Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02814590 2013-04-12
WO 2012/059736 PCT/GB2011/052070
1
PARAMETER SENSING AND MONITORING
The present invention relates to a method and apparatus for monitoring at
least one
parameter associated with a structure. In particular, but not exclusively, the
present
invention relates to a method of monitoring a fibre optic system located on or
in a structure
to derive data indicative of strain and/or temperature in the structure.
There are many technical fields in which it is useful from time to time or
continuously to
monitor one or more parameters associated with a structure. For example, from
time to
time bridges, road surfaces, regions of land, lamp-posts, wind turbine blades,
yacht masts,
suspended power cables or the like should be repeatedly or continuously
monitored so
that information identifying any potential problems with the structure can be
identified and
then remedial action taken.
Another type of structure for which monitoring is desirable is an unbonded
flexible pipe of
the type used in the oil and gas industry in the field of offshore production.
Such flexible
pipe includes a length of flexible pipe body terminated at one or more ends
with an end
fitting. The flexible pipe can be used as a flow-line, riser, jumper or the
like. There is an
increasing desire to monitor the dynamic behaviour of such pipes. Monitoring
strain and/or
temperature and/or some other parameter is a way to assess the past, current
and/or
future performance of the pipe.
In relation to all structures, many different forces will be experienced. This
can lead to very
complex loads and includes, but is not limited to, self-weight, internal
pressure, tension,
vortex induced vibration, flexing, twisting or the like.
One way which has been suggested for monitoring parameters associated with
such
structures is the use of an optical fibre system. The optical fibres can be
used as strain
gauges, temperature gauges, temperature indicators and strain measurements can
be
made which are either localised, distributed or semi-distributed depending
upon the
manner in which the optical fibre is interrogated and regions/sensors in the
optical fibre are
arranged. W02009/068907, the disclosure of which is incorporated herein in its
entirety,
discloses a way in which an optical fibre can be wrapped helically around a
flexible pipe
and certain measurements taken from which parameters associated with the pipe
can be
determined.
Whilst such a system does enable certain parameters associated with the pipe
to be
determined there are limits within which such an optical system can be used.
One reason
for this is because optical fibres are inherently relatively fragile and if
the underlying
structure which is being monitored is prone to substantial mechanical movement
then
mechanical stresses and strains can be induced in the fibre which causes fibre
failure.
CA 02814590 2013-04-12
WO 2012/059736 PCT/GB2011/052070
2
Therefore, the use of optical fibre has until now been limited to uses where
the movement
of the optical fibres has been unduly limited.
Also although the method of spirally wrapping an optical fibre around the body
of a
structure such as a flexible pipe as shown in W02009/068907 can reduce a peak
strain
seen by the optical fibres to a certain extent they are inherently limited in
that they can not
be used to measure along a single axis, deployed onto a circumferentially
discontinuous
structure or provide accurate data if the period of the helix is a poor fit
with the
discrimination length of the optical time domain reflectometer/optical time
domain analyser
system being used.
Strain limitations based on the Ultimate Tensile Strain (UTS) of fibre optic
cables are
currently in the region of 1% according to manufacturers recommendations. The
use of
commercially available optical fibres to measure strains above 1% thus
requires a method
of reducing the amount of strain that the fibre is subjected to thereby
increasing its
capability to measure strain levels beyond its UTS limit.
It is an aim of the present invention to at least partly mitigate the above-
mentioned
problem.
It is an aim of certain embodiments of the present invention to provide a way
of
demagnifying the strain that an optical fibre is subjected to so that an
underlying structure
can be strained, and that strain monitored and measured, without failure of
any part of the
monitoring system.
It is an aim of certain embodiments of the present invention to provide an
apparatus and
method for monitoring parameters associated with an elongate structure, such
as, but not
limited to a flexible pipe, turbine blade, aircraft wing, yacht mast or the
like.
It is an aim of certain embodiments of the present invention to provide an
optical fibre
based parameter measuring/monitoring system which provides a good degree of
resolution, that is to say providing a high number of data points per unit
length of a target
structure, in addition to decoupling strains experienced from an underlying
structure from
the optical fibre monitoring system.
It is an aim of certain embodiments of the present invention to provide a
localised, semi-
distributed or distributed strain measurement system able to utilise Brillouin
scattering
and/or Bragg gratings in a fibre optic system.
It is an aim of certain embodiments of the present invention to provide a
method and
apparatus for monitoring temperature and/or strain and/or some other parameter
associated with an underlying structure.
CA 02814590 2013-04-12
WO 2012/059736 PCT/GB2011/052070
3
According to a first aspect of the present invention there is provided an
apparatus for
monitoring at least one parameter associated with an elongate structure,
comprising:
at least one elongate support body element arranged along a longitudinal
structure axis
associated with an elongate target structure; and at least one optic fibre
element arranged
substantially helically along a longitudinal body element axis associated with
the at least
one support body element.
According to a second aspect of the present invention there is provided a
method of
monitoring at least one parameter associated with an elongate structure,
comprising the
steps of: providing at least one elongate support body element, comprising at
least one
optic fibre element arranged substantially helically along a longitudinal body
element axis
associated with the body element, along a longitudinal structure axis
associated with an
elongate target structure; and via a sensing system, monitoring at least one
characteristic
associated with the fibre element, said characteristic being indicative of a
parameter
associated with the elongate structure.
According to a third aspect of the present invention there is provided a
method of
manufacturing flexible pipe body comprising: providing a fluid retaining
layer; providing at
least one armour layer; and providing at least one elongate support body
element,
comprising at least one optic fibre element arranged substantially helically
along a
longitudinal body element axis associated with the body element, along a
longitudinal pipe
body axis associated with the pipe body.
According to a fourth aspect of the present invention there is provided an
apparatus for
monitoring at least one parameter associated with an elongate structure,
comprising: at
least one optic fibre element arranged substantially helically along a
longitudinal body
element axis of an elongate support body element, said body element being
arranged
along a longitudinal structure axis; wherein a length of the fibre element
between first and
second planes spaced apart along, and perpendicular to, the longitudinal
structure axis, is
greater than a comparable length of the optic fibre element wound, at a
predetermined
pitch, between the first and second planes.
Certain embodiments of the present invention provide the advantage that a
length of
optical fibre which can be provided between chosen points of a target
structure is greater
than a comparable length which prior art techniques can provide. The extra
length relative
to the prior art techniques means that if an underlying structure contracts or
extends in
length by a certain distance there is a proportional contraction/extension in
the optical fibre
which is less than the contraction/extension experienced with prior known
techniques.
CA 02814590 2013-04-12
WO 2012/059736 PCT/GB2011/052070
4
Certain embodiments of the present invention provide the advantage that an
optical fibre
may be wound in a substantially helical fashion around an underlying support
layer which
is then located along a predetermined length of the structure where a
parameter is to be
monitored. This enables the fibre optics to be duly located and monitored in
an efficient
manner.
Embodiments of the present invention will now be described hereinafter, by way
of
example only, with reference to the accompanying drawings in which:
Figure 1 illustrates a free hanging catenary riser;
Figure 3 illustrates regions of a flexible pipe;
Figure 2 illustrates flexing of a bend stiffener and pipe body;
Figure 4 illustrates an optic fibre winding around an underlying cylindrical
body;
Figure 5 illustrates winding an optic fibre;
Figure 6 illustrates winding an optic fibre;
Figure 7 illustrates a support body and fibre optic winding arranged in a
linear fashion;
Figure 8 illustrates a support body and fibre optic winding arranged in a
helical fashion;
Figure 9 illustrates a rectangular support body and fibre optic winding; and
Figure 10 illustrates a system for monitoring parameters associated with a
flexible pipe and
carrying out analysis;
Figure 1 illustrates a flexible pipe (10) which includes a length of flexible
pipe body (11)
terminated at a first end (12) with an end fitting (13) and terminated at a
further end (14)
with a further end fitting (15). The flexible pipe extends from a seabed
region (16) to a
surface region (17). A floating platform (18) is used to secure an upper end
fitting (15) of
the pipe. A bend stiffener (19) is utilised to limit the bending of the
flexible pipe as will be
appreciated by those skilled in the art.
Figure 1 thus illustrates an example of an elongate structure, in this case a
flexible pipe, in
which motion induced in the flexible pipe causes stresses and strains and/or
temperature
fluctuations which from time to time or constantly it is advisable to monitor.
It is to be appreciated that certain embodiments of the present invention are
applicable to a
broad range of structures where one or more parameters associated with those
structures
are to be monitored. For example, instead of a flexible pipe, embodiments of
the present
invention can monitor parts of bridges, road surfaces and/or land regions
and/or lamp-
posts and/or wind turbine blades and/or yacht masts and/or suspended power
cables or
the like.
CA 02814590 2013-04-12
WO 2012/059736 PCT/GB2011/052070
Turning again to the flexible pipe illustrated in Figure 1, a parameter which
might be
determined is fatigue damage to the pipe structure under the bend stiffener as
in such a
system this region is predicted to be the area where maximum fatigue damage to
tensile
layers of the flexible pipe will occur. Certain embodiments of the present
invention provide
5 a system which will collect data which will be stored in a database and
this can be utilised
in real time or at a later point in time to understand the fatigue and
movement behaviour of
the pipe in service. This can be compared to pre-stored predicted values which
will allow
revised life predictions to be made on the pipe system and/or early prediction
of problems
or failure.
The system can be utilised to calibrate system models to more accurately
predict the real
world system behaviour which will allow less conservatism in system design
based on
revised models.
A parameter which it is advantageous to monitor in such a system is the region
of pipe in
high tension low curvature systems is predicted to be inside the bend
stiffener at the top of
the riser. This area is subjected to high tension and the highest topside
curvature which
combines to produce the area of maximum fatigue damage to the tensile layers.
Since the curvature of the pipe decays rapidly over about 5 to 6 meters from
the bend
stiffener tip the maximum curvature will be inferred by measuring the
curvature in that
region and curve fitting the data to a predictive model which will provide an
estimate of the
induced maximum curvature. A modelling system such as OrcaflexTM and/or
locally
generated models can predict the curvature for pipe systems designed and can
produce
similar models for in service systems. Figure 2 illustrates how analysis can
provide a plot
which shows the curvature predictions for a production system (in the example
shown a
riser). The x axis is the meterage of the pipe around the bend stiffener so
Figure 2
illustrates from 6 metre above the flange of the bend stiffener (15) to 11
metres below the
bend stiffener flange (11 metres). The central horizontal line (21) represents
the area
where the bend stiffener covers the pipe. In this system the peak curvature is
predicted at
around 0.9 to 1 metres and this equates to a minimum bending radius of the
pipe of
around 8 metres however in a lower region (20) the measured radius is only
between 50
metres at the 5 metre end and 1,000 metres at the 9 metre end. This what the
curvature
measurement system will measure.
The shape of the curve is predicted to be similar to the system being
monitored so that
although each riser system has a different shape decay curve that curve is
similar for the
different wave patterns the riser will be subjected to. Hence, if the curve
shape is known
and the curvature is measured using an optical fibre system the maximum
curvature is
able to be predicted by using curve fitting algorithms. Combining curvature
data and
CA 02814590 2013-04-12
WO 2012/059736 PCT/GB2011/052070
6
tension allows the fatigue damage at the point of maximum damage to be
calculated. With
the fatigue data it is possible to predict the remaining life of the system.
Actual damage
versus predicted damage. Changes to the pipe behaviour indicating a possible
excursion
which may be damaging to the riser system.
The monitoring system may utilise different types of sensor system. One, two
or more
different types of sensor system can be utilised to provide data points for
further analysis.
For example, tension in the system may be determined using strain gauges or
load cells or
the like which detect the gross tension of the flexible pipe topside or by
using a stress
measurement method such as MAPs which uses magnetic sensors to determine the
stress
induced in the flexible pipe. Another type of sensor which might be used is an
angle of
inclination sensor. This provides useful information which can be an indicator
of vessel or
bend stiffener inclination.
There are one or more methods of determining strain using optical fibres.
Alternatively or
additionally, optical fibres can be utilised to determine temperature at
positions along the
structure. This would be an example of distributed system. Embodiments of the
present
invention are not restricted to such distributed systems. An optic fibre is
utilised as a
distributed strain gauge (or temperature gauge) providing an average strain
value for a
predetermined (for example, 1 metre) length of fibre as a data point. Then the
one metre
average is moved approximately 400 mm and another data point is given.
Therefore a
strain over lm of fibre is provided each 400 mm of the fibre length. An
advantage of this
system is the use of relatively inexpensive optical fibre can be utilised and
a number of
data points produced is high.
Figure 3 illustrates other locations where monitoring of parameters associated
with a
flexible pipe can be utilised. Such locations include sub-sea arches (30)
and/or touchdown
points (31) where the range of strain induced in the flexible pipe may be as
high as plus or
minus 7% or greater and long lengths of hundreds of metres may be monitored.
These
measurements will be required for pipe systems where the predicted high
fatigue damage
locations are not necessarily the topside area but are other locations. Other
regions
including, optionally the whole length, can be monitored.
Brillouin scattering and/or Bragg gratings or other sensing techniques may be
used with
the optic fibres according to certain embodiments of the present invention.
Bragg grating
systems use a fibre which has been written with a discreet grid in regions
which act as
strain gauges (or temperature gauges). These systems work at high frequencies
and are
very accurate as they pick up a strain or temperature along a very small
region (5mm or
smaller). The Bragg gratings can be multiplexed on a single fibre. That is to
say, an
CA 02814590 2013-04-12
WO 2012/059736 PCT/GB2011/052070
7
interrogator can see through one Bragg to a more distant one as long as the
reflected
frequencies do not overlap.
Figure 4 illustrates how one or more optic fibre (40) is wrapped around and
bonded to a
cylindrical support body (41) in a helical formation. Straining the
cylindrical support body
(41) will consequently strain the optic fibre. As an alternative to bonding
the optic fibre (41)
directly to the cylinder a helical groove (50) may be cut into the cylinder to
take the fibre as
shown in Figure 5. Figure 6 illustrates a helical optic fibre positioned in
the internal bore of
a tube and held in place by an adhesive such as epoxy or the like.
As indicated in Figure 4, a cross-section of the support body (41) is
substantially circular in
cross-section having a diameter d. The fibre Length between spaced apart
planes AB
which are axially spaced apart with respect to a longitudinal axis X
associated with the
support member as separated by a distance P which in Figure 4 illustrates the
pitch of the
winding of the optic fibre (40). It will be appreciated that the length of the
fibre is given by:
L = V (z d)2 + P2 Equation 1
This is shown in Figure 4.
Figure 7 illustrates how the optic fibre winding and support body (41)
illustrated in Figures
4 to 6 can be arranged in a linear arrangement along a longitudinal axis Y
associated with
a target structure which is to be monitored. As illustrated in Figure 7, the
fibre length from
two planes A and B spaced apart longitudinally along the axis Y of the target
structure is
given by:
L = ¨H 111(z d)2 + P2 ......................................................
Equation 2
P
Here, H is the distance where strain is measured.
The optic fibre bonded directly along the length of the cylinder (41)
experiences the same
strain as the cylinder. By increasing the length of the fibre by wrapping it
around the
support body the overall strain that the fibre is subjected to is reduced.
Increasing the
amount of wraps on a given length of section results in greater strain de-
amplification.
This method allows a cylinder with bonded optic fibre to be subjected to a
strain around a
radius R which is beyond the breaking strain of the fibre. Aptly, the support
body is of
small enough diameter to allow a minimum of one turn to satisfy a
discrimination length of
a sensing system utilised.
Aptly, the helix is wrapped relatively tightly and in close proximity to the
underlying body to
achieve a high de-amplification co-efficient.
CA 02814590 2013-04-12
WO 2012/059736 PCT/GB2011/052070
8
Aptly, the support body remains elastic over a large strain range.
As the angles needed to achieve high strain rates are large in relation to the
strain axis (for
example, 45 to the strain axis theoretically only results in a geometric de-
amplification co-
efficient of 1.4:1, the actual value is possibly slightly higher than this due
to the narrowing
of the support due to the Poisson effect which is lower than the de-
amplification co-efficient
that is needed to measure large strains in elastomeric or highly bent systems)
the support
body is large enough not to bring about any damage to the fibre or exceed the
critical
angle. The length of fibre and angle of fibre to strain direction may
optionally be
appropriately matched to get the optimum measuring requirements such as, but
not limited
to, sensitivity, resolution and de-amplification.
Aptly, a minimum bend radius of the optic fibre is not exceeded. Aptly, a
radius of
curvature of the optic fibre wound about the support body is not so tight that
the fibre
boundary exceeds a critical angle associated with the optic fibre.
Figure 8 illustrates an alternative way in which the optic fibre and support
structure may be
arranged with respect to the underlying target structure. As illustrated in
Figure 8 rather
than lay the support body in a linear fashion along the longitudinal axis of
the target
structure, the support body and helically wound optic fibre may themselves be
helically
wound around the target structure. This further enhances the introduction of a
greater
fibre length for a given distance between planes along the longitudinal axis
of the target
structure.
For example, as shown in Figure 8 the fibre length from planes A and B
separated by a
pitch distance H is given by:
V(,r ______________________________ D)2 +H2 _________
L¨ \l(t d)2 p2 Equation 3
P
Figure 9 illustrates an alternative embodiment of the present invention in
which an optic
fibre (90) is helically wound around an underlying support body (91) which has
a
substantially rectangular cross-section with rounded end regions (92). A
length of the
support body (91) is b and a width of the support body is d. A fibre length
between
adjacent planes spaced apart along a longitudinal axis of the support body and
substantially perpendicular thereto is P. This is a pitch of winding of the
optic fibre. The
fibre length L is given by:
L=11(7-1-d+2(b¨d))2 +P2 Equation 4
The optic fibre (90) and the rectangular shaped rod (91) of Figure 9 may be
utilised as
described in Figures 7 or 8 noted above. That is to say, as per Figure 7, the
optic fibre and
CA 02814590 2013-04-12
WO 2012/059736 PCT/GB2011/052070
9
rectangular support body may be provided linearly along a longitudinal axis
associated
with the target structure. Thus, at least one optic fibre element is arranged
substantially
helically along a longitudinal body element axis associated with at least one
support body
element with that support body element itself being arranged along a
longitudinal structure
axis associated with an elongate target structure. Alternatively, as shown in
Figure 8, the
optic fibre and rectangular support body may itself be wrapped helically along
a
longitudinal axis of a target structure. Thus, at least one optic fibre
element is arranged
substantially helically along a longitudinal body element axis associated with
at least one
support body element and that support body element is itself arranged along a
longitudinal
structure axis associated with an elongate target structure.
When the optic fibre and rectangular support body are wrapped in a linear
fashion as
shown in Figure 7 the fibre length from A to B (L) is:
L = ¨H111(7 - i - d + 2 (b ¨ d))2 + P2 Equations
P
When the optic fibre and rectangular support body are arranged as illustrated
in Figure 8
the fibre length from A and B which is L is:
L = 11(R- D)2 +H2 ___________________________________________________________
A/1(7rd+ 2 (b ¨ d))2 + P2 Equation 6
P
It will be appreciated that one, two or more optic fibre and support body
arrangements may
be themselves arranged along a longitudinal axis of a structure in which a
parameter is to
be sensed. Each optic fibre is repeatedly or continuously bonded to the
support body
about which it is helically wound.
The following examples have been chosen to achieve measurable strain
sensitivity using
standard measuring equipment.
Examples, assume d = 5 mm , b = 50 mm and H = 500 mm
Then for Figure 4 - L = 500.24 mm (0.05% increase in length L)
for Figure 9 - L = 511.05 mm (2.2% increase in length L compared to Case 1)
If P = 50 mm and d= 5 mm, b= 50 mm and H = 500 mm
Then for Figure 7 as per Figure 4 - L = 524.09 mm (4.8% increase in length L
compared
to Figure 4)
for Figure 7 as per Figure 0- L = 1169.36 mm (134% increase in length L
compared to
Figure 4)
CA 02814590 2013-04-12
WO 2012/059736 PCT/GB2011/052070
If D = 200 mm and P = 50 mm, d = 5 mm, b = 50 mm and H = 500 mm
Then for Figure 8 as per Figure 4 - L = 841.67 mm (68.2% increase in length L
compared
5 to Figure 4)
for Figure 8 as per Figure 9 - L = 1877.9 mm (276% increase in length L
compared to
Figure 4)
10 Where the % increase in L is proportional to the strain demagnification
for the specific
method/winding technique used.
If a parameter being monitored is temperature it is possible to pack more and
more fibres
per unit length of the support body by winding windings of the optic fibre
more tightly. It
will be appreciated that when this is done the angle the winding makes with
respect to the
axis of the support body approaches 90 . This maximises a strain
demagnification effect
and increases resolution of a system. Other parameters may be similarly dealt
with
however when strain is monitored a trade off can be made depending upon the
circumstances (whether strain demagnification, resolution and/or measuring
sensitivity is
most important for a particular use) to select the pitch of winding on the
support body and
thus the number of windings per unit length versus the angle the optic fibre
makes with
respect to the strain direction. Having a helix angle close to normal to a
strain direction will
demagnify a strain on a fibre close to zero, will increase resolution, but
will reduce
sensitivity. Here resolution is an effective distance between measurement
points.
Sensitivity is related to an accuracy of measurements made at those points.
According to certain embodiments of the present invention, in which the
elongate target
structure is a flexible pipe, the flexible pipe may have one or more armour
layers. Such
armour layers are typically formed during a manufacturing phase by wrapping
armour wire
windings helically around an underlying layer. It will appreciated that
embodiments of the
present invention can replace one or more of the armour wire windings with an
optic fibre
and support body having a cross-section compatible with or matching a cross-
section of
the armour wire. In such a circumstance, the pitch at which the optic fibre
and support
body is wound is determined by a pitch selected during the design and
manufacture of the
flexible pipe.
The rectangular-shaped rod with radius corners illustrated in Figure 9 may be
manufactured from a material that can sustain elastic behaviour up to the
maximum strain
levels that are expected to be measured in service. The rod material could,
for example,
be metallic, polymeric or composite or the like. A groove is provided to lay
and fix the
optical fibre into the rod. The fibre is bonded using readily available
adhesives suitable for
the surface of the rod/structure assembly. The path of the groove is designed
so that the
CA 02814590 2013-04-12
WO 2012/059736 PCT/GB2011/052070
11
axial traverse of the group along the length of the rod is the same over the
entire length of
the groove, giving a fixed orientation of the groove relative to the axis of
the rod. The
strain monitoring rod can be temporarily attached, permanently bonded or
directly
incorporated to the structure where strain/displacement is to be monitored.
When the rod is strained due to the application of loads to the structure, the
strain on the
optical fibre that is at an angle to the axis of the rod will be lower and
proportional to the
strain in the rod. The relationship of the strain on the fibre to the strain
on the rod is given
by the following equation:
=017-111:Ti= ( 1¨ v)
2 3+.7t1
- Cos2 where Tant9 = _______________________________________ and
0,1-f ss. 2 ) k 2)
For example, if the thickness of the rod b is 25 mm, the thickness of the rod
d is 5 mm and
a pitch P is a 60 mm in a steel rod (Poisson's ratio V ¨ 0.3) then strain
attenuation (de-
magnification) is:
=-z. 0.4 (40%) Equation 8
R_od
The minimum value of R which is a radius of curvature at the radius ends of
the
rectangular rod depends on a maximum strain that the fibre can sustain.
The simplest form of this development is a grooved cylindrical rod (L= 0).
However, an
achievable amount of de-magnification is low unless the rod diameter is large
as the optic
fibre can only work as a light conduit up to a certain bend radius and as the
bend radius
decreases, the light is gradually lost through walls of the fibre. Use of a
rectangular rod
has an advantage that length of fibre can be increased without increasing the
diameter of
the rod.
The shape of the rod has the benefit that the strain measurement is
insensitive to the
bending of the rod as the tensile and compressive strains cancel out when used
with a
distributed strain sensing system. Cancelling the bending effect applies
equally to both
circular and elongated cross sections of rod. Aptly the averaging distance of
the strain
measurement equals the length L of the fibre over one pitch of spiral.
In such
circumstances only the axial strength of the rod is measured. Aptly, the
system can be
used with a Bragg grating-based discrete sensing system to reduce gross strain
on the
fibre.
CA 02814590 2013-04-12
WO 2012/059736 PCT/GB2011/052070
12
The rod may aptly be manufactured by various methods such as machining,
extrusion then
machining or by use of a number of overlapping rollers with the impression of
the groove
used to form the groove on a pre-formed rod. Alternatively, the rod may be
manufactured
using rapid prototyping techniques such as laser centring or 3D printing.
Figure 10 illustrates a configuration of hardware/software according to
embodiments of the
present invention. One or more sensors are monitored either by a single
monitoring unit
with multiple inputs or a number of monitoring units with a common timebase.
This data is
transferred to a database where the data will be stored in a manner which
allows easy
interrogation. Due to data quantity it is preferable that a short-term
detailed data set will be
kept for a period of, for example, six months which will include all data
recorded then a
further database will be used to store longer term trend data which can be
created by
compressing the short-term data. The short-term data is used in case of
accident or
failure.
Throughout the description and claims of this specification, the words
"comprise" and
"contain" and variations of them mean "including but not limited to", and they
are not
intended to (and do not) exclude other moieties, additives, components,
integers or steps.
Throughout the description and claims of this specification, the singular
encompasses the
plural unless the context otherwise requires. In particular, where the
indefinite article is
used, the specification is to be understood as contemplating plurality as well
as singularity,
unless the context requires otherwise.
Features, integers, characteristics, compounds, chemical moieties or groups
described in
conjunction with a particular aspect, embodiment or example of the invention
are to be
understood to be applicable to any other aspect, embodiment or example
described herein
unless incompatible therewith. All of the features disclosed in this
specification (including
any accompanying claims, abstract and drawings), and/or all of the steps of
any method or
process so disclosed, may be combined in any combination, except combinations
where at
least some of such features and/or steps are mutually exclusive. The invention
is not
restricted to the details of any foregoing embodiments. The invention extends
to any novel
one, or any novel combination, of the features disclosed in this specification
(including any
accompanying claims, abstract and drawings), or to any novel one, or any novel
combination, of the steps of any method or process so disclosed.
The reader's attention is directed to all papers and documents which are filed
concurrently
with or previous to this specification in connection with this application and
which are open
to public inspection with this specification, and the contents of all such
papers and
documents are incorporated herein by reference.
