. At 610,
information is received from a plurality of magnetic sensors. In
some embodiments, the plurality of magnetic sensors includes
sensors having a different levels of sensitivity, or a different
dynamic range, with respect to sensing the magnetic field generated
by current flowing through the conductor. For example, the
plurality of magnetic sensors can be arranged in pairs where each
pair of magnetic sensors includes a first sensor and a second
sensor that are positioned at a predetermined distance from a
spatial axis corresponding to the conductor, wherein the spatial
axis corresponds to a direction of current flow within the
conductor. In such an example, the sensors for different pairs can
be positioned at different distances from the spatial axis.
[0063] At 620, relevant information is selected from the
information received from the plurality of magnetic sensors. As
discussed above, selecting the relevant information can include, at
622, determining that certain magnetic sensors of the plurality of
sensors are saturated, where the information provided by such
saturated magnetic sensors is excluded from the relevant
information. As also discussed above, the relevant information
selected at 620 can include, as shown at 624, information from more
than one pair of magnetic sensors included in the plurality of
sensors.
[0064] At 630, the relevant information is processed to generate
characterization data regarding the current flowing through the
conductor. At 632, such processing is shown to include combining
the information received from more than one pair of magnetic
sensors to arrive at the characterization data for the current. At
634, such a combination is shown to use a weighted average
calculation, where different weighting can be apportioned to
different sensors based on their level of sensitivity, which may be
controlled based on positioning, structure of the sensor, etc.
[0065] FIG. 10 provides a flow chart corresponding to a method for
performing a calibration operation in conjunction with a sensing
apparatus such as those discussed above. At 710, a known current is
sent through a conductor, where the conductor is positioned in a
particular arrangement with a set of magnetic sensors that detect
and measure the magnetic field generated by the current flowing
through the conductor.
[0066] At 720, information is received from the set of sensors. At
730, processing is performed to characterize the current flowing
through the conductor based on the information received from the
sensors. As discussed above, the processing performed at 730 can
include combining information received from multiple sensors in a
manner that provides a wide dynamic range and avoids errors based
on external magnetic fields or imperfections in the sensors.
[0067] At 740, it is determined whether or not the characterization
data generated at 730 is consistent with the known current flowing
through the conductor. For example, if the processing performed at
730 indicates that a certain current having a certain direction and
magnitude is perceived as flowing through the conductor 710, and
that perceived magnitude and direction is consistent with the
actual current known to be flowing through the conductor, the
sensor array, and the processing performed with respect to the
sensor array, is determined to be properly calibrated. If the
sensed current is consistent with the actual current, the method
proceeds to 760 where calibration is complete.
[0068] If it is determined at 740 that the characterization of the
current is not consistent with the actual current flowing through
the conductor, processing parameters are adjusted at 750 in order
to attempt to bring the characterization data in line with the data
that should be expected based on the actual current flow. For
example, the weighting with respect to certain sensors can be
adjusted, or bias/offset values can be adjusted in order to align
the characterization data with the current flow. After adjusting
processing parameters at 750, the processing based on the
information received from the sensors is repeated at 730, and the
characterization data that results is once again checked at 740 to
determine if it is now consistent with the actual current flowing
through the conductor. Based on the comparison performed at 740,
calibration is either completed at 760 or further adjustment to
processing parameters occurs at 750.
[0069] FIG. 11 illustrates a particular embodiment in which a
plurality of sensors 821-827 are arranged within or on a length of
flexible material 805. The thickness (dimension in the Y-direction)
of the material 805 is preferably thin enough such that the
flexible material 805 can be wrapped around a conductor. Such a
wrapping of the flexible material 805 around a conductor 850 is
shown in FIG. 12 in which the conductor lies in the Z-direction. In
some embodiments, the flexible material 805 includes an adhesive
such that the flexible material 805 functions in a manner similar
to tape and is able to self-attach around the conductor 850. In
other embodiments, the flexible material may be a tie wrap, which
can also be referred to as a "zip tie" or "cable tie," such that
the flexible material can be readily attached around the outside of
a conductor. In yet other embodiments, the flexible material is
foam insulation, and the magnetic sensors are included within the
foam insulation.
[0070] Flexible material 805 is also shown to include a port 830,
where the port 830 can be used to output the information collected
by the sensors 821-827. In some examples, the port 830 is an
electrical port into which an interface is plugged to allow the
information from the sensors to be output. In other embodiments,
the port 830 may include a Bluetooth interface, or some other
wireless interface that allows data to be transferred from the
flexible material 805 to a remote processor. In yet other
embodiments, processing circuitry used to process the information
generated by the sensors 821-827 is included in or on the flexible
material 805. In such embodiments, the port 830 can be used to
output processed characterization data corresponding to current
flow through a conductor around which the flexible material 805 is
wrapped. In yet other embodiments, a lights or a display are also
included in or on the flexible material, where the lights or
display are used to provide information regarding the current flow
as characterized by the sensing apparatus. In order to provide
power for circuits or devices on the flexible material, in some
embodiments the flexible material includes circuit elements that
scavenge power from the magnetic field the sensing array is
designed to detect. Thus, in addition to measuring magnetic field
generated by current flow through a conductor, the flexible
material can tap into the energy of the magnetic field and generate
power needed to operate various components that may be included in
or on the flexible material. While this may slightly alter the
current flow being detected, in many applications such an impact is
inconsequential.
[0071] While FIG. 12 shows the flexible material wrapped around the
conductor 850 multiple times such that there are multiple layers of
sensors extending out from the conductor 850, in an example
embodiment where the flexible material is similar to a tie wrap,
only a single wrapping of the flexible material around the wire 850
may exist. Thus, while the embodiment illustrated in FIG. 12
provides for multiple magnetic sensors spaced at different
distances from the conductor 850 based on the multiple wraps of the
flexible material 805, embodiments such as a tie wrap may position
the magnetic sensors differently within the flexible material in
order to achieve a similar effect. Such an embodiment is shown in
FIG. 13. FIG. 13 shows a length of flexible material 905 having a
thickness 906 and in which magnetic sensors 921-929 are formed.
Port 930 functions in a similar manner to port 830 described above
with respect to FIG. 11.
[0072] When the flexible material 905 is wrapped around a conductor
an array of magnetic sensors that around the conductor is
established. As shown in FIG. 13, some of the magnetic sensors are
positioned closer to a first side of the flexible material, whereas
other magnetic sensors are positioned further away from the first
side of the flexible material. Thus, when wrapped around the
conductor, the magnetic sensors 921 and 924 that are close to the
first side of the flexible material end up positioned closer to the
conductor then the other magnetic sensors that are positioned at a
different distance from the first edge within the flexible material
905. Thus, different magnetic sensors having different sensitivity
to magnetic field generated by current flowing within the conductor
are established when the flexible material 905 is wrapped around a
conductor. As discussed above, the magnetic sensors included in the
flexible material 805 and flexible material 905 can be formed to
have different levels of sensitivity, where the sensitivity is
controlled based on positioning of the sensor, the composition of
the sensor, and the presence or absence of buffering material
associated with the magnetic sensors. Thus, rather than including
sensors spaced a different distance from the edge of the flexible
material, sensors having different compositions or different
sensitivities based on other factors can be included in the
flexible material.
[0073] Processing circuitry is used to determine which of the
magnetic sensors are providing useful information regarding the
magnetic field generated by current flowing through the conductor
around which the flexible material is wrapped. Determining which
magnetic sensors are providing useful information can also include
determining which magnetic sensors included in the flexible
material end up in offset positions with respect to each other
after the sensing apparatus is mounted to the conductor. For
example, the processing circuitry can determine that certain pairs
of magnetic sensors are such that they approximate offset pairs of
magnetic sensors such as those shown in FIG. 1. For example,
depending on the thickness of the wire, in the embodiment of FIG.
13, sensors 921 and 924 may comprise a closely matched pair of
magnetic sensors in one instance, where magnetic sensors 921 and
927 present a better matched pair in another example. As noted
above, an optimal pair of magnetic sensors would be equally spaced
from the conductor and offset from each other by approximately
180.degree. with respect to a circle having a center corresponding
to the conductor. While a 180.degree. relationship may not actually
exist for sensors in the flexible material, the positioning of
those sensors still provides significant common mode rejection with
respect to external magnetic fields that could adversely impact
characterization data for the current flow through the conductor.
As such, additional processing that determines which of the
magnetic sensors are best paired to provide common mode rejection
with respect to external magnetic fields can be used in conjunction
with the flexible material embodiments described herein.
[0074] FIG. 14 illustrates yet another example embodiment in which
a sensor array is used to monitor current flow through a conductor.
The circuit 1005 includes a sensing apparatus 1020 and a processing
circuit 1010. As shown, the circuit 1005 is spliced between
conductors 1040 and 1050. Current flowing through conductors 1040
and 1050 also flows through conductor 1022. The sensor array 1021
is positioned with respect to the conductor 1022 such that magnetic
field generated by the current flowing through conductor 1022 can
be monitored by the sensor array 1021 as discussed above. The
information generated by the sensor array 1021 is provided to
processing circuit 1010. In some embodiments, processing circuit
1010 can, based on the information provided by the sensor array,
detect when large spikes in current through conductor 1022 occur.
In one example embodiment, the circuit 1005 is used to monitor
current flow through a high-amperage conductor corresponding to a
motor. Rather than including a fuse between conductors 1040 and
1050 that blows to generate an open circuit when too much current
is applied, the circuit 1050 can used to ensure too much current
does not flow through the conductors 1040 and 1050. By monitoring
the current flow using the sensor array 1021, a disable signal 1012
can be asserted in order to avert the need to blow of physical fuse
and interrupt the connection between conductors 1040 and 1050.
Additional circuitry can then be used to reset the system or change
certain parameters before the disable signal 1012 is de-asserted,
thereby enabling current to once again flow through the conductors
1040 and 1050. While FIG. 14 depicts an example set of components
used to monitor and disable current flow when too much current is
detected, it is understood that other combinations of components
can be used to perform the same or a similar function in other
embodiments.
[0075] As discussed above, by including sensors with different
levels of sensitivity to the magnetic field generated by the
current flowing through the conductor 1022 in the sensor array
1021, a wide dynamic range for the current monitoring circuit 1005
can be achieved. Having the current monitoring circuit 1005
function as a fuse-like device can help to protect certain
circuitry or other devices (e.g. the motor) in a manner that allows
for easier recovery than is possible in a system in which a
physical fuse is blown to create an open circuit.
[0076] FIG. 15 illustrates an embodiment in which a sensing
apparatus is used in a "current loop" configuration in which the
current through a motor 1110 is closely controlled based on a
feedback loop. The circuit includes a motor 1110, an operational
amplifier 1120, and a sensing apparatus 1105. The sensing apparatus
1105 generates a measure of the current flow through the motor 1110
and generates a signal 1122 that is fed back to the operational
amplifier 1120. With a high-gain operational amplifier, this causes
the current through the motor to track very closely to the control
input 1121.
[0077] When a sensing apparatus similar to that shown with respect
to FIG. 14 is employed in the circuit of FIG. 15, additional
protection for the motor 110 can be achieved. If an undesirably
high level of current is detected as flowing through the motor 1110
by the sensing apparatus 1105, a signal 1122 can be provided to the
operational amplifier 1120 that overrides the control input 1121
and ensures that the motor 1110 is not damaged by an oversupply of
current. Such a soft shut down can help to avoid damage to the
motor 1110 while still allowing for a simple reactivation of the
motor 1110 once the issue resulting in the excessive current is
resolved.
[0078] As described herein, a plurality of magnetic sensors are
arranged in an array with respect to a conductor that allows for
varying perspectives on the magnetic field generated by current
flowing through the conductor. In some embodiments, different
levels of sensitivity for the magnetic sensors allow for a wider
dynamic range for the sensor array then can be achieved with a
single sensor. Arranging the sensors in pairs can be used to
provide common mode rejection of signals corresponding to external
magnetic fields unrelated to the current flowing through the
conductor. The different levels of sensitivity for the magnetic
sensors can be adjusted based on numerous techniques, including
their positioning, orientation, composition, and the use of
buffering materials that affect the sensitivity of the magnetic
sensor to the magnetic field. Also disclosed are embodiments in
which the magnetic sensors are included in lengths of flexible
material that can be wrapped or otherwise flexibly placed around
conductors within which current to be characterized is flowing.
Such flexible material embodiments, such as zip ties, tapes, or
other wraps, allow for quick positioning of a sensor array around a
conductor, where the flexible material is adaptable to conductors
of different diameters. Sensitivity of the sensors within the
flexible material can be varied in order to provide an array of
sensors having a large dynamic range suitable for many different
applications.
[0079] Some embodiments described herein utilize multi-axial
sensors that are included on a single substrate (e.g. on the same
semiconductor die) such as those disclosed in U.S. Pat. No.
8,390,283. Having sensors corresponding to all of the X-, Y-, and
Z-axes in a single plane corresponding to the surface of the die
allows for easy placement of the sensors with respect to a
conductor on a printed circuit board or other relatively flat
surface. For example, the sensor die can simply be abutted to, or
stacked on top of, the printed circuit board or die on which the
conductor carrying current to be characterized resides. Such ease
of placement is in sharp contrast to solutions in which a sensor
must be placed perpendicular to the plane in which the conductor
resides, such as a system in which separate, discrete X-, Y-, and
Z-axes sensors must be physically placed in different orientations
with respect to the conductor.
[0080] Providing sensors with very high sensitivity and accuracy in
such embodiments allows for more precise current characterization
with a wide dynamic range. Having sensors corresponding to multiple
axes on the same die also requires less space than embodiments that
utilize distinct sensors or sets of sensors for each axis, as such
distinct-axis sensor embodiments may require the sensors for the
different axes to be positioned in different planes with respect to
each other. Having sensors corresponding to multiple axes on the
same die also provides for a more flexible current sensor that can
be used in a variety of applications, where the flexibility can
promote high volume production that reduces cost. As noted above,
varying the level of sensitivity of sensors used to characterize
current flow can be achieved in many different ways. In some
embodiments corresponding to multiple-axes sensor arrays,
techniques may be employed that allow the sensitivity of sensors
corresponding to one or more of the axes to be varied in a
controlled manner while the sensors corresponding to the other axes
are relatively fixed. For example, the sensitivity corresponding to
the Z-axis can be varied while the sensors for the X-, and Y-axes
are held constant or, in some embodiments, ignored.
[0081] Although the described exemplary embodiments disclosed
herein are directed to a variety of arrangements of magnetic
sensors, the present disclosure is not necessarily limited to the
exemplary embodiments. Thus, the particular embodiments disclosed
above are illustrative only and should not be taken as limitations,
as the embodiments may be modified and practiced in different but
equivalent manners apparent to those skilled in the art having the
benefit of the teachings herein. Accordingly, the foregoing
description is not intended to limit the disclosure to the
particular form set forth, but on the contrary, is intended to
cover such alternatives, modifications and equivalents as may be
included within the spirit and scope of the inventions as defined
by the appended claims so that those skilled in the art should
understand that they can make various changes, substitutions and
alterations without departing from the spirit and scope of the
inventions in their broadest form.
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