Abstrict An improved flow meter and sensor body therefor, the body having
a strain relief portion. A housing of the flow meter defines a fluid
flow passage and a sensor body opening. A sensor body mounting portion
is mounted to the housing. A sensor body sensor supporting portion
is in the fluid flow passage, and supports flow sensor transducers
in the fluid flow. The sensor body relief portion is intermediate
the sensor body mounting and supporting portions, in the sensor
body opening, and adapted to relieve induced strain from external
vibration, whereby the flow meter is substantially insensitive to
external vibration.
Claims What is claimed is:
1. An improved flow meter comprising:
a housing defining a fluid flow passage and a sensor body opening
which opens into the fluid flow passage; and
flow sensor means for sensing fluid flow in the flow passage and
providing a signal in relation to the fluid flow, the flow sensor
means being in the fluid flow passage; and
a sensor body having a mounting portion, a strain relief portion
and a flow sensor supporting portion, the mounting portion being
mounted to the housing external to the housing and the sensor supporting
portion being in the fluid flow passage and supporting the flow
sensor means, the strain relief portion being intermediate the mounting
portion and the sensor supporting portion, the strain relief portion
further being in the sensor body opening and adapted to relieve
induced strain of the sensor supporting portion from external vibration,
whereby the flow meter is substantially insensitive to external
vibration.
2. An improved flow meter as in claim 1 in which the sensor supporting
portion includes an enlarged area loosely fit in the sensor body
opening, to minimize coupling of vibration from the housing to the
flow sensor supporting portion.
3. An improved flow meter as in claim 2 in which the enlarged area
includes surfaces which blend with the contour of the housing to
create continuity in the contour of the housing at the sensor body
opening.
4. An improved flow meter as in claim 1 in which the sensor supporting
portion has a first stiffness and the strain relief portion has
a second stiffness, the second stiffness being substantially less
than the first stiffness.
5. An improved flow meter as in claim 1 in which the sensor supporting
portion has a first major outer dimension in a plane of vibration
and the strain relief portion has a second outer dimension in the
plane of vibration, the second outer dimension being substantially
less than the first outer dimension such that the strain relief
portion of the body is thin relative to the sensor supporting portion.
6. An improved flow meter as in claim 1 in which the sensor body
defines an internal passage for electrical circuitry from the mounting
portion to the sensor supporting portion.
7. An improved flow meter as in claim 1 in which the sensor body
mounting portion includes a section capping the sensor body opening.
8. In a flow meter having a housing defining a fluid flow passage
and a sensor body opening which opens into the fluid flow passage
and flow sensor means for sensing fluid flow in the flow passage
and providing a signal in relation to the fluid flow, the flow sensor
means being in the fluid flow passage, an improved sensor body having
a mounting portion adapted for mounting of the body to the housing
external to the housing, a sensor supporting portion adapted for
supporting the flow sensor means and for being in the fluid flow
passage and a strain relief portion intermediate the mounting portion
and the sensor supporting portion, the strain relief portion further
being adapted for being in the sensor body opening and the strain
relief portion adapted to relieve induced strain of the sensor supporting
portion caused by external vibration, whereby the flow meter is
substantially insensitive to external vibration.
Description BACKGROUND OF THE INVENTION
This invention relates to a volumetric flow meter, and more particularly,
to an improved vortex flow meter.
Volumetric flow meters such as vortex flow meters have employed
strain gauges, capacitors, piezoelectric disks and the like as flow
sensors. Meters of this type have often been sensitive to strain
induced by external vibration. The strain has reached the meters
through the piping in which the meters have been located, from vibration
sources such as wind, control valve turbulence, and reciprocating
machinery including compressors and pumps. Transmission of the vibration
to the flow sensors has caused strain in the sensors, resulting
in erroneous sensor outputs.
SUMMARY OF THE INVENTION
Thus, it is an object of the invention to significantly reduce
the vibration sensitivity of flow meters.
Another object is to accomplish the sensitivity reduction by actually
reducing the strain transmitted to the sensors, rather than electronically
conditioning the sensor signal, to permit the employment of simpler,
less expensive electronic circuitry.
Other objects are to accomplish the desired sensitivity reduction
with a structure which is compatible with existing flow meters,
economical of manufacture, reliable, and resistant to fatigue.
To accomplish these objects, this invention is, in principal aspect,
an improved flow meter, and an improved sensor body for a flow meter.
The sensor body has a mounting portion, a flow sensor supporting
portion and a strain relief portion. The strain relief portion is
preferably located intermediate the mounting portion and the sensor
supporting portion, and is adapted, as by reduction of stiffness,
to relieve induced strain of the sensor supporting portion.
These and other details, aspects, objects and advantages of the
invention are fully set forth in the detailed description, which
follows.
BRIEF DESCRIPTION OF THE DRAWING
The preferred embodiment of the invention is described below in
relation to the accompanying drawing. Briefly, the drawing includes
five figures, or FIGS., as follows:
FIG. 1 is a partially cut-away view of a flow transmitter including
a signal conditioner and flow meter, which incorporates the sensor
body of the preferred embodiment of the invention;
FIG. 2 is a side elevational view of the sensor body of the preferred
embodiment;
FIG. 3 is a front elevational view of the sensor body;
FIG. 4 is a front cross-sectional view of the sensor body; and
FIG. 5 is a cross-sectional view taken along line 5--5 of FIG.
2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1 the preferred embodiment of the invention
is both an improved flow meter 10 and an improved sensor body 12
which may also function as a vortex shedding bluff body. The sensor
body 12 is a part of the flow meter 10 which is joined by a signal
conditioner 14 to form a flow transmitter 16.
As most preferred, the meter 10 employs piezoelectric disks such
as disk 18 as its sensors. Further, as most preferred, the conditioner
14 is cantilevered atop the meter 10 by a bracket 20 and electrical
circuitry such as sensor leads 22 join the disks 18 and the conditioner
14. The leads 22 pass through an internal circuitry passage 24 in
the body 12 and inside a flexible bellows 26 to reach the conditioner
14.
Concentrating on the meter 10 and body 12 the meter 10 includes
a housing 27 of two flanges 28 30 and a central section 32. Two
mounting plates, or bosses, 34 36 are provided atop the section
32 for mounting of the sensor body 12. A sensor body opening 38
opens into the central fluid passage 40 within the section 32.
The sensor body 12 includes a mounting portion 42. The body 12
extends along a central axis 44 as shown in FIG. 2 and the mounting
portion 42 includes a flange 46 extending generally perpendicular
to the axis 44. The flange 46 provides two fastening areas 48 50
where fasteners such as the bolts 52 54 of FIG. 1 are employed
to mount and fasten the flange 46 and thereby the body 12 to the
mounting plates 34 36 and thereby the meter housing 27.
A cylindrical section 56 of the mounting portion 42 extends between
the plates 34 36 from the flange 46 to the upper surface of the
housing central section 32. When the body 12 is mounted, the section
56 caps the opening 38.
Below the section 56 the sensor body 12 includes a sensor supporting
portion 58 an intermediate, strain relief portion 60 and a bottom,
retained end 62. The portion 60 is intermediate the portions 42
58 in that it is between the portions 42 58. This intermediate
location is the preferred location, although it is believed other
locations may be possible.
The sensor supporting portion 58 is rectangular, as best shown
in FIG. 5. The portion 58 includes opposed sidewalls 64 66 and
endwalls 68 70. The sidewalls 64 66 define sensor receiving recesses
72 74. The circuitry passage 24 terminates at the recesses 72
74.
Adjacent the strain relief portion 60 the sensor supporting portion
58 includes an enlarged, generally cylindrical area 76. The opposed
bottom surfaces 78 80 of the area 76 above the endwalls 68 70
are concave, to blend with the contour of the inner wall of the
housing central section 32. As shown in FIG. 1 when the sensor
body 12 is properly located in the housing 27 the sensor supporting
portion 58 is in the central fluid passage 40 while the enlarged
area 76 loosely fits the opening 38 to protect the strain relief
portion 60 from fluid turbulence, and to create continuity in the
contour of the housing inner wall. Continuity eliminates disruption
of the Von Karman vortex street in the fluid passage 40. When the
sensor body 12 is properly located in the housing 27 the strain
relief portion 60 is thus within the opening 38.
The strain relief portion 60 is outwardly cylindrical, and as shown
in FIGS. 1 and 4 annular. The portion 60 is adapted to relieve
strain in the sensor supporting portion 58 from external vibration.
Surprisingly, bending moments induced on piping have been the cause
of strain on the flow sensors. The moments result in sensor body
deflections in the order of millionths of an inch. These deflections,
while nearly infintesimal, cause the sensor strain. The strain relief
portion 60 "absorbs" these deflections, leaving the portion
58 only insignificantly deflected.
To so absorb the deflections, the strain relief portion 60 has
a stiffness substantially less than that of the sensor supporting
portion 58. Thus, the portion 60 acts as a spring. Ideally, the
stiffness would be zero and the portion 60 would absorb all of the
deflections. In reality, the tolerable deflection of the portion
58 is established for the particular sensors in use, and the portion
60 configured to transmit no more than this deflection. Axial stresses,
hydrostatic stresses, operating temperature, material choice and
fatigue are also accommodated. Generally, a smaller circuitry opening
24 and, an axially longer and thinner portion 60 are preferred.
With a steel body 12 the following characteristics of the portion
60 have been found acceptable: for a pipe size ("size")
of one inch, a nominal outer diameter (OD) of 0.207 inches; a nominal
inner diameter (ID) of 0.125 inches, and a nominal length (L) of
0.6 inches; for a size of 11/2 inches, an OD of 0.308", an
ID of 0.188", and a L of 0.7"; for a size of 2 inches,
an OD of 0.36", an ID of 0.26", and a L of 0.7; for a
size of 3 inches, an OD of 0.44", an ID of 0.26", and
a L of 0.6"; for a size of 4 inches, an OD of 0.62"; an
ID of 0.5", and a L of 0.5"; and for a size of 6 inches,
an OD of 0.844", an ID of 0.624", and a L of 0.7".
Tolerances are OD +0.005", ID -0.005", and L +0.006".
As drawn, the outer dimension of the portion 60 is substantially
less than the outer dimensions of the portion 58. Also, as shown,
the strain relief portion 60 is cylindrical, but it will be understood
that other shapes may be utilized. Strain relief with such other
shapes may be accomplished by having the dimensions of the strain
relief portion 60 in the planes of vibration being substantially
less than the corresponding dimensions of the sensor supporting
portion 58 in the planes of vibration. For example, as shown in
FIG. 3 the width of end walls 68 70 is substantially greater than
the corresponding dimension of the strain relief portion 60.
The preferred embodiment is now described. As should be apparent,
a variety of changes could be made to the preferred embodiment,
without departing from the scope of the invention. Therefore, to
particularly point out and distinctly claim the subject matter regarded
as invention, the following claims conclude this specification.
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