Abstrict A vortex flow meter comprises a first diaphragm which divides first
and second pressure chambers from each other; a second diaphragm
which divides third and fourth pressure chambers from each other
and is disposed in such a manner that the direction in which the
second diaphragm is movable is coincident with that in which the
first diaphragm is movable, and that the direction is not coincident
with that of the maximum component of an external force which acts
on the diaphragms; first and second bridge circuits which make outputs
in response to the action of the first and second diaphragms, respectively;
and differential amplifiers which perform the differential amplification
of the outputs from the first and second bridge circuits.
Claims I claim:
1. A vortex flow meter, comprising:
vortex generator means provided in a conduit through which a fluid
to be measured flows for generating Karman vortices;
first pressure chamber;
second pressure chamber;
third pressure chamber;
fourth pressure chamber;
first and second pressure takeout ports for taking out the pressure
of said vortices;
a first pressure passage for transmitting the pressure change caused
at said first pressure takeout port to said first and second pressure
chambers;
a second pressure passage for transmitting the pressure change
caused at said second pressure takeout port to said second and third
pressure chambers;
a first diaphragm provided between said first and second pressure
chamber for acting in response to the pressure difference between
said first and second pressure chambers;
a second diaphragm provided between said third and fourth pressure
chambers for acting in response to the pressure difference between
said third and fourth pressure chambers, said second diaphragm being
movable in a first direction coincident with that in which said
first diaphragm is movable, said first direction is not coincident
with a second direction of a maximum component of an external force
which acts to said first and second diaphragms;
first and second bridge circuits provided on said first and second
diaphragms, respectively, for generating a pair of outputs inverse
to each other in polarity and equal to each other in absolute value
in response to the action of said first and second diaphragms, respectively;
and
differential amplifying means for differentially amplifying the
outputs from said first and second bridge circuits to generate an
output indicative of the period of a pulsation.
2. A vortex flow meter as claimed in claim 1 wherein said differential
amplifying means comprising first and second differential amplifiers
for differentially amplifying said pair of outputs from said first
and second bridge circuits, respectively, and a third differential
amplifier for differentially amplifying the outputs from said first
and second amplifiers.
3. A vortex flow meter as claimed in claim 2 further comprising
a wave-shaping circuit for wave-shaping the output from said third
differential amplifier.
Description BACKGROUND OF THE INVENTION
1. (Field of the Invention)
The present device relates to a vortex flow meter in which diaphragms
are disposed in such a manner that the direction in which the diaphragms
are movable is not coincident with that of the maximum component
of a vibratory force.
2. (Prior Art)
There are various kinds of vortex pressure detection systems. The
Japanese patent application No. 36776/75 or the Japanese Utility
Model patent application No. 3725/79 disclosed a vortex pressure
detection system in which the pressure of vortices is transmitted
to right and a left chambers divided from each other by a diaphragm
to detect the difference in the pressure of the vortices.
In a conventional vortex pressure detection system of such kind,
the sensitivity of a diaphragm needs to be made very high to detect
the pressure of vortices in a range of very low flow rate. However,
if the sensitivity is made very high, the diaphragm responds not
only to the pressure of the vortices but also to an external force
such as a vibratory force. This is a problem.
SUMMARY OF THE INVENTION
The present device was made in order to solve the problem discussed
above.
Accordingly, it is an object of the present device to provide a
vortex flow meter which can measure a very low flow rate with very
small vortex pressure and is high in resistance to external vibration.
The vortex flow meter provided in accordance with the present device
comprises a first diaphragm which divides first and second pressure
chambers from each other; a second diaphragm which divides third
and fourth pressure chambers from each other and is disposed in
such a manner that the direction in which the second diaphragm is
movable is coincident with that in which the first diaphragm is
movable, and that the direction is not coincident with that of the
maximum component of an external force which acts on the diaphragms;
first and second bridge circuits which make outputs in response
to the action of the first and second diaphragms, respectively;
and differential amplifiers which perform the differential amplification
of the outputs from the first and the second bridge circuits.
In the vortex flow meter, the first and second diaphragms cumulatively
act to detect the pressure difference between the first and second
pressure chambers and that between the third and fourth pressure
chambers to detect the pressure of Karman vortices. However, the
first and second diaphragms differentially act against the external
force. The direction in which the first and second diaphragms are
movable are not coincident with that of the maximum component of
the external force which acts on the diaphragms. The outputs made
by the first and second bridge circuits in response to the action
of the first and second diaphragms, respectively, are differentially
amplified by the differential amplifiers so that the vortex flow
meter makes an output.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 a sectional view of a vortex flow meter which is an embodiment
of the present device.
FIG. 2 shows a sectional view of the vortex generating section
of the vortex flow meter.
FIGS. 3 and 4 show mutually perpendicular sectional views of the
vortex pressure detector of the vortex flow meter.
FIG. 5 shows a wiring diagram of the control section of the vortex
flow meter.
FIG. 6 shows an example of the use of the vortex flow meter, which
the meter is installed in a motor vehicle.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
An embodiment of the present device will be hereafter described
with reference to the drawings attached hereto.
FIG. 1 shows a sectional view of a vortex flow meter which is the
embodiment. FIG. 2 shows a sectional view of the vortex generating
section of the vortex flow meter. A fluid 1 to be measured flows
through a conduit 2. A vortex generator 3 is provided in the conduit
2 and extends perpendicularly to the direction of the flow of the
fluid 1 so that Karman vortices 4 are generated downstream of vortex
generator. The pressure of the Karman vortices 4 is detected through
pressure takeout ports 5 and 6 provided in the wall of the conduit
2. A vortex pressure detector 8 communicates with the pressure takeout
ports 5 and 6.
FIGS. 3 and 4 show mutually-perpendicular enlarged sectional views
of the vortex pressure detector 8. Pressure passages 85 and 86 communicate
with the pressure takeout ports 5 and 6. Pressure chambers 81 82
83 and 84 are provided in the vortex pressure detector 8 in such
a manner that the first pressure chamber 81 and the fourth pressure
chamber 84 communicate with the pressure passage 85 and the second
pressure chamber 82 and the third pressure chamber 83 communicate
with the other pressure passage 86. A base plate 88 is provided
between the first and second pressure chambers 81 and 82 and between
the third and fourth pressure chambers 83 and 84 and held between
casing members 89 and 90. A semiconductor chip 87 is provided on
the base plate 88 and has first and second diaphragms 87a and 87b.
The first diaphragm 87a divides the first and second pressure chambers
81 and 82 from each other. The second diaphragm 87b divides the
third and fourth pressure chambers 83 and 84 from each other. The
casing members 89 and 90 define the pressure passages 85 and 86
and the pressure chambers 81 82 83 and 84 and hold the base plate
88. Terminals 91 are connected to wires 92 connected to the terminals
of semiconductor bridge circuits 101 and 102 provided on the surfaces
of the first and second diaphragms 87a and 87b but not shown in
FIGS. 3 and 4.
FIG. 5 shows a wiring diagram of the control section of the vortex
flow meter. Each of the first and second bridge circuits 101 and
102 is composed of four piezoelectric resistors. The output from
the first bridge circuit 101 is applied to the plus and minus input
terminals of a first differential amplifier 103. The output from
the second bridge circuit 102 is applied to the plus and minus input
terminals of a second differential amplifier 104. The outputs from
the first and second differential amplifiers 103 and 104 are applied
to the plus and minus input terminals of a third differential amplifier
105 the output from which is applied to a wave-shaping circuit
106 which shapes the output and provides the output from the vortex
flow meter. A power supply 107 is provided for the first and second
bridge circuits 101 and 102.
FIG. 6 shows an example of the use of the vortex flow meter, in
which the meter 206 is installed in a motor vehicle including an
engine 201 an intake manifold 202 a surge tank 203 a throttle
valve casing 204 a pipe 205 coupling the flow meter to the throttle
valve casing, and another pipe 207 coupling an air cleaner 208 to
the flow meter.
The operation of the vortex flow meter will now be described in
detail. When the fluid 1 flows through the conduit 2 the clockwise
and counterclockwise vortices 4 are alternately generated downstream
of the vortex generator 3 as shown in FIG. 2. The vortices 4 are
generally called the Karman trail. The generation of the Karman
vortices 4 is accompanied by pressure changes. For that reason,
pressure changes are caused on the inside surface of the conduit
2 along the passage for the Karman vortices 4 so that some of the
pressure changes alternately take place at the pressure takeout
ports 5 and 6 provided in the conduit 2 in the face of the passage
for the vortices. The pressure of the vortices 4 is negative in
general. When the clockwise vortex 4 is generated at the pressure
takeout port 5 negative pressure is caused at the port and transmitted
to the first and fourth pressure chambers 81 and 84 through the
pressure passage 85 so that the first and second diaphragms 87a
and 87b deformed toward the first and fourth pressure chambers,
respectively. When the counterclockwise vortex 4 is generated at
the other pressure takeout port 6 negative pressure is caused at
the port and transmitted to the second and third pressure chambers
82 and 83 through the other pressure passage 86 so that the first
and second diaphragms 87a and 87b are deformed toward the second
and third pressure chambers, respectively. It is herein supposed
that when the first and second diaphragms 87a and 87bare deformed
toward the first and the third pressure chambers 81 and 83 respectively,
the outputs from the first and second bridge circuits 101 and 102
have such polarity as shown by arrows v.sub. B in FIG. 5. For that
reason, at the time of the generation of the clockwise vortex 4
the first bridge circuit 101 makes the output v.sub.B and the second
bridge circuit 102 makes the output -v.sub.B. At the time of the
generation of the counterclockwise vortex 4 the first bridge circuit
101 makes the output -v.sub.B and the second bridge circuit 102
makes the output v.sub.B. The outputs from the first and second
bridge circuits 101 and 102 are amplified by the first and second
differential amplifiers 103 and 104 at prescribed amplification
factors, respectively, so that the amplifiers make outputs V.sub.B
and -V.sub.B which are applied to the third differential amplifier
105. When the outputs V.sub.B and -V.sub.B are applied to the plus
and minus input terminals of the third differential amplifier 105
respectively, the amplifier makes an output 2V.sub.B. When the outputs
-V.sub.B and V.sub.B are applied to the plus and minus input terminals
of the third differential amplifier 105 respectively, the amplifier
makes the same output 2V.sub.B. For these reasons, the first and
second diaphragms 87a and 87b cumulatively act for the pressure
of the vortices 4 so that the pressure can be detected even if it
is very small.
The operation of the vortex flow meter in the case that external
pressure except the pressure of the vortices 4 acts on the first
and second diaphragms 87a and 87b is now described. For example,
the external pressure is the pressure which fluctuates in a pulsation
which takes place in the conduit 2 due to the change in the flow
of the fluid 1. Since the pulsation propagates throughout a relatively
large length to the location of the vortex generator 3 from upstream
or downstream thereto, the pulsation is a kind of a completely plane
traveling wave in the conduit 2. For that reason, pressure changes
of the same quantity simultaneously take place at the pressure takeout
ports 5 and 6 and are transmitted to the first and fourth pressure
chambers 81 and 84 through the pressure passage 85 and to the second
and third pressure chambers 82 and 83 through the pressure passage
86. Since the pressure changes of the same quantity are simultaneously
transmitted to the first and second pressure chambers 81 and 82
the first diaphragm 87a is not deformed toward any of the chambers,
so that the first bridge circuit 101 does not make any output from
the pressure changes. As a result, the control section of the vortex
flow meter does not make any output from the pressure changes. Since
the pressure changes of the same quantity are simultaneously transmitted
to the third and fourth pressure chambers 83 and 84 the second
diaphragm 87b is not deformed toward any of the chambers, so that
the second bridge circuit 102 does not make any output from the
pressure changes. As a result, the control section does not make
any output from the pressure changes.
The operation of the vortex flow meter in the case that the vortex
pressure detector 8 is vibrated will now be described. When the
detector 8 is vibrated in such a direction that the first and second
diaphragms 87a and 87b are undeformable, the diaphragms are not
deformed by the vibration, so that the control section does not
make any output from the vibration. When the detector 8 is vibrated
in such a direction that the diaphragms 87a and 87b are deformable,
the diaphragms are deformed by the same quantity in the same direction
at the same time due to the vibration so that the first and second
bridge circuits 101 and 102 make the outputs v.sub.B from the vibration.
In that case, the outputs v.sub.B are amplified by the first and
second differential amplifiers 103 and 104 at the prescribed amplification
factors so that the amplifiers make the outputs V.sub.B which are
applied to the third differential amplifier 105 which generates
an output indicative of the period of a pulsation. Since the outputs
V.sub.B equal to each other are applied to the plus and minus input
terminals of the third differential amplifier 105 in that case,
the amplifier does not make any output from the vibration.
It is difficult to completely equalize the properties of the first
and second diaphragms 87a and 87b to each other in manufacturing
them. If a strong vibratory force acts to the first and second diaphragms
87a and 87b slightly different from each other in mass or piezoelectric
constant, a non-negligible noise is caused in the output from the
third differential amplifier 105. If the vibratory force is not
strong, the noise is negligible.
Air needed by the engine 201 shown in FIG. 6 flows to the vortex
flow meter 206 through the air cleaner 208 and the pipe 207 and
is measured by the meter. The air then flows to the surge tank 203
through the pipe 205 and the throttle valve casing 204 and is entered
into the cylinder of the engine 201 through the intake manifold
202. A vibratory force, which acts to the vortex flow meter 206
in this example of the use thereof, consists of components in mutually
perpendicular directions X, Y and Z. The components are generally
unequal to each other. In this example, the component in the direction
Y is the strongest and that in the direction X is the weakest. Therefore,
if the direction in which the first and second diaphragms 87a and
87b are deformable is made uncoincident with the direction Y or
possibly made coincident with the direction X, the force which acts
on the diaphragms in the direction in which the diaphragms are deformable
can be made so weak that the noise caused in the output from the
third differential amplifier 105 is negligible although the properties
of the diaphragms are not completely equal to each other.
According to the present device, the first and second pressure
chambers of the vortex pressure detector of a vortex flow meter
are divided by a first diaphragm, and the third and fourth pressure
chambers of the detector are divided by a second diaphragm, so that
the diaphragms cumulatively act for the detection of the pressure
of Karman vortices but differentially act against an external force
such as a vibratory force. Besides, the direction of the maximum
component of the external force is made uncoincident with that in
which the diaphragms are deformable. As a result, the meter's capability
to detect the pressure of the Karman vortices in a range of very
low flow rate is enhanced, and the meter's resistance to the external
force is made very high. |