Abstrict An ultrasonic flow meter for determining the flow rate of fluid
flowing through tubings. The ultrasonic flow meter comprises a measuring
tube having a diameter constant in its entire length, and two ring
shaped oscillators disposed longitudinally along the tube so as
to substantially intimately contact the inner peripheral surface
thereof with the outer peripheral surface of the tube. The one of
said two oscillators is energized by electric AC energy to generate
an ultrasonic wave, and the thus generated ultrasonic wave is detected
by means of the other oscillator, and vice versa. Then the time
required for propagating the ultrasonic wave from the upstream oscillator
to the downstream oscillator, and that from the downstream oscillator
to the upstream oscillator is measured, and the difference between
the measured times is calculated by means of an arithmetric circuit
to determine the velocity of the fluid flowing through the measuring
tube.
Claims What is claimed is:
1. An ultrasonic flow meter comprising:
a measuring tube having a uniform outer diameter over the entire
length thereof, said measuring pipe being a straight tube; and
first and second ring shaped oscillators disposed longitudinally
forwardly and rearwardly along, and externally of, an outer peripheral
surface of a wall of the tube so as to substantially intimately
contact inner peripheral surfaces thereof with the outer peripheral
surface of the wall of tube;
wherein the first of said two oscillators is energized by electric
AC energy for generating and propagating a first ultrasonic wave
radially inwardly through the wall of the tube toward a center of
the tube for deflecting at the center of the tube perpendicularly
to the radial direction of inward propagation and for propagating
within the tube, the first ultrasonic wave being detected by the
second oscillator, and wherein the second of said two oscillators
is energized by electric AC energy for generating and propagating
a second ultrasonic wave radially inwardly through the wall of the
tube toward a center of the tube for deflecting at the center of
the tube perpendicularly to the radial direction of inward propagation
and for propagating within the tube, the second ultrasonic wave
being detected by the first oscillator,
the time required for propagating the ultrasonic wave from the
upstream first oscillator to the downstream second oscillator being
measured and the time required for propagating the ultrasonic wave
from the downstream second oscillator to the upstream first oscillator
being measured by measuring circuit, and the difference between
the measured times being calculated by an arithmetic circuit to
determine the velocity of the fluid flowing through the measuring
tube.
2. The ultrasonic flow meter as defined in claim 1 wherein said
first and second ring shaped oscillators surround said outer peripheral
surface of the wall of the tube.
3. The ultrasonic flow meter as defined in claim 2 wherein each
of said first and second ring shaped oscillators is concentric with
the wall of the tube.
4. An ultrasonic flow meter comprising:
a measuring tube having a uniform outer diameter over the entire
length thereof,
said measuring pipe being a straight tube;
first and second ring shaped oscillators having an inner aperture
of a diameter slightly larger than the outer diameter of said measuring
tube, each of said oscillators is disposed along the tube longitudinally
at two positions on the outer periphery of the tube respectively;
and
a substance for facilitating propagation of an ultrasonic wave
being interposed between an inner peripheral surface of each oscillator
and an outer peripheral surface of the measuring tube to achieve
an acoustically engaged condition therebetween,
wherein the first of said two oscillators is energized by electric
AC energy for generating and propagating a first ultrasonic wave
radially inwardly through a wall of the tube toward a center of
the tube for deflecting at the center of the tube perpendicularly
to the radial direction of inward propagation and for propagating
within the tube, the first ultrasonic wave being detected by the
second oscillator, and wherein the second of said two oscillators
is energized by electric AC energy for generating and propagating
a second ultrasonic wave radially inwardly through the wall of the
tube toward a center of the tube for deflecting at the center of
the tube perpendicularly to the radial direction of inward propagation
and for propagating within the tube, the second ultrasonic wave
being detected by the first oscillator,
the time required for propagating the ultrasonic wave from the
upstream first oscillator to the downstream second oscillator being
measured and the time required for propagating the ultrasonic wave
from the downstream second oscillator to the upstream first oscillator
being measured by measuring circuit, and the difference between
the measured times being calculated by an arithmetic circuit to
determine the velocity of the fluid flowing through the measuring
tube.
5. The ultrasonic flow meter as defined in claim 4 wherein the
substance for facilitating the propagation of the ultrasonic wave
comprises grease.
6. The ultrasonic flow meter as defined in claim 5 wherein said
first and second ring shaped oscillators surround said outer peripheral
surface of the wall of the tube.
7. The ultrasonic flow meter as defined in claim 6 wherein each
of said first and second ring shaped oscillators is concentric with
the wall of the tube.
8. The ultrasonic flow meter as defined in claim 4 wherein said
first and second ring shaped oscillators surround said outer peripheral
surface of the wall of the tube.
9. The ultrasonic flow meter as defined in claim 8 wherein each
of said first and second ring shaped oscillators is concentric with
the wall of the tube.
Description FIELD OF THE INVENTION
The present invention relates to the field of flow meter and, in
particular, to ultrasonic flow meters.
BACKGROUND OF THE INVENTION
An ultrasonic flow meter of the type that the generated ultrasonic
wave is caused to propagete through the fluid flowing through the
tublar path, the velocity of the fluid flowing through the tublar
path is determined on the basis of the difference between the rate
of propagation of the ultrasonic wave propagates from the upstream
to the downstream and that propagates from the downstream to the
upstream, and provide the flow rate of the fluid flowing through
the tublar path, is referred to as an ultrasonic flow meter of the
type determining the flow rate from the difference between the rates
of propagation, or an ultrasonic flow meter of the type determining
the flow rate from the difference between the propagation times.
Such type of ultrasonic flow meter is accepted broadly in the art.
The above mentioned type of flow meter can be categorized in its
structure to two generic types of flow meter.
The first type of flow meter has a straight propagation tube and
a pair of ultrasonic oscillators disposed at longitudinally spaced
and diametrically opposite positions on the tube so as to face each
other, as shown in FIG. 6. The generated ultrasonic wave propagates
obliquely to the flowing direction of the fluid fluid flowing through
the tube. The ultrasonic flow meter of this type will be referred
to hereinafter as "flow meter of type 1".
The second type of flow meter has a detector comprising a straight
propagation tube having ultrasonic oscillators at both of its closed
ends, and inflow and outflow tubes connected to the side surface
of the propagation tube, as shown in FIGS. 7 8a, and 9. The ultrasonic
wave generated by means of ultrasonic oscillator will propagate
in parallel with the fluid flowing through the tube. The ultrasonic
flow meter of this type will be referred to hereinafter as "flow
meter of type 2".
The operating priciple adopted in both of the type 1 and the type
2 is referred to as alternately operating method for measuring the
difference between the rates of propagation of the ultrasonic wave.
This method is adopted because of its measuring accuracy and the
cost for it.
In this method, two ultrasonic oscillators are arranged so that
the one of the oscillators may receive the ultrasonic wave generated
by another oscillator, and vice versa. In other words, when one
of the oscillators functions as an ultrasonic oscillator, the other
of the oscillators functions as a receiver for the ultrasonic wave
generated by means of the one oscillator, and vice versa. The flow
rate can be determined by measuring the difference between the time
required for propagating the ultrasonic wave from the one oscillator
to the other oscillator and that from the other oscillator to the
one oscillator. This difference will be referred to hereinbelow
as "propagation time lag".
Each of these flow meters of the type 1 and type 2 has respective
advantages and disadvantages described hereinbelow, so that these
flow meters will be utilized properly for the application.
The primary feature of the flow meter of type 1 is that the components
of the flow meter such as the inflow tube, the propagation tube,
and the outflow tube are included in a continuous straight tube.
In this connection, the flow meter of type 1 has a number of advantages
such that the flow meter can be manufactured economically, the pressure
loss through the flow meter is very little, the cleaning of the
flow meter can easily be carried out, and so on.
However, the smaller the diameter of the tube, the smaller the
distance through which the ultrasonic wave propagates, and the mesuring
accuracy of the propagation time lag will be decreased accordingly.
In this connection, the flow meter of type 1 is not suitable for
the tubings of smaller diameter (i.e. the tubings of lower flow
rate). Actually, a diameter of the tubings of the diameter in the
order of 25 mm is a lower limit for the flow meter of type 1. The
flow meter of type 1 will demonstrate its advantages when applied
to the tubings of larger diameter.
On the other hand, the flow meter of type 2 is complex in its structure,
and inferior to the type 1 in its weight, size, manufacturing cost,
as well as pressure loss and cleaning ability. However, the flow
meter of type 2 is suitable for the tubings of smaller diameter
(i.e. the tubings of lower flow rate), because the propagation distance
of the ultrasonic wave can be set irrespective of the diameter of
the tubing.
In summary, the flow meter of type 1 is for the larger flow rate,
whereas the flow meter of type 2 is for the smaller flow rate.
In the case of the prior flow meter of type 2 for the smaller diameter,
it is necessary to set the distance between two oscillators larger
than a certain distance for assuring predetermined accuracy of the
flow meter. Further, the oscillatory energy larger than the predetermined
value is required for propagating the detectable ultrasonic wave
between the oscillators. It is, therefore, impossible to vary the
length L of the propagation tube and the diameter D of the oscillator.
Although the diameter of the propagation tube can be reduced, if
the diameter of the flow meter shown in FIG. 8a be reduced to the
condition as shown in FIG. 8b, the percentage of the ultrasonic
wave propagating through the fluid is decreased in accordance with
the reduction of the
diameter of the propagation tube, so that the measurement will
be difficult.
The lower limit of the inner diameter of the tubing of the practically
used flow meter of type 2 is in the order of 5 mm.
It is evident from the above description that the most important
improvement to be made on the ultrasonic flow meter is to simplify
the structure of the flow meter as the flow meter of type 1 and
to make the flow meter applicable to the tubings of the smaller
diameter.
OBJECT OF THE INVENTION
The object of the present invention is to provide an ultrasonic
flow meter adapted to be used for the tubings of smaller diameter
of the type determining the flow rate from the difference between
the rates of propagation, or of the type determining the flow rate
from the difference between the propagation times. The flow meter
has a detector defined by a tubing of constant diameter over the
entire length thereof. The flow meter to be provided has a following
advantages.
(a) lower in its manufacturing cost;
(b) higher in its measuring accuracy;
(c) easy in the maintenance and cleaning;
(d) saved the space for dispose it; and
(e) light weight.
SUMMARY OF THE INVENTION
In order to achieve the above object, the ultrasonic flow meter
of the present invention of the type determining the flow rate from
the difference between the rates of propagation, or of the type
determining the flow rate from the difference between the propagation
times, wherein the generated ultrasonic wave is caused to propagete
through the fluid flowing through a measuring tube, the velocity
of the fluid is determined on the basis of the difference between
the rate of propagation of the ultrasonic wave propagates from the
upstream to the downstream and that propagates from the downstream
to the upstream to provide the flow rate of the fluid flowing through
the measuring tube, comprising:
a measuring tube having a uniform diameter over the entire length
thereof, and two ring shaped oscillators disposed longitudinally
forwardly and rearwardly along the tube so as to substantially intimately
contact the inner peripheral surface thereof with the outer peripheral
surface of the tube, wherein an ultrasonic wave is generated by
applying electric AC energy to the one of oscillators, the thus
generated ultrasonic wave is detected by the other oscillator, and
vice versa, to permit and then measuring the time required for propagating
the ultrasonic wave from the upstream oscillator to the downstream
oscillator, and that from the downstream oscillator to the upstream
oscillator, and then to calculate the difference between the measured
times by means of an arithmetric circuit to determine the velocity
of the fluid flowing through the measuring tube. The measuring tube
may be a straight tube or a non-straight tube.
Other objects, features, and advantages will be apparent to those
skilled in the art from a consideration of the following detailed
description and from the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of the ultrasonic flow meter in accordance
with the first embodiment of the present invention;
FIG. 2(a)-2(c) are views of the ultrasonic flow meter in accordance
with the second embodiment of the present invention;
FIG. 3 is a vertical cross-sectional view of a portion of the measuring
tube in which the oscillator is secured;
FIG. 4 is a view showing the relation in time series while the
fluid within the flow meter is stational between AC voltage energizing
either one of the oscillators and electric signals detected by the
other oscillator;
FIG. 5 is a view showing the relation in time series while the
fluid within the flow meter is flowing therethrough between AC voltage
energizing either one of the oscillators and electric signals detected
by the other oscillator;
FIG. 6 is a cross-sectional view of the flow meter of type 1 in
accordance with the prior art;
FIG. 7 is a cross-sectional view of the flow meter of type 2 in
accordance with the prior art;
FIG. 8a is a cross-sectional view of another embodiment of the
flow meter of type 2 and FIG. 8b is an embodiment in which the
diameter of the propagation tube is reduced; and
FIG. 9 is a cross-sectional view of the further embodiment of the
flow meter of type 2.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
A preferred embodiment of the present invention will now be described
with reference to FIGS. 1-5.
In accordance with the first embodiment of the present invention,
the ultrasonic flow meter has a measuring tube 1 comprising a straight
tube of uniform outer diameter over the entire length thereof as
can be seen from FIG. 1. Two ring shaped ultrasonic oscillators
2A and 2B having an inner diameter slightly larger than the outer
diameter of the tube 1 are disposed longitudinally equally spaced
on the tube 1. The clearance defined between an inner peripheral
surface of each ring and an outer peripheral surface of the tube
may be filled with a substance 3 for facilitating the propagation
of the ultrasonic wave to achieve a so-called acoustically engaged
condition. In addition, the substance 3 serves to secure the ultrasonic
oscillators 2A and 2B on the tube 1.
In accordance with the second embodiment of the present invention,
the ultrasonic flow meter has a curved shaped measuring tube as
shown in FIG. 2. A version in which the tube is shaped as "U"
is shown in FIG. 2a, another version in which two U-shaped tubes
disposed in opposite direction are connected with each other is
shown in FIG. 2b, and further version in which the tube is shaped
as a looped coil is shown in FIG. 2c.
In the above-mentioned arrangement, each ultrasonic oscillator
will oscillate radially upon application of electric AC energy thereto,
and generate electric signals similar in their form to the oscillatory
wave upon radial oscillations are applied.
In carrying out the measurement, electric AC energy from an electric
source 4 is applied to either one of the ultrasonic oscillators,
for example, the downstream oscillator 2B to generate ultrasonic
wave.
When the inner lumen of the tube 1 is filled with any fluid, the
ultrasonic wave generated by the ultrasonic oscillator 2B propagates
radially inwardly through the wall of the tube to the fluid, and
once having reached the center of the oscillator (i.e. the center
of the tube), the ultrasonic wave is deflected at right angle and
propagate in parallel to the wall of the tube in both forward and
rearward directions.
The ultrasonic wave is a sort of pressure oscillation, so that
the radially directed pressure fluctuation will also be generated
by the propagation of the ultrasonic wave. The upstream ultrasonic
oscillator 2A will output the corresponding electric signals upon
receiving the pressure fluctuation.
The waveform of the electric energy applied to the oscillator 2B
and the electric signals output from the oscillator 2A are both
input to a propagation time measuring circuit 5A to determine the
time t.sub.1 required for propagating the ultrasonic wave from the
downstream oscillator 2B to the upstream oscillator 2A.
Then the operational mode of ganged switches SW and SW.sub.2 is
shifted to the other circuit to energize the upstream oscillator
2A to generate the ultrasonic wave. Thus generated wave is detected
by the oscillator 2B. The time t.sub.2 required for propagating
the ultrasonic wave from the upstream oscillator 2A to the downstream
oscillator 2B is determined by the propagation time measuring circuit
5A in a same manner as described above with reference to the determination
of time t.sub.1.
When the fluid within the measuring tube is stational (i.e. the
flow rate of the fluid within the tube is equal to zero), the rate
of propagation of the ultrasonic wave through the fluid within the
measuring tube is constant, so that the time t.sub.1 is equal to
the time t.sub.2 as shown in FIG. 4.
On the other hand, when the fluid within the measuring tube is
flowing therethrough, the time t.sub.2 required for propagating
the ultrasonic wave from the upstream oscillator 2A to the downstream
oscillator 2B will be decreased under the effect of the velocity
of the fluid. On the contrary, the time t.sub.1 required for propagating
the ultrasonic wave from the downstream oscillator 2B to the upstream
oscillator 2A will be increased. The velocity of the fluid flowing
through the measuring tube can be obtained by calculating the difference
between the times t.sub.1 and t.sub.2 since the difference will
be increased in proportion to the velocity of the fluid.
The flow meter of the present invention determines the flow rate
from the difference t.sub.1 -t.sub.2 between the time t.sub.1 required
for propagating the ultrasonic wave from the downstream oscillator
2B to the upstream oscillator 2A and the time t.sub.2 required for
propagating the ultrasonic wave from the upstream oscillator 2A
to the downstream oscillator 2B, so that the longer the distance
between the oscillators 2A and 2B, the higher the accuracy of the
measurement.
In the case of a straight measuring tube, lengthening the distance
between oscillators 2A and 2B for achieving high accuracy will lead
to lengthening the entire length of the flow meter in the same plane.
On the contrary, in each curved shaped measuring tube shown respectively
in FIG. 2 having a bend or bends, the apparent length of the flow
meter will not be increased in spite of the fact that the distance
between the oscillators 2A and 2B is increased for achieving high
accuracy.
Specifically, in the version as shown in FIG. 2c, a flow meter
of compact configuration having sufficiently long distances between
oscillators 2A and 2B for increasing the accuracy of the flow meter
can be obtained by repeatedly winding the measuring tube helically.
In the case that the electric circuit for measurement can be disposed
on zone Z (in the version as shown in FIG. 2b, zones Z.sub.1 and
Z.sub.2) defined by the bend or bends of the tube, an unitary ultrasonic
flow meter of very compact size having built-in electric circuit
can be obtained.
In accordance with the present invention, the distance between
two oscillators can be selected independently of the diameter of
the tube on which the oscillators are disposed, and the ring-shaped
oscillators can be manufactured to the outer diameter of the straight
tube, and the flow meter can be adapted to the application in which
a low flow rate of fluid passes through the measuring tube or the
application in which the flow meter include a tube of smaller diameter.
Further, the flow meter of the present invention will provide the
advantages (a)-(e) mentioned in the section of the object of the
present invention.
In accordance with the present invention, a flow meter of still
a smaller diameter than the prior type 2 flow meter can be realized.
This is because reducing the diameter of the tube will not decrease
the percentage of ultrasonic wave propagating through the fluid
within the flow meter, and there is no difficulty in manufacturing
the ultrasonic oscillator of reduced diameter.
While the preferred embodiments of the invention have been illustrated
and described, it will be appreciated that various changes can be
made therein without departing from the spirit and scope of the
invention. The embodiments shown and described are for illutrative
purposes only and are not meant to limit the scope of the invention
as defined by the claims. |