Abstrict A flow meter comprising a fluidic switching device coupled as a
free-running oscillator. The frequency is dependent on the flow
rate of the medium. The device called a fluidistor has a nozzle
(edges) arranged upstream of the control chambers and a first region
downstream of the control chambers, within which first region the
flow of medium lies either on one side or the other side in dependence
upon the pressure conditions and flow conditions prevailing in the
oscillator circuit. A second region is located downstream of said
first region. Mutually spaced apart orifices of a cross-connecting
line, said orifices preferably being arranged transversely to the
flow direction, are arranged at a location at which the stream of
fluid is deflected, in a manner such that said orifices are coupled
together, through a line. In said line is a pressure-sensing device
arranged to generate a signal corresponding to the measuring result
and that said deflection location is placed downstream of the control
chambers.
Claims What is claimed is:
1. A flow meter comprised of a fluidistor coupled as a free-running
oscillator having a frequency responsive to the flow rate of a fluid
medium passing therethrough, said fluidistor including:
at least one control chamber for controlling oscillation of the
fluid medium passing through said fluidistor;
a nozzle located upstream of said control chamber in the direction
of fluid flow through said fluidistor;
a first flow region, located downstream of said control chamber,
in which the flow of fluid medium therethrough oscillates from side
to side of the region in dependence upon the pressure and flow conditions
of the fluid medium within said fluidistor;
a second flow region located downstream of said first region including
a location at which the flow of medium is deflected and a pressure
differential is created across said second region;
a pair of spaced apart orifices disposed transversely to the direction
of fluid flow through said fluidistor and arranged on respective
sides of said second flow region at the deflection location;
a connecting line establishing fluid communication between said
orifices; and
a pressure sensitive device operatively associated with said connecting
line for generating a signal related to the rate of flow of fluid
through said fluidistor.
2. A flow meter according to claim 1 characterised in that the
orifices are located immediately upstream of a constriction in said
second region.
3. A flow meter according to claim 1 characterised in that the
orifices are located downstream of the first region at a distance
from said first region substantially corresponding to the length
of the path of flow for fluid through the first region.
4. A flow meter according to claim 1 characterised in that a metal
object is located in said connecting line and is displaceable to
one side or the other as the result of pressure variations occurring
in the connecting line.
5. A flow meter according to claim 4 characterised in that a sensing
device is located in cooperative relationship with said metal object
and is coupled, via an electric conductor, to a device arranged
to register the frequency of movement of said metal object.
6. A flow meter according to claim 4 characterised in that the
density of the metal object is substantially equal to the density
of the fluid medium.
7. A flow meter according to claim 4 characterised in that the
metal object is a hollow spherical body.
8. A flow meter according to claim 7 characterised in that the
hollow body comprises two parts joined together.
9. A flow meter according to claim 1 characterised in that only
a part of the flow of the total fluid flow to be measured is permitted
to pass through the fluidistor.
Description FIELD OF THE PRESENT INVENTION
The present invention relates to a flow meter and, in particular
to those devices which utilise a fluidic switching device, hereinafter
called a fluidistor, coupled as a free-running or self-oscillating
oscillator. This coupling, which causes the fluidistor to act as
free-running oscillator, comprises either a cross-connection between
the control chambers of the fluidistor or a cross-connection between
an outlet passage and a control chamber. The frequency of such a
free-running oscillator is dependent upon the rate of flow of the
media or the fluid and it is thus a primary desire to construct
the fludistor in a manner such that the frequency is directly dependent
upon and proportional to the rate of flow of the fluid within as
large a range as possible. A prime desire in this respect is to
extend this range in a downward direction, so as also to include
low flow rates.
Although the present invention can be used to measure the flow
rate of media as both gases and liquids, the following description
will be made with reference to liquid as the flowing medium.
A BACKGROUND OF THE PRESENT INVENTION
A fluidistor which satisfies the aforementioned desideratum is
provided upstream of the control chambers with a nozzel, normally
in the form of a constriction of a passage defined by edges, and
forms downstream of the control chambers a first region within which
the flow lies either on one side or the other in dependence upon
the pressure conditions and flow conditions prevailing in the fluidistor
circuit. This region is often called the outlet-passage region since
there is normally provided downstream of the control chambers in
the fluidistor a wedge or stream-divider which defines these outlet
passages. Every fluidistor exhibits a further region located downstream
of the first region. Without the provision of such wedges in a fluidistor,
that side of the stream of fluid remote from the wall portion in
this region is broken up. When the fluidistor is provided with such
wedges, the two streams of fluid are mixed on respective sides of
the stream-divider in said region, immediately when switching occurs
from one outlet passage to the other, to form a jet.
DESCRIPTION OF PRIOR ART
A flow meter is known from the Swedish patent specification No.
7014349. This known fluidistor comprises means which causes the
fluidistor to swing as an oscillator, by arranging a cross connection
between the control chambers of said fluidistor. The fluidistor
has outlet passages on both sides of a stream-divider and by incorporating
a pressure sensing device in a connection between the outlet passages,
in the first region, it is possible, with the aid of this pressure-sensing
device, to acertain the oscillator frequency and thereby to establish
the flow rate of the medium.
A flow meter is particularly sensitive (not porportional) at very
low flow rates, and it is therefore a prime desire to obtain a picture
of the flow through the fluidistor, also at low flow rates, which
is not influenced by the meter, so as to maintain a linear relationship
between frequency and flow.
Thus, the aforementioned Swedish patent specification describes
an arrangement in which the oscillator frequency is sensed in the
first region, within which the flow lies either on one side or the
other, depending upon the pressure conditions prevailing in the
oscillator circuit. By placing the sensing circuit in this first
region and in the streamdivider an adverse effect is obtained on
the picture of the flow in the fluidistor from the aspect of the
measuring results. This is amplified in the aforementioned patent
specification by the fact that the connection line through the stream-divider
is open, and, moreover, downstream of the said connection there
is in said first region a constriction in each respective outlet
passage. This has been done with the intention of amplifying the
pressure difference and optionally to divide a flow through the
connection line. Thus, in the device according to the aforementioned
Swedish patent specifiction the constrictions in the outlet passages
must build up a static pressure difference, this pressure difference
being sensed and measured in the device. The removal of the constrictions
in the first region according to the Swedish patent specification
would mean that only a small, if any difference, in pressure would
occur in the connecting passage.
Since the outlet passage must be provided with a constriction,
it is also necessary to make the stream-divider between the outlet
passages considerably longer than the width of the nozzle, the said
stream-divider in the exemplary embodiment being approximately thirty
times the width of the nozzle.
OBJECTS OF THE PRESENT INVENTION
An object of the primary invention is to provide a flow meter in
which the pressure differences to be utilised are not sensed to
advantage within the first region but within a further, second region.
By this means it is not only possible to exclude the restrictions
in the outlet passages but that a uniform and controllable flow
is ensured within the fluidistor, which means that the linear relationship
between the frequency and flow is amplified in a manner such that
the flow picture in the frequency sensing device does not influence
the flow upstream of the fluidistor oscillator, i.e. in the region
in which the nozzle and control chambers are located.
The present invention also provides the possibility of placing
the cross-connecting line orifices at a distance from each other,
preferably transversely of the flow direction. The said orifices
are also connected to each other via the cross-connecting line in
a manner such that a pressure-sensing device can be incorporated
in said line, said pressure-sensing device being arranged to generate
or initiate a signal corresponding to the measuring result.
For the purpose of creating a measurable pressure, the said orifices
conveniently lie immediately adjacent a location at which the stream
of medium is deflected, normally in a corner, whereby there is generated
a pressure difference. In the exemplary embodiment, this corner
has the form of a slight constriction located downstream of the
said second region. Further, the orifices may be located at a distance
downstream of the first region, corresponding to or substantially
corresponding to the flow length within said first region. Arranged
in the cross-connecting line is a metal object which is displaceable
to one side or the other by variations of pressure occurring in
said line, whilst in connection with said object there is a sensing
device, preferably an inductive transducer. The inductive transducer
is coupled to a device arranged to register and/or indicate the
measurement value, via an electric conductor.
According to the invention, the density of the metal object is
equal to or substantially equal to the density of the medium, such
that the metal object is able to react to any change in the movement
of the medium in the cross-connecting line. The metal object is
preferably a hollow body having a spherical outer configuration.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
An exemplary embodiment exhibiting the significant characterising
features of the present invention will now be described with reference
to the accompanying drawings, in which:
FIG. 1 illustrates the principal of the present invention,
FIG. 2 illustrates a pipe in which there is incorporated a throttle
flange and in which only part of the total flow is allowed to pass
the fluidistor shown in FIG. 3
FIG. 3 illustrates a fluidistor with the surface intended to face
towards and co-act with a planar surface in FIG. 2
FIG. 4 illustrates the fluidistor in the position in which it co-operates
with the planar surface shown in FIG. 2
FIG. 5 is a sectional view of sensing device applied to the fluidistor
shown in FIG. 4 and,
FIG. 6 illustrates two halves of a sphere.
DESCRIPTION OF A PREFERRED EMBODIMENT
Thus the present invention relates to a flow meter incorporating
a fluidistor 1 coupled as a free-running oscillator through a cross-linking
passage 2 extending between the control chambers 3 and 4 thereof.
The oscillator frequency is dependent upon the flow rate of the
fluid, said fluid entering at 5 and passing through a constriction
defined by edges 6 7 the control chambers 3 or 4 and past a first
region 8 into a second region 9 and finally to the outlet 10. As
will be seen from FIG. 1 the fluidistor has a nozzle located upstream
of the control chambers 3 and 4 said nozzle having the form of
the restriction 6 7 and a first region 8 located down-stream of
the control chambers. Within this first region the flow of medium
is such that said flow lies either on one side of said region or
the other, depending upon the pressure conditions and flow conditions
prevailing in the oscillator circuit, there being optionally incorporated
(although not necessarily) in said first region a stream divider
11. In the illustrated embodiment the length of the stream-divider
only corresponds approximately to the width of the constriction
6 7 although there is nothing to prevent the stream-divider from
being longer. Of significance to the present invention is the said
second region 9 located down stream of the first region. In the
absence of a wedge in the fluidistor, the side of the stream remote
from the wall portion is subject to disintegration in the second
region. In the presence of a wedge in the fluidistor the two streams
are mixed on respective sides of the stream divider to form a jet,
this taking place in said second region at the location where switching
from one outlet passage to the other takes place.
In accordance with the present invention, mutually spaced apart
orifices 12 13 of the cross-connecting line, said orifices preferably
being arranged transversely of the flow direction, are arranged
at a location where the stream is deflected. This is particularly
suitable in the second region 9. The orifices 12 13 are connected
together through a line 14 15 in which there is arranged a pressure-sensing
device 16 adapted to generate a signal corresponding to the measured
result.
The orifices 12 13 are arranged adjacent a location where the
stream is deflected in a respective corner, whereby a pressure difference
is generated. In the exemplary embodiment each corner has the form
of a slight constriction located immediately upstream of a construction
17 18 located in the second region 9. The orifices 12 and 13 may
be located at a distance downstream of the first region 8 corresponding
and/or substantially corresponding to the length of the stream or
medium within the first region 8.
Arranged in the line 14 and 15 between the orifices 12 and 13 is
a metal object forming part of a pressure-sensing device. This metal
object is referenced 20. The metal object is displaceable to one
side or the other as a result of variations in pressure occurring
in the lines 14 15 in dependence upon whether the flow is permitted
to pass through the region 8a or the region 8b. Displacement of
the metal object conveniently takes place between stops 21 shown
in the figure and is detected by a inductive transducer.
The inductive transducer conveniently comprises a transducer sold
by Pepper V Fuchs under the trade name NJ4-12GK.
The electrical or inductive transducer 22 is connected through
an electric conductor 23 with a device adapted to register and/or
indicate the measured value, said device being of known construction
and being referenced 24 in FIG. 5.
The density of the metal object 20 is equal to or substantially
equal to the density of the fluid passing through the lines 14
15. The metal object comprises a hollow body, preferably a hollow
sphere. The hollow body may comprise two parts joined together in
some suitable manner. By adapting the thickness of the material
of the hollow sphere to the external volume of the sphere it is
possible to select both size of the sphere and said material thickness
in a manner such that its density coincides with or substantially
coincides with the density of the flowing medium.
In FIG. 2 there is illustrated a pipe through which a total flow
"S" is caused to pass. The pipe 30 is provided with flanges
31 and 32 and has arranged therein a constriction 33 which causes
a part-flow to pass through a pipe 34 and then out through a pipe
35. The pipes 34 and 35 open out on to a flat plate against which
the visible surface of the fluidistor in FIG. 3 shall lie. The pipe
34 communicates with the inlet passage 5 and hence this part-flow
is permitted to pass in through the nozzle 6 and 7 of the fluidistor
and, depending upon the pressure conditions in the control chambers
3 and 4 and the pressure condition in the passage 2 the part-flow
will either lie to the right against part 8a or to the left against
8b. The pressure difference occurring within the second region 9
is sensed via the orifices 12 and 13 before the medium passes through
the outlet 10 and the line 35 back to the pipe.
FIG. 4 illustrates the manner in which the orifices 12 and 13 co-operate
with a sensing device 14 which is shown in cross-sectional view
through the line V--V in FIG. 4.
As will be seen from FIG. 5 the sensing device comprises two parts
41 and 42 the two parts being arranged to be screwed together.
The orifice 12 is arranged to co-operate with the pipe 14 while
the orifice 13 is arranged to co-operate with the pipe 15 which
both form a chamber 15a in which a sphere 20 is placed. In the illustrated
embodiment the sphere 20 can either move towards a wall potion 14'
in the line or against an O-ring 15'. By removing the part 42 the
sphere 20 can be moved into the section 15 of the line into the
correct position. The inductive transducer 22 is insertable in a
hole 22a in the sensing device and is thereby able to detect the
position of the sphere 20. Thus, the transducer is in electrical
connection, through the line 23 with a measuring device 24 the
nature of which forms no part of the present invention and will
not therefore be described in detail.
FIG. 6 shows how the sphere 20 may comprise two parts 20a and 20b.
The two parts are hemi-spherical and are fastened one to the other
in any suitable manner.
The inductive transducer 20 is arranged to emit pulses on the line
23 these pulses being read per unit of time in the measuring unit
24. Since the number of pulses per unit of time is directly proportional
to the part flow through pipes 34 and 35 and this part-flow, in
turn, is directly proportional to the total flow "S,"
as a result of the flange 33 the measuring device 24 is able to
evaluate the flow in the line with great accuracy.
For the sake of clarity, the means for attaching the fluidistor
of FIG. 3 to the plate of FIG. 2 are not shown.
The invention is not restricted to the described embodiment, but
can be modified within the scope of the following claims. |