An improved flow meter has a vertical chamber of relatively constant
cross-section. In this chamber a float resides having a corss-section
only slightly less than the cross-section of the chamber. Fluid
is introduced at the bottom of the chamber and flows to the top
of the chamber. The chamber top is provided with relief port outletting
through a chamber throttle value. Similarly, a passage through the
float has a float throttle valve. The chamber throttle valve controls
the back pressure on the float and provides adjustability to the
lifting of the float at various pressure levels. The throttle valve
provides adjustability to the range of flow to which positioning
of the float responds. A series of apertures configured along the
sides of the chamber open as the float moves upwardly in response
to increasing fluid pressure in the chamber below the float. The
flow meter is digitally sensitive on an analog basis to changes
in flow. One of the chamber walls can be formed from a printed circuit
board which includes apparatus for sensing the position of the float
as well as the flow meter apertures. Calibration of the float sensors
to float position is obviated by this arrangement.
What is claimed is:
1. A device for measuring the flow of fluids, comprising: a housing
defining a chamber of generally constant cross-section, said chamber
having a fluid entrance port communicated at one end and a fluid
exit port communicated at the other end; a float positioned in said
chamber intermediate the fluid entrance and exit ports and being
of lesser but complimentary cross-section to that of said chamber,
said float being biased for movement toward said fluid entrance
port, said chamber including a series of apertures therein that
are at least partially obstructable by said float when said float
is biased toward said fluid entrance port, said float being movable
in response to fluid pressure at said fluid entrance port to successively
uncover said apertures to permit fluid flow from said chamber; and
means for adjustably throttling fluid exiting said other end of
the chamber, whereby the response of said float reacts at varying
pressure ranges to vary the scale of response of said float.
2. The invention of claim 1 wherein said float includes first means
for providing fluid communication between the entrance port and
the exit port through said float, including a passage therethrough;
and second means within said passage for adjusting the rate of fluid
flow through said first means.
3. The invention of claim 1 and including means for sensing the
position of said float in said chamber.
4. The invention of claim 3 wherein the sensing means includes
a number of electrically conductive, spaced, commutating segments
formed on a first portion of an interior surface of said chamber,
a length of conductive material formed on a second portion of the
interior surface of said chamber, and means carried by said float
for establishing electrical communication between the length of
conductive material and ones of the commutating segments as said
float moves within said chamber.
5. The invention of claim 4 including resistance means electrically
coupled to the commutating segments in a manner that causes a decreasing
resistance value to be exhibited at a terminal that is coupled to
said resistance means as said float moves in one direction in said
6. The invention of claim 1 and wherein said fluid entrance port
is at the bottom of said chamber, said fluid exit port is at the
top of said chamber, and said float is gravity biased.
7. A device for measuring the flow of fluids comprising in combination:
a housing defining a vertical chamber of generally constant cross-section,
said chamber having a fluid entrance port communicated to a bottom
section thereof and a fluid exit port communicated to a top section
thereof; a float of lesser but complementary cross-section to the
cross-section of said vertical chamber, said float biased for movement
towards said fluid entrance port and away from said fluid exit port;
said housing having a series of apertures therein and into said
chamber, at least some of the apertures being at least partially
obstructed by said float, said float being movably responsive to
increased fluid pressure at the bottom section of said chamber to
successively uncover said apertures to permit fluid flow from said
chamber; a passageway extending through said float communicating
the bottom section of said chamber to the top of said chamber; means
for adjustably controlling fluid communication through the passageway
of said float.
8. The device according to claim 7 and wherein said float includes
an adjustable passageway therethrough for bypassing a predetermined
amount of fluid from the entrance port side of said float to the
exit port side of said float.
9. The device of claim 7 including means for adjustably restricting
fluid flow through the passageway of the float to the top section
of the chamber.
10. The device of claim 7 wherein said controlling means includes
first fluid restriction means coupled to the float and second restriction
means coupled to the fluid exit port.
11. The invention of claim 7 and wherein said float is gravity
12. The invention of claim 7 and wherein a side of said chamber
is found by a printed circuit board.
13. The invention of claim 12 and wherein said side of said chamber
closed by said printed circuit board includes apertures therein.
14. The invention of claim 13 and wherein said printed circuit
board includes means for the sensing of position of said float within
15. In a flow meter of the type having a sidewall defining a chamber
of constant cross section, said chamber having a fluid entrance
port and a fluid exit port relatively spaced apart from one another;
a float contained in said chamber and between said fluid entrance
and exit ports, said float being biased for movement toward the
fluid entrance port and away from the fluid exit port of said chamber
and having a dimension less than the inside dimension of said chamber
so that said float moves in response to fluid pressure introduced
at said fluid entrance port; the side wall of said chamber having
a series of apertures therein to manifold said chamber; at least
some of the apertures manifolding said chamber being at least partially
obstructable by said float as said float is biased toward said fluid
entrance port, said float being movably responsive to increased
fluid pressure at the fluid entrance port to successively uncover
said apertures to permit fluid flow from said chamber; the float
including means for adjustably controlling fluid exiting from the
fluid exit port of said chamber, whereby the response of said float
reacts at varying pressure ranges to vary the scale of response
of said float.
16. The invention of claim 15 and wherein said float is gravity
17. The invention of claim 15 and wherein at least a portion of
the sidewall of said chamber is formed by a printed circuit board;
said printed circuit board having the apertures of said flow meter
configured therein and having means for sensing the position of
said float along said chamber sidewall.
BACKGROUND OF THE INVENTION
This invention relates to flow meters and more specifically to
a flow meter which has an adjustable range and a digitized indication
of flow over an adjustable range of pressure change.
SUMMARY OF THE PRIOR ART
Float flow meters are known. Assuming that such flow meters are
gravity biased, they usually consist of a vertical chamber with
a float positioned therein. Typically, the chamber is tapered and
the float placed there within to move upwardly with the flow of
air. Air enters at the bottom of the chamber and typically flows
around the float and out through holes at the top. For instance,
a device was described within which the chamber was frustroconical
in shape and became larger in cross-section away from the air entrance
at the bottom of the chamber.
In order to modify or change the operating range of flow meters
of the type to which this invention is directed, it was necessary
to change the operating parts of the flow meter itself. Thus, for
example, either the weight of the float was changed, its geometry,
or both. This could be both time-consuming and expensive, not to
SUMMARY OF THE INVENTION
An improved flow meter has a vertical chamber of relatively constant
cross-section. In this chamber a float resides having a cross-section
only slightly less than the cross-section of the chamber. Fluid
introduced at the bottom of the chamber causes the float to move
upward toward the top of the chamber. A series of apertures, formed
along the sides of the chamber, are opened as the float moves upwardly
in response to increasing fluid pressure in the chamber below the
The chamber top is provided with relief port outletting through
a chamber throttle value. Similarly, a passage through the float
has a float throttle valve. The chamber throttle valve controls
the back pressure on the float and provides adjustability to the
lifting of the float at various pressure levels. The throttle valve
thereby provides adjustability to the range to which positioning
of the float responds. One of the chamber walls can be formed from
a printed circuit board which includes apparatus for sensing the
position of the float as well as the flow meter apertures. Calibration
of the float sensors to float position is obviated by this arrangement
OTHER OBJECTS AND ADVANTAGES
An object of this invention is to provide a flow meter which has
a readily adjustable flow range. According to this aspect of the
invention, a vertical chamber of relatively constant cross-section
has a float placed therein. The float has a cross-section which
is only slightly less than the cross-section of the chamber. A small
and adjustable portion of the fluid introduced at the bottom of
the chamber flows to the top of the chamber around the float. The
top of the chamber is vented to the outlet of the flow meter through
an adjustable valve. Back pressure on the top of the float is adjustably
determined, being the pressure at the outlet of the flow meter plus
the pressure drop caused by the amount of fluid flowing past the
float and through the valve and the adjustable pneumatic resistance
of the valve. The float is buoyantly supported by the difference
between the inlet pressure existing at the bottom of the float and
the adjustable pressure at the top chamber. Since this buoyant force
must be just sufficient to support the float, however, the float
can be supported only when the pressure difference between the inlet
chamber and the outlet chamber of the flow meter rises. The fraction
of that difference appearing across the float can counteract the
gravitational or spring force forcing the float toward the inlet.
An advantage of this aspect of the invention is that by adjusting
the back pressure on the float, the pressure for float movement
is adjustable. Adjustment of the valve has an effect similar to
replacement of the float and the addition of successively heavier
floats, each float being used for different pressure ranges.
A further advantage of chamber back pressure adjustment is that
the entire operating range of the meter is adjustable. Not only
does the threshold or lift off pressure of the flow meter change,
but additionally the increment pressure between the uncovering of
successive ports likewise changes. Adjustability of the entire operating
range of the flow meter results.
A further object of this invention is to disclose in a float having
an adjustable lifting threshold a digitized movement. According
to this aspect of the invention, the chamber is provided with a
series of apertures. These apertures--typically circular--are relatively
spaced along the sidewall of the float and arranged to be successively
uncovered as the float moves upwardly. With greater upward movement,
more apertures are uncovered.
An advantage of this aspect of the invention is that the float
moves upwardly in response to increasing flow within the meter in
a digital fashion. Movement occurs in discrete steps with movement
occurring responsive to small changes in flow with relatively large
changes in height. A flow meter which is ideal for calibrating instruments
to narrow flow and/or pressure changes is disclosed.
A further object of this invention is to disclose a float position
detector which does not require individual adjustment. According
to this aspect of the invention, one of the sides of the enclosure
for the float is made from a PC board. This board is provided with
means for sensing the float position, such as a commutator like
wiper on the float. Once the float is enclosed by the PC board,
both the manifolding apertures to the float chamber and the commutator
for float position are synchronously assembled. Consequently, relative
calibration of these respective apertures is not required.
Other objects, features and advantages of this invention will become
more apparent after referring to the following specification and
attached drawings in which:
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a flow meter constructed according
to this invention illustrating the apparatus in section;
FIGS. 2A and 2B are perspective views of the float, and portions
of the chamber in which the float travels, used in the flow meter
of the present invention, illustrating the use of a commutator structure
to provide an electrical signal that is indicative of float position
in the chamber;
FIG. 3 is a schematic of the electrical circuit used in conjunction
with the commutator structures shown in FIGS. 2A and 2B;
FIG. 4 is a graph illustrating the digitized movement of the float
responsive to changing pressures to the flow meter; and
FIG. 5 is an electrical analog circuit of the flow meter of this
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1 the flow meter of the present invention, designated
generally with the reference numeral 10 is shown as including a
housing A contains a float B within an inlet chamber C with inlet
chamber C being divided by float B into lower chamber C1 and upper
chamber C2. An inlet port D allows passage of a fluid into the lower
chamber portion C1. Air leaks by the float B from lower chamber
C1 and into upper chamber C2. Responsive to the pressure difference
between the lower and upper chambers C1 and C2 caused by this flow
of air, float B is raised. From upper chamber C2 air passes from
exhaust port E into an air discharge chamber F and out through a
relief port H. The exhaust port E from upper chamber C2 is throttled
by a needle valve 14 with needle 16 for adjusting the back pressure
in upper chamber C2 on float B.
Exhaust chamber F and active chamber C are divided by wall 26 that
is provided with a number of linearly disposed apertures 20 collectively
described as manifold J. For reasons that will become clearer below,
the interior surfaces of the apertures 20 are provided with an electrically
conductive plating 21. As here illustrated, manifold J includes
six spaced circular apertures 20. As float B rises corresponding
to increased pressure, successively greater number of apertures
20 are uncovered. With the successive uncovering of these apertures,
an additional and controlled leakage occurs between chamber C and
exhaust chamber F directly through the manifolding, bypassing the
float. As will hereinafter be emphasized more completely, an essentially
"digitized" movement of the float B occurs.
Inlet chamber C is formed from partitions in housing A. The chamber
C is formed by two sidewalls 24 26 a rear wall 27 an upper chamber
wall 25 and a lower chamber wall 29. In addition, a front substantially
planar wall (not shown for reasons of clarity), parallel to the
rear wall 27 extend from and between the walls 24 25 29 and
a side wall 28 (forming, with sidewall 26 discharge chamber F)
to enclose in an airtight manner the two inlet and discharge chambers
C and F. The side walls 24 26 27 and 28 (and a front wall--not
shown) forming chamber C define an essentially rectangular cross-section.
Here, this rectangular cross-section is only slightly greater than
the rectangular cross-section of the float B.
Needle valve 14 is of conventional design, having a housing 15
and needle 16 threadably mounted to the interior of a valve seat
18. By adjustment of the needle 16 back pressure in the upper chamber
C2 is adjustable under the dynamics of fluid flow in the meter.
Such adjustment can typically be made through exhaust port H, with
which the needle valve 14 is axially aligned, by means of a screwdriver.
Float B is configured with an air passage 30 passing therethrough.
Air passage 30 has located at one end a second needle valve 32.
The needle valve 32 by its needle 33 similar to needle valve 14
is shown here as being capable of adjustment. This need not necessarily
be the case; that is, both needle valves 14 and 32 need not be adjustable.
For most cases it may be sufficient to fix one for operation within
a desired range, and to allow the other to remain adjustable so
that operation within selected range can be modified as needed.
The upper chamber wall 25 is provided with an aperture 34 that
is axially aligned with the needle valve 32 to provide access thereto
for adjustment. A threaded plug 35 seals aperture 34 when any necessary
adjustments to the needle valve 32 are completed.
As will hereinafter be emphasized, the needle valves 14 and/or
32 when adjusted, affect the range of differential pressures under
which the meter is operable. These available adjustments provide
a quick, efficient and simple technique for changing the range of
operation of the flow meter 10.
One technique to read the flow meter 10 is to make the walls forming
the housing A transparent so that the relative position of the float
B can be viewed. Markings can be used to translate float position
to flow rate.
FIGS. 2A and 2B illustrate another and preferred method used to
determine the relative position of the float B within the inlet
chamber B and therefore, the fluid flow therethrough. As shown in
FIG. 2A, the float B is provided with continuous channel 50 that
receives a commutator wire 52. The channel 50 is closed at 51 (on
both sides) to inhibit fluid flow around the float B. The ends 54
and 56 of the commutator wire are respectively formed and configured
to slidably engage a commutating bus 60 formed on the interior-facing
surface 24a of the sidewall 24 and a series of commutator segments
62 (FIG. 2B) formed on the surface 26a of the sidewall 26 that faces
the inlet chamber C (FIG. 1).
FIG. 2B shows that the commutator segments 62 are each electrically
connected to the plating 21 of a corresponding aperture 20 by electrical
traces 64. As FIG. 2B also shows (in phantom), the backface 26b
of the sidewall 26 is provided with electrical traces 66 which connect
the platings 21 and therefore the commutator segments 62 to a
resistor array 68. An output terminal 70 extends from the resistor
FIG. 3 illustrates the electrical circuit that incorporates the
electrical connections described above. A source of electrical energy,
here a battery 80 is connected between the commutator bus 60 and
a common G. The resistor array 68 includes resistors R1-R5 connected
to one another in series fashion, and to the commutator segment
62 in parallel--as shown. The terminal 70 of the resistor array
is adapted to be connected to a current meter M, which in turn connects
to the common G. The ends 54 and 56 of the commutator wire 52 (carried
by the float B--see FIG. 2A) rides along the commutator bus 60
engaging certain of the commutator segments 62 thereby providing
an electrical signal at the output terminal 70 that is indicative
of the relative position of the float B.
Preferably, the commutator bus 60 commutator segments 62 electrical
traces 64 and 66 and platings 21 are formed using printed circuit
techniques. The resistor array 68 is preferably formed using a commercially
available resistor package or individual resistors. The values of
the resistances R1-R5 can be chosen to meet any desired parameters.
Finally, the spacings between adjacent ones of the commutator segments
62 and the relative location of these spacings should be such that
the end 56 of the commutator wire 52 will bridge the spacing and
electrically engage two adjacent commutator segments 62 when the
bottom 31 (FIG. 1) of float B is just about to uncover an aperture
Having set forth the construction of the flow meter, its operation
can now be described.
In operation, an inlet fluid is introduced to the flow meter 10
at the inlet port D, through the bottom wall 29 and into the lower
chamber C1. Before float B lifts, the fluid pressure in the lower
chamber C1 must increase until a pressure differential between the
lower and upper chambers C1 and C2 is sufficient to counteract the
weight of float B. When the pressure in the lower chamber C1 exceeds
that of the upper chamber C2 plus the weight of the float B, float
B begins to lift. At this point, there will be a controlled leakage
around the surfaces of float B.
Neglecting any side leakage that may pass through manifolds J,
leakage will occur to upper chamber C2. Exhaust from chamber C2
must occur for the float B to lift properly. At this point it can
be recognized what increased back pressure (as by adjustment of
needle 16 in needle valve 14) will cause. Specifically, it can cause
back pressure in chamber C2 to rise. This in turn will increase
the pressure required to cause float B to lift. Stated in other
terms, the two flow resistances, the first flow resistance being
the constant (and here unadjusted) fluid bypass leakage around the
float B, and the second being the adjustable resistance of the flow
permitted through needle valve 14 function to determine the operating
range of the flow meter 10. Note that these resistances are in series.
The effect of these series of resistances can be readily understood.
Specifically, by increasing the back pressure through adjustment
of the needle valve 14 increasingly higher pressure differences
between the lower chamber C1 and the chamber F will be required
for float B to lift. The effect of this adjustment of needle valve
14 on float B will be as if the float's weight were increased. Thus,
even though float B is effectively "sealed" from the outside,
its effective weight may be adjusted by the penetration of a screwdriver
through exhaust port H to adjust needle 16.
As noted above, the float B may also carry a needle valve 32 which
can be adjusted. The effect of this adjustment is to increase (or
decrease, depending upon the adjustment) the flow resistance presented
by the float B. With decreasing flow resistance--as by opening of
the needle 33 in the needle valve 32--the range over which the float
B is operable increases. Therefore, lifting of the float B must
utilize a greater pressure differential between the lower chamber
C1 and upper chamber C2. In effect, the total range of operable
pressures over which the apertures 20 of manifold J are successively
uncovered is expanded by adjustments of the needle valves 14 and
Assuming adjustment of the paired needle valves 14 and 33 it will
be seen that the valve will operate in a digitized manner. Specifically,
float B will operate to successively uncover apertures 20 in the
manifolding J between the inlet chamber C and exhaust chamber F.
Referring to FIG. 4 assuming a fluid running through the valve,
float height can be plotted as a function of gas flow and/or pressure
across the meter. First, and referring to the ordinant axis, gas
flow is plotted with float height being represented along the abscissa.
Dependent upon the resistance of initially uncovered manifold J
coupling inlet and exhaust chambers C and F, the flow necessary
for the float to lift will be adjustable. In the example here shown,
the resistance is set to lift at 10 units of flow. The reader will
understand that the flow here shown can be set at other initial
Additionally, the force applied to the float and the needle valve
adjustments are chosen so that an increment of lifting occurs at
approximately every two units of flow. Specifically, and by adjusting
needle 33 the pressure differential across the specific increments
of valve movement can be adjusted.
Shown on FIG. 4 are performance curves 80 and 82. Performance curve
80 represents the kind of "digitized" operation that results
from having the manifolding formed by the linear arrangement of
apertures. This digitization can be modified and enhanced by forming
the apertures 20 as narrow slots, with the narrow dimension of each
slot formed parallel to the direction of the float motion. Curve
82 represents a calibration obtained by having apertures 20 arranged
as circular apertures. Other calibrations, linear or nonlinear,
stepped or continuous, can be obtained by adjusting the size, shape
and orientation of apertures 20 to meet the requirements.
Referring to FIG. 5 the operating principles of this invention
can be emulated with reference to the analog circuit diagrams. Let
the pneumatic "circuit" of the invention be represented
by the diagram of FIG. 5 where Q, P, and R represent fluid flow,
pressure and resistance to flow, respectively, and where the subscript
t represents total;
i represents inlet;
o represents outlet;
on represents orifice number;
FB represents float bypass;
v represents valve, adjustable; and
u represents upper chamber.
The float associated with R.sub.FB is biased toward the inlet by
gravitational force, by a spring, or other expedients. As it is
forced by the fluid flow to move away from the inlet, it uncovers
an increasing number of the apertures 20 providing parallel flow
pathways between the inlet chamber C and the exhaust chamber F.
For the float to be supported by the fluid requires that the buoyant
force F be equal to the force F tending to move the float toward
the inlet. That is
where A is the surface area of the bottom 31 of the float.
It is clear from the pneumatic circuit that ##EQU1## from which
we obtain ##EQU2##
It is also clear from the circuit that: ##EQU3## or, from equation
(3) and (4) ##EQU4##
If we design the system so that
the total flow can be described as being dependent on two factors:
that is ##EQU5## is a geometrical factor determined in the initial
design of the instrument, and ##EQU6## is a virtual force pushing
the float toward the inlet and determined by the controllable ratio
of the resistances of the valve, R.sub.v, and the pathway around
the float (or through the float) R.sub.FB.
Thus, the total flow is always directly proportional to the number
N of orifices uncovered by the float, but is adjustably controlled
by the restricting valve coupling the upper chamber to the outlet.
The initial action of the flow meter 10 is dependent on the design.
That is, if the float is initially positioned so as to cover all
of the side wall orifices, the input flow must increase only to
the small valve Q.sub.FB (see above) to lift the float from its
If, however, the initial position of the float is arranged to allow
one orifice to remain uncovered, that orifice providing a flow pathway
between the input and output of the flow meter, the float will not
move until the pressure drop across that orifice is sufficient to
cause Q.sub.FB. The size of this first orifice can be adjusted to
provide a controlled initial bias--allowing the flow meter to act
as a sensitive "vernier" indicator, reading a small flow
range within a much larger total flow.
If the response desired of the flow meter is non-linear, it can
be obtained by adjusting the design either by introducing (a) a
non-linear relationship in the positioning of the wall apertures;
or (b) a variability in the resistance to flow of the several wall
The mounting of the commutator segments 62 onto sidewall 26 of
the chamber C has an unexpected advantage. Specifically, and in
the calibration of such meters in the past, the means for detecting
position of float B and the position of the readout has always heretofore
had to be separately adjusted. In the present invention it can be
seen that adjustment is no longer required. Specifically, the detecting
commentator segment 62 and the location of each of the successive
apertures 20 in the manifold series J is fixed upon manufacture.
Thus, by designing the board to predetermined standards, the relationship
between the apertures 20 forming manifold J and the commentator
segments 62 for the position of the float B can readily be determined.
The reader will understand that this invention will admit a number
of modifications. For example, the float B here illustrated is illustrated
as being preferably biased by gravity. It will be apparent that
the float could be biased by other means, for example, springs and
the like. Moreover, the float has been illustrated as being rectangular
in section moving within a rectangular chamber. It will be appreciated
that the geometry of the float could be circular in cross-sections
or of other geometric configurations as well.
Likewise, in FIGS. 2A and 2B, a preferred embodiment of the invention,
we have illustrated a commutator-like configuration. Other means
of detecting the position of the float could as well be used. In
fact, commutators represent a gross and less sensitive means of
determining float position. However, in many applications such simple
mechanical contacting devices are actually preferred to more sophisticated
means of detecting float position. Other features and natural modifications
of this invention will occur to those having skill in the art.