Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to flowmeters.
A flowmeter suitable for measuring the rate of supply of
fuel to a petrol engine or the rate of supply of spraying liquid
to the boom of agricultural or horticultural spraying equipment
_ 5 includes a bladed rotor element which is rotated by liquid passing
through the meter, the speed of rotation being proportional to the
rate of flow. Such flowmeters may be required to operate over a
range of flow rates from 0.25 to 30 gallons per hour. The lower
end of the range dictates that the maximum diameter of the bore in
which the rotor element is mounted should be generally less than
0.25 inches.
At low flow rates there is an unacceptable drag effect if
an electromagnetic device is used for sensing the speed of
rotation of the rotor element. Although an inductive sensor over-
comes this problem, the element must be made of metal, or must
include a metallic insert. It is then costly to manufacture the
element from a metal which is corrosion resistant and the element
is heavy, which means higher bearing friction and hence poor flow
rate characteristics. It is preferable therefore to make the
rotor element of a plastics material, which offers the advantage
of low cost, Low weight, low production spread in terms of
dimensional accuracy, and a choice of materials which have suitable
chemical and physical properties.
To detect the speed of rotation of the rotor element an
optical sensing device has been proposed as an alternative to
an inductive or electromagnetic device. In the optical device a
beam o~ light is transmitted across the bore so that it is
interrupted by the rotating blades o the rotor element. A photo-
- detector to which the beam is applied generates an electrical
signal of frequency representing the frequency at which the beam
is interrupted, and hence the speed at which the element is
rotated. For satisfactory operation, this optical device relies
upon a high degree of transparency of the liquid passing through
the meter. Further, spurious signals are produced if the liquid
includes gas bubbles which interrupt the light beam. It is found
that there may be errors of up to 25%, particularly if the "lens
effect" of liquid within the bore is used to focus the light beam
: ~ on to the photodetector.
According to the present invention there is provided a flow-
meter comprising a bladed rotor element mounted in a bore formed
in a body so that fluid flowing through the bore causes the element
to rotate at a speed representative of the rate of flow of the
fluid, a source of electromagnetic radiation, means for directing
radiation from the source into the bore and towards the rotor
element so that a radially outer face of at least one rotor blade
moves across the path of the radiation during each rotation of the
rotor element, a detector of electromagnetic radiation, and means
for directing radiation reflected by the said face of the or each
blade to the detector, the means for directing radiation from the
source and the means for directing reflected radiation comprising
at least one elongated guide member having a refractive index
greater than the refractive index of the medium in which the
member i9 disposed.
Preferably, the or each guide member is Eormed integrally
with the said body.
The means for directing radiation from the source and the
means for directing reflected radiation may comprise respective
- first and second elongated guide members, each having a refractive
index greater than the refractive index of the medium in which the
member is disposed.
Alternatively, the means for directing radiation from the
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source may comprise a limb and the body o~ a generally
Y-shaped guide member having a refractive index greater
than the re~ractive index of the medium in which the
member is disposed, and the means for airecting re-
flected radiation then comprise the other limb and thebody of the generally Y-shaped guide memher.
Preferably, the part of the or each blade from
which radiation is reflected to the detecting means has
a higher coef~icient of re~lection than a hub upon which
the blade or blades is supported.
Suitably, the part of the or each blade from which
radiation is reflected is adjacent to a side wall
through which the radiation enters the bore during the
time within which radiation is reflected therefrom,
whereby the radiation travels only a short distance
through fluid flowing through the bore.
The or each guide member may comprise a rod of
glass or plastics material.
The electromagnetic radiation is suitably visible
or infra-red radiation.
The invention will now be described, by way of
example, with reference to the accompanying drawings, in
which:-
Figure 1 is a p~an view of a flowmeter according
to the invention, part of a housin~ o~ the flowmeterbeing removed;
Figure 2 is an axial section of a rotor element in
the flowmeter of Figure l;
Figures 3, 6 and 7 are diagrammatic side ele-
vations of ~urther flowmeters according to theinvention; Figure 7 is shown on the sheet illustrating
Figure 3; and
Figures 4 and 5 are transverse sections of further
flowmeters according to the invention; Figure 4 is shown
on the sheet illustrating Figure 2.
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The flowmeter shown in Figure 1 of the drawings is
suitable for use in measuring the rate of supply of fuel
to a petrol engine or the rate of supply of spraying
liquid to a boom in agricultural or horticultural
spraying e~uipment. Included in this flowmeter is
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a tubular body 1 which, in use, is connected into a line along
which the fuel or spraying liquid is passed. Within a bore 3 of
the body 1 is a bladed rotor element 5 so arranged that liquid
flowing through the bore causes the element to rotate at a speed
proportional to the rate of flow of liquid. For measuring the
speed of rotation, a light source 7 is mounted outside the body 1
and a guide member 9 is arranged to direct a beam of light from the
source into the bore 3 so that a radially outer face of each blade
~ 11 on the element 5 moves across the beam once during each rotation
of the element. Light reflected from a radially outer face of each
blade 11 is directed by a further guide member 13 to a photo-
sensitive detector 15 which produces an electrical output signal
whose frequency is proportional to the speed of rotation of the
element 5, and hence proportional to the rate of flow of liquid.
15Figure 2 shows an axial section of the rotor element 5 in the
flowmeter of Figure 1. The element 5 includes a hub 17 which is
moulded from a plastics material having a low coefficient of
reflection, preferably black material. Supported by the hub 17
are three helical blades 11 of a plastics material having a high
coefficient of reflection, preferably a white plastics`material
or a plastics material impregnated with a reflective substance to
produce a highly reflective surface.
Referring now to Figure 1, each of the light guide members 9
and 13 is moulded lntegrally with the tubular body 1, the axes of
the mernbers lying in a plane which inc]udes the axis of the body 1
and the axis of the rotor element 5.
A housing 27 of opaque material houses the light source 7 and
the photosensitive detector 15 and also receives the light guide
members 9 and 13. The housing 27 is formed of a base part 29,
shown in plan view in Figure 1, and a cover part (not shown).
The base part 29 of the housing 27 ls formed with cavities
31 and 33 for housing the source 7 and the detector 15, respectively,
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and with channels 35 and 37 for receiving respective members 9 and
13. An inner section 39 of the channel 35 has a reduced diameter
which is only slightly larger than the diameter of the guide member
9 so that no light from the source 7 can reach the element 5 unless
it has travelled via the guide 9. Similarly, an inner section 41
of the channel 37 has a reduced diameter for preventing reflected
light other than light which travels along the guide member 13 from
reaching the detector 15.
~ In the flowmeter of Figure 1 the body 1 and guide members 9and 13 are made of glass or transparent plastics material. The
guide members 9 and 13 are about 1 mm diameter~
Upstream of the rotor element 5 (to the right as viewed in
Figure 1) is a flow straightener and rotor support 43. The
support 43 has a central, generally cylindrical section 45, whose
external diameter is smaller than the diameter of the bore 3, and
four longitudinally extending ribs 45, which engage an inner
surface of the bore 3. At one end of the section 45 is ~n insert
47, which serves as a bearing support for one end of a spindle 49
upon which the element 5 is mounted.
Downstream of the element 5 is a second flow straightener and
rotor support 51, which likewise is formed with longitudinally
extending ribs 53 and which has an insert 55 to provide a bearing
support for the splndle 49.
The light source 7 and the detector 15 are electrically
connected to electrical circuit components on a printed circuit
board 57.
When the flowmeter of Figure 1 is in use, liquid flowing
through the bore 3 in the body 1 impinges against the bl~des 11 of
the element 5 and causes the element to rotate. The speed of
rotation is proportional to the rate of flow of liquid along the
bore 3. A beam of light from the source 7 is directed into the
bore 3 by the guide member 9 and is reflected into the further
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guide member 13 and on to the detector 15 each time one of the
blades 11 moves across the beam, i.e. three times per revolution
of the element 5. The detector 15 produces an electrical output
signal which varies periodically at a frequency equal to the
frequency at which pulses of radiation are applied thereto. The
signal is applied via suitable circuits on the board 57 in the
case of a simple flowrate indicator to a meter (not shown) which
gives a reading representative of the frequency of the output
- ~ signal, and hence representative of the speed of rotation of the
element 5, and the rate of flow of the liquid along the bore 3.
Figure 3 is a second embodiment of the invention which has
a tubular body 1, a rotor element 5, a light source 7 and a
photosensitive-detector 15 of the form shown in Figure 1. In the
flowmeter of Figure 3, however, a Y-shaped guide member 59
replaces the guide members 9 and 13 of Figure 1. This guide
member 59 is arranged so that light from the source 7 travels along
one limb and the body of the "Y" and enters the bore 3 o~ the body
1 in a radial direction. Light reflected from a radially outer
face of each blade 11 on the rotor element 5 reenters the body of
the member 59 and a part of this light then travels via a second
limb of the "Y" to the detector 15.
The guide'member 59 of Figure 3 is moulded from transparent
plastics material. The included angle between the two limbs of
the "Y" is less than half the critical angle of the material in
air so that light from the source 7 does not enter the second limb
and interfere with the reflected light. Light can be directed
accurately towards the element 5 by means of the member 59.
Figure 4 is a section at right'angles to the axis of a
- further flowmeter according to the invention which has a rotor
element 5 and a tubular body 1 of the form shown in previous
embodiments. Moreover, there are light guide members 61 and 63
which are formed'integrally with the body 1. In the flowmeter
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of Figure 4, however, the axes of the members 61 and 63 lie in a
plane which is perpendicular to the axes of the rotor element 5
and the body 1.
Marked in Figure 4 are the paths of rays of light which are
incident upon the rotor element 5 and which are reflected there-
from at various angular positions of the element. First, there
is a divergent cone of rays which emerges from the guide member 61
and impinges upon the radially outer face of a blade 11 when the
element 5 is in the angular position shown in Figure 4. The
periphery of the cone is indicated by the points A and Bo Light
reflected Erom the blade 11 diverges further and illuminates a
generally circular area of the wall of the bore 3 in the body 1,
designated by the points C and D in Figure 4. Part of this
reflected light enters the guide member 63 and is directed towards
the detector 15.
When the element 5 has rotated from the position shown in
Figure 4, light from the member 61 impinges upon the hub 23 of the
element, illuminating an area of the hub whose periphery is
indicated by the points F and L. From the llub 23 the Light is
reflected on to an area of the bore 3 extending angularly between
the points I and K. The arc IK is approximately 205 whilst the
arc CD is only approximately 18 . There is therefore.a ratio of
approximately 11:1 between the area of the bore 3 illulllinated by
the reflected light when the element 5 is in the angular position
shown in Figure 4 and the area illuminated when the element has
been rotated from this position.
Figure 5 is an embodiment of the invention wherein the guide
members 61 and 63 of Figure 4 are replaced by a Y-shaped guide
member 65 corresponding to the guide member 59 of Figure 3. The
member 65 is formed integrally with the body 1 and is arranged
with the axes of the body and limbs of the member in a plane
perpendicular to the axis of the body 1 and the rotor element 5.
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Figure 6 is an embodiment suitable for use with a tubular
body 1 and rotor element 5 thereof at an ambient temperature
greater than the temperature at which a photosensitive detector 15
can be operated. In this embodiment the detector 15 is located
remotely of the body~l and the rotor element 5. Light reflected
from the element 5 is guided to the detector by means of a
plastics or glass optical guide member 67 of extended length.
The guide member 67 has a short initial section which is
made of glass or thermoplastics material and is formed integrally
with the body 1. Connected to this initial section is an
elongated section made of a series of glass fibre optical guides
` or of thermoplastics material.
In Figure 7 of the drawings there is an embodiment which
corresponds to the embodiment of Figure 1 except that the body 1
is replaced by an opaque tubular body 69 having a window 71 of
transparent material through which radiation can be transmitted to
and from the element 5. Guide members 9 and 13 are formed
integrally with the window 71.
In further embodiments a photosensitive detector and a light
source are both remote from the rotor element and the body
containing the element. In one of these embodiments there is a
single extended light guide, formed integrally with the body,
which is connected to a Y-shaped guide member. In another
embodiment there is a first extended guide member for directing
light from the source to the rotary element and a further extended
guide for directing reflected light to the detector. At least part
of each guide member is~formed integrally with the body 1 housing
the rotary element
In the embodiments described above the axes of the light
guide members are disposed in a plane which includes the axis of
the body 1 or is perpendicular thereto. It will be appreciated
that alternative arrangements can be employed. For example, the
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guide members can be arranged with the axes of the guides lying in
a plane which is inclined at 45 to the axis of the body 1.
It will be appreciated that a rotor element having a hub and
a plurality of radially extending blades can be used in place of
the element 1 with helical blades described above. The tubular
body 1 can be made of opaque materLnl hflving gl~ss or pl~lstics
windows through which light is directed on to the rotor element.
Infra-red or ultraviolet radiation can be used instead of
visible radiation.
The guide member or members can be made separately from the
body 1 and secured thereto by adhesive, care being taken to avoid
loss of light due to internal reflections and refraction. In some
cases it may be possible to have the guide member or members spaced
a short distance from the body 1.
