Method and apparatus for measuring liquid flow

A method and apparatus for measuring liquid flow, particularly milk, includes directing the liquid to flow through one or more flow channels, while exposing the liquid to electromagnetic radiation; measuring the transparency to electromagnetic radiation of the liquid flowing through the flow channel; and measuring the momentary attenuation of electromagnetic radiation by the liquid flowing through the flow channels, to determine the momentary volume of the liquid flowing through the flow channel. The momentary velocity of the liquid flowing through the flow channels is also determined, thereby permitting a determination of the momentary flow rate of the liquid flowing through the flow channels.

FIELD AND BACKGROUND OF THE INVENTION 
The present invention relates to a method and apparatus for measuring 
liquid flow. The invention is particularly useful for measuring the flow 
of milk, and is therefore described below particularly with respect to 
this application, but it will be appreciated that the invention could 
advantageously be used for measuring the flow of other liquids, 
particularly mixtures. 
Existing methods of measuring milk flow are generally based on mechanical 
type measuring devices. One way of electrically measuring milk flow is to 
subject the milk to electromagnetic radiation and to measure the 
attenuation of the electromagnetic radiation by the milk. However, the 
composition of the milk varies substantially from cow to cow, and even 
from the same cow during the same milking process. Such variations in 
composition affect the attenuation of the electromagnetic radiation by the 
milk and thereby affect the measurements in a significant manner. 
OBJECTS AND BRIEF SUMMARY OF THE INVENTION 
An object of the present invention is to provide a method, and also an 
apparatus, for measuring liquid flow in which variations in the 
composition of the liquid do no significantly affect the measurements. 
Another object of the present invention is to provide a method and 
apparatus which not only produces a relatively accurate measurement, in 
real time, of the flow of a liquid despite variations in the liquid 
composition, but which also provides additional information useful in 
indicating the composition of the liquid whose flow rate is being 
measured. A further object is to provide a method and apparatus of 
measuring milk flow particularly useful for accurately measuring flow 
rates of milk in a real time manner. 
According to one aspect of the present invention, there is provided a 
method of measuring liquid flow, comprising the steps: (a) directing the 
liquid to flow through a flow channel of known dimensions while exposing 
the liquid to electromagnetic radiation; (b) measuring the momentary 
attenuation of the elecromagnetic radiation by the liquid flowing through 
the flow channel; (c) measuring the relative transparency to 
electromagnetic radiation of the liquid flowing through the flow channel 
for calibration purposes; (d) determining from the foregoing measurements 
the momentary volume of the liquid flowing through the flow channel; (e) 
determining the momentary velocity of the liquid flowing through the flow 
channel; and (f) determining from steps (d) and (e) the momentary flow 
rate of the liquid flowing through the flow channel. 
According to further features in the preferred embodiment of the invention 
described below, the transparency is measured by subjecting a known volume 
of the liquid to the electromagnetic radiation and measuring its 
attentuation. More particularly, the transparency of the liquid is 
measured by measuring the attenuation by the liquid of the electromagnetic 
radiation while the liquid flows through and fills a conduit of known 
dimensions. 
In the described embodiment, the latter channel is a calibrating channel 
separate from the flow channel. It is contemplated, however, that the flow 
channel, or one of the flow channels (if a plurality are provided), could 
also be used as the calibrating channel if the transparency measurement is 
taken when that channel is full. 
The preferred embodiment of the invention described below provides further 
important features, including the following: in step (a), the liquid is 
directed to flow through a plurality of the flow channels in parallel to 
each other; in step (b), the momentary attenuation of the electromagnetic 
radiation is measured in each of the plurality of flow channels; and in 
step (d), the momentary volume of the liquid flowing through all the flow 
channels is measured to determine the momentary volume of the liquid 
flowing through all the flow channels. 
According to still further features in the described preferred embodiment, 
in step (b) the momentary attenuation of the electromagnetic radiation 
measured in at least some of the flow channels is of different 
frequencies, to thereby provide information useful in indicating the 
composition of the liquid flowing through the flow channels. 
In the preferred embodiment of the invention described below, the 
electromagnetic radiation source is a source of infrared light. 
As will be described more particularly below, the method of the present 
invention is particularly useful for measuring the flow rate of milk since 
the results are not significantly affected by changes in composition of 
the milk from cow to cow, or even from the same cow. Moreover, the results 
produced by the method also provide information useful in indicating the 
actual composition of the milk whose flow rate is being measured. Thus, 
the latter feature makes it possible to estimate the milk's different 
components, such as relative percentages of fat and protein, since these 
relative percentages influence the absorption of the light from the light 
source. 
The invention also provides apparatus for measuring liquid flow in 
accordance with the above method. 
Further features and advantages of the invention will be apparent from the 
description below.

DESCRIPTION OF A PREFERRED EMBODIMENT 
The apparatus illustrated in the drawings is particularly useful for 
measuring the flow rate of milk and also for indicating its composition, 
e.g., the relative percentages of fat and protein. 
The apparatus illustrated in FIG. 1 includes a measuring head, generally 
designated 2, having an inlet 4 connected to a conduit 6 leading from a 
source of the milk (e.g., a cow milking machine), and an outlet 8 
connected to an outlet conduit 10 (e.g., leading to a container for 
receiving the milk). As the milk flows through measuring head 2, its flow 
rate is continuously measured in a real time manner despite variations in 
the composition of the milk. 
The outlet conduit 10 would normally be connected to a vacuum source. Thus, 
when the flow of milk through the measuring head 2 is not continuous, air 
"bubbles", or milk "pulses", would be produced in the flow of the milk 
through the measuring head. 
Measuring head 2 includes, adjacent to its inlet end 4, a plurality of 
partitions 12 which divide the inflowing milk into a plurality of parallel 
flow channels 14. Each of the flow channels 14 is of known dimensions, in 
that both its width and height are known. However, the flow channels 14 
are designed, as compared to the range of flow rate of the milk to be 
measured, so that the channels are not completely filled by the milk at 
the time the measurements are made. Accordingly, the volume of each 
channel will vary in accordance with the flow rate of the milk through 
that channel. 
Measuring head 2 further includes two lines of electromagnetic radiation 
sources, such as infrared light sources, each aligned with, and on one 
side of, each of the flow channels 14. In the example illustrated in FIG. 
1, there are seven flow channels 14, and therefore there is a first line 
of seven light sources 20, and a second line of seven light sources 22 
spaced from line 20 towards the outlet end 8 of the housing. The distance 
between the two lines of light sources 20, 22 is precisely known. This 
enables a determination of the velocity of the milk flow to be made, as 
will be described more particularly below. Each of the light sources 20, 
22 is aligned with a light detector 24, 26, at the opposite side of the 
respective channel 14, so that each detector 24, 26 measures the 
attenuation of the light produced by the milk passing through the 
respective channel 14. 
Measuring head 2 includes a further channel 30, serving as a calibrating 
channel, through which the milk is directed after it leaves the seven flow 
channels 14. Calibrating channel 30 is also of known dimensions, but in 
this case the channel is completely filled with milk when measurements are 
taken, as distinguished from the flow channels 14 which may not be 
completely filled with milk during the normal working ranges of the 
illustrated apparatus. Calibrating channel 30 is used for measuring the 
relative transparency of the milk. For this purpose, the calibration 
channel 30 is also equipped with a light source 32 and a detector 34 on 
the opposite sides of the channel. 
The milk, after passing through calibration channel 30, passes through 
another calibration station 36 between the calibration channel 30 and the 
housing outlet 8. Calibration station 36 is also equipped with a light 
source 38 and detector (40, FIG. 2). The light source 38 and its 
corresponding detector 40 are subjected to the same temperature as the 
milk flowing through channels 14 and 30, but they are physically insulated 
from the milk so that the detected radiation is influenced, not by the 
attenuation of the radiation caused by the milk, but only by the 
temperature variations of the milk. 
The overall system including the measuring head 2 illustrated in FIG. 1, is 
more particularly illustrated in the block diagram of FIG. 2. It will thus 
be seen that the radiation from the line of light sources 20 passes 
through the milk flowing through the flow channels 14, so that the 
radiation detected by each of the detectors 24 at the opposite side of 
reach channel provides an indication of the momentary attenuation produced 
by the milk flowing through the respective channel. A similar measurement 
is provided by the second line of light sources 22 and their respective 
detectors 26. Since the distance between the two lines of light sources is 
known, the velocity of the milk flowing through the flow channels 14 can 
be determined. 
This is more particularly illustrated in FIG. 3, wherein it will be seen 
that the broken-line waveform, corresponding to the outputs of detectors 
26 cooperable with the line of light sources 22 lags the full-line 
waveform, correspond to the outputs of detectors 24 cooperable with the 
line of light sources 20 because of the distance between the two lines of 
light sources and detectors. Since this distance is known, and since this 
lag can be measured, the velocity of the milk flowing through the flow 
channels 14 can be determined. 
The outputs of the two groups of detectors 24, 26 are fed, via an amplifier 
50 and an analog-to-digital converter 52, to a microprocessor 54 which 
makes this determination. 
Detector 34, aligned with light source 32 in the calibration channel 30, 
also produces an output which is applied, via amplifier 50 and converter 
52, to the microprocessor 54. As described earlier, since the calibration 
channel 30 is always full of milk, the output of its detector 34 will not 
provide an indication of the relative volume of the channel occupied by 
the milk, but rather of the relative transparency of the milk flowing 
through that channel. Thus, the higher the percentage of fat in the milk, 
the lower will be the relative transparency of the milk to the radiation, 
and therefore the higher will be the attentuation resulting from the 
passage of the radiation through the milk. 
Microprocessor 54 receives the outputs from the two groups of detectors 24, 
26, and also from the calibration detector 34. Microprocessor 54 includes 
a non-volatile memory 56 that contains a table for converting the 
measurements of detectors 24, 26, and also of a calibration detector 34, 
to the relative volume of the flow channels 14 occupied by the milk 
passing through these channels. Since microprocessor 54 also determines 
(from the two lines of detectors 24, 26) the velocity of the milk passing 
through these channels, the microprocessor is able to determine the flow 
rate of the milk at any instant irrespective of its transparency. 
The amount of light absorbed by the milk flowing through the flow channels 
14 is dependent, not only on the relative volume of the milk actually 
occupying the respective channel and the composition (transparency) of the 
milk in the channel, but also on the frequency of the radiation of its 
respective source (20, 22). Thus, the light sources 20 and their detectors 
24 in some or all of the channels could be selected to operate at 
different frequencies, so that the information received by their 
respective detectors 24 will provide an indication of the relative 
composition of the milk then being measured, e.g., the relative percentage 
of fat and protein. 
Detector 40 feeds it output, which varies with the temperature, to a 
stabilization unit 58. This unit controls the energy supplied to all the 
light sources 20, 22, 32 and 38, in order to compensate the measurements 
for changes in temperature and ageing effects. 
In order to obtain a precision of .+-. one percent, which is generally more 
than adequate for the consumer, it is possible to use low sample rates, in 
the region of 3-30 Khz, and a data word width of eight bits. These sample 
rates and data widths enable the use of standard low cost 
analog-to-digital components and microprocessors. The radiation sources 
and detectors may change by ageing. Ageing can be measured by examining 
the values obtained in the receivers while the channels are empty, and may 
also be compensated for by updating the table stored in the memory 56. 
While the invention has been described with respect to one preferred 
embodiment, it will be appreciated that many variations and other 
applications of the invention may be made.