U.S. patent application number 10/848600 was filed with the patent office on 2005-02-10 for load monitoring systems and methods.
This patent application is currently assigned to BBNT SOLUTIONS LLC. Invention is credited to Hanna, Douglas S., Madden, Richard, Whittemore, David H..
Application Number | 20050028607 10/848600 |
Document ID | / |
Family ID | 31887624 |
Filed Date | 2005-02-10 |
United States Patent
Application |
20050028607 |
Kind Code |
A1 |
Hanna, Douglas S. ; et
al. |
February 10, 2005 |
Load monitoring systems and methods
Abstract
A system (200) monitors a load associated with a load carrying
member. The system (200) may include a voltage divider (240) and a
computer device (250). The voltage divider (240) measures
inductance associated with load sensing elements (210) that monitor
the load carrying member. The computer device (250) determines
displacements of the load sensing elements (210) based on the
inductance associated with the load sensing elements (210) and
determines the load associated with the load carrying member based
on the displacements of the load sensing elements (210). The system
may be designed to be portable and/or DC powered.
Inventors: |
Hanna, Douglas S.; (Mystic,
CT) ; Whittemore, David H.; (Yarmouthport, MA)
; Madden, Richard; (Groton, MA) |
Correspondence
Address: |
ROPES & GRAY LLP
ONE INTERNATIONAL PLACE
BOSTON
MA
02110-2624
US
|
Assignee: |
BBNT SOLUTIONS LLC
Cambridge
MA
|
Family ID: |
31887624 |
Appl. No.: |
10/848600 |
Filed: |
May 17, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10848600 |
May 17, 2004 |
|
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|
10228669 |
Aug 26, 2002 |
|
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|
6748809 |
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Current U.S.
Class: |
73/794 |
Current CPC
Class: |
G01L 5/164 20130101;
G01L 5/165 20130101; G01L 1/14 20130101; B63B 21/502 20130101; E21B
19/09 20130101 |
Class at
Publication: |
073/794 |
International
Class: |
G01N 003/00 |
Claims
What is claimed is:
1. A system that monitors a load associated with a load carrying
member, a plurality of load sensing elements that monitor the load
carrying member, the system comprising: a voltage divider
configured to measure inductance associated with the load sensing
elements; and a computer device configured to: determine
displacements of the load sensing elements based on the inductance
associated with the load sensing elements, and determine the load
associated with the load carrying member based on the displacements
of the load sensing elements.
2. The system of claim 1, wherein the voltage divider includes: a
reference resistor, and an impedance determined based on at least a
resistor and an inductor corresponding to the load sensing
elements.
3. The system of claim 2, wherein the load sensing elements connect
to the computer device via a plurality of cables; and wherein the
impedance is determined further based on a resistor, a capacitor,
and an inductor corresponding to the cables.
4. The system of claim 2, wherein the inductor corresponding to the
load sensing elements includes a variable inductor with an
inductance that changes based on changes in displacement of the
load sensing elements.
5. The system of claim 1, wherein when determining the load, the
computer device is configured to: identify a plane through the
displacements using a Least Mean Square process, and determine the
load associated with the load carrying member using the plane.
6. The system of claim 1, wherein the load associated with the load
carrying member includes tension and bending associated with the
load carrying member.
7. The system of claim 6, wherein the tension is determined based
on a stiffness value and a displacement component due to
tension.
8. The system of claim 6, wherein the bending is determined based
on a bending stiffness value and one or more displacement
components due to bending.
9. The system of claim 6, wherein the load associated with the load
carrying member further includes orientation of bending associated
with the load carrying member.
10. The system of claim 9, wherein the orientation of bending is
determined based on a plurality of displacement components due to
bending.
11. The system of claim 1, wherein the system is a portable system
and the computer device includes a portable computer device.
12. The system of claim 1, further comprising: a DC power supply
configured to provide power to the voltage divider and the computer
device.
13. The system of claim 1, wherein the voltage divider and the
computer device operate in an absence of AC line voltage.
14. A system for monitoring a load associated with a load carrying
member, a plurality of load sensing means that monitor the load
carrying member, the system comprising: means for determining
inductance associated with the load sensing means using voltage
division; means for determining displacement of the load sensing
means based on the inductance associated with the load sensing
means; and means for determining the load associated with the load
carrying member based on the displacement of the load sensing
means.
15. A method for monitoring a load associated with a load carrying
member, a plurality of sensors that monitor the load carrying
member, the method comprising: measuring inductance associated with
each of the sensors using voltage division; determining
displacements of the sensors based on the inductance associated
with each of the sensors; and determining the load associated with
the load carrying member based on the displacements of the
sensors.
16. The method of claim 15, wherein the voltage division uses a
reference resistance and an impedance that is determined based on
at least a resistance and an inductance corresponding to the
sensors.
17. The method of claim 16, wherein the inductance corresponding to
the sensors includes a variable inductance that changes based on
changes in displacement of the sensors.
18. The method of claim 15, further comprising: identifying a plane
through the displacements using a Least Mean Square process.
19. The method of claim 18, wherein the determining the load
includes: using the plane to determine the load associated with the
load carrying member.
20. The method of claim 15, wherein the load associated with the
load carrying member includes tension and bending associated with
the load carrying member.
21. The method of claim 20, wherein the tension is determined based
on a stiffness value and a displacement component due to
tension.
22. The method of claim 20, wherein the bending is determined based
on a bending stiffness value and one or more displacement
components due to bending.
23. The method of claim 20, wherein the load associated with the
load carrying member further includes orientation of bending
associated with the load carrying member.
24. The method of claim 23, wherein the orientation of bending is
determined based on a plurality of displacement components due to
bending.
25. The method of claim 15, wherein the method is performed by a
portable device.
26. The method of claim 15, wherein the method is performed by a
device that is powerable by DC battery power.
27. The method of claim 15, wherein the method is performed by a
device that operates in an absence of AC line voltage.
28. A portable load monitoring system that monitors a load
associated with a load carrying member, a plurality of load sensing
elements being associated with the load carrying member, the system
comprising: a voltage divider configured to measure inductance
associated with the load sensing elements; and a portable computer
device configured to: determine displacements of the load sensing
elements due to the load based on the inductance associated with
the load sensing elements, and determine the load associated with
the load carrying member based on the displacements of the load
sensing elements.
29. A system that monitors a load associated with a load carrying
member, a plurality of load sensing elements being associated with
the load carrying member, the system comprising: a DC power source;
a voltage divider connected to the DC power source and configured
to measure inductance associated with the load sensing elements;
and a computer device connected to the DC power source and
configured to: determine displacements of the load sensing elements
due to the load based on the inductance associated with the load
sensing elements, and determine the load associated with the load
carrying member based on the displacements of the load sensing
elements.
30. The system of claim 29, wherein the DC power source includes a
battery.
Description
REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 10/228,669, filed on Aug. 26, 2002, the
specification of which is incorporated by reference herein in its
entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to load monitoring
and, more particularly, to systems and methods for signal
conditioning and processing of load monitoring signals
[0004] 2. Description of Related Art
[0005] Load and tension monitoring of load carrying members are
very important in some applications. For example, load and tension
monitoring of moorings and risers is important in offshore oil
production platforms. One such monitoring system includes variable
reluctance sensors placed around the periphery of a load carrying
member to measure the load associated with that member. This system
uses a resonant circuit to process signals from the sensors and
report results to a marine monitoring system.
[0006] The electronics used in such a system are sophisticated and
expensive. The electronics are typically housed in a fixed cabinet
and powered by an AC line voltage. Therefore, the electronics are
rendered inoperable in the event of line voltage failure, which may
occur in critical situations, such as in a severe storm.
[0007] As a result, there is a need for a monitoring system that is
inexpensive, portable, and/or capable of being powered by DC
power.
SUMMARY OF THE INVENTION
[0008] Systems and methods consistent with the present invention
address this and other needs by providing a monitoring system that
is inexpensive, portable, and/or capable of being powered by DC
power.
[0009] In accordance with the principles of the invention as
embodied and broadly described herein, a system monitors a load
associated with a load carrying member. The system may include a
voltage divider and a computer device. The voltage divider measures
inductance associated with load sensing elements that monitor the
load carrying member. The computer device determines displacements
of the load sensing elements based on the inductance associated
with the load sensing elements and determines the load associated
with the load carrying member based on the displacements of the
load sensing elements.
[0010] In another aspect of the invention, a portable load
monitoring system monitors the load associated with a load carrying
member. The system includes a voltage divider and a portable
computer device. The voltage divider is configured to measure
inductance associated with load sensing elements that are
associated with the load carrying member. The portable computer
device is configured to determine displacements of the load sensing
elements due to the load based on the inductance associated with
the load sensing elements, and determine the load associated with
the load carrying member based on the displacements of the load
sensing elements.
[0011] In a further aspect of the invention, a system monitors a
load associated with a load carrying member. The system includes a
voltage divider and a computer device connected to a DC power
source. The voltage divider is configured to measure inductance
associated with load sensing elements associated with the load
carrying member. The computer device is configured to determine
displacements of the load sensing elements due to the load based on
the inductance associated with the load sensing elements, and
determine the load associated with the load carrying member based
on the displacements of the load sensing elements.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The accompanying drawings, which are incorporated in and
constitute a part of this specification, illustrate the invention
and, together with the description, explain the invention. In the
drawings,
[0013] FIG. 1 is an exemplary diagram of an environment in which
systems and methods consistent with the present invention may be
implemented;
[0014] FIG. 2 is an exemplary diagram of a system in which systems
and methods consistent with the present invention may be
implemented;
[0015] FIG. 3 is an exemplary diagram of the load measurement unit
of FIG. 2 according to an implementation consistent with the
present invention;
[0016] FIG. 4 is an exemplary diagram of the upper sensor ring of
FIG. 3 according to an implementation consistent with the present
invention;
[0017] FIG. 5 is an exemplary diagram of a sensor of FIG. 4
according to an implementation consistent with the present
invention;
[0018] FIG. 6 is an exemplary detailed diagram of the signal
conditioning system of FIG. 2 according to an implementation
consistent with the present invention;
[0019] FIG. 7 is an exemplary diagram of a sensor plane that may be
constructed to facilitate determination of displacement according
to an implementation consistent with the principles of the
invention;
[0020] FIG. 8 is a flowchart of exemplary processing for
determining tension, bending, and orientation of bending associated
with a load carrying member according to an implementation
consistent with the present invention; and
[0021] FIG. 9 is an exemplary diagram of a sensor according to
another implementation consistent with the principles of the
invention.
DETAILED DESCRIPTION
[0022] The following detailed description of the invention refers
to the accompanying drawings. The same reference numbers in
different drawings may identify the same or similar elements. Also,
the following detailed description does not limit the invention.
Instead, the scope of the invention is defined by the appended
claims and equivalents.
[0023] Systems and methods consistent with the present invention
provide load monitoring that may be used to monitor the load
associated with load carrying members, such as moorings and risers
of offshore oil production platforms. The systems and methods may
include inexpensive circuitry with DC power capability. In certain
critical situations, such as in a severe storm, uncertainty in the
determination of the load associated with a load carrying member
may be unacceptable. The DC power capability permits the monitoring
to occur in situations, such as where there is AC line voltage
failure.
[0024] The systems and methods consistent with the present
invention also provide a portable, compact configuration for
deployment to remote locations. Field personnel can use the
portable configuration as a diagnostic and/or troubleshooting tool
to quickly localize problems at various points in the cabling. In
other implementations, the portable configuration may be enclosed
in a protective container and deployed for load measurements at
locations, such as in underwater mooring and riser systems at or
near the sea floor.
Exemplary Environment
[0025] FIG. 1 is an exemplary environment 100 in which systems and
methods consistent with the principles of the invention may be
implemented. As shown in FIG. 1, environment 100 may be associated
with a floating production system, such as a floating offshore oil
platform 110. Platform 110 may be secured to the sea floor via
chains or tendons, such as moorings 120. Oil, gas, and/or water may
be extracted and provided to platform 110 and/or exported via one
or more tubes, such as riser 130. It may be important to monitor
the load and tension associated with moorings 120 and riser 130 to
make sure that moorings 120 and riser 130 are not loose or
overstrained, possibly, to the point of breakage, and that platform
110 is stable.
[0026] While systems and methods consistent with the principles of
the invention will be described within environment 100, such
systems and methods are not so limited. In fact, systems and
methods consistent with the present invention may be used in any
environment where it may be useful to monitor the load of a load
carrying member.
Exemplary Load Measurement Unit Configuration
[0027] FIG. 2 is an exemplary diagram of a system 200 in which
systems and methods consistent with the principles of the invention
may be implemented. System 200 includes one or more load
measurement units 210, one or more cables 220, junction box 230,
signal conditioning system 240, and computer system 250. Computer
system 250 and/or signal conditioning system 240 may be powered by
AC power or DC power, such as a battery (not shown). The DC power
permits computer system 250 and/or signal conditioning system 240
to operate in the event of AC power failure.
[0028] Generally, load measurement unit 210 may generate signals
indicative of displacement associated with a tendon or tube, such
as mooring 120 or riser 130. Cable 220 may connect load measurement
unit 210 to junction box 230 within platform 110. Cable 220 may
include one or more underwater connectors. Junction box 230 may
provide connection points between one or more load measurement
units 210 and signal conditioning system 240. A typical platform
110 may include one or more junction boxes 230.
[0029] Signal conditioning system 240 may gather data for
determining inductance associated with load measurement unit 210
based on the signals from load measurement unit 210. Computer
system 250 may determine the inductance associated with a load
measurement unit 210 and, from this, the load associated with
mooring 120 or riser 130. For example, computer system 250 may
determine tension, bending, and orientation of bending associated
with mooring 120 or riser 130.
[0030] These components will now be described in more detail.
Load Measurement Unit
[0031] FIG. 3 is an exemplary diagram of load measurement unit 210
according to an implementation consistent with the principles of
the invention. Load measurement unit 210 may be located on a load
carrying member, such as mooring 120 or riser 130, approximately
100 or more feet underwater. Load measurement unit 210 may include
upper sensor ring 310 and lower sensor ring 320 that form rings
around the periphery of the load carrying member. Load measurement
unit 210 may generate signals indicative of the displacement
between upper sensor ring 310 and lower sensor ring 320.
[0032] FIG. 4 is an exemplary diagram of upper sensor ring 310
according to an implementation consistent with the principles of
the invention. Sensor ring 310 may include approximately three to
twelve load sensing elements, such as sensors 410, located around
the periphery of the load carrying member (e.g., mooring 120 or
riser 130). The actual number of sensors 410 included may be a
number sufficient to obtain good estimates of tension, bending, and
the orientation of the bending of the load carrying member.
[0033] FIG. 5 is an exemplary diagram of a section of sensor 410
according to an implementation consistent with the principles of
the invention. Sensor 410 may include a variable reluctance sensor
or capacitive sensor. Sensor 410 may include C-shaped magnetic core
510, I-shaped magnetic core 520, brackets 530 and 540, and windings
550. C-shaped magnetic core 510 may be constructed, for example, of
a highly permeable laminated transformer material. C-shaped core
510 may be mounted on upper sensor ring 310 via bracket 530 with
the ends of the C-shape pointed downward or in a direction
generally parallel to the direction of force within the load
carrying member.
[0034] I-shaped magnetic core 520 may be constructed, for example,
of a highly permeable laminated transformer material. I-shaped
magnetic core 520 may be mounted on lower sensor ring 320 via
bracket 540. I-shaped core 520 may be positioned so that narrow
gaps exist between each end of C-shaped core 510 and a facing
portion of I-shaped core 520. In an implementation consistent with
the principles of the invention, the widths of the gaps are small
as compared with any transverse dimension of the ends of C-shaped
core 510. Further, the cross-sectional dimensions or areas of the
ends of C-shaped core 510 may be smaller than those of the facing
portion of I-shaped core 520.
[0035] A winding 550 may be mounted around each end of C-shaped
core 510 closely adjacent to the respective gap. Windings 550 may
connect in series so that their electromotive forces add. As will
be understood by those skilled in the art, C-shaped core 510 and
I-shaped core 520 may be highly permeable and, thus, the gaps
between cores 510 and 520 may constitute most of the reluctance in
the magnetic circuit linking windings 550. Thus, the inductance
exhibited may be directly dependent on the widths of the gaps in
the direction of the magnetic flux in the gaps (i.e., the vertical
direction in FIG. 5).
[0036] As an axial load is applied to sensor 410, the width of the
respective gap between each end of C-shaped core 510 and the
adjacent portion of I-shaped core 520 increases or reduces. As the
gaps are reduced, the inductance exhibited increases.
[0037] Both of the gaps may be used in determining the value of
inductance. As a result, small increases in the length of one gap
can compensate or offset for small decreases in the length of the
other gap. Accordingly, sensor 410 may be relatively insensitive to
bending moments applied thereto (i.e., around a horizontal axis
perpendicular to the paper as illustrated in FIG. 5). Bending
moments around the orthogonal horizontal axis lying in the plane of
the paper only produce changes in width as a function of
displacement across the surfaces of the ends of both gaps but not
changes in the average width of each gap, to a first order
approximation.
Cable
[0038] Cable 220 may include a marine cable that connects load
measurement unit 210 to junction box 230 within platform 110. Cable
220 may include conductors that connect to sensors 410 of load
measurement unit 210. Cable 220 may also include one or more
underwater connectors with active or inactive components to relay
signals between segments of cable 220.
Junction Box
[0039] Junction box 230 may include a set of connection points that
connect cables 220 to signal conditioning system 240. One or more
junction boxes 230 may be located within platform 110. For example,
one junction box 230 may be located in the control room of platform
110 and another junction box 230 may be located in the lower
regions of platform 110, such as where cables 220 come into
platform 110.
Signal Conditioning System
[0040] FIG. 6 is an exemplary diagram of signal conditioning system
240 according to an implementation consistent with the principles
of the invention. Signal conditioning system 240 may gather data
for determining the inductance and the operational status of
sensors 410 and communicate this data to computer system 250.
[0041] Signal conditioning system 240 may include interface 610,
filters 620, driver 630, resistors 640, and switches 650. Interface
610 is shown as a component of signal conditioning system 240. In
an alternate implementation, interface 610 may be part of computer
system 250.
[0042] Interface 610 may include a Personal Computer Memory Card
International Association (PCMCIA) interface that facilitates the
connection of signal conditioning system 240 to computer system
250. Interface 610 may include one or more digital-to-analog (D/A)
channels that may be used to operate components of signal
conditioning system 240. If interface 610 includes more than one
D/A channel, each D/A channel may correspond to a different one of
sensors 410.
[0043] Interface 610 may also include one or more analog-to-digital
(A/D) channels that may be used to capture data, such as data used
in determining the inductance of a sensor 410. In the example of
FIG. 6, interface 610 includes N+1 A/D channels that correspond to
N different ones of sensors 410. A/D channel 0 may be used for
calibrations and data acquisition, as will be described in more
detail below. Interface 610 may also include ground (GND)
connections.
[0044] Filters 620 may include conventional low pass filters that
are designed to remove noise and aliased components of the signal.
Driver 630 may include a sensor line driver that drive signals from
the D/A channel.
[0045] Resistors 640 may be reference resistors (RR) having a known
resistance. Switches 650 may include calibration switches that are
used to switch the components of signal conditioning system 240
between calibration and data acquisition modes. As shown in FIG. 6,
switches 650 may be in the up position during the calibration
mode.
[0046] Signal conditioning system 240 may view sensor 410 and cable
220 as a combination of resistors, capacitors, and inductors. For
example, cable 220 may be represented by a capacitor CC, a resistor
RC, and an inductor LC. The features of cable 220 may be measured
and remain constant. Therefore, the capacitance, resistance, and
inductance of cable 220 are known. Sensor 410 may be represented by
a resistor RS and an inductor LS. The resistance of sensor 410 may
be measured and remain constant. The inductance of sensor 410 is a
variable inductance that changes based on changes in displacement,
as described above. The impedance of cable 220 and sensor 410 may
be represented by ZSC.
[0047] Signal conditioning system 420 uses a voltage divider
circuit made up of the resistor RR and impedance ZSC to gather data
for determining the inductance of sensor 410. The transfer function
TF of the voltage divider may be represented by: 1 TF Vm Vi = Z SC
R R + Z SC ,
[0048] where Vi refers to a reference voltage input and Vm refers
to a response voltage sample. The sensor and cable impedance ZSC
may be represented by: 2 Z SC = Z CC ( R C + Z LC + R S + Z LS ) Z
CC + R C + Z LC + R S + Z LS ,
[0049] where ZCC refers to the impedance of the capacitance of
cable capacitor CC, ZLC refers to the impedance of cable inductor
LC, and ZLS refers to the impedance of sensor inductor LS. From
these equations, the impedance of inductor LS (ZLS) can be
determined. The inductance of inductor LS may then be determined
from the following: 3 L S = ( R R ( 1 / TF - 1 ) - R R / Z CC - R C
- R S ) / j - L C .
[0050] Signal conditioning system 240 provides the measurements
used in determining the transfer function TF in the above equation
to computer system 250 via the appropriate one(s) of the A/D
channels.
Computer System
[0051] Computer system 250 may include a computer device, such as a
personal computer, laptop, personal digital assistant, etc. To make
system 200 portable, computer system 250 may include a portable
device, such as a laptop or a personal digital assistant. Computer
system 250 may determine inductance, displacement, and load
associated with a load carrying member, such as mooring 120 or
riser 130. Computer system 250 may determine displacement at a
number of different locations around the periphery of the load
carrying member. Computer system 250 may convert determined sensor
inductance values to displacement due to tension and displacement
due to bending.
[0052] Computer system 250 may calibrate the components of signal
conditioning system 240 in the calibration mode. For example,
switches 650 and the A/D channels may be placed into the
calibration mode. Computer system 250 may output a reference signal
via the D/A channel. Computer system 250 may then determine
magnitude and phase corrections for all channels relative to the
reference A/D channel 0.
[0053] Thereafter, during the data acquisition mode, computer
system 250 may obtain the measurements for determining the transfer
functions for the voltage dividers from signal conditioning system
240. Computer system 240 may use the transfer functions to
determine the inductance of sensors 410. For a given inductance
value, computer system 240 may estimate the corresponding
displacement for sensor 410 based on prior calibrations of that
sensor 410.
[0054] Computer system 250 may then determine displacement due to
tension and displacement due to bending. FIG. 7 is an exemplary
diagram of a sensor plane that may be constructed to facilitate
determination of displacement according to an implementation
consistent with the principles of the invention.
[0055] Computer system 250 may determine the displacement of each
sensor 410 based on its inductance and then subtract out the
displacement for that sensor 410 under zero load. As a result,
computer system 250 may determine just how much each sensor 410 is
displaced under load. The displacement of a sensor(i) may be
represented by:
Z.sub.i=Ax.sub.i+By.sub.i+C,
[0056] where x.sub.i and y.sub.i are positions of sensor(i) in the
X and Y planes, respectively; A and B are displacement components
due to bending; and C is a displacement component due to tension.
Computer system 250 may use a Least Mean Square process, or another
process, to identify a plane through the displacements: 4 E = i = 1
N [ Z i - ( Ax i + By i + C ) ] 2 .
[0057] Once the variables A, B, and C are known, then computer
system 250 may determine tension, bending, and orientation of
bending associated with riser 130. Tension (T) may be determined
based on:
T=K.sub.axialC,
[0058] where K.sub.axial may refer to a stiffness value associated
with load measurement unit 210. Bending (Be) may be determined
based on:
Be=K.sub.bend{square root}{square root over (A.sup.2+B.sup.2)},
[0059] where K.sub.bend may refer to a bending stiffness value
associated with load measurement unit 210. A load measurement unit
210 may be calibrated beforehand to determine values for
K.sub.axial and K.sub.bend. Orientation of bending may be
determined based on A and B (i.e., the displacement components due
to bending).
[0060] Computer system 250 may present information to an operator
via a graphical user interface. The display parameters of the
graphical user interface may include individual sensor status,
inductance, and calculated load, tension and bending values
associated with a load carrying member (instantaneous or averaged),
and/or other information that may be useful to the operator.
Exemplary Processing
[0061] FIG. 8 is a flowchart of exemplary processing for
determining tension, bending, and orientation of bending associated
with a load carrying member, such as a mooring 120 or riser 130,
according to an implementation consistent with the present
invention. Processing may begin with the calibration of the
components of signal conditioning system 240 (act 810). Computer
system 250 may instruct signal processing system 240 to enter the
calibration mode. Computer system 250 may then input digitized data
via the D/A channel of interface 610 and simultaneously calibrate
the components of signal conditioning system 240 to determine
magnitude and phase corrections for all of the channels relative to
the reference A/D channel 0.
[0062] Thereafter, computer system 250 may instruct signal
processing system 240 to enter the data acquisition mode. In the
data acquisition mode, sensor inductance may be determined using
the voltage divider of signal conditioning system 240 (act 820).
For example, the D/A channel of interface 610 may apply a
band-limited random or sine input to the cable ends through driver
630. The reference voltage input (Vi) and the response voltage
samples (Vm) may then be measured at the A/D channels of interface
610. Reference voltage input (Vi) may be measured at the A/D
channel 0 and the reference voltage samples (Vm) may be
simultaneously measured at the A/D channels 1-N.
[0063] Computer system 250 may perform a discrete Fourier transform
on the data obtained during the calibration mode and the data
obtained during the data acquisition mode at the excitation
frequency. Computer system 250 may divide the complex amplitude of
the data from each of the channels obtained during the data
acquisition mode by the complex amplitude of the data from each of
the channels obtained during the calibration mode to obtain a set
of N complex transfer functions TF. The TF values may be used in
the equation for LS (identified above) to obtain the inductance of
each sensor 410.
[0064] Once sensor inductance has been determined, sensor
displacement may be determined (act 830). Sensor displacement may
be estimated from information gathered during the
previously-conducted sensor calibrations. The displacements of
several sensors 410 may then be used to construct a plane through
the displacements using a Least Mean Square algorithm, as described
above. Construction of the plane may facilitate the determination
of the displacement components due to bending and tension, as
described above.
[0065] Once the displacement components due to bending and tension
are determined, the tension, bending, and orientation of bending
associated with the load carrying member may be determined (act
840). As described above, the tension may be determined based on a
stiffness value and the displacement component due to tension. As
also described above, the bending may be determined based on a
bending stiffness value and the displacement components due to
bending, and the orientation of bending may be determined based on
the displacement components due to bending.
Load Cell Configuration
[0066] Thus far, a load measurement unit has been described as the
vehicle for measuring the load associated with a load carrying
member, such as a mooring or riser. In an alternate implementation
consistent with the principles of the invention, a load cell may be
used. In this load cell configuration, one or more load cells may
be associated with each load carrying member. Instead of being
located along the periphery of the load carrying member, the load
cells are connected to the load carrying member at a point where
the load carrying member connects to something else, like the
platform. Like the load measurement unit, the load cells measure
the load associated with the load carrying member.
[0067] FIG. 9 is an exemplary diagram of a sensor 900 according to
an implementation consistent with the principles of the invention.
Sensor 900 may include a variable reluctance sensor, such as the
one described in U.S. Pat. No. 5,359,902. Sensor 900 may include a
hollow cylinder 910 connected to rigid end caps 920 and 930. Hollow
cylinder 910 may be of circular cross-section and act as an elastic
element for forces applied in a direction along the axis of
cylinder 910. Cylinder 910 may, for example, be constructed of a
high grade steel that has a very repeatable and essentially linear
elasticity. Cylinder 910 may act essentially as a lossless spring.
While the spring constant will typically be very high as understood
by those skilled in the art, the forces intended to be measured may
also be quite high.
[0068] End caps 920 and 930 connect to the ends of cylinder 910. In
another implementation consistent with the present invention, end
caps 920 and 930 are not separate from, but are integral with,
cylinder 910. At least one of end caps 920 and 930 may connect to
the load carrying member.
[0069] Within cylinder 910, sensor 900 may include C-shaped
magnetic core 940, I-shaped magnetic core 950, brackets 960 and
970, and windings 980. C-shaped magnetic core 940 may be
constructed, for example, of a highly permeable laminated
transformer material. C-shaped core 940 may be mounted on upper end
cap 920 via bracket 960 with the ends of the C-shape pointed
downward or in a direction generally parallel to the direction of
force within the wall of cylinder 910.
[0070] I-shaped magnetic core 950 may be constructed, for example,
of a highly permeable laminated transformer material. I-shaped
magnetic core 950 may be mounted on lower end cap 930 via bracket
970. I-shaped core 950 may be positioned so that narrow gaps exist
between each end of C-shaped core 940 and a facing portion of
I-shaped core 950. In an implementation consistent with the
principles of the invention, the widths of the gaps are small as
compared with any transverse dimension of the ends of C-shaped core
940. Further, the cross-sectional dimensions or areas of the ends
of C-shaped core 940 may be smaller than those of the facing
portion of I-shaped core 950.
[0071] A winding 980 may be mounted around each end of C-shaped
core 940 closely adjacent to the respective gap. Windings 980 may
connect in series so that their electromotive forces add. As will
be understood by those skilled in the art, C-shaped core 940 and
I-shaped core 950 may be highly permeable and, thus, the gaps
between cores 940 and 950 may constitute most of the reluctance in
the magnetic circuit linking windings 980. Thus, the inductance
exhibited may be directly dependent on the widths of the gaps in
the direction of the magnetic flux in the gaps (i.e., the vertical
direction as shown in FIG. 9).
[0072] As an axial load is applied to sensor 900, cylinder 910
compresses or expands and the width of the respective gap between
each end of C-shaped core 940 and the adjacent portion of I-shaped
core 950 reduces or increases. As the gaps are reduced, the
inductance exhibited increases.
[0073] Because the facing portion of I-shaped core 950 opposite
each end of C-shaped core 940 is broader in transverse dimensions
than the facing end of the C-shaped core 940, the inductance value
of sensor 900 may be insensitive to small displacements of C-shaped
core 940 in directions transverse to the axis of cylinder 910 and
to the widths of the gaps. Both of the gaps may be used in
determining the value of inductance. As a result, small increases
in the length of one gap can compensate or offset for small
decreases in the length of the other gap. Accordingly, sensor 900
may be relatively insensitive to bending moments applied thereto
(i.e., around a horizontal axis perpendicular to the paper as
illustrated in FIG. 9). Bending moments around the orthogonal
horizontal axis lying in the plane of the paper only produce
changes in width as a function of displacement across the surfaces
of the ends of both gaps but not changes in the average width of
each gap, to a first order approximation.
[0074] In this load cell configuration, sensor 900 may connect to a
signal conditioning system and a computer system, which may be
configured and operate similar to signal conditioning system 240
(FIG. 2) and computer system 250 described above.
CONCLUSION
[0075] Systems and methods consistent with the present invention
may provide portable signal conditioning and signal processing
components for variable reluctance load measurement. The systems
and methods determine inductance and operational status of sensors
used to measure the load of a load carrying member, converts the
sensor inductance into displacement, and performs a Least Mean
Square process to identify a plane through the displacements. The
systems and methods may use this information to determine tension,
bending, and orientation of bending associated with the load
carrying member.
[0076] Systems and methods consistent with the principles of the
invention may be configured with a laptop computer to provide a
portable load measurement device or as a compact standalone device
for deployment to remote areas or areas that are not easily
accessible. For example, the compact standalone device may be
remotely operable and capable of being placed within a pressure
vessel for deployment at or near the sea floor.
[0077] Further, systems and methods consistent with the present
invention include inexpensive circuitry that is amenable to
operation on both line AC power and DC battery power. The DC power
capability makes the systems and methods operable in the event of
line voltage failure that may occur in critical situations, such as
during a severe storm.
[0078] The foregoing description of preferred embodiments of the
present invention provides illustration and description, but is not
intended to be exhaustive or to limit the invention to the precise
form disclosed. Modifications and variations are possible in light
of the above teachings or may be acquired from practice of the
invention. For example, while a series of acts has been described
with regard to FIG. 8, the order of the acts may differ in other
implementations consistent with the present invention. For another
example, load forces upon the load sensors or load cells need not
be vertical. The load sensors or load cells may operate in any
orientation relative to Earth vertical.
[0079] No element, act, or instruction used in the description of
the present application should be construed as critical or
essential to the invention unless explicitly described as such.
Also, as used herein, the article "a" is intended to include one or
more items. Where only one item is intended, the term "one" or
similar language is used. The scope of the invention is defined by
the claims and their equivalents.
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