Abstrict A flow meter comprising a cavity, an inlet to the cavity and an
outlet from the cavity, and two oval rotors mounted within the cavity
between the inlet and the outlet. The rate of rotation of the rotors
is substantially proportional to the flow of fluid through the meter.
The rotors are provided with magnets. Electrical inductors, which
are capable of detecting the magnets, are arranged outside the cavity
to monitor rotation of the rotors without being mechanically linked
thereto, and to provide a measure of the flow of fluid through the
meter. A division ratio adjuster is included in electrical circuitry
of the meter to vary the calibration of the measurement in dependence
upon the flow rate through the meter.
Claims I claim:
1. A fluid meter comprising:
(a) wall means defining a cavity;
(b) an inlet to the cavity and an outlet from the cavity;
(c) a rotor mounted within said cavity between said inlet and said
outlet to rotate at a rate which is substantially proportional to
flow of fluid through the meter;
(d) detectable means fixed in relation to said rotor;
(e) detector means capable of detecting said detectable means,
arranged outside said cavity to provide a signal in dependence upon
rotation of said rotor without being mechanically linked thereto;
(f) measuring means connected to said detector means to provide
a measure of the volume of fluid which flows through the meter from
the signal from the detector means;
(g) a flowrate indicator connected to said detector means to provide,
from the signal therefrom, a signal indicative of the flowrate of
fluid through the meter; and
(g) a calibration adjuster connected between said flowrate indicator
and said measuring means to adjust the calibration of said measuring
means in dependence upon the signal from said flowrate indicator.
2. A meter according to claim 1 wherein there are two oval rotors
mounted in said cavity to rotate in opposite senses about axes which
are transverse in relation to fluid flow through the meter, the
major axes of said two oval rotors being at substantially 90.degree.
to one another when one of them is at right angles to the direction
of flow.
3. A meter according to claim 2 wherein intermeshing parts are
provided on said two rotors to keep the second of rotation of each
rotor the same as the other.
4. A meter according to claim 1 wherein the cavity wall means,
the rotor, and the rotor shaft and bearings comprise a synthetic
plastics material.
5. A meter according to claim 4 wherein the cavity wall means
comprise a case and a bulkhead injection moulded as one part.
6. A meter according to claim 4 wherein the meter has a rotor
shaft injection moulded in nylon.
7. A meter according to claim 4 wherein said rotor is provided
with an encapsulated sintered magnet.
8. A fluid meter comprising:
(a) wall means defining a cavity;
(b) an inlet to the cavity and an outlet from the cavity;
(c) a rotor mounted within said cavity between said inlet and said
outlet to rotate at a rate which is substantially proportional to
flow of fluid through the meter;
(d) detectable means fixed in relation to said rotor;
(e) detector means capable of detecting said detectable means,
arranged outside said cavity to generate at least one electrical
pulse for each revolution of said rotor without being mechanically
linked thereto;
(f) a counter connected to said detector means to count pulses
generated by the detector means so as to provide a measure of the
volume of fluid which flows through the meter from the signal from
the detector means;
(g) a display connected to the counter to display the count in
the said counter;
(h) a frequency-to-voltage converter connected to the detector
means to provide a voltage signal having a magnitude in dependence
upon the rate at which pulses are produced by the detector means;
and
(i) a division ratio adjuster having an input connected to said
frequency-to-voltage converter and an output connected to said counter
to adjust the calibration of said counter in dependence upon the
signal from said frequency-to-voltage converter.
Description This invention relates to a fluid flow meter, especially a liquid
flow meter which is suitable for domestic application by the various
national water authorities.
The advances in the usage, recycling and control of water in recent
years reflect the need for control of water as a limited commodity
caused by the continuing increases in population coupled with increased
demands by agriculture and industry. This need is also made evident
by political pressure sponsored by public demand for the cost effectiveness
of continued support of the water services by public money. These
trends may well lead to the sale or lease of water based on measured
usage.
Future policies may well be dictated by the attention currently
being focussed on energy conservation that could open up a completely
new area in the utilisation of a pressurised water supply as a source
of energy to enhance or replace electrical domestic equipment. The
availability of cold water detergent may herald the design of a
washing machine powered and programmed by water. Again, the desirability
of metered water is highlighted.
Such arguments that have been put forward hiterto for the adoption
of domestic meters have been, and are being, parried by statements
of cost. For example, 80 per installation has recently been quoted,
which is formidable even with individual, or government, underwritten
expense. These estimates are based on currently availble meters
which are invariably manufactured from metals using a larger number
of machined mechanical parts.
One previously-proposed meter adopts the well proven principle
of displaced volume effected by two oval rotors in a cavity of known
volume. The rotors rotate in opposite senses and are at 90.degree.
to one another when one is at right angles to the direction of flow.
A meter which uses this principle is known as a rotating oval flow
meter. Such a flow meter is driven by the flow of water or other
fluid passing through it, the speed of rotation of the rotors being
in direct proportion to the amount of water displaced. Hitherto,
the measurement of flow has been achieved as indicated diagrammatically
in FIG. 1 of the accompanying drawings, by means of a drive 1 from
one of the rotors (not shown in FIG. 1) through a sealed bearing
in a wall 2 of the cavity 2 to a gear train in a gear box 3 arranged
to actuate a mechanical counter 4 set in a display window (not shown
in FIG. 1) via a counter-to-gear-train coupling 5.
The foregoing meter tends to exhibit one or more of the following
drawbacks:
(a) rotor bearing wear resulting in seizure and flow restriction,
because of the kind of bearing needed for coupling one of the rotors
to the gear train;
(b) breakdown of the seal on the drive shaft between the cavity
and a housing for the gearbox and/or display;
(c) use of metals in the construction which may either have an
adverse effect on the water or may be adversely affected by the
water to the detriment of the rotors and bearings;
(d) limitation on the selection of metals which can be used without
incurring detrimental electrolytic effects;
(e) the need for a large number of machined parts resulting in
high manufacturing costs;
(f) the need for a large number of moving parts which reduce the
"Mean Time between Failure" factor, thus reducing reliability;
(g) no facilities for calibration by adjusting the ratio between
rotor turns and turns of the counter, this being an inherent factor
of design although the accuracy of the meter is directly proportional
to the allowed manufacturing tolerances.
The present invention aims to provide a flow meter which is less
susceptible to one or more of these drawbacks. One way it accomplishes
this is to replace the mechanical linkage between one of the rotors
of the meter and the counter by a magnet or other detectable device
in or on one of the rotors and an electrical inductor or other detector
outside the cavity.
Thus, according to one aspect of the present invention, there is
provided a flow meter comprising a cavity, an inlet to the cavity
and an outlet from the cavity, and a rotor mounted within the cavity
between the inlet and outlet, the rate of rotation of which rotor
is proportional to the flow of fluid through the meter, in which
the rotor is provided with a magnet or other detectable device,
and an electrical inductor or other detector, which is capable of
detecting the detectable device, is arranged outside the cavity
to monitor rotation of the rotor without being mechanically linked
thereto. The cavity may therefore be completely sealed with no linkage
member extending through its wall or walls.
The rotor may be one of two oval rotors mounted in the cavity for
rotation about axes which are transverse in relation to fluid flow
through the meter, in opposite senses and at 90.degree. to one another
when one of them is at right angles to the direction of flow.
Another way in which this invention accomplishes its aim is by
making the cavity wall or walls, the rotor or rotors, and/or the
rotor shaft or shafts and bearings out of synthetic plastics material
or materials.
For example, the cavity wall or walls and a case and bulkhead of
the meter may be injection moulded as one part in polypropylene
or a similar material. The meter may have rotor shafts injection
moulded in nylon, and rotor ovals moulded in polypropylene with
encapsulated sinterred magnets.
An example of a flow meter in accordance with the present invention
is illustrated in FIGS. 2 to 11 of the accompaying drawings, in
which:
FIG. 2 is a diagram showing the basic layout of the flow meter;
FIG. 3 is a rear view of the meter with a rear plate and gear wheels
of rotors of the meter removed for the sake of clarity;
FIG. 4 shows the arrangement of two rotors of the meter in greater
detail;
FIG. 5 shows a rear end cap of the meter;
FIG. 6 shows an axial sectional view through the flowmeter;
FIG. 7 shows an axial sectional view of one of the rotors of the
flowmeter, a section at right angles to that shown in unbroken lines
being shown by the broken lines;
FIG. 8 shows a rear view of the flowmeter;
FIG. 9 shows a front view of the flowmeter;
FIG. 10 shows a side view of the flowmeter; and
FIG. 11 is a block circuit diagram of the electronic circuitry
of the meter .
The flow meter shown diagrammatically in FIG. 2 comprises a meter
cavity 10 with a bulkhead 12 as one of the cavity walls dividing
the cavity 10 from an electronic components and counter housing
14. A liquid crystal display counter 16 connected to a printed circuit
board 18 is mounted within the housing 14. A number of electrical
and electronic components are attached to the printed circuit board
18 including an electrical inductor or pick-up coil 20 field effect
transistors 22 and other semi-conductor or electronic components
24 connected to perform the functions which are described herein.
The construction of the flow meter is shown in greater detail in
FIGS. 3 to 10 of the accompanying drawings.
A polypropylene cavity and housing wall 26 of the meter is oblong
in a section perpendicular to a central axis through the meter,
as shown in FIG. 3. This section comprises two semi-circular portions
28 spaced apart by two straight parallel portions 30. A bulkhead
32 divides the spaced within the wall 26 into the meter cavity 10
and the electronic components and counter housing 14. The bulkhead
32 and cavity and housing wall 26 are injection moulded as one part.
A rear end cap 34 shown in FIG. 5 closes off the meter cavity 10
from the exterior, and a front plate 35 closes off the housing 14.
The front plate 35 has a display window 36 shown in FIG. 9 to reveal
the liquid crystal display counter 16. The cavity 10 is provided
with an inlet 37 and an outlet 38 provided respectively in the opposite
straight portions 30 of the wall 26.
Two polypropylene rotors 39 and 40 are mounted within the cavity
10 so as to be rotatable about their respective shafts 42 and 44.
These axes lie in the planes in which the semi-circular portions
28 of the cavity wall 26 meet the straight portions 30. The rotors
are the same size as one another, both being oval in transverse
section. The major axis of each oval is equal to the interior radius
of each semi-circular portion 28 and the sum of the major axis
and the minor axis is equal to the distance between the shafts 42
and 44. The geometry of the oval shape is such that, starting from
positions in which the major axis of one oval is parallel to the
straight portions 30 of the cavity and housing wall 26 and the major
axis of the other oval is at right angles to those straight portions,
the ovals always touch one another along a line parallel to and
between the shafts 42 and 44 for equal rotations of the two rotors
in opposite senses.
FIG. 4 shows respective intermeshing gear wheels 46 and 48 fixed
to the rear sides of the rotors 39 and 40 to ensure that the two
rotors always rotate in opposite senses to one another by the same
angular amount. The gear wheels may each be made with the corresponding
rotor as one part. Respective sintered magnets 50 and 52 are encapsulated
in the rotors 39 and 40 close to an outer extremity of the major
axis in each case, with weights 54 and 56 counterbalancing the magnets
close to the opposite extremities of the major axes.
FIG. 6 shows how the various parts of the meter are assembled together
with injection moulded 60.degree. nylon pin bearings 58 60 62
and 64 at the ends of the shafts 42 and 44 one bearing 58 or 60
for each shaft being sunk in the bulkhead 32 and another 62 or 64
in the rear cap 34.
On one side of the bulkhead 32 in the electronic component and
counter housing 14 the printed circuit board 18 is mounted in the
bulkhead, with the pick-up coil 20 field-effect transistors 22
and other electronic components 24 and also the liquid crystal
display counter 16. The pick-up coil 20 is accommodated in a recess
in the bulkhead 32 on the dry side thereof. A further recess, diametrically
opposite the first, houses a second pick-up coil 66 connected to
charge an integral nickel-cadmium cell 68 via a rectifier (not shown
in FIG. 6). The cell is connected to power the various electronic
components on the printed circuit board 18 including the liquid
crystal display counter 16.
Operation of the flow meter is as follows.
As water under pressure enters the meter cavity 10 via the inlet
37 it drives the rotors 39 and 40 in opposite senses as indicated
by the arrows in FIG. 3 to move around the inside of the semi-circular
portions 28 of the cavity wall 26 before passing to the opposite
side of the rotors and out of the cavity 10 via the outlet 38. Since
the amount of water transferred in this from the inlet to the outlet
is substantially the same for each full turn of the rotors 39 and
40 the flow of water through the meter is directly proportional
to the speed of rotation of the rotors, or expressing this in another
way, the total volume of water displaced is proportional to the
total number of turns of the rotors. The gear wheels 46 and 48 or
the rotors 39 and 40 respectively ensure that the rotors always
turn through the same angles, albeit in opposite directions, over
any given period of time. This ensures that the ovals are always
touching one another along a line which is parallel to and between
the shafts 42 and 44.
The number of times the rotors rotate over any given period of
time is counted by means of the scintered magnet 50 in the rotor
39 which creates an electrical pulse in the pick-up coil 20 each
time it passes by the latter. The coil 20 is thus able to detect
the magnet 50. The pulses from the coil 20 are counted electronically
and the stored total is displayed by means of the liquid crystal
display counter 16 on the printed circuit board 18. The display
thus gives a reading of the total volume of water which has passed
through the meter since the counter 16 was last set to zero. The
counter 16 is calibrated so that the reading on the display shows
this volume in cubic meters.
The pulsed output from the other pick-up coil 66 created as the
sintered magnet 52 in the rotor 40 passes by the coil, maintains
a charge level in the nickel-cadmium cell 68. In addition to acting
as a power source for the various electronic parts of the meter,
the cell 68 maintains the stored total in the counter 16 during
long periods of non-use.
This construction of the meter, with its reduced number of moving
parts and self-powering features which eliminate the need for a
driveshaft and gear train, retains the benefits of the previous
meter while offering enhanced performance and reliability. It has
the advantage of being capable of mass production by methods which
cut out skilled assembly. The net result is a product that can now
be produced at a fraction of the cost of equivalent existing models.
FIG. 11 shows electronic circuitry which may be used in the meter.
The first pick-up coil is connected to an electronic counter 70
of the liquid crystal display counter 16 of FIGS. 2 to 10. This
counter 70 drives a liquid crystal display 72 and is also readable,
via a telephone interface 74 by means of the user's telephone line.
This allows the meter to be read directly by a central computer.
The second pick-up coil 66 has a first output line to a rectifier
76 which charges the nickel-cadmium cell 68 and a second output
line to a frequency/voltage converter 78. The cell 68 is connected
to apply an operating voltage to the various parts of the circuitry.
The frequency/voltage converter 78 is connected to apply a control
voltage to a division ratio adjuster 80. The latter supplies a control
signal to the counter 70 to adjust the division ratio of the latter.
This calibrates the rate of count according to the flow rate through
the meter, correcting for errors which would otherwise tend to arise
for rates of flow at the upper and lower extremes of the meter's
range.
Instead of using the frequency/voltage connector 78 to control
the division ratio adjuster 80 the latter could be controlled directly
by the frequency of the signal from the pick-up coil 66. It is also
possible to use some other form of cell in place of the nickel-cadmium
cell, and some other form of pick-up in place of the pick-up coils.
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