Abstrict A dual sensor vortex flow meter providing fluid connections for
two sensors and containing isolation valves providing the further
capability of separate valve control of the fluid communication
to each of the dual sensors is herein disclosed. The vortex flow
meter is mounted onto a flow meter body having an existing sensor
cavity for housing a single sensor. The vortex flow meter is fitted
into the existing sensor cavity by means of a dummy-cast sensor.
On either side of the dummy sensor are apertures coupled to flow
passages that transmit the alternating differential pressure fluctuations
caused by the vortices from each side of the dummy sensor to the
corresponding sides of each of the dual sensors. The dual sensor
vortex flow meter may also include valves for controlling the process
flow transmission to each of the sensors.
Claims We claim:
1. A flow-metering apparatus of the vortex-shedding type comprising:
a) a flow-pipe section fluidly connected to a process flow, said
flow-pipe section having a single divided cavity for allowing communication
with the process flow, said single divided cavity forming a single
fluid connection to said process flow;
b) a vortex-generating body mounted in said flow-pipe section for
generating alternating differential pressure fluctuations;
c) a plurality of sensor elements, each of said sensor elements
having first and second sides, said first and second sides being
on opposite sides of said sensor element, each of said first and
second sides subjected independently to the alternating differential
pressure fluctuations from said single fluid connection;
d) a mounting support, removably mounted to said flow-pipe section,
housing said sensor elements and securing said sensor elements to
said flow-pipe section, said sensor elements removably mounted within
said mounting support, said sensor elements positioned spatially
apart from each other in said mounting support, said mounting support
having flow passages for transmitting the alternating differential
pressure fluctuations to said sensor elements, said flow passages
communicating with the process flow through said single divided
cavity;
e) electrical transmission means connected to said sensor elements
to conduct signals representative of said process flow; and
f) computation means connected to said electrical transmission
means, and removably mounted to said mounting support, for processing
said signals transmitted from said electrical transmission means
and producing electronic signals indicative of physical measurement
quantities of said process flow.
2. A flow-metering apparatus as in claim 1 wherein said mounting
support further comprises a flow divider positioned in said single
divided cavity of said flow-pipe to maintain differential flow through
said flow passages by dividing the cavity.
3. A flow-metering apparatus as in claim 1 wherein said sensor
elements comprise first and second sensor elements fluidly connected
to a single divided cavity, and
wherein said flow passages of said mounting support comprise a
first pair of flow passages for transmitting the alternating differential
pressure fluctuations to said first sensor element, and a second
pair of flow passages for transmitting the alternating differential
pressure fluctuations to said second sensor element,
said first pair of flow passages having a first high flow passage
and a first low flow passage, said first high flow passage transmitting
high pressure fluctuations of said alternating differential pressure
fluctuations to said first side of said first sensor element, and
said first low flow passage transmitting low pressure fluctuations
of said alternating differential pressure fluctuations to said second
side of said first sensor element, and
said second pair of flow passages having a second high flow passage
and a second low flow passage, said second high flow passage transmitting
high pressure fluctuations of said alternating differential pressure
fluctuations to said first side of said second sensor element, and
said second low flow passage transmitting low pressure fluctuations
of said alternating differential pressure fluctuations to said second
side of said second sensor element.
4. A flow-metering apparatus as in claim 3 wherein said computation
means comprises a first and second computation element, said first
computation element electrically connected to said first sensor
element, and said second computation element electrically connected
to said second sensor element.
5. A flow-metering apparatus as in claim 3 wherein said mounting
support further comprises a first and second valve control device
for controlling transmission of the alternating pressure fluctuations
to said first and second sensor elements,
said first valve control device coupled to said first set of flow
passages, and
said second valve control device coupled to said second set of
flow passages.
6. A flow-metering apparatus as in claim 1 wherein said mounting
support further comprises a plurality of valve control devices,
coupled to said sensor elements and said flow passages, for controlling
the transmission of the alternating differential pressure fluctuations
to said sensor elements.
7. A vortex flow meter comprising:
a) a flow-pipe section fluidly connected to a process flow, said
flow-pipe section having a single divided cavity for allowing communication
with the process flow;
b) a vortex-generating body mounted in said flow-pipe section for
generating alternating differential pressure fluctuations;
c) a first and second sensor means fluidly connected to said fluid
flow at said single divided cavity for detecting the alternating
differential pressure fluctuations and for producing electronic
signals representative thereof,
said first sensor means having a first side and a second side,
said first side of said first sensor means opposite said second
side of said first sensor means,
said second sensor means having a first side and a second side,
said first side of said second means opposite said second side of
said second sensor means, and
said first and said second sensor means positioned spatially apart
from each other;
d) a first and second computation means for processing said electronic
signals, said first computation means electrically connected to
said first sensor means, and said second computation means electrically
connected to said second sensor means; and
e) a manifold for removably housing said first and second sensor
means, comprising:
i) body means;
ii) a first and second pair of flow passages extending longitudinally
through said body means for fluidly connecting said process flow
at said single divided cavity to said first and second sensor means,
said flow passages communicating with the process flow through said
cavity,
said first pair of flow passages, transmitting low pressure fluctuations
of said alternating pressure fluctuations to said first side of
said first sensor means, and transmitting high pressure fluctuations
of said alternating pressure fluctuations to said second side of
said first sensor means,
said second pair of flow passages transmitting low pressure fluctuations
of said alternating pressure fluctuations to said first side of
said second sensor means, and high pressure fluctuations of said
alternating pressure fluctuations to said second side of said second
sensor means;
iii) a first and second mounting means in said body means, said
first mounting means removably attaching said manifold to said flow-pipe
section, and said second mounting means removably attaching said
manifold to said first and second computation means.
8. A manifold as in claim 7 further comprising first and second
valves for controlling transmission of the alternating pressure
fluctuations to said first and second sensing means,
said first valve fluidly connected to said first pair of flow passages,
and
said second valve fluidly connected to said second pair of flow
passages.
9. A manifold as in claim 7 wherein said first mounting means further
comprises an attachment means and a dummy-cast sensor element positioned
in said single divided cavity of said flow-pipe section, to act
as a flow divider to divide said single divided cavity and to maintain
differential flow through said flow passages.
Description BACKGROUND
1. Technical Field
This invention relates to a flow measuring apparatus, and, more
particularly, to vortex shedding flow meters having sensor means
for detecting vortices generated according to fluid flow.
2. Background Art
For many industrial processes, it is common practice to measure
a process flow within a pipe using the principle of vortex shedding.
Numerous types of vortex flow meters have been designed utilizing
this principle to measure the physical characteristics of the fluid
flow by sensing the frequency of the vortex formation. Typically,
these vortex meters comprise a vortex-shedding body mounted in a
flow pipe together with a sensor for detecting the frequency of
vortex formation. The sensors used to detect the vortices often
contain two highly corrosion resistant process isolation diaphragms
which serve to transmit the alternating differential pressure fluctuations
caused by the shedding vortices to an internal sensor element through
either the sensors internal fill fluid or through mechanical coupling.
The fluid flow velocity is proportional to the frequency of vortex
shedding.
An example of such a vortex flow meter is The Foxboro Company's
E83 series vortex flow meter with optional isolation manifold, described
in The Foxboro Company, Product Specification Sheet, PSS 1-8A1 D.
This flow meter contains a pipe section containing a shedding plate
for generating alternating vortices. A sensor, mounted slightly
above the shedder plate, is used for sensing the vortices and generating
an electronic signal representative of the shedding frequency. This
signal is then transmitted to a processing element contained in
an electronic housing for amplification and conditioning of the
signal. An isolation manifold is provided for valve control of the
fluid communication to the sensors. The isolation manifold is beneficial
when the sensor requires maintenance, repair, replacement, or the
like, since it disengages the process flow from the sensor without
requiring the entire process to be shut off.
A constraint of this type of vortex flow meter is that the measurements
depend on the accuracy of one sensor. Sensors do not always operate
accurately as they are subject to breakage and malfunctions. In
these instances, the measurement of the process flow is interrupted
in order to either replace, repair, clean, calibrate, or maintain
the sensor. This interruption of the process flow measurement is
a limitation on the above vortex flow meter.
It is an object of this invention to provide a vortex flow meter
with redundant sensor capability for continuous measurement of a
process flow.
It is another object of this invention to provide a vortex flow
meter with redundant sensor capability with continuous measurement
from a common source point in the process flow.
A more specific object of the invention is to provide dual sensors
for use in a vortex flow meter having a process flow such that the
sensors enable the process to remain operational despite the malfunction
or failure of one of the sensors and to provide a cross check on
the computational accuracy of each of the sensors.
A more specific object of the invention is to provide dual sensors
for use in a vortex flow meter having isolation valves which can
isolate the sensors from the process flow such that either one or
both sensors can be replaced without shutting down the process,
and without interrupting the measurement of the process flow rate.
A further object of the invention is to provide a cost effective
dual sensor vortex flow meter that does not require additional modification
to the flow meter body.
SUMMARY
This invention results from the realization that redundant sensor
capability enables continuous process measurement despite sensor
malfunction or the need for periodic maintenance.
The first embodiment features a dual sensor vortex flow meter containing
a support base housing two sensors and providing process fluid connections
to the two sensors. The vortex flow meter is mounted onto a flow
meter body containing an existing cavity which normally houses a
single sensor. The support base is fitted into the existing sensor
cavity by means of a dummy-cast sensor. On either side of the dummy-cast
sensor are apertures coupled to flow passages that transmit the
alternating differential pressure fluctuations caused by the vortices
from each side of the dummy-cast sensor to the corresponding sides
of each of the dual sensors.
The second embodiment features the dual sensor vortex flow meter
of the first embodiment with the additional feature of dual isolation
valves. The isolation valves allow for the replacement of either
one of the sensors without having to shut down the process flow
or lose the process flow measurement. There is an isolation valve
for each sensor which is connected to the sensor's process fluid
flow passages. A valve handle for each sensor provides the capability
of disengaging the process fluid from the sensor when sensor replacement,
maintenance, repair or the like are required.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other objects, features and advantages of the
invention will be apparent from the following more particular description
of two preferred embodiments of the invention, as illustrated in
the accompanying drawings in which like reference characters refer
to the same parts throughout the different views. The drawings are
not necessarily to scale, emphasis instead being placed on illustrating
the principles of the invention.
FIG. 1 is an end view of a vortex flow meter with the dual sensor
manifold according to the first preferred embodiment of the invention.
FIG. 2 is an exploded perspective view of the vortex flow meter
of FIG. 1 further depicting all the component parts.
FIG. 3 is a side elevation of the dual sensor manifold as used
in the first preferred embodiment.
FIG. 4 is a vertical cross-sectional view of the manifold of FIG.
3.
FIG. 5 is a plan view of the dual sensor manifold as used in the
first embodiment.
FIG. 6 is a bottom view of the dual sensor manifold as used in
both embodiments.
FIG. 7 is a side elevation of a dual sensor manifold having isolation
valves as used in the second preferred embodiment.
FIG. 8 is a vertical cross-sectional view of the manifold of FIG.
7.
FIG. 9 is a plan view of the dual sensor manifold of the second
embodiment.
FIG. 10 is an exploded cross-sectional view of the dual sensor
manifold with isolation valves of FIG. 8 further depicting all the
component parts for the left-sensor branch.
DESCRIPTION OF THE ILLUSTRATED EMBODIMENT
A dual sensor vortex flow meter providing fluid connections for
two sensors and containing isolation valves providing the further
capability of separate valve control of the fluid communication
to each of the dual sensors is herein disclosed.
FIG. 1 is an end view of a vortex flow meter according to a first
embodiment containing flow meter body 10 for use in a flow pipe
having a process flow, and shedder bar 12 for generating alternating
differential pressure vortices. Manifold 20 is mounted on top of
flow meter 10. Manifold 20 is a Y-shaped structure containing a
right branch 18 and a left branch 22. The elements contained in
each branch are structurally and operationally identical. In each
branch is a sensor for detecting the shedding frequencies produced
from shedder bar 12. Right branch 18 contains a supporting base
16 onto which is mounted electronic housing 26a containing electronic
circuitry for amplifying and conditioning signals produced from
one sensor. Similarly, left branch 22 contains a supporting base
24 onto which is mounted electronic housing 26b containing electronic
circuitry for amplifying and conditioning signals produced from
the second sensor.
Referring to FIG. 2 manifold 20 is mounted on top of flow meter
body 10 through cylindrical opening 28. At the bottom of manifold
20 is an integrally cast dummy sensor and flow divider 36. For the
purposes of this application, the terms cast dummy sensor, dummy-cast
sensor, cast of dummy sensor, sensor casting, and cast dummy sensor
and flow divider, are used synonymously. The cast of dummy sensor
36 is used to fit manifold 20 to the flow meter body without requiring
a modification to the flow meter body. This design has the economic
advantage of making the flow meter body easily adaptable for either
a dual or single sensor configuration. U-shaped gasket 34 preferably
fabricated of a high-temperature material, is fitted around dummy-cast
sensor 36 providing a pressure barrier which causes the alternating
differential pressure to be established across the faces of dummy-cast
sensor 36. Circular gasket 32 is placed over cylindrical opening
28 between flow meter body 10 and manifold 20. Manifold 20 with
U-shaped gasket 34 fitted around sensor casting 36 is positioned
into flow meter body 1 through cylindrical opening 28 having circular
gasket 32 between the respective contact surfaces.
Referring to FIGS. 2 and 6 manifold 20 is bolted onto flow meter
body 10 by four bolts, 48a, 48b, 48c, 48d, which pass through holes
46a, 46b, 46c, 46d in manifold mounting base 72 and are threaded
into holes 30a, 30b, 30c, 30d respectively in meter body 10.
FIG. 5 is a plan view of the supporting bases of each branch of
the manifold. Referring to FIGS. 2 and 5 supporting base 16 of
right branch 18 consists of sensor slot 42 with four threaded holes
44a, 44b, on one side of slot 42 and threaded holes 44c, 44d on
the opposite side. Supporting base 24 of left branch 22 is identical
having sensor slot 43 with threaded holes 45a, 45b on one side of
slot 43 and threaded holes 45c, 45d on the opposite side.
Positioned in sensor slot 42 is a vortex sensor 54a, and in sensor
slot 43 is vortex sensor 54b, both having a sensor housing containing
a sensor element (not shown). The sensor housing has two highly
corrosion resistant process isolation diaphragms which serve to
transmit the alternating differential pressure fluctuations caused
by the shedding vortices to an internal sensor element through the
sensor's internal fill fluid, or through mechanical coupling. The
sensor element generates a signal representative of the shedding
frequency of the vortices, which is proportional to the flow velocity,
through a cable to appropriate circuitry contained in electronic
housing 26a, 26b. An example of one such sensor is found in U.S.
Pat. No. 5209125 to Kalinoski et al.
The sensor elements, the components used for mounting the sensor
elements to the manifold, and their electronic housings are identical
for both branches of the manifold. Therefore, for the purposes of
this application, a description of these elements is presented for
one branch since they are identical in the second branch.
Referring to FIGS. 2 and 5 the bottom portion of sensor 54a is
fitted with U-shaped gasket 52 preferably made of high-temperature
material, which serves to create a pressure barrier between the
two sides of the sensor, so that the sensor experiences essentially
the same alternating differential pressure as dummy-cast sensor
36. Sensor gasket 50 is placed between the contact surfaces of the
sensor when the sensor is seated into manifold 20. Bonnet 70 is
placed over sensor 54a and bolted onto manifold 20 thereby securing
sensor 54a to manifold 20. Bonnet 70 is bolted onto manifold 20
by four bonnet mounting bolts 60a, 60b, 60c, 60d which pass through
bonnet holes 58a, 58b, 58c, 58d and are threaded into tapped holes
44a, 44b, 44c, 44d in manifold 20.
FIG. 6 is a bottom view of manifold 20 and depicts apertures 82
83 84 85 located on either side of dummy-cast sensor 36. Referring
to FIGS. 2 and 6 each aperture is coupled to a flow passage providing
fluid communication to sensor 54. These passages transmit the alternating
pressure fluctuations caused by the flow vortices generated by shedder
plate 12 from each side of dummy-cast sensor 36 to the respective
sides of sensor 54. The purpose of these apertures and flow passages
is to transmit the alternating pressure fluctuations to sensors
54a, 54b simultaneously as if each sensor was in the position of
dummy-cast sensor 36. This purpose then enables sensors 54a, 54b
to make redundant measurements from a common source point in the
process flow.
The vortices produced by the shedder bar create an alternating
differential pressure between the left side, 35 and the right side
37 of dummy-cast sensor 36. At one instant of time, the left side,
35 experiences the maximum or high pressure while the right side,
37 experiences the minimum or low pressure. One half of a vortex
shedding cycle later the left side, 35 experiences the minimum
pressure, while the right side, 37 experiences the maximum pressure.
Hence, a sinusoidal pressure fluctuation occurs across dummy-cast
sensor 36. For purposes of the following discussion, the vortex
shedding cycle will be frozen in time such that side 35 will be
denoted the high pressure side and side 37 the low pressure side.
With reference to FIGS. 4 and 6 apertures 82 83 are located on
the high side of dummy-cast sensor 36 and serve to transmit the
high pressure to the high sides of sensors 54a, 54b simultaneously.
Aperture 82 is coupled to flow passage 78 and aperture 83 is coupled
to flow passage 80. Flow passage 78 is coupled to high side 74 of
sensor 54b at chamber 69 and flow passage 80 is coupled to high
side 76 of sensor 54a at chamber 65.
Similarly, apertures 84 85 are located on the low side of dummy-cast
sensor 36 and serve to transmit the low pressure to the low sides
of sensors 54a, 54b. Aperture 84 is coupled to flow passage 79 and
aperture 85 is coupled to flow passage 81. Flow passage 79 is coupled
to low side 75 of sensor 54b at chamber 71 and flow passage 81 is
coupled to low side 77 of sensor 54a at chamber 67.
The operation of the vortex flow meter will now be described in
detail. The process fluid flows through the flow pipe to shedder
plate 12 which generates the alternating vortex pressure fluctuations.
These vortices are transmitted through two internal meter body chambers
(not shown) to opposite sides of dummy-cast sensor 36. The high-pressure
vortex fluctuations transmitted to side 35 are transmitted simultaneously
through apertures 82 83 through flow passages 82 80 to the high
sides of sensors 54a, 54b respectively. Simultaneously, the low-pressure
vortex fluctuations transmitted to side 37 of sensor 36 are transmitted
through apertures 84 85 through flow passages 79 81 to the low
sides of sensors 54a, 54b respectively. These pressure fluctuations
are, in turn, detected by sensors 54a, 54b. An electronic signal,
representative of the shedding frequency, is then transmitted from
the sensors to processing elements contained in electronics housing
26a, 26b respectively.
The second preferred embodiment extends the vortex flow meter described
in the above first embodiment with isolation valves, providing valve
control of the fluid passages to the sensors. This additional capability
is beneficial for isolating one or both of the sensors from fluid
communication or flow when sensor maintenance, repair, replacement,
or the like is needed. It also makes it feasible to replace the
sensor without interrupting the process flow or its measurement.
The second embodiment of the manifold incorporates some of the
same structural features used in the first embodiment. Specifically,
the sensor bonnet 70 electronic housings 26a, 26b, and the corresponding
mounting bolts and gaskets which secure the sensor and the electronic
housings to the manifold are identical as described above in the
first embodiment. Likewise, the shape of the manifold is similar.
With reference to FIGS. 7 and 10 manifold 109 is of a Y-shape
structure having a right branch 115 and a left branch 117. However,
right and left branches 115 117 are of an elongated length as they
house a valve control mechanism.
With reference to FIGS. 8 and 10 each sensor has a ball valve
control mechanism, coupled to each of the respective sensor flow
passages, for isolating one or both of the sensors from the process
flow. It should be noted that this embodiment is not limited to
a ball-valve type of valve mechanism. Other valve types may be used,
such as, but not limited to, needle-type valves, and flat circular-disc
valves. The ball valve consists of a stainless steel ball, 121
having two circular flow passages, 131 133 that function as fluid
conduits. The ball is positioned in housing, 143 secured by seals
138a, 138b. The ball's flow passages, 131 133 are of the same
width as the sensor's flow passages, 78 79 80 81. When the ball
is in the open position, as shown by ball 121a, flow passages 131
133 are aligned with flow passages 80 81 providing a fluid conduit
for the process flow to be transmitted to the sensor. When the ball
is in the closed position, as shown by ball 121b, flow passages
131 133 are not aligned with flow passages 78 79 thereby blocking
fluid communication to the sensor. Referring to FIG. 10 seals 138a,
138b are made of a high temperature resistant material having a
pair of flow passages 132 134 that are coupled to flow passages
78 79 respectively, forming a flow passage for the process fluid
to reach the sensor. Seal 138b is positioned at the bottom of housing
143 having the bottom surface of ball 121b resting in semi-circular
cavity 128b. Seals 138a, 138b serve to isolate the process fluid
contained in each flow passage from one another ensuring that the
differential pressure measurement is not attenuated by leaks from
one flow passage to the other flow passage. They also serve to prevent
external leakage of the process fluid when the valve is in the closed
position.
Ball 121 and seals 138a, 138b are secured into housing 143 and
manifold 109 by valve bonnet 137 which is fitted onto manifold 109.
Gasket 136 is placed between the surface of valve bonnet 137 and
manifold 109 in order to prevent external leaks. Valve bonnet 137
is bolted to manifold 109 by means of bolts 140a, 140b which pass
through holes 141a, 141b on valve bonnet 137 and are threaded into
holes 142a, 142b on manifold 109. Valve bonnet 137 contains sensor
chamber 144 used for housing sensor element 54b. The bottom base
of valve bonnet 137 contains two flow chambers 124 126 which are
coupled to flow passages 78 79 through conduits 131-132 133-134
respectively. Flow chambers 124 126 serve to transmit the alternating
differential pressure fluctuations to both sides of sensor 54b in
sensor chamber 144.
With reference to FIGS. 2 and 10 sensor 54b is secured into sensor
chamber 144 by bonnet 70 in an identical manner as described above
in the first embodiment. Likewise, electronic housing 26b is mounted
onto bonnet 70 having electronic circuitry for amplfying and conditioning
signals produced from senor 54b.
With reference to FIG. 10 the ball valve also comprises valve-handle
mechanism 113 having valve stem 113h, for rotating the ball valve
to the open or closed position. Valve stem 113h contains a protrusion
122 that fits into rectangular indent 135 of ball 121b, thereby
aligning valve-handle mechanism 113 and ball 121b on the same horizontal
rotational axis. Valve stem 113h is further secured to manifold
109 by a series of washers, gaskets, and nuts: interior gasket 113g,
exterior gasket 113f, washer 113e, Belleville spring washer 113d,
valve handle 113c, lock washer 113b, and nut 113a. Belleville spring
washer 113d serves to create a spring load, compressing gaskets
113f, 113g thereby forming a seal securing valve stem 113h to manifold
109 in order to prevent process fluid leakage. Nut 113a and lock
washer 113b serve to securely fasten valve handle 113c to the valve
stem and manifold 109.
Referring to FIG. 8 the operation of the ball valve relies on
its horizontal rotational axis, 129. To turn the valve on, as shown
by ball 121a, valve handle 113 is rotated at a certain angle in
one direction, thereby aligning the ball's internal chambers 131
133 with the sensor's flow passages 80 81. To eliminate fluid
communication, as shown by ball 121b, valve handle, 113 is rotated
at a certain angle in the opposite direction, thereby blocking flow
passages 78 79 and the process fluid from flowing to the sensor.
The dual sensor vortex flow meter as described above has the advantages
of redundant sensor capability enabling continuous flow measurement
despite the malfunction of one of the sensors, and provides a cross
check on the computational accuracy of each of the sensors. The
redundant flow measurement is made from a common source point in
the process flow thereby enhancing the accuracy of both measurements.
The isolation valves provide separate valve control of the fluid
communication to each of the dual sensors. This is advantageous
for sensor replacement, repair, maintenance or the like. This vortex
flow meter has the additional economic advantage of not requiring
any modification to the flow meter body.
Although the preferred embodiments of the invention have been described
hereinabove in detail, it is desired to emphasize that this is for
the purpose of illustrating the invention and thereby to enable
those skilled in this art to adapt the invention to various different
applications requiring modifications to the apparatus described
hereinabove; thus, the specific details of the disclosures herein
are not intended to be necessary limitations on the scope of the
present invention other than as required by the prior art pertinent
to this invention. |