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 three
ring shaped oscillators disposed longitudinally along the tube so
as to intimately contact the inner peripheral surface thereof with
the outer peripheral surface of the tube. The central oscillator
of said three oscillators is energized by electric AC energy to
generate an ultrasonic wave. The thus generated ultrasonic wave
is detected by means of forward and rearward oscillators. The ultrasonic
wave detected by the forward oscillator and that detected by the
rearward oscillator are processed by means of a comparator to obtain
the flow rate 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; and
three oscillators disposed longitudinally 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 the tube;
said oscillators including a central oscillator and forward and
rearward oscillators; wherein:
the central oscillator of said three oscillators is energized by
electric AC energy and is ring shaped for generating and propagating
an 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 in forward and rearward directions
parallel to the wall of the tube;
said forward and rearward oscillators are ring shaped for detecting
the ultrasonic wave propagating in said forward and rearward parallel
directions and for outputting signals indicative thereof; and
the signals indicative of the ultrasonic waves detected by the
forward oscillator and by the rearward oscillator are processed
by a comparator to obtain the flow rate of the fluid flowing through
the measuring tube.
2. An ultrasonic flow meter as defined in claim 1 wherein the measuring
tube is a straight tube.
3. An ultrasonic flow meter as defined in claim 1 wherein the measuring
tube is a non-straight tube.
4. An ultrasonic flow meter comprising:
a measuring tube of uniform outer diameter over the entire length
thereof;
said measuring pipe being a straight tube,
three ring shaped oscillators having an inner aperture of a diameter
slightly larger than the outer diameter of said measuring tube,
said oscillators disposed along the tube longitudinally at three
positions on the outer periphery the tube respectively; and
a substance for facilitating propagation of an ultrasonic wave
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,
said ring shaped oscillators including a central oscillator and
forward and rearward oscillators;
wherein: the central oscillator of said three oscillators is energized
by electric AC energy to generate an ultrasonic wave propagating
inwardly through the tube; the thus generated ultrasonic wave is
detected by said forward and rearward oscillators; and the ultrasonic
waves detected by the forward oscillator and by the rearward oscillator
are processed by a comparator to obtain the flow rate of the fluid
flowing through the measuring tube.
5. An ultrasonic flow meter as defined in claim 4 wherein the substance
for facilitating the propagation of the ultrasonic wave comprises
a semifluid.
6. An ultrasonic flow meter as defined in claim 4 wherein the substance
for facilitating the propagation of the ultrasonic wave comprises
a semisolid.
7. An ultrasonic flow meter as defined in claim 5 wherein the
substance for facilitating the propagation of the ultrasonic wave
comprises grease.
8. An ultrasonic flow meter as recited in claim 1 wherein said
measuring tube is curved.
9. An ultrasonic flow meter as recited in claim 8 wherein said
measuring tube is U-shaped.
10. An ultrasonic flow meter as recited in claim 8 wherein said
measuring tube includes two U-shaped tubes, connected to each other,
and wherein said central oscillator is located at a point of connection
of said two U-shaped tubes to each other.
11. An ultrasonic flow meter as recited in claim 8 wherein said
measuring tube includes at least one looped coil.
12. An ultrasonic flow meter as recited in claim 4 wherein said
tube is defined by a wall, said three ring shaped oscillators mounted
externally of said wall for propagating said ultrasonic wave through
said wall radially to a center of the tube for deflection at right
angle in the center and for propagating in parallel to the wall.
Description FIELD OF THE INVENTION
The present invention relates to the field of flow meters and,
in particular, to ultrasonic flow meters.
BACKGROUNG 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. 7. The generated ultrasonic wave propagates
obliquely to the flowing direction of the 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. 8 9a, and 10. 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 principle 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 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. 9a be reduced to the
condition as shown in FIG. 9b, 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 three ring shaped oscillators disposed longitudinally
along the tube so as to intimately contact the inner peripheral
surface thereof with the outer peripheral surface of the tube, wherein
an ultrasonic wave is generated by means of the central oscillator
of said three oscillators, the thus generated ultrasonic wave is
detected by means of forward and rearward oscillators, and then
processing the ultrasonic wave detected by the forward oscillator
and that detected by the rearward oscillator by means of a comparator
to obtain the flow rate of the fluid flowing through the measuring
tube. The measuring tube may be a straight tube or a non-straight
tube.
Particularly, when electric AC energy is applied to the central
oscillator in pulse or intermittently, the times required to propagate
the ultrasonic wave from the central oscillator to the forward or
rearward oscillator are detected.
Further, when the AC voltage of constant frequency is applied to
the central oscillator, the phase difference between the waveform
of the electric signals and output from the forward or rearward
oscillator is detected.
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;
FIGS. 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
the central oscillator 2B and electric signals detected by upstream
oscillator 2C and downstream oscillator 2C;
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 the central oscillator 2B and electric signals detected
by upstream oscillator 2C and downstream oscillator 2C;
FIG. 6 is a phase difference between waveforms;
FIG. 7 is a cross-sectional view of the flow meter of type 1 in
accordance with the prior art;
FIG. 8 is a cross-sectional view of the flow meter of type 2 in
accordance with the prior art;
FIG. 9a is a cross-sectional view of another embodiment of the
flow meter of type 2 and FIG. 9b is an embodiment in which the
diameter of the propagation tube is reduced; and
FIG. 10 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. 1-6.
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. Three ring shaped ultrasonic oscillators
2A, 2B, and 2C 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, 2B, and 2C on the tube 1. Substance 3 may be a semifluid
(such as grease) or a semisolid.
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 the centrally disposed ultrasonic 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 centrally disposed 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 forward and rearward
ultrasonic oscillator 2A and 2C will output the corresponding electric
signals upon receiving the pressure fluctuation, and each signal
is amplified through the amplifier 5A and 5C, and then input to
the comparator circuit 6.
When the fluid within the measuring tube is stational (i.e. the
flow rate of the fluid within the tube is equal to zero) and the
distance between oscillators 2A and 2B, and that between oscillators
2B and 2C are equal, the electric signal generated by the central
generator 2B propagates symmetrically in both forward and rearward
directions, so that the electric signals output from the forward
and rearward oscillator 2A and 2C are equal as shown in FIG. 4.
On the other hand, when the fluid within the measuring tube is
flowing through, a certain time lag will be created between the
output signal generated by the upstream oscillator 2A and that of
the downstream oscillator 2C as shown in FIG. 5. This time lag will
increase in proportion to the flow rate of the fluid.
In conclusion, the flow rate of the fluid flowing through the measuring
tube can be measured by detecting the time lag by the comparator
circuit 6.
In this embodiment, the ultrasonic wave is generated in shot or
intermittently, and the flow rate may be calculated from the time
lag.DELTA. t between the first arrival times of the forward and
rearward oscillators. However, the comparator circuit may adopt
the phase difference detecting process utilized in such apparatus
as optical rangefinders in order to detect the flow rate.
In accordance with the phase difference detecting process, there
are implemented the steps of energizing the central oscillator 2B
with the AC voltage of constant frequency, analyzing the waveform
Fa and Fc as shown in FIG. 6 of the electric signals output from
forward and rearward oscillators 2A and 2C by Fourier analysis,
detecting the time lag defined between the oscillatory waveform
as the phase difference, and accurately determining the time lag
therebetween.
Unlike the above-mentioned method in which there is calculated
the time lag between the first arrival times of the forward and
rearward oscillators, in this phase difference detecting process,
ultrasonic wave is remained generated, so that the variation of
the flow rate can be detected upon occurrence.
Owing to the recent progress in the art of semiconductor technology,
this process can be practiced broadly and economically by employing
the microprocessor.
In the above discussed embodiments, it is assumed that the distance
from the central oscillator to each of the forward and rearward
oscillators is equal. However, if compensation can be carried out
in calculating the flow rate from the time lag, the distance need
not be equal.
The flow meter of the present invention measures the flow rate
from the difference T.sub.A -T.sub.C between the times T.sub.A and
T.sub.C required for the ultrasonic wave generated by the oscillator
2B to arrive at each of the oscillators 2A and 2C, so that the longer
the distance between the oscillators 2A and 2B and the distance
between oscillators 2B and 2C, the higher the accuracy of the measurement.
In the case of a straight measuring tube, lengthening the distance
between oscillators 2A and 2B and the distance between oscillators
2B and 2C 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 oscillators 2A and 2B is increased for achiving 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 and between oscillators 2B and 2C 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, a 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
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 includes 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, flow meter of further
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. |