US2016041234A1PendingUtilityA1
Calibration of sensitivity and axial orthogonality for magnetometers
Assignee: HALLIBURTON ENERGY SERVICES INCPriority: Aug 8, 2014Filed: May 19, 2015Published: Feb 11, 2016
Est. expiryAug 8, 2034(~8 yrs left)· nominal 20-yr term from priority
Inventors:Wenquan LiRandal Thomas BesteJesse Kevin HensarlingBrian RobersonJohn Harrison FarrahTony Vu
G01R 33/0035G01V 13/00G01V 3/081
49
PatentIndex Score
0
Cited by
0
References
0
Claims
Abstract
A reduced-cost apparatus for calibrating the sensitivity and orthogonality of a triaxial magnetometer, and a method for adjusting the distance between the two coils of a Helmholtz coil and other related parameters are described herein. A method can include positioning a calibrated magnetometer within a mounting fixture between two coils of a Helmholtz coil, the two coils arranged in mutually parallel planes and separated by the radius of the Helmholtz coil, the mounting fixture mounted such that a position of the mounting fixture is adjustable along an axis orthogonal to the mutually parallel planes; adjusting the position of the mounting fixture over at least some of the positions and measuring the magnetic field at each position to generate a set of magnetic field measurements associated with the positions; and adjusting the first distance based on the first set of magnetic field measurements. Additional apparatuses, systems, and methods are disclosed.
Claims
exact text as granted — not AI-modifiedWhat is claimed is:
1 . A method comprising:
positioning a calibrated magnetometer within a mounting fixture between two coils of a Helmholtz coil, the two coils arranged in mutually parallel planes and being separated by a distance equal to an estimated radius of the Helmholtz coil, the mounting fixture being mounted such that a position of the mounting fixture is adjustable to a plurality of positions along a center axis of the Helmholtz coil that is orthogonal to the mutually parallel planes; adjusting the position of the mounting fixture between the two coils over at least a subset of the plurality of positions; providing an excitation signal to the Helmholtz coil, subsequent to adjusting the position of the mounting fixture to each of the plurality of positions, to generate a magnetic field at the calibrated magnetometer; measuring the magnetic field using the calibrated magnetometer to generate a first set of magnetic field measurements associated with the plurality of positions; and adjusting the distance between the two coils based on the first set of magnetic field measurements.
2 . The method of claim 1 , wherein adjusting the distance comprises:
generating a value for a separation distance between the two coils according to a mathematical relationship between the first set of magnetic field measurements, a radius of the Helmholtz coil, and the separation distance between the two coils; and adjusting the distance between the two coils to correspond to a true radius of the Helmholtz coil obtained through a data fitting algorithm.
3 . The method of claim 2 , further comprising:
adjusting the position of the mounting fixture subsequent to having adjusting the distance between the two coils based on the first set of magnetic field measurements.
4 . The method of claim 3 , wherein adjusting the position of the mounting fixture comprises:
moving the position of the mounting fixture through a plurality of positions; measuring the magnetic field, using the calibrated magnetometer mounted inside the mounting fixture, at each of a plurality of positions to generate a second set of magnetic field measurements associated with the plurality of positions; and adjusting the position of the mounting fixture according to a center location of the Helmholtz coil, the center location having been calculated using a mathematical relationship based on the second set of magnetic field measurements.
5 . The method of claim 4 , further comprising:
positioning a triaxial magnetometer to be calibrated inside the mounting fixture, subsequent to calibrating the position of the mounting fixture, the mounting fixture having an aperture configured to align the X-axis, the Y-axis, and the Z-axis of a triaxial magnetometer to the axis of the Helmholtz coil, respectively one axis at a time, when the triaxial magnetometer is inserted in the mounting fixture; using the Helmholtz coil to apply magnetic field to each axis of the triaxial magnetometer, one axis at a time, to generate a third set of magnetic field measurements; and generating a compensation matrix that contains data representative of misalignment errors based on the third set of magnetic field measurements.
6 . The method of claim 5 , wherein applying the magnetic field to the triaxial magnetometer includes:
applying the magnetic field to the X-axis of the triaxial magnetometer and recording the magnetic field measured by the X, Y and Z axes of the triaxial magnetometer; applying the magnetic field to the Y-axis of the triaxial magnetometer and subsequently recording the magnetic field measured by the X, Y and Z axes of the triaxial magnetometer; and applying the magnetic field to the Z-axis of the triaxial magnetometer, and subsequently recording the magnetic field measured by the X, Y and Z axes of the triaxial magnetometer.
7 . The method of claim 6 , wherein the magnetic field is applied along the X-axis, Y-axis, and the Z-axis by rotating the triaxial magnetometer between each application of the magnetic field.
8 . The method of claim 6 , further comprising:
calculating the measured magnetic field based on the compensation matrix.
9 . An apparatus comprising:
a Helmholtz coil including a first coil and a second coil arranged in mutually parallel planes and spaced a distance from each other along an axis orthogonal to the parallel planes, the first coil and the second coil slidably engaged with a first rail and a second rail such that the first coil and the second coil move along the first rail and the second rail to adjust the distance; and a mounting fixture including an aperture for mounting a magnetometer, the mounting fixture being slidably mounted to a third rail, the third rail passing through the first coil and through the second coil parallel to the axis such that the mounting fixture moves along the third rail to adjust a distance between the mounting fixture and each of the first coil and the second coil.
10 . The apparatus of claim 9 , wherein the aperture is shaped such that a magnetometer inserted into the aperture is rotationally adjustable to rotate about an origin of the mounting fixture.
11 . A system comprising:
a one-dimensional (1D) Helmholtz coil including a first coil and a second coil arranged in mutually parallel planes and spaced a distance from each other along an axis orthogonal to the parallel planes, the first coil and the second coil slidably engaged with a first rail and a second rail such that the first coil and the second coil slidably move along the first rail and the second rail to adjust the distance; and a mounting fixture including an aperture for mounting a magnetometer, the mounting fixture being slidably mounted to a third rail, the third rail passing through the first coil and through the second coil parallel to the axis such that the mounting fixture slidably moves along the third rail to adjust a distance between the mounting fixture and each of the first coil and the second coil; and a magnetometer, inserted into the aperture, to provide magnetic field measurements; and a signal generator to providing a driving signal to the 1D Helmholtz coil.
12 . The system of claim 11 , further comprising:
one or more processors to process magnetic field measurements of the calibrated magnetometer, and memory to store the magnetic field measurements.
13 . The system of claim 12 , further comprising a spectrum analyzer to analyze and display data representative of magnetic field measurements.
14 . The system of claim 13 , further comprising:
a triaxial magnetometer to mount inside the mounting fixture; and a lock-in amplifier to couple to the triaxial magnetometer to receive measurement signals from the triaxial magnetometer through at least a portion of a calibration procedure.
15 . A non-transitory computer-readable medium comprising instructions that, when implemented on a machine, cause the machine to perform operations including:
receiving a first set of magnetic field measurements that have been generated by a one-dimensional Helmholtz coil having two coils with a radius, the two coils being spaced from each other by the radius of the Helmholtz coil; and generating a calculated value for a separation distance by which the two coils are to be separated based on a relationship between the first set of magnetic field measurements, the radius, and the separation distance.
16 . The non-transitory computer-readable medium of claim 15 , wherein the relationship between the first set of magnetic field measurements, the radius, and the separation distance includes a mathematical relationship defined according to:
B
(
x
,
s
)
=
ϖ
0
INR
2
2
[
(
R
2
+
x
2
)
-
3
2
+
⌈
R
2
+
(
s
-
x
)
2
⌉
-
3
2
]
,
where B(x, s) is the received magnetic field measurement at a point x, s is the separation distance, R is the radius of each of the two coils, I represents a value for electrical current in the Helmholtz coil, N is the number of turns on each of the two coils, and μ 0 is the permeability of free space.
17 . The non-transitory computer-readable medium of claim 16 , further comprising instructions, that, when implemented on the machine, cause the machine to:
generate a best fit curve based on the first set of magnetic field measurements; and determine the calculated value for the distance based on the best fit curve.
18 . The non-transitory computer-readable medium of claim 15 , further comprising instructions that, when implemented on a machine, cause the machine to perform operations including:
providing the calculated value for the distance to a display.
19 . The non-transitory computer-readable medium of claim 15 , further comprising instructions that, when implemented on a machine, cause the machine to perform operations including:
receiving a second set of magnetic field measurements from the Helmholtz coil, the separation distance between the two coils having been adjusted to equal the calculated value for the separation distance; and generating a calculated value for a center of the Helmholtz coil based on a relationship between the second set of magnetic field measurements, the radius, and the separation distance.
20 . The non-transitory computer-readable medium of claim 19 , wherein the relationship between the second set of magnetic field measurements, the radius, and the separation distance includes a mathematical relationship defined according to:
B
(
x
,
s
)
=
μ
0
INR
2
2
[
[
R
2
+
(
x
0
+
k
Δ
x
)
2
]
-
3
2
+
[
R
2
+
[
R
-
(
x
0
+
k
Δ
x
)
]
2
]
-
3
2
]
,
where B(x, s) is the received magnetic field measurement at a point x, s is the separation distance, R is the radius of each of the two coils, I is electrical current in the Helmholtz coil, N is the number of turns on each of the two coils, μ 0 is the permeability of free space, x 0 is the offset of a first coil of the two coils from the center of the Helmholtz coil, Δx is a length, and k is an integer.Join the waitlist — get patent alerts
Track US2016041234A1 — get alerts on status changes and closely related new filings.
We store only your email — no account needed. See our privacy policy.