The vortex flow meter includes a conduit for the passage of a fluid
therethrough and a vortex generator disposed in said conduit at
the upstream end thereof. The vortex generator includes a plurality
of vortex amplifying plates which are disposed at right angles to
the flow of fluid through the conduit and a pair of symmetrically
disposed hot wires are mounted under tension on posts protruding
from the surface of the downstream plate in spaced relation to the
surface of the plate.
1. A vortex flow meter comprising a conduit for the passage of
a fluid therethrough from an upstream end to a downstream end, vortex
generating means disposed in said conduit and having a surface at
the downstream end thereof disposed at right angles with respect
to the axis of said conduit, a plurality of posts secured to said
surface and protruding therefrom in the downstream direction and
hot wire means comprised of two wires symmetrically disposed with
respect to each other on said posts under tension in a substantially
zigzag fashion and in spaced relation to said surface for detecting
the frequency of Karman's vortices generated downstream of said
vortex generator means.
BACKGROUND OF THE INVENTION
The present invention is directed to a vortex flow meter and more
particularly to the vortex detecting elements within the flow meter.
Vortex flow meter devices are generally operative to generate a
frequency signal proportionate to the flow rate or velocity of a
fluid passing through a conduit. In such devices a plurality of
vortices are generated downstream from a vortex generator which
is inserted into the fluid to be measured. There are a number of
methods for detecting the vortices in terms of changes in pressure,
flow velocity, transmission of ultrasonic waves, radiation of heat-sensitive
elements or the like. However, an accurate frequency signal cannot
be produced unless a sensor for producing such an electric output
signal corresponding to the frequency of the aforementioned vortices
is properly positioned within the conduit. An example of a method
for properly positioning the sensor is explained in detail in Japanese
Patent Publication No. 54-38513. An excellent method for measuring
the frequency of Karman's vortices is a hot wire system which is
highly responsive but inexpensive and is suitable over a wide flow
rate range from a very low flow rate to a very high flow rate.
One of the problems with such a hot wire system is that the hot
wires are easily broken when they are extended under tension since
they are extremely thin. Also, if the hot wires are extended under
tension directly on the conduit through which the fluid to be measured
flows, the hot wires will break unless their thermal expansion is
identical to that of the conduit for the fluid. Furthermore, the
hot wires themselves tend to deteriorate rapidly when they are exposed
directly to the pressure of the fluid passing through the conduit.
In order to avoid the aforementioned problems, it has been proposed
to deposit platinum or the like directly on the surface of the vortex
generator. However, in such a method, the responsiveness of the
hot wire system deteriorates since the heat of the deposited platinum
is transferred to the vortex generator. In order to raise the temperature
of the deposited conductive material an additional amount of current
must be supplied which renders the system uneconomical.
SUMMARY OF THE INVENTION
The present invention provides a new and improved vortex flow meter
utilizing a hot wire system for detecting and measuring the frequency
of the vortices which eliminates the aforementioned problems while
carrying out the detection and measurement in a simple and economical
The present invention provides a new and improved vortex flow meter
utilizing a hot wire system wherein the hot wires are disposed downstream
of the vortex generator out of the direct path of the fluid while
being supported in spaced relation from the vortex generator in
a manner which minimizes the heat transfer from the wires to the
The foregoing and other objects, features and advantages of the
invention will be apparent from the following more particular description
of a preferred embodiment of the invention as illustrated in the
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic side elevation view, partly in section of
the vortex flow meter according to the present invention.
FIG. 2 is an end view of the vortex amplifying plate having the
hot wires mounted thereon.
FIG. 3 is a sectional view taken along the line A--A of FIG. 2.
DETAILED DESCRIPTION OF THE INVENTION
A vortex generator 2 is located within a conduit 1 for the purpose
of generating a series of vortices 3 as shown in FIG. 1. The vortex
generator 2 is comprised of a generating column 2a which extends
coaxially of the conduit 1 and is supported by a grid 4 at the upstream
end of the conduit. The grid 4 may contain suitable filter elements
or the like and the fluid is directed into the conduit in the direction
of the arrow as shown in FIG. 1. The vortex generator is further
comprised of a plurality of vortex amplifying plates 2b, 2c and
2d which are arranged to amplify the series of Karman's vortices.
On the downstream side of the vortex amplifying plate 2d there
are mounted a plurality of posts 5 to which the hot wires 6 are
symmetrically secured under tension for the purpose of detecting
the frequency of the vortices as they pass downwardly through the
conduit as viewed in FIG. 1.
The vortices 3 are alternately generated on opposite sides of the
vortex generator and as they move downstream past the amplifying
plates, the hot wires 6 will be alternately cooled as each vortex
passes. The alternate cooling of the hot wires through which an
electric signal is passed varies the conductivity of the hot wires
to thereby vary the current. The changes in current in each wire
may be detected by a suitable circuit (not shown) for producing
an output signal indicative of the frequency of the vortices passing
through the conduit.
As mentioned previously, the hot wires 6 are mounted on the posts
5 under tension and may generate a form similar to the letter V
or the letter N. It is also possible for the hot wires to be located
about the posts 5 in a plurality of turns extending substantially
parallel with the vortex generator plate. The portions of the hot
wire leading to the posts may follow any suitable path outwardly
of the conduit which will protect the wires 6 from being broken.
The material of the vortex amplifying plate 2d may be chosen so
as to minimize the possiblity of wire breakage due to thermal expansion.
Since the hot wires are carried by the posts 5 on the amplifying
plate in spaced relation to the amplifying plate 2d the wires do
not lose their heat to the amplifying plate and therefore their
responsiveness is not affected and extra heating of the wires is
not required. Since the hot wires are disposed in the wake of the
fluid to be measured, that is, on the downstream face of the vortex
amplifying plate 2d, they are not subjected directly to the pressure
of the fluid thereby increasing their durability.
Even though the vortex generator 2 has been described as being
comprised of a plurality of parts and even though a plurality of
hot wires are utilized, similar results can be obtained with a onepiece
generator and a single hot wire.
While the invention has been particularly shown and described with
reference to a preferred embodiment thereof, it will be understood
by those in the art that various changes in form and details may
be made therein without departing from the spirit and scope of the