Note: Descriptions are shown in the official language in which they were submitted.
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
DIFFERENTIAL PRESSURE TRANSMITTER WITH INTRINSIC VERIFICATION
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority to and the benefit of U.S.
Patent
Application Number 16/152,969, filed on October 5, 2018, which is a
continuation-in-
part application of U.S. Patent Application No.15/727,449, filed on October 6,
2017,
which in turn claims priority as a continuation application to U.S. Patent
Application No.
14/957,191, filed on December 2, 2015, now U.S. Patent No. 9,784,633, issued
October
10, 2017, which is a continuation-in-part of 13/883,043, filed on December 10,
2013,
now U.S. Patent No. 9,207,140, issued December 8, 2015, which is in turn a 371
of
International application PCT/U52011/059114, filed November 3, 2011, which
claims
priority to U.S. Provisional Patent Application No. 61/409,631, filed November
3, 2010.
Each of the above applications are herein incorporated by reference in its
entirety.
FIELD OF THE INVENTION
[0002] The invention relates to improved differential pressure transmitters
with improved
accuracy, process containment, innovative remote calibration, their methods of
use and
manufacture preferably for industrial uses.
BACKGROUND OF THE INVENTION
[0003]Differential pressure transmitters have a significant error envelope for
service
within their operating limits, require a great deal of care and maintenance to
satisfy their
intended purposes. It is common practice for differential pressure
transmitters to be
removed from the application or field installation and transported to well-
equipped
calibration laboratories to assure the accuracy of their measurement. This
practice has
1
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
limitations, is costly and disruptive. Furthermore, calibration laboratories
rarely
simultaneously duplicate the combined actual process conditions of a specific
transmitter
to determine performance under actual operating conditions. Having no accepted
means
of conducting simultaneous combined influences, they test one influence at a
time and
add the results. Calibrations are violated during inadvertent over-range when
re-installing
the transmitter on-line and unknowingly compromise "assurance" of accuracy
provided
by the calibration. The very precaution to assure highest performance
unknowingly
induces an error. Often, a compromised partial calibration is conducted,
whereupon the
output of the transmitter is adjusted for a zero value by a technician at the
transmitter
having equalized the pressure upon the transmitter. The industry is subjected
to a
significant error envelope in conducting asset management inducing
unacceptable
financial unknowns.
[0004]Unfortunately, measurement accuracy is influenced by the combination of
many
environmental process and environmental conditions such as process pressure,
process
temperature, environmental temperature, solar radiation, local neighboring
thermal
radiation, inadvertent over-range, electronic/mechanical drift and enclosure
distortion due
to process pressure or bolting stresses. All these influences are only
evaluated under
steady state conditions, even though these influences are interdependent. The
user or field
technician is not routinely provided with standard techniques or methods to
properly
compensate for these interdependencies, and usually does not have the required
facilities.
Without means for managing the interdependencies, they are usually considered
as being
independent and result in a challenge to calibrate while any condition is not
at a steady
state condition.
-2-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
[0005]The present practice is to compensate for these influences without
considering
their interdependencies. This is pragmatically achieved by erroneously
applying
independent corrections for the prominent influences. This neglect of the
interdependency of the various influences increases measurement errors.
Accurate
compensation requires considering the actual combined environmental and
process
conditions that might be at transient or steady state.
[0006]Conventional differential pressure transmitters having a single sensor
exacerbate
these detrimental influences. For example, most of the existing single sensor,
dual fill
fluid volume differential pressure transmitters tend to have differences in
the fill fluid
volumes, operate with differences in temperature of these fill fluid volumes,
differences
in the spring rates and effective areas of the pressure sensitive elements of
the high and
low sides. These differences limit their capabilities for they produce
erroneous
differential pressures due to process pressure, process temperature or
enclosure distortion
acting upon these differences. Similarly, within single sensor, single fill
fluid volume
differential pressure transmitters having a significant difference in the
spring rate of
pressure sensitive elements of the high and low side isolation diaphragms will
also
produce a detrimental differential pressure due to process pressure,
transmitter
temperature or enclosure distortion acting upon these differences.
[0007]These conditions impact asset management, the environment and product
quality.
A user, until now, has had no recourse other than to accept these poor
conditions.
-3-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
SUMMARY OF THE INVENTION
[0008] The many environmental and process influences referred to earlier, are
exacerbated by current differential pressure transmitters employing a single
differential
pressure sensor with dual isolation diaphragms. A single sensor differential
pressure
transmitter cannot compensate for process or environmental influences without
determining the actual process pressure and temperature to determine the
compensation
factors and are typically limited to steady state conditions. A novel
differential pressure
transmitter is proposed that inherently eliminates these environmental
influences and the
compensation for these environmental influences does not require an awareness
of the
process pressure or a need for a process pressure sensor nor a temperature
measurement.
[0009] Specifically, the object of the present invention is to provide a dual
sensor
differential pressure transmitter with a single fill fluid volume that
inherently eliminates
process and environmental performance influences while operating in steady
state or
transient environment, minimizes zero/span over-range, provides increased
signal level,
improved process containment and a substantial reduction in product costs.
[0010] In a first embodiment, the proposed differential pressure transmitter
can provide
the desired improved performance, process containment at low product cost. In
a second
embodiment, the invention provides enhancements satisfying more demanding
applications. In a third embodiment, the invention provides capabilities
presently
unavailable in the industry and satisfies the most demanding applications.
This novel
system provides remote calibration, traceable to NIST, at actual combined
operating
conditions and without interrupting signal output.
-4-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
[0011] Thus, the proposed differential pressure transmitter intrinsically
eliminates
detrimental process and environmental influences and provides an optional
remotely
activated assurance of the elimination of these environmental influences
traceable to
NIST within +/- 0.005% of reading without the need for a technician in the
field, while at
combined simultaneous operating conditions and without interruption of signal
output.
[0012] The proposed dual sensor, single fill fluid volume differential
pressure transmitter,
compensation does not require monitoring of the process pressure and
temperature. The
object of the present invention is to provide a differential pressure
transmitter that
intrinsically eliminates process and environmental performance influences,
increases
signal level while substantially reducing product costs and provides a means
for
conducting calibration audits at actual operating conditions, remotely without
a
technician in the field.
[0013] In a first embodiment, the differential pressure transmitter comprises
a body, and
first and second cavities within said body connecting to a first and a second
port,
respectively on the exterior of said body. The transmitter further comprises
first and
second flexible element assemblies within and sealed to said first and second
cavities in a
planar housing minimizing influence of vibration that would exist if aligned
in an axial
manner, thereby forming a third and a fourth cavity and a fifth cavity
connecting said
third and said fourth cavities. The transmitter further comprises a fill fluid
having a fluid
fill volume within and connecting said third, said fourth and said fifth
cavities and means
of sensing the first and second position of a first and a second flexible
element end within
said third and said fourth cavities. The transmitter further comprises means
of providing a
conditioned response from the said first and said second position of a first
and a second
-5-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
flexible element end, wherein, the said conditioned response of said first and
said second
flexible element end position is proportional to the desired measurement of
the said
differential pressure applied to said differential pressure transmitter.
[0014] In a second further embodiment the differential pressure transmitter of
the
invention, said aforementioned means of sensing the position of said first and
said second
flexible element end is achieved by sensing the capacitance between the said
first and
said second flexible element end and a first and second electrode. In one
aspect said first
and said second electrode is located within and is electrically insulated and
attached to
said third and said fourth cavity. In one aspect, a first and a second
electrical conductor
is electrically attached to said first and said second electrode and said
first and said
second electrical conductor is sealed to contain said fill fluid within said
third and said
fourth cavities and electrically insulated from said body. An electronic
module external
to said body and electrically connected to said first and said second
conductor and said
body can also be provided. The electronic module senses the capacitance
between said
first and said second flexible element end and said first and said second
electrode and
provides a conditioned response indicative of the said differential pressure.
The change
in position of said first and said second flexible element end produces a said
first and said
second change in capacitance between said first and said second flexible
element end and
said first and said second electrode and said first and said second change in
capacitance is
conditioned to provide a response that is proportional to the desired
measurement of said
differential pressure having minimal undesireable influences from the process
variables.
[0015] In a third, further embodiment, a change in said fill fluid volume due
to
temperature variation, process pressure, enclosure or bolting distortion
produces equal
-6-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
and opposing influences upon said first and said second flexible element
assemblies
which are produced or compensated to appear to have equal ratios of spring
rate to
effective areas, thereby causing said temperature variation and said process
pressure
variation and said enclosure distortion or bolt variation to have minimal
influence upon
differential pressure measurement.
[0016] The dual sensor single fill volume has many benefits not found in
present
transmitters, such as:
[0017]a. The single fill volume responds to undesireable influences such as
the process
temperature, process pressure and their variation by inherently applying
induced change
in the pressure developed by said influences and their variation equally to
each sensor.
The said pressure being applied equally to both sensors assures no
differential pressure
due to said influences being applied upon the sensors.
[0018]b. The dual sensors capture the desired differential pressure by sensing
the
differential pressure upon one of the sensors experiencing an increasing
capacitance
signal due to a decreasing sensing gap when input pressure to be sensed is
increasing, and
upon the remaining sensor having a decreasing capacitance signal due to an
increasing
sensing gap when input pressure is increasing. Thus, the output of the dual
sensors is
composed of the difference of the output of the dual sensors which are of
opposite sign.
This is a significant benefit, for it rejects common mode influences while
doubling the
output of the signal providing improved resolution.
[0019]c. Obtaining the desired output by acquiring the difference of the two
sensors
provides a means of rejecting any common mode undesireable influences if the
gain of
-7-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
each of the dual sensors is assured to be identical by innovative
compensation. The gain
of the two sensors may be assured to be identical by many approaches. For
example,
first, the signal of each of the dual sensors may be sequentially captured,
and their
average value then calculated. Second, this average value is subtracted from
each of the
captured values, causing these signals to appear to be equally displaced from
a zero-point
reference position. Although of opposing sign, equal gain is assured. Third,
if the
common mode undesireable influences are not precisely compensated, a zero-
point
residual will develop upon subtracting. This condition is eliminated by
subtracting any
such zero-point value from all values, thereby eliminating any zero-value
residuals while
retaining equal gain having opposing sign of the dual sensors.
[0020]d. The undesirable over range influence upon zero-point and span has
been
significantly improved within the limits of operation of temperature and
process pressure.
This has been achieved by improved support maintaining the elastic properties
of the
flexible elements during the over range.
[0021]The invention further contemplates an electronic module. In one
embodiment, the
electronic module comprises means for sensing said first capacitance between
said first
flexible element end and said first electrode and a said second capacitance
between said
second flexible element end and said second electrode; means for determining
the first
and second position of said first and said second flexible element end by
sensing said first
and said second capacitance; means for determining a reference zero point
condition
position of said first and said second flexible element end while at reference
temperature
and reference common pressure and no applied said differential pressure; means
for
determining operating zero point condition position of said first and said
second flexible
-8-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
element end while at operating temperature and operating common pressure and
no
applied said differential pressure; means for determining reference
differential pressure
condition position of said first and said second flexible element end while at
reference
temperature and reference common pressure and said differential pressure;
means for
determining operating differential pressure condition position of said first
and said
second flexible element end while at operating temperature, operating pressure
and said
differential pressure; a means for determining a first and a second difference
in operating
position between said operating differential pressure condition position and
said
operating zero condition position of said first and said second flexible
element end; a
means for providing an output proportional to said first and a second
difference in
operating position between said operating differential pressure condition
position and
said operating zero condition position of said first and said second flexible
element end; a
means for determining a first and a second difference in reference position
between said
reference differential pressure condition position and said reference zero
point condition
position of said first and said second flexible element end; and a means for
providing an
output proportional to the said first and a second difference in reference
position between
said reference differential pressure position and said reference zero point
position of said
first and said second flexible element end.
[0022]In another embodiment, the electronic module of the invention comprises
means
for determining said fill fluid temperature; means for determining said fill
fluid pressure
without a dedicated pressure sensor; means for calculating the change in said
operating
differential pressure condition from reference zero condition due to a change
in said fill
fluid temperature; means for calculating the change in said operating
differential pressure
-9-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
condition from said reference zero point condition due to a change in said
fill fluid
pressure; means for providing an output of said temperature; means for
providing an
output of said pressure; and means for providing an output of said reference
zero point
condition thereby determining a reference zero point condition.
[0023]The differential pressure transmitter of the invention may optionally
further
comprise a three-position valve. In one embodiment the three-position valve
comprises:
a valve body having a first external port and a second external port to
external pressures
and said body having two internal transmitter ports a first internal port and
a second
internal port connecting to said differential pressure transmitter; a rotary
valve plug
having two internal flow conduits; and means of positioning said rotary valve
plug to any
of three-positions. In one aspect, the three positions of the valve are as
follows: a first
position wherein the first external port is connected to the first internal
port and the
second external port is connected to the second internal port; a second
position wherein
the first internal port is connected to the second internal port and no
connection made
between the first and second external ports; and a third position wherein the
first external
port is connected to the second internal port and the second external port is
connected to
the first internal port. In this aspect, normal operation of said differential
pressure
transmitter is configured per said first position, process isolation and said
differential
pressure transmitter equalization is configured per said second position and
reverse
operation of said differential pressure transmitter is configured per said
third and wherein
prior to entering said first or third positions said three-position valve
enters said second
position
-10-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
[0024]In another aspect, the aforementioned three position valve may further
comprise
means of determining said reference zero position by isolation of said
differential
pressure transmitter from said process while maintaining process pressure upon
said
differential pressure transmitter and equalization of the said differential
pressure upon
said differential pressure transmitter in said second position of said three
position valve
and whereby, without any said differential pressure or constant said
differential pressure,
the said differential pressure transmitter output in said normal operation is
compared to
the said differential pressure transmitter output in said reverse operation
and provides an
indication of the differences in density and/or liquid height of process fluid
in the impulse
lines connected to said differential pressure transmitter and thereby provides
a means for
the compensation of impulse line density and level influences.
[0025]In one aspect the above-mentioned electronic module implements a method
for
compensating the combined influence of said temperature and said pressure due
to said
change in said fill fluid fill volume, said spring rates and said effective
areas of said first
and said second flexible element assemblies. In one embodiment the method
comprises
isolating said differential pressure transmitter from said process while
maintaining said
process pressure and said temperature within said differential pressure
transmitter and
allowing equalization of said high side and said low side; sensing said
process pressure
with a process pressure sensor; sensing said temperature with a process
temperature
sensor; sensing said operating zero condition of said first and said second
flexible
element at said process pressure and said temperature; calculating the
deflection of said
first and second flexible element due to said process pressure; calculating
the deflection
of said first and second flexible elements due to said process temperature;
calculating the
-11-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
ratio of said spring rate to said effective area of said first and second
flexible elements;
calculating the said spring rates of said first and second flexible elements;
calculating the
said areas of said first and second said flexible elements; and generating and
applying
compensation factors for said first and said second flexible elements for said
process
pressure and said temperature. The aforementioned-method provides compensation
for
the said differential pressure transmitter for influences of the combined
influence of said
temperature and said pressure due to said change in said fill fluid fill
volume, said
effective areas and said spring rates of said first and said second flexible
element
assemblies.
[0026] In another embodiment the differential pressure transmitter of the
invention may
optionally comprise a three-position actuator. In one embodiment, the three-
position
actuator comprises a first cylinder having a first piston and a first pressure
port, the first
cylinder having a stop for limiting axial motion of said first piston; and a
second cylinder
having a second piston, said second cylinder having an axial slot and said
second piston
having a radial extension positioned within said axial slot of said second
cylinder; and a
third cylinder having a third piston and a second pressure port the third
cylinder further
comprising a stop for limiting axial motion of said third piston. A first
actuator position
is obtained by pressure being applied to said first cylinder through said
first port, a
second actuator position is obtained by pressure being applied to said third
cylinder
through said second port and a third position is obtained by pressure applied
to said first
cylinder through said first port and to third cylinder though said second
port. Positioning
of said center piston moves said three-position valve to said position one,
said position
-12-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
two or said position three and said radial extension of said second piston
provides a
means of moving an external device to any of the said three positions.
[0027]In another embodiment, the transmitter may optionally include a
gravitational
pressure reference source. In one aspect, the gravitational pressure reference
source
comprises: a body; an internal cavity having a post; a sphere having a hole
containing
termination of said post that is attached to said sphere is sealed to said
post; a cylinder
having enlarged internal diameters at each end; a stepped cylindrical post
attached to said
cylinder; a cylindrical weight with an internal diameter accepting said
stepped cylindrical
post; and a means of securing said stepped cylindrical post to said
cylindrical weight,
wherein said cylinder, said stepped cylindrical post and said cylindrical
weight comprise
a gravitational reference assembly. The gravitational pressure reference
source further
comprises an internal cylindrical magnet within a cavity in said body and
vertically
below and concentric with said gravitational reference assembly wherein the
said internal
cylindrical magnet can be raised by an external magnet field with opposing
magnetic
poling and said raising of said internal magnet raises said gravitational
reference
assembly relative to said sphere and wherein upon a change of said external
magnet field
the said internal cylindrical magnet falls rapidly due to gravity and the said
change in said
external magnet field and wherein the gravitational reference assembly falls
under the
action of gravity producing a reference pressure in the said cavity of the
said cylinder and
wherein said reference pressure is applied to the internal cavity of the post.
The
gravitational pressure reference source may also include a means of measuring
temperature by capturing the time of the descent for a known distance of the
said
gravitational reference assembly and a means for converting the said time of a
descent for
-13-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
a said known distance to an average velocity of the said fill fluid through
said
gravitational reference assembly and from said average velocity through said
gravitational reference assembly determine a viscosity of said fill fluid and
from said
viscosity determine said temperature from known viscosity versus temperature
relationships. The response of the differential pressure transmitter upon the
application
of the gravity pressure reference provides a means of sensing said reference
pressure for
verifying calibration and determining said temperature of said fill fluid.
[0028]The differential pressure transmitter may also further comprise an
actuator for
actuating said gravitational pressure reference. In one embodiment the
gravitational
pressure reference actuator comprises: (a) a piston having a longitudinal
axis, said piston
having four cavities with an axis of symmetry perpendicular to and
intersecting said
longitudinal axis of said piston and said axis of symmetry of said four
cavities and said
longitudinal axis are parallel and said piston having four magnets contained
within the
said cavities and the magnetic poling of each said magnet alternates along
said piston
longitudinal axis; and (b) a cylinder with a first and a second closed end
wherein said
piston and said magnets are contained within said cylinder and said piston and
said
cylinder having means for preventing rotation of said piston within said
cylinder. The
cylinder has a first and a second pneumatic port located at a first and second
closed end
of said cylinder respectively. By applying pneumatic pressure to the first
pneumatic port
the piston is moved to the second closed end. Likewise, by applying pneumatic
pressure
to the second pneumatic port the piston is moved to the first closed end of
the cylinder.
[0029]In one aspect, the magnets of the aforementioned gravitational pressure
reference
actuator, within said process enclosure are raised by external magnets by
providing an
-14-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
axial opposing magnetic field. Likewise, said magnets within a said process
enclosure
are lowered by said external magnets by providing an axial additive magnetic
field and
means provided for actuating said gravitational pressure reference.
[0030]In one aspect of the invention, the invention calculates a correction
factor to
eliminate undesireable influences as follows. An external, equal and common
pressure is
applied to the said first and second flexible element assemblies. The
deflection of each of
said flexible element assemblies, because of said compression of said fill
fluid due to said
pressure, is sensed. The difference in the ratio of spring rate to effective
area of a said
first and second flexible element assemblies is determined by comparing the
said
displacements of the said pair of flexible element ends in response to the
said common
pressure. A correction factor consisting of the ratio of spring rate to
effective areas of
said first and second flexible element assemblies is produced and is used to
compensate
for said deflections of said first and second flexible element assemblies in
the sensing of
said differential pressures.
[0031]In addition to process and environmental influences, over-range of the
differential
pressure transmitter is a major influence and presently usually not specified
or
considered. If specified, it usually does not apply to worst-case conditions
resulting from
a combination of maximum working pressure while at maximum process
temperature.
The proposed differential pressure-sensing concept minimizes these over-range
concerns
due to hysteresis from over stressing by an assurance that the proposed
concept is not
highly stressed and well supported during the over-range. Zero and span return
errors
from overstressing as in present practice are significantly minimized. Thus,
an
improvement in over-range performance is inherent in the proposed differential
pressure-
-15-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
sensing concept and resolves the worst-case condition of maximum process
pressure
over-range at maximum process temperature.
[0032]The proposed dual sensor, single fill fluid volume differential pressure
transmitter
is shown in FIG. 1 and the dual sensor concept is shown in cross-section in
FIG. 2. This
proposed dual sensor concept does not eliminate the undesirable change in fill
fluid
volume occurring with changes in process pressure, temperature or enclosure
distortion
but it does inherently compensate to eliminate the undesirable error
influence. Any
differential pressure developed due to the change in fill fluid volume for
whatever cause
is applied equally and opposingly to the high and the low side flexible
element
assemblies with no differential pressure being sensed by the differential
pressure
transmitter. Ideally, if the combined response of spring rates and effective
areas of the
high and low side flexible element assemblies are matched, there cannot be a
differential
pressure developed in the proposed concept due to the detrimental influences.
[0033]Optimization of the proposed concept requires design and manufacturing
considerations to assure this match of the combined response of spring rates
and effective
areas of the high and low side flexible element assemblies of (3 A) and (3B)
of FIG. 2.
Although these efforts may produce a good match, it cannot be assured to be
insignificant. However, an innovative simple manufacturing procedure assures
these
differences in the spring rates and effective areas of the high and low side
flexible
element assemblies due to manufacturing tolerances are insignificant. During
the
manufacturing process, a high pressure is simultaneously applied to the high
and low side
flexible element assemblies while monitoring the deflections of the high and
low side
flexible element ends resulting from the compression of the fill fluid. The
difference in
-16-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
the deflection of the flexible element ends provides a means of compensating
for the
difference in the effective areas and spring rates of the flexible element
assemblies. The
compensation process equation will be developed further in the discussion to
illustrate
how the compensation is implemented. Thus, the difference in the spring rates
and
effective areas of the flexible element assemblies due to manufacturing
tolerances is
minimized and ideally eliminated assuring a high level of performance.
Furthermore, this
process can also be applied in the field. Thus, a user can verify high
performance upon
receipt and during routine maintenance.
[0034]The difference in the spring rates and effective areas of the flexible
element
assemblies due to manufacturing tolerances is minimized and ideally eliminated
assuring
a high level of performance by a very simple approach during actual operation
by
considering one sensor as a reference and applying a compensation factor to
the
remaining sensor achieving an ideal match. This compensation is best described
shortly
after an awareness of important details of operation are presented.
[0035] The proposed dual sensor, single fill fluid volume differential
pressure transmitter
is simple in construction. A single fill fluid volume exists between the high
side flexible
element assembly and low side flexible element assembly. Within this single
volume,
there are fixed electrodes (4a) and (4b) of FIG. 2 that are in close proximity
to each of the
flexible element ends (8A) and (8B). The sensing is achieved by simultaneously
measuring the differential change in capacitance due to the deflection of the
flexible
element end with respect to the fixed electrode for the high and the low side.
A pressure
applied to the high side deflects the flexible element end of the high side
inwardly
towards the fixed electrode and simultaneously the fill fluid causes the low
side flexible
-17-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
element end to deflect outwardly away from the fixed electrode due to the
equal
displaced volume of the flexible element assemblies.
[0036] Operation of the differential pressure transmitter in a flow or level
application, is
categorized by four conditions that may be defined:
[003711. When the transmitter is assured to be at a reference temperature,
reference
process pressure and no differential pressure, the output is defined as
"reference zero
condition".
[003812. When the transmitter is assured to be at a known temperature, known
process
pressure and no differential the output is defined as "operating zero
condition".
[003913. When the transmitter is assured to be at a known temperature, known
process
pressure and a known differential pressure with respect to "reference zero
condition" is
defined as "reference differential pressure condition".
[004014. When the transmitter is assured to be at a known temperature, known
process
pressure and at a differential pressure being measured, it is defined as
"operating
differential pressure condition".
[0041] The proposed advanced and premium differential pressure transmitter
concepts
will satisfy the requirements of more demanding applications. The advanced and
premium differential pressure transmitters are composed of the standard
differential
pressure transmitter with ancillary devices.
-18-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
[0042]There are three ancillary devices. The advanced and premium product has
an
actuator that remotely operates a three-position valve for normal, equilibrate
or reverse
position. The equilibrate-position isolates the transmitter from the process.
[0043]The premium product also incorporates a gravitational pressure reference
that
verifies calibration traceable to National Institute of Standards with an
actuation device
that provides remote operation of the gravitational pressure reference without
a
technician at the site.
[0044]The proposed premium dual sensor, single fill fluid volume differential
pressure
transmitter concept provides capabilities that presently are not available in
the industry
and will now be described.
[0045]Differential pressure transmitters have been improved in recent years.
An example
is provided in U.S. Pat. No. 6,321,585 Sgourakes for a Differential Pressure
Generator.
This improvement eliminates all detrimental combined interdependent process
and
environmental influences of differential pressure transmitters by remotely
verifying
measurement accuracy within +/-0.005% of reading traceable to National
Institute of
Standards while transmitter is on-line at process and environmental operating
conditions
for flow and liquid level applications.
[0046]The present invention integrates U.S. Pat. No. 6,321,585 Sgourakes
Differential
Pressure Generator within the proposed premium differential pressure
transmitter and
with the addition of proposed ancillary devices, provides an exceptional high-
performance premium differential pressure transmitter for flow and liquid
level
applications with remote calibration assurance that is not in any existing
product.
-19-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
[0047]The premium differential pressure transmitter provides significant
advancements
in performance. Some of the advancements enhancing the remote calibration
verification
of U.S. Pat. No. 6,321,585 Sgourakes for a Differential Pressure Generator
are:
[004811. A reference zero condition value is available with each differential
pressure
observation providing an ability to monitor zero-point value during each
differential
pressure measurement.
[004912. Detrimental influences of environmental temperature, process
temperature and
process pressure are inherently eliminated from the differential pressure
transmitter.
[005013. Automatically scheduled sensor calibrations can be achieved remotely
during
routine sustained operation.
[005114. Reverse flow capability. The three-position valve provides an ability
to
measure normal or reverse flows.
[005215. Elimination of density or level differences in impulse lines is
assured. This is
achieved by comparing the zero condition in normal and reverse positions of
the three-
position valve. Any difference can be attributed to density or level
differences in the
impulse lines and the influence compensated.
[005316. The transmitter provides greater range limits by providing lower span
capability achieved by a significant reduction of the error envelope, avoiding
the cost and
complexity of multiple transmitters with intermediate spans.
[005417. Minimal over-range influence of zero and span.
-20-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
[005518. A very low cost of manufacture achieved based upon manufacturing
major
components from bar stock that is automatically machined without need for
presence of a
machinist.
[005619. Calibration is assured to be within +/-0.005% of reading traceable to
National
Standards Institute, achieved from remote locations with an unattended
computer,
scheduled as desired, without a technician present at transmitter, at actual
combined
operating conditions, on-line and without signal interrupt for flow or level
applications.
[0057110. Pro-active maintenance can warn if a trend of concern develops in
sequential
calibration assurances or from monitoring of the zero value at each
differential pressure
acquisition.
[0058111. Instantaneous assurance of proper operation can be remotely verified
within
minutes during crisis conditions without signal interruption.
[0059112. Eliminates the need for travel to the site, flights, accommodations,
rental
vehicle, well equipped lab or an interruption of signal. The transmitter
continues
operation in process line, eliminates hand written manual calibration history
management, eliminates lengthy evaluations in a calibration laboratory
requiring the
simulation of process pressures and environmental temperatures.
[0060113. Provides a capability for remotely achieved customer/buyer audits
eliminating
skilled operators, costly travel, hotel accommodations and seasoned resources.
[0061114. The present capacitive single sensor concepts are typically a
stretched
diaphragm with an effective area of approximately 1/3 inch squared with non-
linear
-21-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
deflection. Conversely, the proposed capacitive concept has an effective area
of 3.5
inches squared with linear deflection. Thus, providing a factor of ten
improved
sensitivity.
[0062]According to one aspect, there is disclosed a method of compensating for
undesired influences in a pressure transmitter wherein the pressure
transmitter comprises
a body for housing a high-pressure sensor and a low-pressure sensor each of
which is in
fluid communication with a port and in further fluid communication with each
other
through a connector tube containing a fill fluid. The method may comprise
acquiring a
first deflection signal from the high-pressure sensor in response to an
applied pressure
then instantly acquiring a second deflection signal from the low-pressure
sensor in
response to the applied pressure, computing an average value of said first and
second
deflection signals, subtracting said average value from said first and said
second
deflection signals so as to generate normalized first deflection signal and
normalized
second deflection signal, respectively, subtracting a high-pressure zero point
offset from
said normalized first deflection signal to generate offset-corrected
normalized first
deflection signal, subtracting a low-pressure zero point offset from said
normalized
second deflection signal to generate offset-corrected normalized second
deflection signal,
multiplying said offset-corrected normalized first deflection signal by a
first
compensation scaling factor to obtain scaled offset-corrected normalized first
deflection
signal, multiplying said offset-corrected normalized second deflection signal
by a second
compensation scaling factor to obtain scaled offset-corrected normalized
second
deflection signal, and subtracting said first scaled offset-corrected
normalized first
-22-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
deflection signal from said second scaled offset-corrected normalized second
deflection
signal to derive a compensated differential pressure.
[0063]In some embodiments, the method of compensating may further comprise
multiplying said compensated differential pressure by a conversion factor to
obtain said
compensated differential pressure in desired units of measure.
[0064]In some embodiments, any of said high-pressure and low-pressure zero
offsets
may be determined via regression analysis of previously obtained signals from
said high
pressure sensor and said low-pressure sensor, respectively, in response to
applied
pressures. In other embodiments, said high-pressure and low-pressure zero
offset may be
determined from an initial calibration.
[0065]In some embodiments, said first compensation scaling factor may be
proportional
to a predefined standard deflection associated with said high-pressure sensor
and may be
inversely proportional to a full span deflection associated with said high
pressure sensor
obtained via regression analysis of previously obtained signals from said high-
pressure
sensor.
[0066]In some embodiments, said second compensation scaling factor may be
proportional to a predefined standard deflection associated with said low-
pressure sensor
and may be inversely proportional to a full span deflection associated with
said low-
pressure sensor obtained via regression analysis of previously obtained
signals from said
low-pressure sensor.
-23-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
[0067]According to another embodiment, there is provided a method of
compensating for
undesired influences in a pressure transmitter wherein the pressure
transmitter comprises
a low-pressure sensor and a high-pressure sensor in further fluid
communication with
each other through a connector tube containing a fill fluid. The method
comprises
acquiring deflection signals from the high-pressure sensor and the low-
pressure sensor,
computing an average value of the deflection signals, generating normalized
deflection
signals based on the average value, generating offset-corrected normalized
deflection
signals, scaling said offset-corrected normalized deflection signals, and
deriving a
compensated differential pressure output based on the scaled offset-corrected
normalized
deflection signals.
[0068]In some embodiments, the method may further comprise converting said
compensated differential pressure output to desired units of measure.
[0069]In some embodiments, generating said normalized deflection signals may
comprise equalizing the gains of the high-pressure sensor and the low-pressure
sensor.
[0070]In some embodiments, generating offset-corrected normalized deflection
signals
may further comprise determining zero offsets for the high-pressure sensor and
the low-
pressure sensor. In some embodiments, determining zero offsets may comprise
performing regression analysis of previously obtained signals from the high-
pressure
sensor and the low-pressure sensor.
[0071]In some embodiments, scaling said offset-corrected normalized deflection
signals
comprises multiplying said offset-corrected normalized deflection signals for
each of the
-24-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
high-pressure sensor and the low-pressure sensor by respective compensation
scaling
factors.
[0072] In some embodiments, the compensation scaling factor for the high-
pressure
sensor may be proportional to a predefined standard deflection associated with
said high-
pressure sensor and may be inversely proportional to a full span deflection
associated
with said high pressure sensor obtained via regression analysis of previously
obtained
signals from said high-pressure sensor. The compensation scaling factor for
the low-
pres sure sensor may be proportional to a predefined standard deflection
associated with
said low-pressure sensor and may be inversely proportional to a full span
deflection
associated with said low-pressure sensor obtained via regression analysis of
previously
obtained signals from said low-pressure sensor.
[0073]In some embodiments, a method according to the present invention can
further
include sensing a compression of the fill fluid by any of said high-pressure
or low-
pres sure zero offset to provide a measure of the process pressure after
compensating for
any influence of temperature on the fill fluid. In some such embodiments, a
temperature
sensor is employed to measure the temperature of the fill fluid.
[0074]In some embodiments, a method according to the present teachings can
further
include providing a differential pressure sustained by each of said dual
sensors by
employing a relation predicting the internal pressure upon said dual sensors.
[0075] In many embodiments, the steps of methods according to the present
teachings are
performed by a digital processor.
-25-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
BRIEF DESCRIPTION OF THE DRAWINGS
[0076]FIG. 1 is an isometric view of the differential pressure transmitter.
[0077]FIG. 2 is a cross sectional view of the proposed differential pressure
sensor of the
differential pressure transmitter.
[0078]FIG. 3 is an isometric view of the premium differential pressure
transmitter with
integrated three-position valve and valve operator and gravitational reference
with
operator.
[0079]FIG. 4 is a schematic view illustrating the three position hydraulic
connections.
[0080]FIG. 5 is a view showing the three-position valve components in the
normal
position.
[0081]FIG. 6 is an isometric view of the three position valve components in
the
equilibrate position.
[0082]FIG. 6A is a cross sectional view of the three position valve in the
equilibrate
position with center piston positioned in center position.
[0083]FIG. 7 is a cross sectional view of the gravitational pressure reference
with the
actuator in the normal run position.
[0084]FIG. 8 is a cross sectional view of the gravitational pressure reference
with the
actuator having raised the weight and cylinder assembly and prepared to
initiate
development of the gravitational pressure reference.
-26-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
[0085]FIGS. 9A to 9C are charts illustrating a compensation process according
to an
embodiment, showing the initial conditions, slope equalization and offset
elimination
according to aspects of the present disclosure.
[0086]FIG. 10 is a schematic diagram illustrating one embodiment of a method
of
compensating for undesired influences in a pressure transmitter according to
aspects of
the present disclosure.
[0087]FIG. 11 is an example illustration of digital electronic circuitry or
computer
hardware that can be used with the embodiments disclosed herein.
DETAILED DESCRIPTION OF THE INVENTION
[0088] The proposed dual sensor, single fill fluid volume differential
pressure transmitter
(1) is illustrated in FIG. 1 with the major components shown as a body (2),
two process
interface assemblies (3A) and (3B), high pressure process port (12), and low
pressure
process port (13).
[0089] The dual sensor, single fill fluid volume differential pressure
transmitter (1) of
FIG. 1 is very compact and optimized to accommodate present impulse line
spacing of
2", 2 us" and 2 1/4" between high-pressure process port (12) and low-pressure
process
port (13). The flexible element assembly (3A) of FIG. 2, is composed of a
flexible
element end (8A) and two convolutions (9AA) and (9AB). The flexible element
assembly (3A) is attached to a base (15A) having an isolation groove (16A)
that
minimizes influences from distortion of the body (2) due to process pressure
or
process/environmental temperature. Additional components are the fill fluid
(14), fill
fluid connecting tube (11) and fill fluid filling ports (10A) and (10B).
-27-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
[0090]The dual sensor measures the differential pressure by sensing the
capacitance
change due to the deflection of flexible element end (8A) with respect to the
fixed
electrode (4A) as shown in cross section 2-2 of FIG. 2. and simultaneously the
deflection
of flexible element end (8B) with respect to the fixed electrode (4B). The
flexible
element assemblies (3A) and (3B) thereby provide process isolation and a
differential
pressure sensing capability. The said fixed electrode and said flexible
element end may
be configured to provide improved shielding from undesired environmental
electronic
charges.
[0091]The flexible element assembly (3A) has an electrode (4A) mounted upon an
insulator (5A) that is attached to the base (15A). The electrode (4A) has an
electrical
conductor (6A) providing electrical continuity from the electrode (4A) to an
electrical
termination (17A) of hermetic seal (7A). The electrical conductor (6A) has a
stress relief
(not shown) that minimizes thermal expansion and pressure expansion influences
to
assure reliable connectivity between electrode (4A) and the electrical
termination (17A)
of the hermetic seal (7A). Additionally, the electrical conductor (6A) is
contained within
an insulator (18A) to minimize undesirable capacitive coupling and restrict
relative
motion between the conductor (6A) and the body (2).
[0092]A fill fluid (14) hydraulically couples the flexible element assembly
(3A) of the
high side to the flexible element assembly (3B) of the low side. Thus, a high
pressure
applied to a flexible element assembly (3A) of the high side causes an inward
deflection
while the opposing flexible element assembly (3B) experiences an outward
deflection.
-28-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
[0093]All ancillary devices are contained within an assembly (14) of FIG. 3.
They will
be described sequentially in the following description.
[0094]The three-position valve configures the proposed differential pressure
transmitter
(1) for normal, equilibrated or reverse operation and are shown schematically
in FIG. 4.
The main components of the proposed three-position valve and valve operator
(20) are
shown in FIG. 5 and now considered.
[0095]The normal position of FIG. 4. connects a high-pressure process port to
a high-
pressure differential pressure transmitter port and a low-pressure port to a
high-pressure
differential pressure transmitter with a normal flow direction.
[0096]Equilibrate position of FIG. 4. connects a high-pressure differential
pressure
transmitter port to a low-pressure differential pressure transmitter port
equilibrating
pressures and no differential pressure being applied to the differential
pressure
transmitter.
[0097]Reverse position of FIG. 4. connects a high-pressure process port to a
high-
pressure differential pressure transmitter port and a low-pressure process
port to a low-
pres sure differential pressure transmitter port providing reverse flow
measurement
capability. Although the differential pressure transmitter (1) remains in the
same
position, the high-pressure and low-pressure ports of the reverse position of
the
differential pressure transmitter (1) are opposite the high-pressure and low-
pressure ports
of the normal position.
-29-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
[0098]The three position valve and operator (20) as shown in FIG. 5 is
composed of a
fixed valve seat (21) that is restricted from rotation by a matching key way
in the body
(2) that is not shown and provides the ports for communication with the
differential
pressure transmitter (1), a selector disc (22) that is rotated to configure
the desired
positions of FIG. 4, a compensation plate that is not shown, provides axial
compensation
for thermal and pressure deflections and torsionally couples selector disc
(22) to rotor
(24), an axial spring (23) that provides a load to selector disc (22) and
rotor (24) assuring
that selector disc (22) achieves a seal with valve seat (21) while
compensating for thermal
and pressure deflections, rotor (24) is driven by a crank (26) of three
position actuator.
[0099]The novel three-position actuator of the three-position valve (20) is
shown in cross
section 2-2 of FIG. 6A for the equilibrate position. The center piston (29) is
driven to the
equilibrate position by applying pressure to port (33) that acts upon piston
(30) forcing it
to the right until arrested by stop (35) in cylinder of lower molding (32) and
simultaneously applying pressure to port (34) that acts upon piston (31)
forcing it to the
left until arrested by stop (36) in the cylinder of lower molding (32).
[0100]The normal and reverse positions of the valve actuator are achieved by
motion of
three pistons (30), (31) and (32) having an innovative sequence. Referring to
FIG. 6A,
when the pneumatic port (33) on the left is pressurized, the left piston (30)
travels to the
right and engages the center piston (29) and sequentially engages the right
piston (31) and
continues to the right until piston (30) is limited by a stop (35) at this
time the pressure is
applied to center piston (29) through path (38A) and piston (31) is then
driven to the right
termination of the cylinder. Similarly, when the pneumatic port (34) on the
right is
pressurized, the right piston (31) travels to the left and engages the center
piston (29) and
-30-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
sequentially engages the left piston (30) and continues to the left until
piston (31) is
limited by a stop (36) at this time the pressure is applied to center piston
(29) through
path (38B) and piston (30) is then driven to the left termination of the
cylinder.
[0101]Motion of piston (29) of FIG. 6A actuates the valve. A post (37) of the
center
piston (29) is attached to valve plate (28) and valve plate (28) is coupled to
a crank (26).
As post (37) is positioned to the left, center and the right, it rotates the
crank (30) of the
three-position valve (20). The crank (26) turns the rotor (24) that positions
the selector
disk (22) to the desired valve position. The valve may also be operated
manually by
positioning valve plate (28) by hand. Valve plate (28) provides an indication
of the
position of the valve.
[0102]The three-position valve (20) provides the ability to determine and
remove the
influence of level or density in impulse lines. With a constant flow or
ideally no flow,
the three position valve (20) is first positioned in the normal position and
the normal
value of the differential pressure transmitter (1) is determined. Then the
three-position
valve (20) is positioned in the reverse position and the reverse value of the
differential
pressure transmitter (1) is determined. The results are compared, and a
correction is
made to minimize any level or density differences in the impulse lines.
[0103]The gravity pressure reference (40) shown in cross section 3-3 of FIG.
7, functions
is described in detail in U.S. Pat. No. 6,321,585 Sgourakes for a Differential
Pressure
Generator. However, the basic operation is as follows:
[0104]The weight and cylinder assemblies (43A) and (43B) are raised with
respect to
fixed spherical pistons (41A) and (41B) and then allowed to descend under the
action of
-31-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
gravity thereby producing a traceable, reliable reference pressure within the
cylinders
(42A) and (42B) that is applied to the differential pressure transmitter (1).
[0105]The principle of operation is simple. The weight and cylinder assembly
(43A) on
the high side has the same volume as the weight and cylinder assembly (43B) on
the low
side. The desired reference differential pressure is developed by a density
difference of
the weight and cylinder assembly (43A) with respect to the weight and cylinder
assembly
(43B). The density of the fill fluid changes significantly due to volume
changes with
respect to pressure or temperature. However, the fill fluid changes produce
equal
influences upon the assemblies and therefore do not influence the desired
reference
differential pressure. Thus, the reference differential pressure is not
influenced by fill
fluid density variations that occur with temperature or process pressure.
[0106]Innovative concepts have now been provided to enhance the raising and
the
descent of the weight and cylinder assemblies (43A) and (43B) of FIG. 7.
Located within
the enclosure are internal magnets (45A) and (45B) that are raised by an
opposing magnet
field or lowered by an attractive magnetic field. These magnetic fields are
produced
externally.
[0107]Positioning an external magnet (48) having an opposing magnetic
orientation to
the internal magnet (45) produces an opposing magnetic field that raises the
internal
magnet. Positioning an external magnet (48) having an attractive magnetic
orientation to
the internal magnet (45) produces an attractive magnetic field that lowers the
internal
magnet.
-32-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
[0108]The positioning of the external magnets with respect to the internal
magnets is
simply done by shuttling the external magnets horizontally left or right a
distance equal to
the one half the horizontal distance between the internal magnets (45A) and
(45B). This
motion is illustrated in FIG. 7 illustrating the relationship in normal
operation desiring to
capture the internal magnets by providing an attractive field and reduce
vibration of the
internal magnets. Fewer magnets could be used but the desired advantage of
capturing
the internal magnets in normal operation thereby reducing pressure pulsations,
would not
be achieved.
[0109]In the moment prior to the descent of the weight and cylinder assemblies
(43A)
and (43B) the internal magnets are held in a position illustrated in FIG. 8.
To initiate a
descent the external magnets (48) are quickly returned to the normal position.
At this
time the weight assemblies (43A) and (43B) experience a gravitational force
that is
applied upon the effective area defined by the sphere within the cylinder
thereby
producing the desired differential pressure.
[0110]The positioning of the external magnets is achieved by pneumatic
pressure applied
to either end of the piston (47) carrying the external magnets (48).
[0111]A transmitter which may be a gauge pressure, absolute pressure or
differential
pressure transmitter is disclosed having an innovative compensation process
assuring
improved performance by eliminating undesired influences due to process
temperature,
process pressure, ambient temperature, over range, distortion of the sensor
enclosure due
to process pressure or bolting, changes in spring rates or effective areas of
the dual
sensors, while in the steady or the dynamic state.
-33-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
[0112] In various embodiments of the innovative compensation process disclosed
herein,
one of the flexible element assemblies may be used as a reference.
[0113] The output of the transmitter is composed of a differential signal of
the high-
pressure sensor minus the low-pressure sensor. The compensation process
considers that
any common undesirable input of the same value and polarity is therefore self-
cancelling,
while desired signals of opposing polarity are additive and retained. However,
it may not
be realistic, due to manufacturing limitations, to consider that the gain of
deflection due
to pressure of the dual sensors being a function of the sensor spring rate and
effective
area are of the same value.
[0114] The innovative process disclosed herein overcomes this concern such
that the
gain is made to appear to be opposite in sign but equal and any existing zero
offset is
eliminated. The gain can then be adjusted to a standard value devoid of
undesirable
influences due to process temperature, process pressure, ambient temperature,
over range,
distortion of the sensor enclosure due to process pressure or bolting, changes
in spring
rates or effective areas of the dual sensors, while in the steady or the
dynamic state.
[0115] The compensation of the dual sensors without the use of a common
reference for
each of the sensors is unduly complex and causes confusion. Embodiments
disclosed
herein address this difficulty by innovative means of achieving a common
reference for
comparison of the high-pressure sensor response to that of the low-pressure
sensor. The
high-pressure sensor is referred to as being the high side, and similarly the
low-pressure
sensor referred to as being the low side.
-34-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
[0116]The volume displacement of the low side flexible element produces an
identical
volume displacement as the high side flexible element. Applying this fact, the
applied
pressure PH will now be developed as the desired common reference, then used
to
develop the equation for determining the differential pressure from
deflections of the dual
sensors, followed by the development of the compensation process:
DEFINITIONS
[0117] PH = applied pressure
PI = internal pressure of fill fluid
P = process pressure
AVH = volume displaced by high side
AVL = volume displaced by low side
AH =effective area high side
AL=effective area low side
KH=spring rate high side
KL=spring rate low side
DH = deflection of high side
DL = deflection of low side
DHP = deflection of high side due to PH
-35-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
DLP = deflection of low side due to PH
[0118]An applied differential pressure causes the high side flexible element
to displace a
volume of the fill fluid inward resulting in an identical volume displacement
of the low
side flexible element outward. This provides a sign convention that the
displacement
inward of the high side flexible element due to a positive applied
differential pressure, is
considered negative and the resulting displacement outward of the low side
flexible
element is considered positive. Thus, the volumes are equal in value and of
opposite sign:
-AVH = AVL EQ 100
DH* AH = DL * AL EQ 101
[0119]The high side deflection equation predicting its decrease is given by:
AH
DH = (-PH-P+PI) * ¨ EQ 102
KH
[0120] The low side deflection equation predicting its increase is given by:
AL
DL = (PI-P) * ¨ EQ 103
KL
[0121] Substituting DH and DL into -DH * AH = DL * AL produces the following
volume equality:
AH2 AL2
(-PH-P+PI) * ¨ = (PI-P) * ¨ EQ 104
KH KL
[0122] Solving for internal pressure PI, as a common function in terms of PH
for the
deflection of high and low sides provides the desired common reference:
-36-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
AH2
P1= PH AL-, AH-
? KH _E +P EQ 105
KL KH
[0123] Next, equations to determine differential pressure are developed.
Solving for the
deflection of the high side in terms of the applied differential pressure PH
finds that the
process pressure P is not a factor and high side deflection is given by:
AL2 AH , (AH2 . AL2)
[0124] DHP = -rõ n --/ ¨1-- EQ 106
KL KH KH KL
[0125] Similarly, the deflection of the low side in terms of the applied
pressure PH is
given by:
AH2
AL
DLP
= PH(AH2KHAL2 _______________________ ) EQ 107 KL
KH + KL
[0126] The total deflection in terms of the applied differential pressure PH,
is given by:
AH2 AL2
( H-K 2)-\
DLP-DHP=PH v + PL4AH2KLAL2 ) EQ 108
AH2 AL KL KH
KH KL KH+ KL
[0127] Thus, the deflection due a differential pressure is determined with a
common
reference of PH which eases the analysis. When this total deflection of DLP-
DHP is
multiplied by a proportioning factor, it will provide an equation for the
total differential
pressure in desired units of measure.
[0128] The high side and low side flexible element deflection responses can
now be
visualized with respect to PH as seen in FIGS. 9A - 9C and described further
below.
ADDITIONAL DEFINITIONS
-37-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
[0129]DHR=Position of high side flexible element end with PH
DHZ=Position of high side flexible element end without PH
DLR=Position of low side flexible element end with PH applied to high side
DLZ=Position of low side flexible element end without PH
[0130]It will now be shown how the compensated equation inherently eliminates
the
detrimental influences of process and environmental influences.
[0131]A change in the common fill fluid pressure due to process and
environmental
influences will apply an equal pressure and related deflection upon each of
the flexible
element assemblies but will not cause any change in the differential pressure
upon the
flexible element assemblies. This is an important and basic benefit, for
process
temperature, process pressure, environmental temperature and enclosure
distortion will
change the common fill fluid volume but not the differential pressure being
sensed.
Therefore, the detrimental performance influences are inherently eliminated.
[0132]Equations describing the detrimental influences will now be provided.
The
deflection due to process pressure changing the compression of the fill fluid
volume can
be determined from the following equations:
-P*PW AH
DPH = ________________________________________________________________ EQ 109
AL2 AH2 KH
__F_
KL KH
-P*P*17 AL
DPL ¨ ________________________________________________________________ EQ 110
AL2 AH2 KL
__F_
KL KH
-38-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
[0133]Similarly, the deflection due to temperature of the fill fluid expanding
or
contracting the fill fluid volume can be determined from the following
equations:
T*a*V AH
DTH = AL2 AH2 KH EQ
111
KL + KH
DTLT*a*V AL
= EQ 112
AL2 AH2 KL
KL + KH
[0134] Including these influences within the basic equation provides:
AL2
AH2
DLPC+DHPC=[PH KH + ______ + T*a*V 1 AL +i-PH KL -P*P*V T*a*V 1 AH
AL2 AH2 AL2 AH2 AL2 AH2L KL L AL2 AH2 AL2 AH2 AL2 AH2] ¨101
L_d__
K KH KL KH KL KH KL KH KL KH KL KH
EQ 113
[0135]The distortion due to pressure or temperature of each housing produces
deflections
HsgH and HsgL upon the high side and the low side, respectively. Any
distortion due to
bolting produces deflections BCH and BCL on the high side and the low side,
respectively. The reference sensor position associated with zero condition
determined by
manufacturing variations or changes with time is identified as CH and CL for
the high
side and the low side, respectively.
[0136]The complete equation is now presented with all undesireable influences
of
significance prior to compensation:
AH2
j_ AL2 1
DLPC+DHPC=[PH KH AL
+HsgL+BCL+CL+
AL-, AH-, + A AH2] AL2 *I3A* H142 1 T*a*V KL
KL + KH KL+ KH KL+ KH
AL2
KL -P*P*V T*a*V 1 ¨HsgH¨BCH¨CH EQ
114
AH
[PH AL2 AH2
KH AL2 AH2 ¨ AL2 AH2]
KL + KH KL + KH KL + KH
-39-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
[0137]Following compensation, all influences are eliminated and the output is
doubled:
AH2 AL2
AL 4_ KL AH1
DLPC+DHPC, PH f ________ , ,
= AL-
KHAH- KL ' AL2 AH2 KIP EQ 115
KL+ KH KL KH
[0138]In one embodiment, an innovative seven step compensation process
achieves the
desired results of eliminating all influences while doubling the output. In
one
embodiment, the compensation process may include seven steps, comprising:
[0139] 1A. Acquire DH output of high side in response to PH and all influences
at
operating point.
[0140]1B. Acquire DL output of low side in response to PH and all influences
at same
operating point. FIG. 9A is a chart showing the low side deflection signal DL
and the
high side deflection signal DH as a function of the applied pressure PH. As
shown in the
initial conditions chart of FIG. 9A, DL and DH have different slopes. Further,
the
deflection signals have non-zero offsets; DL has an offset of BL, and DH has
an offset of
BH.
[0141] 2. Compute the average of DH and DL as acquired with DA,(DH+DL)/2.
[0142] 3A. Subtract DA from the value of DH just acquired, thus producing a
value of
DHA.
[0143]3B. Subtract DA from the value of DL just acquired, thus producing a
value of
DLA. FIG. 9B shows a chart of the normalized deflection signals DLA and DHA
for the
low side and the high side, respectively. The normalization step equalizes the
slopes, as
-40-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
shown in FIG. 9B. That is, DHA and associated DLA will now have equal but
opposite
polarity gain. Further, although the zero values may be non-zero, they will be
equal, as
shown by BL and BH in FIG. 9B.
[0144] 4A. Obtain by regression analysis of available DHA data or by other
means, their
zero-point value and subtract this zero-point value from present DHA producing
DHAZ
at present operating point. Thus, a linear relationship is produced,
containing all the
values of DHAZ passing through zero-value without an offset and defined by
DHAZ=
mH*PH, wherein mH possesses the gain of linear relation of DHAZ versus PH,
from
regression analysis of all updated available data or by other means.
[0145]4B. Obtain by regression analysis of available DLA data or by other
means, their
zero-point value and subtract this zero-point value from present DLA producing
DLAZ at
present operating point. Thus, a linear relationship is produced containing
all the values
of DLAZ passing through zero-value without an offset and defined by DLAZ=
mL*PH,
wherein mL possesses the negative gain of linear relation of DLAZ versus PH,
from
regression analysis of all updated available data or by other means. FIG. 9C
shows a
chart of the offset-corrected normalized deflection signals DLAZ and DHAZ for
the low
side and the high side, respectively. As shown in the chart, the slopes are of
equal value
and opposite sign, and the offsets are eliminated. The output is now available
as a
function of deflection that is proportional to PH having an equation DLAZ-DHAZ
without a zero offset and not influenced by any undesirable influences such as
process
temperature, ambient temperature, process pressure, over range, distortion of
the sensor
enclosure and distortion due to bolting. However, it is susceptible to sensor
change
influences which will be removed by Step 5.
-41-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
[0146]5A. Calculate a proportioned value DHAZP= Stroke*DHAZ/DHAZPFS wherein
"Stroke" equals a standardized deflection at full span that theory and/or
typical response
would anticipate. DHAZ is that realized from Step 4A and DHAZPFS is the full
span
value continuously computed by regression analysis of all acquired results of
4A or by
other means.
[0147] 5B. Calculate a proportioned value DLAZP= Stroke*DLAZ/DLAZPFS wherein
"Stroke" equals a standardized deflection at full span that theory and/or
typical response
would anticipate. DLAZ is that realized from Step 4B and DLAZPFS is the full
span
value continuously computed by regression analysis of all acquired results of
4B or by
other means.
[0148] 6. Calculate the Output = DLAZP-DHAZP in inches of deflection, which is
now
continuously compensated to eliminate undesired sensor influences of spring
rate and
effective area as they might occur.
[0149] 7. This Output can now be multiplied by an appropriate factor, to
obtain desired
units of measure.
[0150]At every acquisition of the output, there is now available the present
actual zero-
point value of each acquisition.
[0151]In another embodiment, an alternative compensation process is provided,
comprising:
[0152]1. Acquire DH output of high side sensor in response to PH and all
influences.
-42-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
[0153] 2. Subtract the zero-point value of the high side sensor from the value
of DH just
acquired, thus producing a value of DHZ.
[0154] 3. Acquire DL output of low side sensor in response to PH and all
influences.
[0155] 4. Subtract the zero-point value of the low side sensor from the value
of DL just
acquired, thus producing a value of DLZ.
[0156] 5. From the values of DHZ determine the negative gain from the full
span value
minus the zero-point value divided by the full span value of PH.
[0157]6. From the values of DLZ determine the gain from the full span value
minus the
zero-point value divided by the full span value of PH.
[0158]7. Compensate the gain of the low side by multiplying all values by the
ratio of the
low side gain divided by the high side gain producing a value of DHZG.
[0159] 8. The values of low side and high side compensated for zero-point and
gain, can
now be processed as shown in initial compensation process to provide output in
desired
units of measure.
[0160]FIG. 10 is a schematic diagram illustrating one embodiment of a method
100 of
compensating for undesired influences in a pressure transmitter according to
aspects of
the present disclosure. The method 100 comprises acquiring deflection signals
from high
and low pressure sensors, as shown at 102. The deflection signals DH and DL
are
acquired in response to an applied pressure PH, as well as other influences
(e.g., DT, DP,
HsgH, HsgL, CH, CL, BCH and BCL as discussed above). The method 100 further
-43-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
comprises computing an average value of the deflection signals DH and DL, as
shown at
104. The resulting signal is DA = (DH+DL)/2. The method 100 further comprises
generating normalized deflection signals as shown at 106, so as to equalize
the slopes as
was shown and discussed in relation to FIG. 9B. Generating the normalized
deflection
signals may include subtracting the average value DA of the deflection signals
from each
of the deflection signals DH and DL. The normalized deflection signal for the
high side is
computed as DHA = DH-DA, and the normalized deflection signal for the low side
is
computed as DLA = DL-DA.
[0161]The method 100 further comprises generating offset-corrected normalized
deflection signals as shown at 108, so as to eliminate the offsets as shown
and discussed
in relation to FIG. 9C. Generating offset-corrected normalized deflection
signals may
comprise subtracting zero-point offsets from the normalized deflection
signals. For
example, an offset-corrected normalized deflection signal for the high side
may be
computed as DHAZ = DHA-BHA, as discussed above. Similarly, an offset-corrected
normalized deflection signal for the low side may be computed as DLAZ = DLA-
BLA.
The zero offset values BLA and BHA may be obtained, for example, from an
initial
calibration. In other embodiments, the zero offset values may be obtained
based on
regression analysis of previously obtained signals from each of the high and
low pressure
sensors.
[0162]The method 100 further comprises scaling the offset-corrected normalized
deflection signals as shown at 110. Scaling the offset-corrected normalized
deflection
signals may comprise multiplying the offset-corrected normalized deflection
signals by
compensation scaling factors. For example, the scaled offset-corrected
normalized
-44-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
deflection signal DHAZP for the high side may be obtained by multiplying DHAZ
by a
first compensation scaling factor. The scaled offset-corrected normalized
deflection
signal DLAZP for the low side may be obtained by multiplying DLAZ by a second
compensation scaling factor. In one embodiment, the first compensation scaling
factor
may be proportional to a predefined standard deflection associated with the
high-pressure
sensor, and may be inversely proportional to a full span deflection associated
with the
high pressure sensor obtained via regression analysis of previously obtained
signals from
the high-pressure sensor. In one embodiment, the second compensation scaling
factor
may be proportional to a predefined standard deflection associated with the
low-pressure
sensor and may be inversely proportional to a full span deflection associated
with the
low-pressure sensor obtained via regression analysis of previously obtained
signals from
the low-pressure sensor.
[0163] The method 100 further comprises deriving a compensated differential
pressure
output as shown at 112. The output may be obtained by subtracting the high
side scaled
offset-corrected normalized deflection signal from the low side scaled offset-
corrected
normalized deflection signal, that is Output = DLAZP-DHAZP.
[0164] In some embodiments, the method 100 may comprise additional steps. For
example, the method 100 may further comprise obtaining the differential
pressure in a
desired unit, for example by multiplying the compensated differential pressure
by a
conversion factor.
[0165] In various embodiments disclosed herein, the deflections DHP and DLP,
produced by application of PH, are sensed by their respective flexible element
capacitive
-45-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
deflection sensing means. However, it is recognized that other types of
sensors for
sensing the deflection could be considered by those skilled in the art.
[0166] Various embodiments disclosed herein assure that any pressure due to
undesirable
influences is applied equally to the high side as well as the low side sensors
by means of
a construction having a common fill fluid. It is assured that the undesirable
influences
acting in a common mode are equally applied to both sensors.
[0167] The desired applied pressure is determined by obtaining the difference
between
the low side and the high side sensors. However, the high side sensor has a
portion of the
desired applied pressure in addition to the pressure of the undesirable
influences. The low
side sensor also has a portion of the desired applied pressure in addition to
the pressure of
the undesirable influences. The differential sensing of the low side and high
side sensors
thereby eliminates any contribution of the undesirable influences from
influencing the
desired applied pressure, only if the gain of the low side and high side
sensors are of
equal value and opposite sign.
[0168] The present disclosure recognizes that the gain of the low side and
high side
sensors cannot be assured of being identical due to manufacturing limitations.
However,
this issue is resolved with an innovative concept for compensating the
absolute gain of
the low side sensor to equal that of the high side sensor.
[0169] The deflections DH being acquired are composed of the desired pressure
inputs
DHP and undesired influences from process temperature DTH, ambient temperature
DTA, process pressure DTPH, over range ORH, distortion of the sensor enclosure
HsgH,
-46-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
changes due to bolting BCH and changes in spring rates or effective areas of
the high side
DKAH, while in the steady or the dynamic state.
[0170] The deflections DL being acquired are composed of the desired pressure
inputs
DLP and undesired influences from process temperature DTL, ambient temperature
DTA, process pressure DTPL, over range ORL, distortion of the sensor enclosure
HsgL,
changes due to bolting BCL and changes in spring rates or effective areas of
the low-side
DKAL, while in the steady or the dynamic state.
[0171] The compensation is initiated by deflections DH and DL being averaged
to
produce a common value DA at each position sensed. This value DA is subtracted
from
each of the sensed deflections of DH and DL for all values within the span
producing a
linear relationship in DHA and DLA having equal gain of opposite polarity and
equal
values at zero value which may be offset.
[0172] At this stage of the compensation, both plots are a mirror image of
equal absolute
value about the PH axis having a positive gain for the low side and a negative
gain for the
high side, as shown and discussed in relation with FIG. 9B. Although the
greater portion
of common mode undesirable influences of low side or high side have now been
rejected,
there can be a residual influence due to gain differences prior to achieving
equal slopes
with opposite polarity. So, prior to finalizing the output, these undesirable
minimum
residual values of DH such as DHP, DTH, DPH, HsgH, BCH and CH are removed from
the values of DHA as well as DLP, DTL, DPL, HsgL, BCL and CL are removed from
values of DLA.
-47-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
[0173] These minimal offsets or "zero-shifts" are easily removed by
subtracting any
residual "zero shift values" that might exist in any of the values of DHA and
DLA, as
determined by regression analysis or other means, thus producing the plots of
DHAZ and
DLAZ with equal value but opposing polarity and having no zero-offset value,
as shown
and discussed in relation with FIG. 9C.
[0174] Additionally, an innovative means of eliminating the difference in
response of the
dual sensors induces a constant full span value of deflection "Stroke" of the
output, and
the values of DHAZ and DLAZ are scaled to produce a proportional output of
DHAZP
and DLAZP. This scaling is achieved by proportioning each value of DLAZ by a
term
defined by the specific value of deflection multiplied by "Stroke", divided by
the full
span value of DLAZFS. Similarly, scaling is achieved by proportioning each
value of
DHAZ by a term defined by the specific value of deflection multiplied by
"Stroke",
divided by the full span value of DHAZFS. This proportioning provides a
consistent full
span value of the "Output" that eliminates calibration changes due to
effective area and
changes of spring rate of the sensor in an ongoing manner into the future.
[0175] The single fill fluid dual sensor concept assures influences of DTL,
DTH, DPL,
DPH are equally applied to each of the flexible element assemblies. When
combined with
the disclosed compensation concept of the flexible element assemblies, there
is an
assurance of the compensation in an on-going manner of all undesirable
performance
influences from process or ambient temperature, or process pressure (DH, DPH,
DTL and
DPL) while in the steady or the dynamic state, as well as changes in
calibration due to
changes in the effective areas or changes in spring rates of the non-reference
sensor,
-48-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
influences of housing distortion HsgH, BCH, BCL and HsgL and the reference
positions
of sensors CH and CL.
[0176]In some embodiments, the above methods for compensating for undesirable
influences in a passive transmitter can be implemented on a computer. By way
of
example, FIG. 11 schematically depicts an example of a computing device 200
that can
be employed to implement compensation methods according to the present
teachings.
The computing device 200 includes a processor 202, at least one random access
memory
(RAM) module 204, a permanent memory 206, and a data acquisition interface 208
for
receiving data from a differential transmitter, e.g., deflection data
associated with the
flexible assemblies. A bus 210 allows communication between the processor and
various
components of the computing device. In some embodiments, instructions for
implementing compensation methods according to the present teachings can be
stored in
the permanent memory, and can be loaded into the RAM module for operating on
the
data received from a differential sensor in accordance with the present
teachings.
[0177]The processor 202 can be any suitable processor available in the art.
The processor
202 can be configured to carry out various functions described herein. These
functions
can be carried out and implemented by any suitable computer system and/or in
digital
circuitry or computer hardware. The processor 202 can implement and/or control
the
various functions and methods described herein. The processor 202 can be
connected to a
permanent memory 206. The processor 202 and the permanent memory 206 can be
included in or supplemented by special purpose logic circuitry.
-49-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
[0178] The processor 202 can include a central processing unit (CPU, not
shown) that
includes processing circuitry configured to manipulate and execute various
instructions.
For example, the processor 202 can be a general and/or special purpose
microprocessor
and any one or more processors of any kind of digital computer. Generally, the
processor
202 can be configured to receive instructions and data from a memory module
(e.g., a
read-only memory or a random access memory or both) and execute the
instructions.
The instructions and other data can be stored in the memory.
[0179] The permanent memory 206 can be any form of non-volatile memory
included in
machine-readable storage devices suitable for embodying data and computer
program
instructions. For example, the permanent memory 206 can be a magnetic disk
(e.g.,
internal or removable disks), magneto-optical disk, one or more of a
semiconductor
memory device (e.g., EPROM or EEPROM), flash memory, CD-ROM, and/or DVD-
ROM disks.
[0180]Various embodiments disclosed herein can be implemented in digital
electronic
circuitry or in computer hardware that executes software, firmware, or
combinations
thereof. The implementation can be as a computer program product, for example
a
computer program tangibly embodied in a non-transitory machine-readable
storage
device, for execution by, or to control the operation of, data processing
apparatus, for
example a computer, a programmable processor, or multiple computers. In some
embodiments, transmission and reception of data, information, and instructions
can occur
over the communications network.
-50-
CA 03117915 2021-04-27
WO 2020/072911 PCT/US2019/054710
[0181] Accordingly, embodiments disclosed herein provide a higher level of
performance
that does not exist in pressure transmitters.
[0182] The present disclosure is not to be limited in terms of the particular
embodiments
described in this application, which are intended as illustrations of various
aspects. Many
modifications and variations can be made without departing from its spirit and
scope, as
will be apparent to those skilled in the art. Functionally equivalent methods
and
apparatuses within the scope of the disclosure, in addition to those
enumerated herein,
will be apparent to those skilled in the art from the foregoing descriptions.
Such
modifications and variations are intended to fall within the scope of the
appended claims.
It is also to be understood that the terminology used herein, is for the
purpose of
describing particular embodiments only, and not intended to be limiting.
-51-
