Abstrict A flow meter in which a bluff body of elongated cross-section extends
substantially normal to the axis of a conduit through which a fluid,
which may be a liquid or a gas, passes so that vortices or whirls
alternatingly breaking away from the body are formed in the fluid
to opposite sides of the body, and in which the frequency of the
alternatingly breaking vortices is proportionate to the speed, respectively
the volume per time unit, of the fluid passing through the conduit.
This frequency is measured by at least one feeler arranged in a
measuring conduit located outside the first-mentioned conduit and
in which the measuring conduit communicates through bores with the
interior of the first-mentioned conduit to opposite sides of the
bluff body.
Claims What is claimed as new and desired to be protected by Letters Patent
is set forth in the appended claims:
1. In a flow meter for measuring the speed of a fluid passing through
a conduit, a combination comprising a turbulence producing bluff
body extending substantially normal to the axis of the conduit through
the interior of the latter to produce in the fluid passing through
the conduit to opposite sides of said body vortices which alternatingly
break away from the body and the frequency of which is proportionate
to the speed of the fluid passing through said conduit, said body
having a front face adapted to be impinged by the fluid passing
through the conduit; a measuring conduit outside said first-mentioned
conduit, said measuring conduit having a pair of open ends; a pair
of bores each having one end communicating with the respective open
end of said measuring conduit and another end communicating with
the interior of said first-mentioned conduit, the other end of one
of said bores communicating with said first-mentioned conduit to
one side of said bluff body and slightly upstream of the front face
thereof and the other end of the other of said bores communicating
with the interior of said first-mentioned conduit at the other side
of said bluff body and slightly downstream of said front face; and
a feeler for measuring said frequency located in said measuring
conduit.
2. A combination as defined in claim 1 wherein said bluff body
has an elongated cross-section in the direction of the flow of fluid
passing through said first-mentioned conduit, and wherein the other
end of said other bore is located at about the first third of the
cross-section of the bluff body, as seen in the direction of the
fluid passing through said first-mentioned conduit.
3. A combination as defined in claim 1 wherein said bluff body
has a substantially T-shaped cross-section.
4. A combination as defined in claim 1 and including a feeler
head fixedly mounted on said first-mentioned conduit, said measuring
conduit and said feeler being located in said feeler head.
5. A combination as defined in claim 4 wherein said bores extend
substantially parallel to said bluff body.
6. A combination as defined in claim 4 and including tubular support
means passing in a sealed manner through said measuring head for
supporting said feeler, said tubular support means having an outer
end projecting beyond said measuring head and a pair of conductors
connected to said feeler and passing through said tubular support
means to the outside of said measuring head.
7. A combination as defined in claim 1 wherein two pairs of bores
are provided, wherein the other ends of one pair of said bores are
mirror-symmetrically arranged with respect to the other ends of
the other pair and wherein the one end of one pair communicates
respectively with the open ends of a first measuring conduit and
the one end of the other pair communicates with the open ends of
a second measuring conduit, and a feeler in each measuring conduit.
Description BACKGROUND OF THE INVENTION
The present invention relates to a flow meter, in which a bluff
body of elongated cross-section extends substantially normal to
the axis of a conduit through which a fluid, which may be a liquid
or a gas, passes, so that vortices are formed in the liquid to opposite
sides of the body which alternatingly break away from the latter.
The frequency of the alternatingly breaking vortices is proportionate
to the speed, respectively the volume per time unit, of the fluid
passing through the conduit and this frequency is measured by at
least one feeler arranged in a measuring conduit located outside
the first-mentioned conduit and in which the outer ends of the measuring
conduit communicate through bores with the interior of the first-mentioned
conduit to opposite sides of the bluff body.
Such a flow meter has the advantage that the feeler is arranged,
not as usual on or in the bluff body and therewith in the mainstream
passing through the conduit, but in which the feeler is located
in a measuring conduit provided outside of the main conduit. In
this way the feeler may be easily exchanged during the operation
of the flow meter and in addition it is protected from any mechanical
damage, which may be caused by particles taken along by the fluid
passing through the main conduit.
In flow meters of the aforementioned kind it is known to arrange
the ends of the bores which communicate with the main conduit at
the rear region of the bluff body, as considered in the direction
of the flow of the fluid flowing through the main conduit, whereby
both inner ends are arranged in a plane which is normal to the longitudinal
axis of the main conduit, that is, both inner ends are located directly
in the region of the leading vortices. The vortices which, according
to Karman's street of vortices detach itself alternatingly from
the bluff body, will cause at the bores alternating pressure variations,
which will produce in the measuring conduit, due to the momentarily
produced pressure difference, an alternating fluid stream, the frequency
of which is sensed by the feeler and indicated as a measurement
for the speed of the fluid passing through the main conduit.
Due to the irregularity of the departing vortices directly in the
vortex region, such irregularities are transmitted through the bores
also onto the movement of the fluid in the measuring conduit, so
that a usable signal output is only obtainable at low frequencies,
that is, at a large nominal width of the flow meter. However, at
small monimal widths and therewith connected high vortex frequencies,
a sure signal reception is not assured, since the irregularities
of the movement of the fluid occurring in the measuring conduit,
which are due to the not always simultaneously occurring of plus
and minus impulses, lead to super impositions and therewith to disturbances
in the measuring conduit. In addition it is possible, since the
fluid medium in the measuring conduit only pendulates, that during
measuring of gas, condensate and during measuring of liquid, gas
carried thereby will accumulate in the measuring conduit, so that
the signal will be changed or completely extinguished.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a flow meter
operating according to the above-mentioned principle, which at all,
that is also at high vortex frequencies will assure a perfect indication
of the speed of the fluid passing through a conduit.
With these and other objects in view, which will become apparent
as the description proceeds, the flow meter for measuring the speed
of the fluid passing through a conduit mainly comprises a turbulence
producing bluff body extending normal to the axis of a conduit through
the interior of the latter to produce in the fluid passing through
the conduit to opposite sides of the body vortices which alternatingly
brake away from the body and the frequency of which is proportionate
to the speed of the fluid passing through the conduit, a measuring
conduit outside the first-mentioned conduit in which open ends of
the measuring conduit communicate through a pair of bores with the
interior of the first-mentioned conduit and in which an inner end
of one of the bores communicates with the first-mentioned conduit
at one side of the bluff body and slightly upstream of a front face
thereof, whereas an inner end of the other of the bores communicates
with the interior of the first-mentioned conduit at the other side
of the bluff body and slightly downstream of the mentioned front
face and in which a feeler for measuring the frequency of the alternatingly
breaking vortices is located in the above-mentioned measuring conduit.
The bluff body has an elongated cross-section in the direction
of flow of the fluid passing through the first-mentioned conduit
and the inner end of the other bore is preferably located at about
the first third of the cross-section of the bluff body.
The inner end of the one bore which is located slightly upstream
of the front face of the bluff body will receive very uniform and
smooth pressure variations, which are released by the vortices street
of Karman and which extend to this inner end. The inner end of the
other bore located in the region of the bluff body will receive,
due to its nearness to the vortex zone, very strong pressure variations,
however, with disturbing waves of low and high frequency superimposed
since the Karman street of vortices produces a hydrodynamic instability
so that necessarily additional and secondary vortices are present.
Due to the cooperation of the two displaced inner ends of the bores,
the two essentially diferent forms of the pressure variations, that
is, in the front smooth and uniform, but relatively weak and in
the rear slightly varying, but rather strong, are combined to a
proper signal. The different impulses support each other in the
measuring conduit, as shown by experiments, in a surprising manner
so favorably that a clear well-defined strong signal is obtained,
even at high frequencies. Due to the static pressure difference,
which is always present between the inner ends of the first and
the second bore, an advancing impulse wave is created, which is
initiated by the rear bore and which is formed by the front bore.
Thereby any disturbing additional pulsations are smoothed, respectively
filtered out.
Due to the static pressure difference between the two bores, the
measuring conduit will also be automatically ventilated, if the
flow meter is used for measuring the speed of a liquid passing therethrough,
or drained, if the speed of a gas is to be measured.
Preferably, two pairs of bores may be provided in which the inner
ends of one pair of bores are mirror-symmetrically arranged with
respect to the inner ends of the other pair, whereas the outer ends
of the bores are respectively connected to two separate measuring
conduits, in each of which a feeler is located. In this way two
signals in phase opposition are created, which, by means of a simple
circuit, can be used for surveyance of the signals so that a disturbance
in the function may be immediately indicated. With the two signals
produced in phase opposition it is also possible to obtain, by means
of a differential circuit, an extremely high signal amplitude, which
will assure even at above normal frequency regions still a proper
signal.
The novel features which are considered as characteristic for the
invention are set forth in particular in the appended claims. The
invention itself, however, both as to its construction and its method
of operation, together with additional objects and advantages thereof,
will be best understood from the following description of specific
embodiments when read in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates in cross-section a first embodiment of a flow
meter according to the present invention;
FIG. 2 is a cross-section taken along the line II--II of FIG. 1;
FIG. 3 illustrates in cross-section a second embodiment according
to the present invention;
FIG. 4 is a cross-section taken along the line IV--IV of FIG. 3;
and
FIG. 5 is a cross-section taken along the line V--V of FIG. 3.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawing and more specifically to FIGS. 1 and
2 it will be seen that the flow meter illustrated therein comprises
a vortex producing bluff body 1 extending normal to the axis of
a conduit 2 through the interior of the latter and the conduit 2
is flown through by fluid, that is a liquid or a gas, the speed
of which has to be measured by the flow meter. The bluff body 1
produces to opposite sides 3 and 4 thereof vortices alternatingly
breaking away from the body 1 the frequency of which is proportionate
to the speed of the fluid passing through the conduit 2. This frequency
is transmitted by means of two bores 5 and 6 through the wall of
the conduit 2 and a measuring conduit 7 located outside of the main
conduit 2 to a feeler element 8 located in the measuring conduit
7. The measuring conduit 7 and the feeler 8 are located in a feeler
head 9 connected in any convenient manner, not shown in the drawing,
to a flattened outer surface portion of the main conduit 2. The
feeler element 8 is mounted in a tubular support 10 (FIG. 2) which
is inserted in a sealed manner in a bore provided in the feeler
head 9 and the tubular support 10 is held in position by a screw
bushing 11 screwed into a properly threaded portion of the aforementioned
bore. The inpulses imparted to the feeler 8 are transmitted to the
outside by electrical conductors 12 which may be connected to an
indicator instrument of known construction, not shown in the drawing.
The bores 5 and 6 are preferably parallel to the longitudinal axis
of the bluff body 1.
According to the present invention the bore 6 communicates at its
inner end with the space 4 in the interior of the conduit 2 to one
side of the bluff body 1 and slightly upstream of a front face 13
of the bluff body 1 which is adapted to be impinged by the fluid
passing through the interior of the conduit 2. The inner end of
the bore 5 communicates with the interior of the conduit 2 at the
other side 3 of the bluff body 1 and slightly downstream of the
front face 13 of the latter, preferably at the border of the vortex
zone about in the first third of the elongated bluff body 1 as
measured in the direction of the fluid flow passing through the
interior of the conduit 2.
In the embodiment shown in FIGS. 3-5 two pairs of bores, that is
the bores 5 6 and 14 15 are provided which are arranged mirror-symmetrically
with respect to each other. The bores 5 and 6 are connected to each
other by a measuring conduit 7 with a feeler element 8 provided
therein, whereas the bores 14 and 15 are connected by means of a
measuring conduit 16 to act on a feeler element 17 provided in the
conduit. The feeler element 8 is supported in the manner as described
in connection with FIG. 2 and the feeler element 17 likewise is
supported in a tubular support 18 located in a sealed manner in
a corresponding bore in the feeler head 9 and held in place by a
screw bushing 19. Both tubular supports 10 and 18 may easily be
assembled or disassembled with the remainder of the flow meter,
even during operation of the latter, so that the feeler elements
8 and 17 may be replaced any time such a replacement appears necessary.
It will be understood that each of the elements described above,
or two or more together, may also find a useful application in other
types of flow meters differing from the types described above.
While the invention has been illustrated and described as embodied
in a flow meter, it is not intended to be limited to the details
shown, since various modifications and structural changes may be
made without departing in any way from the spirit of the present
invention.
Without further analysis, the foregoing will so fully reveal the
gist of the present invention that others can by applying current
knowledge readily adapt it for various applications without omitting
features that, from the standpoint of prior art, fairly constitute
essential characteristics of the generic or specific aspects of
this invention.
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