Abstrict A flow meter, for measuring fluid flow rates, having a housing
through which the fluid flows and is caused to impinge on an impeller
or rotor for rotating the impeller at a rotational velocity representative
of the fluid flow rate. The impeller or rotor has a plurality of
teeth on which a light beam is reflected. A photosensitive device
receiving the reflected chopped light produces at its output a signal
whose frequency is a function of the rotational velocity of the
impeller.
Claims I claim:
1. A flow meter comprising a body, a first chamber in said body,
a fluid inlet in communication with said first chamber, a second
chamber in said body, a fluid outlet in communication with said
second chamber, a rotor member disposed in said second chamber,
at least one orifice for flowing fluid from said first chamber into
said second chamber, said orifice being a channel having an inlet
in said first chamber and an outlet in said second chamber, said
channel being arranged to provide a swirling motion to the fluid
flow from said first chamber to said second chamber, said rotor
being disposed such as to be acted upon by the fluid in swirling
motion for causing said rotor to rotate at a velocity proportional
to the fluid flow rate through said orifice, a toothed wheel formed
integrally with said rotor, a light source, means for projecting
a light beam from said light source upon the periphery of said toothed
wheel whereby said light beam is periodically reflected from said
toothed wheel, a photosensitive element and means for transmitting
said periodically reflected light beam to said photosensitive element,
said photosensitive element providing at its output a signal of
a frequency proportional to the velocity of rotation of said toothed
wheel.
2. The flow meter of claim 1 wherein said first chamber is annular.
3. The flow meter of claim 2 wherein said annular chamber is formed
between a cylindrical bore surface in said body and a cylindrical
peripheral surface on a plug member disposed in said first chamber,
said rotor being mounted on the end of said plug.
4. The flow meter of claim 3 wherein said means for transmitting
said light from said light source and for transmitting said periodically
reflected light to said photosensitive element are optical fibers.
5. The flow meter of claim 3 wherein said first chamber and said
second chamber are substantially coaxial, said first chamber is
of larger diameter than said second chamber, and an annular abutment
is formed between said first chamber and said second chamber, and
wherein said orifice is in an annular plate removably mounted on
the end of said plug and said channel is in the form of a groove
formed in a face of said annular plate in engagement with said annular
surface.
6. The flow meter of claim 5 wherein said rotor comprises a smooth-rimmed
wheel having a peripheral portion disposed in a circular recess
in said annular plate.
7. The flow meter of claim 6 wherein said means for transmitting
said light from said light source and for transmitting said periodically
reflected light to said photosensitive element are optical fibers.
8. The flow meter of claim 5 wherein said means for transmitting
said light from said light source and for transmitting said periodically
reflected light to said photosensitive element are optical fibers.
9. The flow meter of claim 1 wherein said means for transmitting
said light from said light source and for transmitting said periodically
reflected light to said photosensitive element are optical fibers.
10. The flow meter of claim 9 wherein said optical fibers are disposed
in a tubular member located in a radial bore in said body.
11. The flow meter of claim 10 wherein said optical fibers comprises
a bundle of fibers conveying said light from said light source,
and a single fiber conveying said reflected light to said photosensitive
element.
Description BACKGROUND OF THE INVENTION
The present invention relates to a flow meter for measuring the
flow rate of a fluid such as a liquid fluid or a gaseous fluid,
for example.
Known flow meters are subjected to any number of a plurality of
disadvantages such as, for example, lack of accuracy except within
a very narrow range of measured flow rates, high pressure losses,
lack of linearity of the signal output, and unreliable indication
of low flow rates, for example. In addition, most flow meters available
on the market utilize a rotor provided with vanes or blades which
are interposed in a light beam between a light source and a photosensitive
device which measures the fluid flow rate as a function of the number
of times the light beam is interrupted by the vanes or blades in
a given time basis. Because the light beam travels a considerable
distance within the fluid, it is subject to substantial absorption
and dispersion while passed through liquid fluids lacking adequate
light transmissivity.
SUMMARY OF THE INVENTION
The present invention provides a flow meter capable of providing
a substantially linear signal output over a wide range of fluid
flow rate, which utilizes a reflected interrupted or chopped light
beam travelling through a very thin film of the fluid, and which
is adaptable to a variety of flow rate ranges through substitution
of a simple orifice plate providing a swirling flow of fluid impinging
upon an impeller, preferably in the form of a smooth-rimmed wheel.
A toothed wheel, which may be substituted for the smooth-rimmed
wheel but which, preferably, is formed as a unit with the smooth-rimmed
wheel, has a plurality of teeth on which a light beam channeled
through optical fibers is directed and reflected, via a receiver
optical fiber, to a light-sensitive detector.
The many objects and advantages of the present invention will become
apparent to those skilled in the art when the following description
of the best modes contemplated for practicing the invention is read
in conjunction with the accompanying drawing wherein:
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is an elevation view of a flow meter according to the present
invention;
FIG. 2 is a section therethrough as seen from line 2--2 of FIG.
1 including a schematic representation of the optical system associated
therewith;
FIG. 2a is a partial section from line 2a--2a of FIG. 2;
FIG. 3 is a section, at an enlarged scale, along line 3--3 of FIG.
2;
FIG. 4 is a partial section from line 4--4 of FIG. 3;
FIG. 5 is a partial section from line 5--5 of FIG. 3; and
FIG. 6 is a partial view similar to FIG. 3 but showing a modification
thereof.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the drawing, and more particularly to FIG. 1 a flow
meter according to the present invention comprises a body or housing
10 having an inlet for connection to a fluid inlet 12 and an outlet
for connection to a fluid outlet 14. An enclosure 16 is mounted
on a side of the body 10 and contains the optical system, shown
schematically at 18 FIG. 2 associated with the flow meter for
measuring flow rate through the body 10 from the inlet 12 to the
outlet 14.
As further shown in more details at FIGS. 2 and 3 the body 10
has a longitudinal cylindrical bore 20 of relatively large diameter
axially disposed with a longitudinal blind bore 22 of relatively
smaller diameter, a step annular surface 21 being formed between
the bores 20 and 22. The bore 20 has an open end provided with a
thread 24 accepting the peripherally threaded portion 26 of a plug
28 provided with, for example, an hexagonal head 30. The plug 28
has a peripheral annular groove 32 disposed proximate its hexagonal
head 30 in which is placed an elastomeric O-ring 34 providing an
effective seal against leakage of fluid from the inside of the bore
20. The other end of the plug 28 has a cylindrical reduced diameter
peripheral surface 36 terminating into a further reduced diameter
portion 38 FIG. 3 supporting an annular orifice plate 40. The
orifice plate 40 has an annular end face 42 engaged with the annular
step surface 44 between the plug large diameter cylindrical surface
36 and the plug reduced diameter cylindrical end portion 38 around
which is installed the annular orifice plate 40 the plug reduced
diameter end portion 38 fitting in the cylindrical opening 43 of
the annular orifice plate 40. Preferably, the peripheral surface
46 of the orifice plate 40 is flush with the peripheral cylindrical
surface 36 of the plug 28 such as to form, with the surface of the
bore 20 an annular chamber 48 in fluid communication with the inlet
12 through a channel 50.
The annular orifice plate 40 has a face 52 provided with one or
more tangential grooves 54 four of which are shown at FIG. 4. The
face 52 is engaged with the annular surface 21 between the body
large diameter bore 20 and the small diameter bore 22 when the plug
28 is installed within the bore 20 thus maintaining the annular
orifice plate 40 solidly in position and causing the fluid flowing
from the annular chamber 48 into the bore 22 to flow in a swirling
motion into the open portion of the orifice plate cylindrical opening
43 such as to tangentially impact upon the smooth cylindrical surface
56 of the wheel portion 58 of an impeller or rotor 60 thus causing
the rotor 60 to rotate at a velocity representing the flow velocity
through the tangential nozzles formed by the grooves 54 and the
portions of the annular surface 21 closing the top of the grooves
54. The rotor 60 is supported from a stationary hub, FIG. 5 in
the form of a pin 62 by bearing means such as ball bearings 64
the pin 62 having a retainer end portion 66 engaging the inner race
of the ball bearings 64 on the end of a slender body portion 68
fitted in an axially disposed bore 70 in the plug 28. FIGS. 3 and
6 a radially disposed set screw 72 threading in a radial bore 74
holding the body portion 68 of the pin 62 securely in position.
The rotor 60 comprises a toothed wheel 76 as shown at FIGS. 3
and 5 formed integral with or attached to the smooth-rimmed wheel
58 and provided with a plurality of peripheral teeth 78 which is
rotated in unison with the smooth-rimmed wheel 58. The fluid flowing
from the annular chamber 48 through the nozzles formed by the grooves
54 tangential to the periphery of the smooth-rimmed wheel 58 and
causing the rotor 60 to rotate, flows into the bore 22 to the outlet
14 via a channelway 80.
A light tube 82 FIGS. 2 and 5 is disposed within a radial bore
84 through the flow meter body or housing 10 in alignment with the
toothed wheel 76. The light tube 82 carries a bundle 86 of optical
fibers, FIGS. 2 and 2a, for example seven in number. Six optical
fibers 88 are peripherally disposed in the light tube 82 relative
to a single centrally disposed fiber 90 for example, and the peripheral
fibers 88 form a secondary bundle where they emerge from the light
tube 88 and directed with an end proximate to a light source, such
as light bulb 92. The bundle of optical fibers 88 transmits light
from the light bulb 92 to the end of the light tube 82 disposed
proximate the periphery of the toothed wheel 76. The center optical
fiber 90 transmits the interrupted or chopped light reflected from
the teeth 78 of the toothed wheel 76 to a photosensitive device
93 such as a photovoltaic or photoresistive photocell. The signal
at the output of the photocell 93 is fed to a utilization circuit,
FIG. 2 forming no part of the present invention, through, for example,
an appropriate signal amplifier 94 a square wave generator 96 transforming
the signal into square wave pulses for counting the number of pulses
within a predetermined time basis in a counter 98 and for eventual
numerical display in a display device 100 indicating the fluid flow
rate through the flow meter, or for any other appropriate utilization,
such as controlling a flow valve or the like.
The number of teeth 78 of the toothed wheel 76 of the rotor 60
may be arbitrarily chosen according to the desired flow rate definition
and degree of accuracy for low flow rates. It has been found experimentally
that twelve teeth are sufficient to cover considerable flow rate
ranges. With the structure according to the invention, a curve representing
flow rate as a function of, for example, pulses per second at the
output of the photodetector 93 is substantially linear and accurate
for flow rate range ratios as high as 20 to 1. The useful flow rate
range can be easily changed and the flow meter of the invention
adapted to any fluid flow rate range merely by substituting the
annular orifice plate 40 by another. Orifice plates 40 may be provided
with any number of grooves 54 from one groove and, preferably two,
to three, four or more grooves to accommodate diverse ranges of
flow rate within several orders of magnitude. The width and the
depth of the grooves 54 may also be varied from one orifice plate
40 to another, such that by simply inserting the appropriate orifice
annular plate 40 for a predetermined range of flow rates on the
end of the plug 28 the flow meter of the invention may be tailored,
without any modification of elements, to accommodate a plurality
of flow rate ranges and measures such flow rates within a range
with high accuracy.
As illustrated at FIG. 6 the rotor 60 may consist simply of the
toothed wheel 76 rotatably mounted on the end of the plug 28 within
the reduced diameter bore 22 in the body 10 such that the toothed
wheel 76 is disposed within the reduced diameter bore 22 relatively
proximate the outlet of the grooves 54 in the aperture plate 40
thereby in the swirling flow of fluid, with the teeth 78 optically
aligned with the optical axis of the light tube 82.
It will be appreciated that only a very thin film of the fluid
circulating through the flow meter of the invention is interposed
between the end of the optical fibers 88 and 90 in the light tube
82 and the peripheral surface of the toothed wheel 76 with the
result that the direct light beam and the reflected light beam need
not travel through a substantial thickness of fluid, as is the case
in flow meters utilizing a light beam traversing a considerable
thickness of fluid from a light emitting device to a photosensitive
device, and wherein the light beam is interrupted by vanes or teeth
disposed on the periphery of a rotor. Because of the short distance
travelled by the light within the fluid, the flow meter of the invention
is capable of accurately measuring flow rates of relatively opaque
fluids. The light may be visible light or it may be infrared radiation.
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