Abstrict A vortex flow meter comprises a first diaphragm which divides a
first and a second pressure chamber from each other; a second diaphragm
which divides a third and a fourth pressure chambers from each other;
a first and a second bridge circuits which receive the action of
the first and the second diaphragms, respectively; a first and a
second variable amplifiers which amplify the outputs from the first
and the second bridge circuits, respectively; and a differential
amplifier which receives the outputs made by the first and the second
variable amplifiers, inverse to each other in polarity and nearly
equal to each other in magnitude.
Claims What is claimed is:
1. A vortex flow meter, comprising:
a vortex generator provided in a conduit through which a fluid
to be measured flows;
first and second pressure takeout ports for picking up the pressure
of Karman vortices generated in the fluid downstream of said vortex
generator in said conduit;
first, second, third and fourth pressure chambers;
a first pressure passage for transmitting a first pressure change
caused at said first pressure takeout port to said first and fourth
pressure chambers;
a second pressure passage for transmitting a second 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
chambers for detecting the difference in the pressure of said karman
vortices;
a second diaphragm provided between said third and fourth pressure
chambers for detecting the difference in the pressure thereof;
first and second bridge circuits for generating an output in response
to the action of said first and second diaphragms, respectively;
first and second variable amplifiers for receiving the output from
said first and second bridge circuits;
a differential amplifier for differentially amplifying the outputs
from said first and second variable amplifiers, inverse each other
to in polarity and nearly equal to each other in magnitude to generate
an output representing the period of a pulsation which takes place
along with the generation of said vortices; and
first and second adjusting resistors provided in said first and
second variable amplifiers for adjusting the amplification factors
of said first and second variable amplifiers, respectively, to equalize
the outputs from said first and second variable amplifiers to each
other.
2. A vortex flow meter as claimed in claim 1 further comprising
a wave-shaping circuit for wave-shaping the output from said differential
amplifier.
3. A vortex flow meter, comprising:
a vortex generator provided in a conduit through which a fluid
to be measured flows;
first and second pressure takeout ports for picking up the pressure
of Karman vortices generated in the fluid downstream of said vortex
generator in said conduit;
first, second, third and fourth pressure chambers;
a first pressure passage for transmitting a first pressure change
caused at said first pressure takeout port to said first and fourth
pressure chambers;
a second pressure passage for transmitting a second 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
chambers for detecting the difference in the pressure of said Karman
vortices;
a second diaphragm provided between said third and fourth pressure
chambers for detecting the difference in the pressure thereof;
first and second bridge circuits for generating output signals
in response to the action of said first and second diaphragm, respectively;
and
a variable differential amplifying circuit for differentially amplifying
the outputs from said first and second bridge circuits, said variable
differential amplifying circuit having gain adjusting means for
performing gain adjustment to equalize the outputs from said first
and second bridge circuits to each other even if a force except
the vortex pressure is applied to said first and second diaphragm.
4. A vortex flow meter as claimed in claim 3 wherein said gain
adjusting means comprises gain adjusting resistors.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
The present device relates to a vortex flow meter in which two
diaphragms cumulatively act for a signal output but differentially
act against a noise to make the difference between noise outputs
zero.
2. Prior Art
There are various kinds of vortex pressure detection systems. The
Japanese Patent Application No. 36776/75 or the Japanese Utility
Model Application No. 3725/79 disclosed a flow meter in which the
pressure of vortices is transmited to a right and a left chambers
divided from each other by a diaphragm to detect the difference
in the pressure.
In a conventional flow meter 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.
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 according to the present invention comprises
a first diaphragm which divides a first and a second pressure chambers
from each other; a second diaphragm which divides a third and a
fourth pressure chambers from each other; a first and a second bridge
circuits which receive the action of the first and the second diaphragms,
respectively; a first and a second variable amplifiers which amplify
the outputs from the first and the second bridge circuits, respectively;
and a differential amplifier which receives the outputs made by
the first and the second variable amplifiers, inverse to each other
in polarity and nearly equal to each other in magnitude.
In the vortex flow meter provided in accordance with the present
device, the changes in the pressure of Karman vortices are transmitted
to the first, the second, the third and the fourth pressure chambers.
The pressure difference between the first and the second pressure
chambers and that between the third and the fourth pressure chambers
are detected by the first and the second diaphragms, respectively.
The first and the second bridge circuits make outputs from the action
of the first and the second diaphragms, respectively. The first
and the second variable amplifiers amplify the outputs from the
first and the second bridge circuits, respectively. The amplification
factors of the first and the second variable amplifiers are adjusted
so that outputs made by the amplifiers in response to an external
force such as a vibratory force and acting to the first and the
second diaphragms are equalized to each other. The differential
amplifier performs the differential amplification of the outputs
from the first and the second variable amplifiers.
Further, the vortex flow meter according to the present device
comprises a first and a second pressure takeout ports opened downstream
to both the sides of a vortex generator in a conduit through which
a fluid to be measured flows; a first pressure passage through which
the first pressure takeout port communicates with a first and a
fourth pressure chambers; a second pressure passage through which
the second pressure takeout port communicates with a second and
a third pressure chambers; a first diaphragm which divides the first
and the second pressure chambers from each other; a second diaphragm
which divides the third and the fourth pressure chambers from each
other; a first and a second bridge circuits which make outputs in
response to the action of the first and the second diaphragms, respectively;
and a variable differential amplifier which performs the differential
amplification of the inputs supplied thereto on the basis of the
outputs from the first and the second bridge circuits and has gain
control resistors for performing gain control to equalize the inputs
to each other even if a force except the pressure of vortices acts
to the diaphragms.
In the vortex flow meter provided in accordance with the present
device, the pressure of vortices downstream to both the sides of
the vortex generator in the conduit is transmitted to the pressure
chambers through the pressure takeout ports and the pressure passages
so that the first and the second diaphragms act in mutually reverse
directions. As a result, the first and the second bridge circuits
produces the outputs inverse to each other in polarity so that the
inputs supplied to the variable differential amplifier on the basis
of the outputs from the first and the second bridge circuits are
cumulatively processed by the variable differential amplifier. When
the external force except the pressure of the vortices acts to the
diaphragms, the outputs from the first and the second bridge circuits
change in the same direction of increase or decrease at the same
time so that the action of the external force is cancelled by the
variable differential amplifier. If the outputs from the first and
the second bridge circuits are not equal to each other, the gain
control is performed by the gain control resistors to equalize the
outputs to each other.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 and 2 show mutually-perpendicular sectional views of a
vortex flow meter according to an embodiment of the present device;
FIGS. 3 and 4 show mutually-perpendicular sectional views of the
vortex pressure detector of the vortex flow meter;
FIGS. 5 and 6 show mutually-different sectional views of the vortex
pressure detector;
FIG. 7 shows a wiring diagram of the vortex flow meter according
to another embodiment of the present invention; and
FIG. 8 shows a wiring diagram of the vortex flow meter according
to a further embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiments of the present device will be described with reference
to the drawings attached hereto.
FIGS. 1 and 2 show mutually-perpendicular sectional views of a
vortex flow meter which is the embodiment. A measured fluid 1 such
as intake air flows through a conduit 2 in the flow meter. A vortex
generator 3 is provided in the conduit 2 and extends perpendicularly
to the direction of the flow of the fluid 1. Karman vortices 4 are
generated in the fluid 1 downstream to the vortex generator 3. A
first and a second pressure takeout ports 5 and 6 are provided in
the wall of the conduit 2 downstream to the vortex generator 3 to
detect the pressure of the Karman vortices 4. A vortex pressure
detector 8 communicates with the pressure takeout ports 5 and 6
and is provided outside the conduit 2. The body of the detector
8 is made of casing members 89 and 90 integrally coupled with each
other, as shown in FIGS. 3 and 4. A first and a second pressure
passages 85 and 86 are provided in the casing member 90 and communicate
with the pressure takeout ports 5 and 6 respectively. A first and
a third pressure chambers 81 and 83 are provided in the casing member
90. A second and a fourth pressure chambers 82 and 84 are provided
in the other casing member 89. As shown in FIGS. 5 and 6 the first
and the fourth pressure chambers 81 and 84 communicate with the
first pressure passage 85 and the second and the third pressure
chambers 82 and 83 communicate with the second pressure passage
86. A base plate 88 fitted with a semiconductor chip 87 is provided
between the casing members 89 and 90. The semiconductor chip 87
has a first and a second diaphragms 87a and 87b. The first diaphragm
87a divides the first and the second pressure chambers 81 and 82
from each other. The second diaphragm 87b divides the third and
the fourth pressure chambers 83 and 84 from each other. Semiconductor
bridge circuits 101 and 102 are provided on the first and the second
diaphragms 87a and 87b, respectively. The terminals of the bridge
circuits 101 and 102 are connected to an external circuit through
wires 92 and terminals 91.
FIG. 7 shows a wiring diagram of the control section of the vortex
flow meter according to one embodiment of the present invention.
The control section includes the first and the second bridge circuits
101 and 102 each composed of four piezoelectric resistors. A first
and a second differential amplifiers 103 and 104 receive the outputs
from the first and the second bridge circuits 101 and 102 respectively.
A first variable amplifier 105 regulates the output from the first
differential amplifier 103. A second variable amplifier 106 regulates
the output from the second differential amplifier 104. Gain control
resistors 105a and 106a are provided in the first and the second
variable amplifiers 105 and 106 respectively. A third differential
amplifier 107 receives the outputs from the first and the second
variable amplifiers 105 and 106. A wave-shaping circuit 108 receives
the output from the third differential amplifier 107. A power supply
109 is provided for the first and the second bridge circuits 101
and 102.
The operation of the vortex flow meter is described in detail from
now on. When the fluid 1 flows through the conduit 2 the clockwise
and counterclockwise vortices 4 are alternately generated downstream
to the vortex generator 3 as shown in FIG. 2. The vortices 4 are
generally called the Karman trail. The generation of the vortices
4 is accompanied by pressure changes. For that reason, pressure
changes take place on the inside surface of the conduit 2 along
the passage for the Karman vortices 4. Because of the alternate
generation of the clockwise and counterclockwise vortices 4 pressure
changes alternately take place at the pressure takeout ports 5 and
6 opened into 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 port
5 negative pressure is caused at the port and is transmitted to
the first and the fourth pressure chambers 81 and 84 through the
pressure passage 85 so that the first and the second diaphragms
87a and 87b are deformed toward the first and the fourth pressure
chambers 81 and 84 respectively. When the counterclockwise vortex
4 is generated at the other pressure takeout port 6 negative pressure
is caused at the port and is transmitted to the second and the third
pressure chambers 82 and 83 through the pressure passage 86 so that
the first and the second diaphragms 87a and 87b are deformed toward
the second and the third pressure chambers 82 and 83 respectively.
It is herein supposed that when the first and the second diaphragms
87a and 87b are deformed toward the first and the third pressure
chambers 81 and 83 respectively, the outputs from the bridge circuits
101 and 102 have such polarity as shown by arrows v.sub.B in FIG.
7. For that reason, at the time of the generation of the clockwise
vortex 4 the bridge circuit 101 makes the output +v.sub.B101 and
the other bridge circuit 102 makes the output -v.sub.B102. At the
time of the generation of the counterclockwise vortex 4 the bridge
circuit 101 makes the output -v.sub.B101 and the other bridge circuit
102 makes the output +v.sub.B102.
The input V.sub.B105 to the plus input terminal of the third differential
amplifier 107 and that V.sub.B106 to the minus input terminal of
the amplifier are expressed as follows:
In the equations (1) and (2), .alpha..sub.103 .alpha..sub.104
.beta..sub.105 and .beta..sub.106 denote the amplification factors
of the first differential amplifier 103 the second differential
amplifier 104 the first variable amplifier 105 and the second variable
amplifier 106 respectively. Since the inputs V.sub.B105 and V.sub.B106
to the plus and minus input terminals of the third differential
amplifier 107 are inverse to each other in polarity, the output
V.sub.B107 from the amplifier is expressed as follows:
Therefore, the first and the second diaphragms 87a and 87b cumulatively
act so that lower vortex pressure can be detected. The absolute
values of the input voltages V.sub.B105 and V.sub.B106 do not need
to be equal to each other.
The operation of the vortex flow meter in the case that external
pressure except the pressure of the vortices 4 acts to the first
and the 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 the fourth pressure
chambers 81 and 84 through the pressure passage 85 and to the second
and the third pressure chambers 82 and 83 through the pressure passage
86 respectively. When the pressure changes of the same quantity
are transmitted to the first and the second pressure chambers 81
and 82 divided from each other by the first diaphragm 87a, the diaphragm
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. When the pressure changes
of the same quantity are transmitted to the third and the fourth
pressure chambers 83 and 84 divided from each other by the second
diaphragm 87b, the diaphragm 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 of the vortex
flow meter 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 is now described. When the detector
8 is vibrated in such a direction that the first and the second
diaphragms 87a and 87b are underformable, the diaphragms are not
deformed by the vibration, so that the control section of the vortex
flow meter 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 in the same
direction as each other so that the first and the second bridge
circuits 101 and 102 make the outputs v.sub.B101 and v.sub.B102.
Since the amplification factors of the first and the second differential
amplifiers 103 and 104 and the first and the second variable amplifiers
105 and 106 are as mentioned above, the output V.sub.B107 from the
third differential amplifier 107 at the time of the deformation
of the diaphragms 87a and 87b is expressed as follows:
If the inputs V.sub.B105 and V.sub.B106 to the plus and minus input
terminals of the third differential amplifier 107 are equal to each
other, the output V.sub.B107 therefrom is zero, namely, the amplifier
does not make any output from the vibration, so that a noise is
not caused in the signal output from the amplifier, by the vibration.
However, the first and the second diaphragms 87a and 87b cannot
be completely equalized to each other in dimensions, form and piezoelectric
constant, in manufacturing them. For that reason, an inequality
exists as follows:
The amplification factors of the first and the second differential
amplifiers 103 and 104 cannot be equalized to each other, either.
Nevertheless, the inputs V.sub.B105 and V.sub.B106 to the third
differential amplifier 107 can be equalized to each other by adjusting
the amplification factors of the first and the second variable amplifiers
105 and 106. For that purpose, the amplification factors of the
variable amplifiers 105 and 106 are preset to establish an equation
as follows: ##EQU1## For the presetting, the vortex pressure detector
8 is vibrated by a prescribed force and the control resistors 105a
and 106a of the first and the second variable amplifiers 105 and
106 are trimmed so that the inputs to the plus and minus input terminals
of the third differential amplifier 107 are equalized to each other.
FIG. 8 shows a wiring diagram of the vortex flow meter according
to the other embodiment of the present invention. Each of the first
and the second bridge circuits 101 and 102 is composed of four piezoelectric
resistors. A first and a second differential amplifiers 103 and
104 receive the outputs from the first and the second bridge circuits
101 and 102 respectively. A variable differential amplifier 105
receives the outputs from the first and the second differential
amplifiers 103 and 104 respectively, and has gain control resistors
111 and 112. A wave-shaping circuit 108 receives the output from
the variable differential amplifier 105. A power supply 107 is provided
for the first and the second bridge circuits 101 and 102.
The operation of the vortex flow meter is described in detail from
now on. When the fluid 1 flows through the conduit 2 the clockwise
and counterclockwise vortices 4 are alternately generated downstream
to the vortex generator 3 as shown in FIG. 2. The vortices 4 are
generally called the Karman trail. Because of the generation of
the Karman vortices 4 pressure changes are caused in the fluid
1. Therefore, pressure changes are also caused on the inside surface
of the conduit 2 along the flow of the fluid 1. Thus, pressure changes
alternately take place at the pressure takeout ports 5 and 6 facing
the flow of the fluid 1. 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 is transmitted
to the first and the fourth pressure chambers 81 and 84 through
the pressure passage 85 so that the first diaphragm 87a is deformed
toward the first pressure chamber and the second diaphragm 87b is
deformed toward the fourth pressure chamber. When the counterclockwise
vortex 4 is generated at the pressure takeout port 6 negative pressure
is caused at the port and is transmitted to the second and the third
pressure chambers 82 and 83 through the pressure passage 86 so that
the first diaphragm 87a is deformed toward the second pressure chamber
and the second diaphragm 87b is deformed toward the third pressure
chamber.
It is herein supposed that when the first diaphragm 87a is deformed
toward the first pressure chamber 81 and the second diaphragm 87b
is deformed toward the third pressure chamber 83 the outputs from
the first and the second bridge circuits 101 and 102 have such polarity
as shown by arrows V.sub.B in FIG. 7. For that reason, at the time
of the generation of the clockwise vortex 4 the first and the second
bridge circuits 101 and 102 make the outputs +V.sub.B101 and -V.sub.B102
respectively. At the time of the generation of the counterclockwise
vortex 4 the first and the second bridge circuits 101 and 102 make
the outputs -V.sub.B101 and +V.sub.B102 respectively. The input
V.sub.B103 to the plus input terminal of the variable differential
amplifier 105 and that V.sub.B104 to the minus input terminal thereof
are expressed as follows:
In the equations (5) and (6), .alpha..sub.103 and .alpha..sub.104
denote the amplification factors of the differential amplifiers
103 and 104 respectively. Since the inputs V.sub.B103 and V.sub.104
to the plus and minus input terminals of the variable differential
amplifier 105 are inverse to each other in polarity, the output
therefrom is expressed as follows:
Therefore, the outputs made by the first and the second differential
amplifiers 103 and 104 in response to the deformation of the first
and the second diaphraqms 87a and 87b act cumulatively so that very
small vortex pressure can be detected. The absolute values of the
inputs V.sub.B103 and V.sub.B104 do not need to be equal to each
other.
The operation of the vortex flow meter in the case that external
pressure except the pressure of the vortices 4 acts to the first
and the second diaphragms 87a and 87b is now described. For example,
the external pressure is the pressure which fluctuates in a pulsation
which takes place 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, the second, the
third and the fourth pressure chambers 81 82 83 and 84 through
the pressure passages 85 and 86. When the first and the second pressure
chambers 81 and 82 divided from each other by the first diaphragm
87a receive the pressure changes of the same quantity at the same
time, the diaphragm is not deformed toward any of the pressure chambers,
so that the first and the second bridge circuits 101 and 102 do
not make any output from the pressure changes. As a result, the
vortex flow meter does not make any output from the pressure changes.
When the third and the fourth pressure chambers 83 and 84 divided
from each other by the second diaphragm 87b receive the pressure
changes of the same quantity at the same time, the diaphragm is
not deformed toward any of the pressure chambers, so that the first
and the second bridge circuits 101 and 102 do not make any output
from the pressure changes. As a result, the vortex flow meter 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 is now described. When the detector
8 is vibrated in such a direction that the first and the second
diaphragms 87a and 87b are undeformable, the diaphragms are not
deformed by the vibration, so that the vortex flow meter does not
make any output from the vibration. When the detector 8 is vibrated
in such a direction that the first and the second diaphragms 87a
and 87b are deformable, the diaphragms are deformed in the same
direction as each other by the vibration so that the first and the
second bridge circuits 101 and 102 make the outputs V.sub.B101 and
V.sub.B102 respectively. Since the amplification factors of the
first and the second differential amplifiers 103 and 104 are as
mentioned above, the output V.sub.B105 from the variable differential
amplifier 105 is expressed as follows:
If the inputs V.sub.B103 and V.sub.B104 to the plus and minus input
terminals of the variable differential amplifier 105 are equal to
each other, the output V.sub.B105 therefrom is zero so that the
vortex flow meter does not make any output from the vibration. Therefore,
no noise is caused by the vibration. However, since the first and
the second diaphragms 87a and 87b cannot be completely made equal
to each other in dimensions, form, piezoelectric resistor constant
and so forth in manufacturing them, the outputs V.sub.B101 and V.sub.B102
from the first and the second bridge circuits 101 and 102 are not
equal to each other but nearly equal to each other. Besides, the
amplification factors of the first and the second differential amplifiers
103 and 104 cannot be equalized to each other. Nevertheless, the
differential output from the variable differential amplifier 105
can be made zero by adjusting the gain of the amplifier, even if
the inputs thereto are not equal to each other. If the output from
the first differential amplifier 103 is higher than that from the
second differential amplifier 104 the gain of the variable differential
amplifier 105 at the input terminal thereof for the output from
the second differential amplifier is increased by adjusting the
gain control resistor 112 to make the differential output from
the variable differential amplifier zero. If the output from the
first differential amplifier 103 is lower than that from the second
differential amplifier 104 the gain of the variable differential
amplifier 105 at the input terminal thereof for the output from
the first differential amplifier is increased by adjusting the gain
control resistor 111 to make the differential output from the variable
differential amplifier zero. For these purposes, the vortex pressure
detector 8 is vibrated by a prescribed force, and the gain control
resistors 111 and 112 are adjusted to make the differential output
from the variable differential amplifier 105 zero, before the vortex
flow meter is put into practical use.
As described above, according to the present device, a first and
a second diaphragms are provided between a first and a second pressure
chambers and between a third and a fourth pressure chambers, respectively,
in a vortex flow meter 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 amplification factors of a first and a second variable amplifiers
are preset so that outputs based on the external force acting to
the first and the second diaphragms are equalized to each other.
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 difference between the diaphragms and the irregularity of the
control section of the vortex flow meter are prevented from being
harmful, to make the meter very reliable against the external force.
Further, according to the present device, a first diaphragm divides
a first and a second pressure chambers from each other, and a second
diaphragm divides a third and a fourth diaphragms from each other,
so that the first and the second 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 gains for the inputs from bridge circuits, which respond to
the strains of the diaphragm under the external force, can be preset
to equalize the inputs to each other. As a result, the sensitivity
to detect the pressure of the Karman vortices in a range of very
low flow rate is enhanced, and noise is prevented from being caused
by the diaphragms under the external force or by the irregularity
of circuit properties. |