Abstrict A flow meter pickoff assembly for nulling a flow meter zero offset
is provided. The flow meter pickoff assembly includes a mounting
device affixed to a first flow meter portion of a flow meter and
a first pickoff sensor half adjustably affixed to the mounting device
and configured to interact with a second pickoff sensor half affixed
to a second flow meter portion. At least one relative angle of the
first pickoff sensor half in relation to the second pickoff sensor
half can be adjusted by adjusting the first pickoff sensor half
to the mounting device according to at least one adjustment axis.
The flow meter pickoff assembly further includes an adjustment means
for enabling the first pickoff sensor half to adjust with respect
to the mounting device along the at least one adjustment axis in
order to adjust the at least one relative angle.
Claims We claim:
1. A flow meter pickoff assembly for nulling a flow meter zero
offset, the flow meter pickoff assembly comprising: a mounting device
affixed to a first flow meter portion of a flow meter; a first pickoff
sensor half adjustably affixed to the mounting device and configured
to interact with a second pickoff sensor half affixed to a second
flow meter portion, wherein at least one relative angle of the first
pickoff sensor half in relation to the second pickoff sensor half
can be adjusted by adjusting the first pickoff sensor half to the
mounting device according to at least one adjustment axis; and an
adjustment means for enabling the first pickoff sensor half to adjust
with respect to the mounting device along the at least one adjustment
axis in order to adjust the at least one relative angle.
2. The flow meter pickoff assembly of claim 1 wherein the first
pickoff sensor half is adjustably affixed to the mounting device
by one or more threaded fasteners.
3. The flow meter pickoff assembly of claim 1 wherein the adjustment
means comprises a portion of the first pickoff sensor half.
4. The flow meter pickoff assembly of claim 1 wherein the adjustment
means comprises a portion of the mounting device.
5. The flow meter pickoff assembly of claim 1 wherein the at least
one relative angle comprises two relative angles and wherein an
orientation of the first pickoff sensor half can be adjusted relative
to the mounting device according to two adjustment axes.
6. The flow meter pickoff assembly of claim 1 with the adjustment
means comprising a protrusion positioned between the first pickoff
sensor half and the mounting device.
7. The flow meter pickoff assembly of claim 1 with the adjustment
means comprising an at least partially elongated ridge positioned
between the first pickoff sensor half and the mounting device.
8. The flow meter pickoff assembly of claim 1 with the adjustment
means comprising a spacer positioned between the first pickoff sensor
half and the mounting device.
9. The flow meter pickoff assembly of claim 1 with the adjustment
means comprising a spacer positioned between the first pickoff sensor
half and the mounting device and wherein the spacer is formed of
an electrically non-conductive material.
10. The flow meter pickoff assembly of claim 1 wherein the adjustment
means is substantially compressible.
11. The flow meter pickoff assembly of claim 1 wherein the adjustment
means comprises a deformable spacing shape.
12. The flow meter pickoff assembly of claim 1 wherein the adjustment
means comprises a deformable tab.
13. The flow meter pickoff assembly of claim 1 wherein the adjustment
means comprises a plurality of spacers.
14. The flow meter pickoff assembly of claim 1 wherein the adjustment
means comprises a one or more spacers and a projection.
15. The flow meter pickoff assembly of claim 1 wherein the adjustment
means comprises one or more springs.
16. The flow meter pickoff assembly of claim 1 wherein the adjustment
means comprises a projection and at least one spring.
17. A flow meter adjustment method for nulling a flow meter zero
offset, the method comprising: affixing a mounting device to a first
flow meter portion of a flow meter; adjustably affixing a first
pickoff sensor half to the mounting device, with the first pickoff
sensor half being configured to interact with a second pickoff sensor
half affixed to a second flow meter portion, wherein at least one
relative angle of the first pickoff sensor half in relation to the
second pickoff sensor half can be adjusted by adjusting the first
pickoff sensor half to the mounting device according to at least
one adjustment axis; and providing an adjustment means for enabling
the first pickoff sensor half to adjust with respect to the mounting
device along the at least one adjustment axis in order to adjust
the at least one relative angle.
18. The method of claim 17 wherein the first pickoff sensor half
is adjustably affixed to the mounting device by one or more threaded
fasteners.
19. The method of claim 17 wherein the adjustment means comprises
a portion of the first pickoff sensor half.
20. The method of claim 17 wherein the adjustment means comprises
a portion of the mounting device.
21. The method of claim 17 wherein the at least one relative angle
comprises two relative angles and wherein an orientation of the
first pickoff sensor half can be adjusted relative to the mounting
device according to two adjustment axes.
22. The method of claim 17 with the adjustment means comprising
a protrusion positioned between the first pickoff sensor half and
the mounting device.
23. The method of claim 17 with the adjustment means comprising
an at least partially elongated ridge positioned between the first
pickoff sensor half and the mounting device.
24. The method of claim 17 with the adjustment means comprising
a spacer positioned between the first pickoff sensor half and the
mounting device.
25. The method of claim 17 with the adjustment means comprising
a spacer positioned between the first pickoff sensor half and the
mounting device and wherein the spacer is formed of an electrically
non-conductive material.
26. The method of claim 17 wherein the adjustment means is substantially
compressible.
27. The method of claim 17 wherein the adjustment means comprises
a deformable spacing shape.
28. The method of claim 17 wherein the adjustment means comprises
a deformable tab.
29. The method of claim 17 wherein the adjustment means comprises
a plurality of spacers.
30. The method of claim 17 wherein the adjustment means comprises
a one or more spacers and a projection.
31. The method of claim 17 wherein the adjustment means comprises
one or more springs.
32. The method of claim 17 wherein the adjustment means comprises
a projection and at least one spring.
Description BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a flow meter, and more
specifically to a flow meter pickoff assembly and flow meter pickoff
adjustment method for nulling a flow meter zero offset.
[0003] 2. Statement of the Problem
[0004] It is known to use Coriolis mass flow meters to measure
mass flow and other information of materials flowing through a pipeline
as disclosed in U.S. Pat. No. 4491025 issued to J. E. Smith, et
al. of Jan. 1 1985 and Re. 31450 to J. E. Smith of Feb. 11 1982.
These flow meters have one or more flow tubes of different configurations.
Each conduit configuration may be viewed as having a set of natural
vibration modes including, for example, simple bending, torsional,
radial and coupled modes. In a typical Coriolis mass flow measurement
application, a conduit configuration is excited in one or more vibration
modes as a material flows through the conduit, and motion of the
conduit is measured at points spaced along the conduit. The vibrational
modes of the material filled systems are defined in part by the
combined mass of the flow tubes and the material within the flow
tubes.
[0005] When there is no material flowing through the flow meter,
all points along a flow tube oscillate with an identical phase.
As a material begins to flow through the flow tube, Coriolis forces
cause each point along the flow tube to have a different phase with
respect to other points along the flow tube. The phase on the inlet
side of the flow tube lags the driver, while the phase on the outlet
side leads the driver. Sensors are placed at different points on
the flow tube to produce sinusoidal signals representative of the
motion of the flow tube at the different points. A phase difference
of the signals received from the sensors is calculated in units
of time. The phase difference between the sensor signals is proportional
to the mass flow rate of the material flowing through the flow tube
or flow tubes.
[0006] However, there can be inaccuracy in this phase difference.
One source of error can come from imperfections in the flowtube
apparatus. Another source of error can come from improperly aligned
sensor components. Yet another source of error can come from variability
in the meter electronics.
[0007] One way of detecting inaccuracy in the flow meter is by
vibrating the empty flowtube apparatus and measuring the resulting
phase difference. This phase difference in the flowtube apparatus,
such as for air, for example, is termed a zero offset. Ideally,
the zero offset will be zero for a no flow condition (i.e., for
air). However, this is usually not the case. Multiple manufacturing
tolerances, material variations, improper sensor alignments, and
electronic component tolerances can combine to produce a zero offset
ranging away from ideal. In addition, the zero offset can be affected
by temperature. Unfortunately, the greater the zero offset, the
more the zero offset is likely to be affected by temperature.
[0008] Although the FCF is currently compensated for these temperature
effects, the zero offset is typically not adjustable in a prior
art flow meter and the zero offset cannot be mechanically compensated.
In the prior art, the problem is typically approached by the user
of the flow meter being required to re-zero the flow meter when
the temperature changes by more than 20 degrees Centigrade.
[0009] Significant work has been done over the years relating to
the reduction and/or elimination of zero offset in Coriolis flow
meters. The prior art has taken two approaches. The first prior
art approach has been to minimize the zero offset of a flow meter
through small tolerances and rigorous manufacturing methods. The
second prior art approach has been to address the zero offset problem
through advanced signal processing, such as modal filtering, compensating
for residual flexibility, etc. However, both prior art approaches
are costly, complex, and not satisfactorily accurate and successful.
SUMMARY OF THE SOLUTION
[0010] The above and other problems are solved and an advance in
the art is achieved through the provision of a flow meter and method
for nulling a flow meter zero offset.
[0011] A flow meter pickoff assembly for nulling a flow meter zero
offset is provided according to an embodiment of the invention.
The flow meter pickoff assembly comprises a mounting device affixed
to a first flow meter portion of a flow meter and a first pickoff
sensor half adjustably affixed to the mounting device and configured
to interact with a second pickoff sensor half affixed to a second
flow meter portion. At least one relative angle of the first pickoff
sensor half in relation to the second pickoff sensor half can be
adjusted by adjusting the first pickoff sensor half to the mounting
device according to at least one adjustment axis. The flow meter
pickoff assembly further comprises an adjustment means for enabling
the first pickoff sensor half to adjust with respect to the mounting
device along the at least one adjustment axis in order to adjust
the at least one relative angle.
[0012] A flow meter pickoff adjustment method for nulling a flow
meter zero offset is provided according to an embodiment of the
invention. The method comprises affixing a mounting device to a
first flow meter portion of a flow meter and adjustably affixing
a first pickoff sensor half to the mounting device. The first pickoff
sensor half is configured to interact with a second pickoff sensor
half affixed to a second flow meter portion. At least one relative
angle of the first pickoff sensor half in relation to the second
pickoff sensor half can be adjusted by adjusting the first pickoff
sensor half to the mounting device according to at least one adjustment
axis. The method further comprises providing an adjustment means
for enabling the first pickoff sensor half to adjust with respect
to the mounting device along the at least one adjustment axis in
order to adjust the at least one relative angle.
DESCRIPTION OF THE DRAWINGS
[0013] The same reference number represents the same element on
all drawings. The drawings are not necessarily to scale.
[0014] FIG. 1 illustrates a Coriolis flow meter comprising a flow
meter assembly and meter electronics;
[0015] FIG. 2 is a chart of some of the factors that affect a flow
meter zero offset;
[0016] FIG. 3 shows a flow meter pickoff assembly according to
an embodiment of the invention;
[0017] FIG. 4 shows a flow meter pickoff assembly according to
another embodiment of the invention;
[0018] FIG. 5 shows a spacer according to an embodiment of the
invention;
[0019] FIG. 6 shows a spacer according to an embodiment of the
invention;
[0020] FIG. 7 is a chart of a flowtube apparatus without any zero
offset compensation (upper line) and a flowtube apparatus wherein
the zero offset is compensated for by adjusting the relative angle
.theta. (lower line);
[0021] FIG. 8 shows a spacer according to another embodiment of
the invention;
[0022] FIG. 9 shows a flow meter pickoff assembly wherein the adjustment
means comprises a rib or protrusion that can be moved with respect
to the mounting device;
[0023] FIG. 10 shows a flow meter pickoff assembly wherein the
adjustment means comprises a deformable spacing shape;
[0024] FIG. 11 shows a flow meter pickoff assembly wherein the
adjustment means comprises another embodiment of a deformable spacing
shape;
[0025] FIG. 12 shows a flow meter pickoff assembly wherein the
adjustment means comprises a deformable tab;
[0026] FIG. 13 shows a flow meter pickoff assembly wherein the
adjustment means comprises a plurality of spacers;
[0027] FIG. 14 shows a flow meter pickoff assembly wherein the
adjustment means comprises spacers and a projection such as a rib
or bump;
[0028] FIG. 15 shows a flow meter pickoff assembly wherein the
adjustment means comprises one or more springs; and
[0029] FIG. 16 shows a flow meter pickoff assembly wherein the
adjustment means comprises a projection, such as a rib or bump,
and at least one spring.
DETAILED DESCRIPTION OF THE INVENTION
[0030] FIGS. 1-16 and the following description depict specific
examples to teach those skilled in the art how to make and use the
best mode of the invention. For the purpose of teaching inventive
principles, some conventional aspects have been simplified or omitted.
Those skilled in the art will appreciate variations from these examples
that fall within the scope of the invention. Those skilled in the
art will appreciate that the features described below can be combined
in various ways to form multiple variations of the invention. As
a result, the invention is not limited to the specific examples
described below, but only by the claims and their equivalents.
[0031] FIG. 1 illustrates a Coriolis flow meter 5 comprising a
flow meter assembly 10 and meter electronics 20. Meter electronics
20 is connected to meter assembly 10 via leads 100 to provide density,
mass flow rate, volume flow rate, totalized mass flow and other
information over path 26. Flow meter assembly 10 includes a pair
of flanges 101 and 101', manifold 102 and flow tubes 103A and 103B.
Connected to flow tubes 103A and 103B are driver 104 and pick-off
sensors 105 and 105'. Brace bars 106 and 106' serve to define the
axes W and W' about which each flow tube 103A and 103B oscillates.
[0032] When flow meter assembly 10 is inserted into a pipeline
system (not shown) which carries the material being measured, material
enters flow meter assembly 10 through flange 101 passes through
manifold 102 where the material is directed to enter flow tubes
103A and 103B, flows through flow tubes 103A and 103B, and back
into manifold 102 where it exits meter assembly 10 through flange
101'.
[0033] Flow tubes 103A and 103B are selected and appropriately
mounted to manifold 102 so as to have substantially the same mass
distribution, moment of inertia, and elastic modulus about bending
axes W-W and W'-W' respectively. The flow tubes extend outwardly
from the manifold in an essentially parallel fashion.
[0034] Flow tubes 103A-B are driven by driver 104 in opposite directions
about their respective bending axes W and W' and at what is termed
the first out of phase bending mode of the flow meter. Driver 104
may comprise one of many well known arrangements, such as a magnet
mounted to flow tube 103A and an opposing coil mounted to flow tube
103B. An alternating current is passed through the opposing coil
to cause both tubes to oscillate. A suitable drive signal is applied
by meter electronics 20 via lead 110 to driver 104. The force pattern
generated by driver 104 is fixed over the life of the sensor (i.e.,
Cp is constant). Driver 104 generates a constant force and the pick-offs
105 or 105' measure the tube displacement.
[0035] Meter electronics 20 receives the right and left velocity
signals appearing on leads 111 and 111', respectively and the tube
displacement over lead 112. Meter electronics 20 produces the drive
signal on lead 110 which causes driver 104 to oscillate the flow
tubes 103A and 103B. The present invention as described herein can
produce multiple drive signals from multiple drivers. Meter electronics
20 processes left and right velocity signals and a tube displacement
signal to compute mass flow rate and provide the validation system
of the present invention. Path 26 provides an input and an output
means that allows meter electronics 20 to interface with an operator.
[0036] FIG. 2 is a chart of some of the factors that affect a flow
meter zero offset. The zero offset can be affected by the flowtube
geometry and manufacturing tolerances (depicted by the tube zero
arrow), variations in the attachment of the magnet base to a flowtube
(depicted by the base zero arrow), variations in the magnet attachment
angle to the flowtube (depicted by the magnet attach zero arrow),
and flexing/changes in a mounting glue (depicted by the glue zero
arrow) due to changes in an ambient temperature, pressure, etc.
These various factors in some cases will cancel each other out to
some degree, but alternately can add together to produce a large
zero offset value. As previously discussed, the approach in the
prior art has been to measure the zero offset at the factory and
simply reject flow meters that have a zero offset that is greater
than an acceptable threshold. This is costly and inefficient.
[0037] FIG. 3 shows a flow meter pickoff assembly 105 according
to an embodiment of the invention. The flow meter pickoff assembly
105 includes a first pickoff sensor half 110 and a second pickoff
sensor half 140. The first pickoff sensor half 110 can be affixed
to a first flow meter portion 150 such as a flowtube 150 of a flow
meter apparatus, for example. The first pickoff sensor half 110
can be affixed to the first flow meter portion 150 by a mounting
device 151 such as a bracket, a flange, a U-bolt clamp, etc. The
mounting device 151 can be affixed to the first flow meter portion
150 by a weld, glue, clamping, etc.
[0038] The second pickoff sensor half 140 can likewise be affixed
to a second flow meter portion 152. In the case of a single flowtube
flow meter, the second pickoff sensor half 140 can be affixed to
a second flow meter portion 152 such as a flange, casing, brace
bar, etc. Alternatively, it should be understood that the pickoff
halves can be swapped and the mounting device 151 can be affixed
to the second flow meter portion 152.
[0039] In order to compensate for or to eliminate a zero offset
characteristic of the flow meter, it is desirable to be able to
adjust at least a relative angle .theta. between the first pickoff
sensor half 110 and the second pickoff sensor half 140. For example,
the relative angle .theta. may need to be eliminated in order to
minimize or eliminate the zero offset. In the past, the relative
angle .theta. was minimized only through rigorous manufacturing
and quality control procedures. However, according to the invention,
the first pickoff sensor half 110 can be moved and therefore at
least the relative angle .theta. can be adjusted. The relative angle
.theta. can be adjusted while monitoring or measuring the zero offset.
The zero offset therefore can be accurately compensated for on an
individual meter basis, under test conditions.
[0040] The first pickoff sensor half 110 in the embodiment shown
includes a sensor portion 112 affixed to a base 114 and an adjustment
means 116. The sensor portion 112 can comprise a magnet coil. It
should be understood that although the sensor portion 112 is shown
as a magnet coil and the second pickoff sensor half 140 is shown
as a magnet (such as a permanent magnet), the first and second pickoff
sensor halves 110 and 140 can be interchanged.
[0041] The adjustment means 116 is positioned between the first
pickoff sensor half 110 and the mounting device 151. The adjustment
means 116 can be clamped between the two portions, can be part of
the base 114 or can be part of the mounting device 151. The first
pickoff sensor half 110 is removably and adjustably affixed to the
mounting device 151 by one or more fasteners 118. Through the combination
of the adjustment means 116 and the one or more fasteners 118 the
orientation of the first pickoff sensor half 110 can be adjusted
in relation to the mounting device 151. The orientation adjustment
is accomplished in one embodiment by screwing the fasteners 118
into or out of the mounting device 151 in order to change at least
the relative angle .theta..
[0042] The adjustment means 116 in one embodiment comprises a protrusion.
The adjustment means 116 can comprise a rib, ridge, or other elongated
shape extending from the base 114. The adjustment means 116 can
be formed of a material having a sufficient hardness wherein the
adjustment means 116 does not deform or shift under load of adjustment.
In addition, the hardness can ensure that the pickoff assembly alignment
and spacing does not change over time. In one embodiment, the adjustment
means 116 comprises a length of dowel, such as a metal dowel. The
dowel can be chosen according to a desired cost and tolerance. A
small diameter metal dowel can provide a sufficient material hardness
and can result in minimal lateral movement at time of adjustment.
The adjustment means 116 can extend partially or fully across the
base 114 (see FIG. 5) or can extend partially or fully across the
mounting device 151. Such an elongated shape generally permits motion
of the base 114 along only one axis, especially if two fasteners
118 are used, as shown. The axis of motion in this embodiment extends
vertically out of the figure, parallel to the adjustment means 116
and allows the relative angle .theta. to be adjusted.
[0043] In another embodiment, the adjustment means 116 comprises
a substantially semi-hemispherical bump, a substantially conical
bump, a substantially pyramidal bump, etc. In these embodiments,
the first pickoff sensor half 110 can be adjusted in two dimensions,
i.e., along a vertical axis Y and along a horizontal axis X that
generates the relative angle .theta. (see FIG. 6). Three or more
fasteners 118 can be used to affix the base 114 to the mounting
device 151 in these embodiments and therefore allow orientation
adjustment along the two adjustment axes.
[0044] The adjustment means 116 in any of the various embodiments
can be formed of any material. In one embodiment, the adjustment
means 116 comprises part of the base 114 and is formed of the same
material. In another embodiment, the adjustment means 116 is formed
of a different material than the base 114 and is bonded to the base
114 is cast into the base 114 etc. In one alternative embodiment,
the adjustment means 116 is similarly formed on or as part of the
mounting device 151. In another alternative embodiment, the adjustment
means 116 is a separate component that is merely clamped between
the first pickoff sensor portion 110 and the mounting device 151.
[0045] In one embodiment, the adjustment means 116 is formed of
an at least partially compressible or deformable material. As a
result, the distance between the base 114 and the mounting device
151 can be modified (i.e., the adjustment means 116 can be squeezed
down if the first pickoff sensor half 110 is to be moved closer
to the mounting device 151). In addition, the deformation of the
adjustment means 116 can also allow the orientation of the first
pickoff sensor half 110 to be adjusted.
[0046] FIG. 4 shows a flow meter pickoff assembly 405 according
to another embodiment of the invention. In this embodiment, the
flow meter pickoff assembly 405 further includes a spacer 404 positioned
between the first pickoff sensor half 110 and the mounting device
151. The spacer 404 has a thickness and includes an adjustment means
416. The spacer 404 therefore can be used with a conventional first
pickoff sensor half 110 and enables the orientation of the conventional
first pickoff sensor half 110 to be adjusted in relation to the
mounting device 151 as previously discussed. The spacer 404 in
one embodiment is formed of an electrically non-conductive material
and therefore electrically isolates the first pickoff sensor half
110 from the first flow meter portion 150. The spacer 404 can include
fastener apertures 408 that are used to hold the spacer 404 between
the first pickoff sensor half 110 and the mounting device 151. Alternatively,
in another embodiment the spacer 404 fits between the fasteners
118 and is clamped between the first pickoff sensor half 110 and
the mounting device 151.
[0047] FIG. 5 shows a spacer 404 according to an embodiment of
the invention. In this embodiment, the spacer 404 includes a body
401 two fastener apertures 408 and a transverse, elongated adjustment
means 416 in the shape of a rib. The adjustment means 416 enables
the spacer 404 to pivot along only one adjustment axis X (see figure).
The spacer 404 can therefore be used to adjust one angle, i.e.,
the relative angle .theta. shown in FIGS. 3 and 4. The spacer 404
in one embodiment is formed of a material that provides a sufficient
stiffness so that the spacer 404 does not deflect or deform during
adjustment so that the first pickoff sensor half 110 cannot improperly
or undesirably contact the second pickoff sensor half 140.
[0048] FIG. 6 shows a spacer 604 according to an embodiment of
the invention. In this embodiment, the spacer 604 includes a body
601 three or more fastener apertures 608 and a bump-type adjustment
means 616. The bump-type adjustment means 616 enables the spacer
604 to pivot according to two adjustment axes X and Y. The spacer
604 can therefore be used to fully adjust the orientation of the
first pickoff sensor half 110 in relation to the mounting device
151.
[0049] FIG. 7 is a chart of a flowtube apparatus without any zero
offset compensation (upper line) and a flowtube apparatus wherein
the zero offset is compensated for by adjusting the relative angle
.theta. (lower line). It can be seen from the graph that by compensating
for the zero offset, the zero offset changes very little over the
measured temperature range. In contrast, the upper line, having
no zero offset compensation, shows how the zero offset can vary
an undesirable amount over a particular temperature range, affecting
the accuracy of the flow meter. This temperature range is generally
very small for traditional metal flow meters. The data shown in
the figure is for a plastic flow meter, for which the zero offset
temperature effect is approximately 100 times the temperature zero
offset for a metal flow meter.
[0050] FIG. 8 shows a spacer 804 according to another embodiment
of the invention. In this embodiment, the adjustment means 816 comprises
a substantially sharp-edged rib and has a substantially triangular
or non-circular cross-section. The cross-section can alternatively
be rectangular or even irregular in shape. Alternatively, the adjustment
means 816 can be formed of bevels, curved faces, or angled faces
formed on the body 801. As was previously discussed, the adjustment
means 816 can comprise a separate element bonded to or formed in
the body 801 or can comprise a portion of the spacer 804.
[0051] FIG. 9 shows a flow meter pickoff assembly 905 wherein the
adjustment means 116 comprises a rib or protrusion that can be moved
with respect to the mounting device 151. As a result, two or more
fasteners 118 can clamp the first pickoff sensor half 110 to the
mounting device 151 at various orientations.
[0052] FIG. 10 shows a flow meter pickoff assembly 1005 wherein
the adjustment means 116 comprises a deformable spacing shape 116.
The deformable spacing shape 116 can be compressed by two or more
fasteners 118 in order to achieve a desired orientation of the first
pickoff sensor half 110. The deformation can occur along one or
two adjustment axes, depending on the number and location of the
fasteners 118. The deformable spacing shape 116 can optionally be
formed of a resilient, deformable material.
[0053] FIG. 11 shows a flow meter pickoff assembly 1105 wherein
the adjustment means 116 comprises another embodiment of a deformable
spacing shape 116. The deformable spacing shape 116 in this embodiment
comprises a resilient deformable material, and is formed in a curved
shape to facilitate a return to an original shape in the absence
of compression on the deformable spacing shape 116. Other geometries
of the deformable spacing shape 116 are contemplated and included
within the scope of the accompanying claims.
[0054] FIG. 12 shows a flow meter pickoff assembly 1205 wherein
the adjustment means 116 comprises a deformable tab 116. The deformable
tab 116 includes a portion 1216 that is welded or bonded to either
the mounting device 151 or to the first pickoff sensor half 110.
As a result, the deformation of the deformable tab 116 pivots around
the portion 1216. The deformable tab 116 can optionally be formed
of a resilient, deformable material.
[0055] FIG. 13 shows a flow meter pickoff assembly 1305 wherein
the adjustment means 116 comprises a plurality of spacers 116. The
spacers 116 can be selected and added to achieve a desired orientation
of the first pickoff sensor half 110. The spacers 116 can be of
any desired thickness. In addition, multiple different spacer thicknesses
can be used in order to achieve a desired spacing. In the embodiment
shown, the spacers 116 include an aperture that receives a fastener
118. As a result, through the use of two or more fasteners 118 and
associated spacers 116 the orientation of the first pickoff sensor
half 110 can be adjusted.
[0056] FIG. 14 shows a flow meter pickoff assembly 1405 wherein
the adjustment means 116 comprises spacers 116a and projection 116b
such as a rib or bump. In this embodiment, the spacers 116a can
be used to achieve a desired orientation of the first pickoff sensor
half 110 with respect to the rib or bump 116b (i.e., the relative
angle .theta. can be changed by adding or subtracting spacers 116a).
Alternatively, the projection 116b can be replaced by a deformable
shape or tab.
[0057] FIG. 15 shows a flow meter pickoff assembly 1505 wherein
the adjustment means 116 comprises one or more springs 116. The
one or more springs 116 are positioned between the first pickoff
sensor half 110 and the mounting device 151 such as straddling
a fastener 118. In this embodiment, the fasteners 118 can be used
to change the orientation of the first pickoff sensor half 110 against
the biasing forces provided by the springs 116. If three or more
fasteners 118 are employed, the first pickoff sensor half 110 can
be oriented along two adjustment axes.
[0058] FIG. 16 shows a flow meter pickoff assembly 1605 wherein
the adjustment means 116 comprises a projection 116a, such as a
rib or bump, and at least one spring 116b. The at least one spring
116b can be held in position by a corresponding fastener 118 passing
through the spring 116b. The first pickoff sensor half 110 can pivot
on the rib or bump 1116a, as controlled by the at least one spring
116b and the fasteners 118. Alternatively, the at least one spring
116b can be replaced by a deformable shape or tab.
[0059] It should be understood that other embodiments and variations
of the adjustment means are contemplated and included within the
scope of the invention and the accompanying claims.
[0060] The zero offset nulling according to the invention can be
implemented according to any of the embodiments in order to obtain
several advantages, if desired. The zero offset nulling according
to the invention provides a simple, low cost, and effective mechanical
nulling. The zero offset nulling of the flow meter enables the zero
offset to be compensated for or eliminated. The zero offset nulling
according to the invention, by compensating for or eliminating the
zero offset, makes the flow meter less sensitive to changes in temperature.
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