Note: Descriptions are shown in the official language in which they were submitted.
CA 02341501 2001-02-23,.,e
The Sweaisn ram~~~ ~~~
PCT International Appll~ation
1 ~ _ '~i ~ ; 1
Z 4 -~~' 2000
FLUID SENSING DEVICE AND METHOD FOR USE IN PARTICULAR IN
MILHING MACHINES
The present invention relates to a fluid sensing device and method for use in
S particular in milking machines of the type mentioned in the preamble of
claims 1
and 11.
In milking machines it is necessary to regularly clean the pipe system leading
from
the milked animals udder to the milk storage container. This is done by
flushing the
system with cleaning fluids and it is important to be able to distinguish
between
water, milk, milk diluted with water, cleaning fluid, air, etc. in the hoses
or pipes so
that milk is not inadvertently sent to a container intended for waste products
and so
that waste products, cleaning fluid or contaminated milk are not sent to
containers
intended for pure milk. It is often also important to detect when a teat or
udder has
finished supplying milk to prevent excessively prolonged stimulation of the
empty
teat or udder.
Patent document US-A 4 756 274 describes an end of milking detector for use in
a
pipe in which a horizontally directed infra-red light source sends a beam of
infra-red
light to a detector on the opposite side of the pipe. If the fluid in the pipe
reaches or
passes above the level of the infra-red light source the beam is prevented
from
reaching the detector and it is assumed that the pipe is full of milk. This
device can
only determine that there is an absence or presence of milk (or other light
blocking
substance) above the level of the detector in a pipe. It cannot accurately
measure
how full the pipe is and it cannot measure the composition of the substance
blocking
the light beam.
Patent document US-A 5 116 119 describes a device for measuring liquid flow.
This
device has one or more channels through which the fluid flows and each channel
contains a pair of sensors. Each sensor comprises an emitter of
electromagnetic
radiation and a receiver positioned on the side of the channel opposite the
emitter.
AMENDED SHEET
CA 02341501 2001-02-23
WO 00/13011 2 PCT/SE99/01451
The attenuation of the radiation received by the receiver is used as a measure
of the
momentary volume of the fluid flowing through the channel. This device is
unsuitable for detecting the presence and flow of clear fluids.
The device and method of the present invention have the object of solving the
problems of the prior art.
The object is achieved according to the present invention by means of a device
and
a method having the features mentioned in the characterising parts of the
independent claims. Further developments and improvements of the present
invention are mentioned in the dependent claims.
The invention will be described more closely with the help of examples of
embodiments and the appended figures in which:
Figure 1 is a schematic perspective lateral view, partly in section, of one
embodiment of a sensing device according to the invention;
Figure 2 shows a graph displaying the output against time of the sensing
device of
figure 1;
Figure 3 shows a schematic side view of an embodiment of a sensing device in
accordance with the invention in a supply line.
The sensing device 1 shown in Figure 1 comprises a light source 3, such as a
visible
light emitting diode, on one side of a transparent container 5, such as a
transparent
glass or plastic pipe having a circular cross-section, holding the fluid 7
being
examined and a light detecting means 9 e.g. a light sensitive resistor or a
photo
diode, mounted on the opposite side of the container, which is sensitive to
the light
emitted by the light source and which generates an output signal 11, e.g. a
voltage,
proportional to the light it receives. Light detecting means 9 is preferably
directly
CA 02341501 2001-02-23
PCT/SE99/01451
wo 00/13011 3
opposite light source 3. Preferably light detecting means 9 and light source 3
are
arranged with one vertically above the other so that even small quantities of
fluid in
the container 5 interrupt the path of the light between the detecting means 9
and
light source 3 and can be detected. In the example shown in figure 1 the pipe
5 is
intended to be part of a milking device and the fluid 7 could be air, water,
cleaning
fluid, milk or the like which is flowing through the pipe 5. The output signal
11 is
represented here symbolically by a trace 13 on an oscilloscope screen 15 but
in the
preferred embodiment the output signal 11 is processed by calculating means
such
as a computer 17. The trace 13 varies as the composition of the fluid between
the
light emitting source 3 and the light detecting means 9 varies. While for the
sake of
simplicity the light source 3 and detecting means 9 have been shown spaced a
distance from the pipe 5 in practice the best results can be achieved by
having them
in contact with the pipe 5 and, possibly, mounted in blind recesses formed in
the
wall of the pipe 5. In the latter case the base of the recesses prevent the
fluid in the
pipe 5 from coming into contact with these components. In order to prevent
ambient
light affecting the light detecting means the device in accordance with the
present
invention is preferably surrounded by a light-tight casing or cover 10.
The amount of light received by light detecting means 9 is dependent on a
number
of variables, such as, for example, the strength of the light source 3 and the
distance
between the light source 3 and light detecting means 9, the opacity of the
fluid 7 in
the container 5 etc. If all the other variables are kept constant then any
variation in
the amount of light detected by light detecting means 9 is dependent on the
composition of fluid 7. The output signal or voltage 11 generated by this
light can
be analysed, for example by comparison to the signals received from
calibration
mixtures of known composition, in order to determine the composition of the
fluid
in the pipe. This comparison can be performed manually by an operator, for
example by comparing an output signal against calibration charts showing
output
signals obtained for different fluids of known composition. Alternatively one
or
more threshold levels can be set which corresponds to one or more desired
opacities
of the fluid being tested. Then when the detected light passes a certain
threshold a a
CA 02341501 2001-02-23
PCT/SE99/01451
w0 00/1301 i
visual signal such as a lamp or strobe light and/or an audible signal such as
a bell or
buzzer can be activated. This embodiment has the advantage that it is easy to
implement without requiring the use of a computer. However in the preferred
embodiment of the invention the comparison is performed by automated means
such
as computer 17. Once the composition of the fluid in the pipe 5 has been
determined
it is possible to use this information to control valves (not shown) so that
the fluid 7
is guided to the correct destination. It is also possible to control valves to
change the
composition of the fluid e.g. by opening or shutting a cleaning fluid supply
valve or
a milk supply valve.
Calibration of the device can be performed by passing calibration fluids of
known
composition through the device and comparing the output signal against the
expected output signal.
Figure 2 shows a graph of how an output voltage signal for a sensing device
according to the invention could vary as different fluids pass through the
pipe 5.
When the pipe 5 contains only air (as shown in the section of the graph marked
"air") a certain voltage Vair will be generated and when the pipe 5 is
completely
filled with a clear fluid such as water which has a refractive index which is
different
to the refractive index of air the pipe 5 will act as a magnifying lens to
concentrate
the light onto the detector and a higher voltage Vwater will be generated (as
shown
in the section of the graph marked "water"). When the pipe S is completely
filled by
an opaque fluid such as milk (as shown in the section of the graph marked
"milk")
then a lower voltage Vmilk will be generated and this voltage will rise
towards
Vwater if the milk is diluted with water and vice versa. Thus the voltage
generated
can be used to determine what percentage of milk and water is in the pipe. By
using
a sufficiently sensitive light detecting means 9 the sensing device can be
made to
detect extremely small instantaneous variations (such as "var" as shown in the
enlarged part of fig. 2) in the opacity of the fluid 7 and, since milk or milk
and water
always has some tiny variations in opacity, it can also detect if the fluid is
moving.
In the region of the graph between Vair and V water each generated voltage
could
CA 02341501 2001-02-23
WO 00/13011 5 PCT/SE99/01451
correspond to a mixture of air and water or a mixture water and mills. It is
possible
to determine which type of mixture is present by checking which valves are
open or
by studying the variation "var" in the signal which has different
characteristics
depending on whether a clear mixture of air and water is present or an opaque
mixture of milk and water.
Figure 3 shows an embodiment of a device in accordance with the present
invention
for use in a system which is subject to large variations in flow rate and
composition
of the fluid passing through it. Such large variations are common in milking
systems
in which slugs of milk are followed by bursts of air and in which the milk
flow rate
can varies from zero up to several litres per minute. The device shown
generally by
31 is fitted across a comparatively narrow bypass-tube 33 which is below a
larger
diameter supply tube. As the bypass-tube 33 is below the supply tube 35 then
liquids in the supply tube will tend to fill up the bypass tube before they
start
flowing through the supply tube. Preferably the sensing device 31 is
positioned at
the lowest point of bypass-tube 33 so that only a small volume of fluid is
required to
fill the cross-section of the bypass-tube 33 by the sensing device
3l.Therefore even
with small flow rates it is possible to accurately sample the fluid as long as
the
volume of fluid which collects in the bypass-tube 33 is sufFcient to fill the
cross-
section by the sensing device 31. When the flow of fluid in the supply tube 35
then
most of the fluid will pass through the bypass-tube 3. As the fluid flow
increases
more and more of the fluid will flow through the supply tube 35. It is useful
to have
a large diameter supply tube 35 as this reduces the pressure losses in the
system
while the use of a narrow diameter bypass-tube 33 allows accurate sampling of
small quantities of fluid.
The presence of blood or other coloured contamination can be detected by using
a
suitable, preferably removable, colour filter or a providing more sensing
devices
according to the invention, each having a filter or light source adapted to
enable the
~0 de:ection of different contaminants.
CA 02341501 2001-02-23
WO 00/13011 6 PCT/SE99/01451
Clotting of milk can be detected by analysis of the signal as the passage of
clumps
of clotted milk will cause easily detected dips in the signal.
Accurate measurement of the velocity of the fluid can be obtained by using two
or
more sets of light sources and detector spaced a known distance apart in the
direction of flow of the fluid being examined. By comparing the signals
generated
by the spaced apart detectors in order to identify similar irregularities in
the signals
the speed of the flow can be calculated from the time it takes for
irregularities in the
waveform of the first generated signal to appear in the second generated
signal.
As the light source and sensing means are on the outside of the pipe there are
no
problems in keeping them clean and no special sealing arrangements are
required.
The lens effect of the circular cross-section makes it possible to determine
if the
pipe contains air or water. This is because a water-filled pipe 5 acts as a
converging
lens and more of the light emitted by the light source 3 is focused onto the
detecting
means 9 than is the case with an air-filled pipe 5. While the invention has
been
illustrated with an example of a pipe with a circular cross-section, a
magnifying
effect can also be achieved by using a pipe with another suitable cross-
section e.g.
oval, semi-circular, convex, bi-convex etc. Alternatively if a triangular (or
other
mufti-sided) cross-section pipe with straight sides is used then the pipe will
act as a
prism and will refract the incident light through an angle which depending on
how
full of fluid it is. By providing a continuous line of spaced-apart light
sensing means
in a line corresponding to the possible paths that the refracted light can
take it is
possible to measure the degree of fullness of the pipe as well as the
composition of
the fluid in it.
The invention has been illustrated by an example of an embodiment in which the
container is made of a transparent material. It is also conceivable to make
the
container material from a translucent material. It is furthermore conceivable
to use
an electromagnetic radiation source which does not produce visible light e.g.
a
CA 02341501 2001-02-23
WO 00/13011 7 PCT/SE99/01451
source of infra-red radiation or ultra-violet radiation instead of, or in
combination
with, the visible light source mentioned above. In order to reduce the effects
of the
material acting as a light guide it is conceivable that it can be necessary to
surround
the detector with a light-proof shield or use some other shielding means to
ensure
that only light which passes through the fluid in the container is received by
the
detector.
In another embodiment of the invention (not shown) a single sensor according
to the
invention can be used to measure the flow in a pipe. This can be achieved by
providing a pipe with such a large cross-sectional area that it never becomes
completely filled by fluid during normal use. It is therefore possible to
measure the
depth of fluid as it passes between the source and detecting means. This depth
can
be used to calculate the flow rate if the size of the pipe and the force
causing the
flow, e.g. a head of pressure or a suction, are known.
While the invention has been illustrated as detecting the composition of
moving
fluids it is also suitable for modification to analyse static fluids. In other
words a
device in accordance with the present invention could be constructed in a
container
which can be filled with a sample of the fluid of interest which can then be
analysed. The device could be used to sense the mixing of an opaque fluid or
powder in a clear liquid, wherein the transparency of the liquid decreases as
the
opaque fluid or powder is mixed in. The output signal will therefore diminish
in
strength as the mixing takes place and complete mixing is indicated by the
output
signal reaching a steady-state.
