Note: Descriptions are shown in the official language in which they were submitted.
~Z3Z2~
:
The present invention relates to an apparatus for
measuring components of liquid samples based on the ability of
these components to absorb infrared radiation at certain
frequencies. The apparatus according to aspects of this in~ention which
~may be used for analyzing liquid samples in general is
specifically, but not exclusively,intended for use in
analyzing liquid milk samples or determining components thereo~.
Analyzing apparatuses for automatic determination
and registration of various components, e.g. fat, protein,
and lactose, of milk samples being exposed to infrared
radiation, are known. In such known apparatus infrared radiation
from a radiation source is divided into two separate beams
which by means of a system of mirrors are passed through a
component filte~ and a reference filter, respectively. The
component filter admits a narrow band of infrared wave lengths
at which the radiation absorbing ability of the component to
be measured is relatively high, and the reference filter admits
a narrow band of wave lengths at which the radiation
absorbing ability of said component is substantially lower.
These filtered infrared radiation beams are interrupted by a
. . .
rotating reflecting chopper disc at a frequency of 12.5 Hz, and
the component and reference light pulses thus generated are
directed through a transparent cuvette containing the milk
sample and thereafter focused on a pyroelectric radiation
~kL detector ~hich generates an electric signal in response to
the radiatlon pulses received. A radiation attenuating'col~like
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member extends into the reference beam and may be displaced by a DC servomotor
which is energized by the electrical signal from the radiation detector. When
unbalance of the sample and reference beams occurs because of a change in sam-
ple component absorption the amplified signal causes the servomotor to drive
the attenuating comb-member further into or out of the reference beam until
balance is restored. The component of the sample is then determined as a
function of the position of the comb-like member in the reference beam when
balance has been obtained.
The known analyzing apparatus with the dual beam system described
above is of a rather complicated structure containing ten different mirrors,
the positions of which must be accurately adjusted. Furthermore, the accur-
acy of a dual beam system inplies, inter alia that the condition of the beam
directing mirrors associated with each of the t~o~,beams does not change non-
uniformly, for example due to dust or other changes in reflexion ability.
m e prior art also discloses an infrared single beam analyzer for
determining one component of a gas flowing through a transparent gas cell. An
infrared radiation beam is directed from an infrared source through the gas
cell by means of optical lenses and focused on an indium antimonide detector.
The radiation beam is chopped at a chopping frequency of 600 Hz, and inter-
ference filters selected for the measurement and reference wave lengths are
interposed alternately in the radiation beam at a frequency at about 6 Hz so
that the detector receives chopped energy at a level corresponding alternate-
ly to the measuremant and reference transmission levels. Consequently, the
output signal of the
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detector is a 600 Hz carrier modulated at 6 Hz~ The signal
generated by the detector is supplied to signal processing cir-
cuits for determining the component to be measured on the basis
of said signal.
The present invention is a broad aspect thereof provides a
simplified infrared analyzing apparatus of the single beam t~pe
for determining a plurality of components of a li~uid sample.
The apparatus according to an aspect of this invention comprises
a source of infrared radiation, transparent sample receiving
means, means for directing a beam of radiation from said source
through said sample receiving means, means for chopping said
beam at a predetermined frequency at a position between said
source and said sample receiving means, a plurality of pairs of
; optical filters, each of said pairs being associated with the
respective one of ~aid components and comprising a component
ilter for passing infrared radiation at a narrow frequency band
at which the radiation absorbing ability of said component is
relatively high, and a reference filter for passing infrared
radiation at a different narrow frequency band at which the radia-
tion absorbing ability of said component is low, means for
successively positioning said filters of at lèast one pair in
said radiation beam between said source and said sample receiving
means and for maintaining each filter on said radiation beam for
a period of time comprising a plurality of cycles of said chopp-
ing means, a thermopile radiation detector arranged so as to
receive radiation having passed said sample receiving means and
for providing a signal on said period of time in response to the
radiation received and means for calculating values of the com-
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ponent associated with said one pair of filters on the basis of
two said si~nals related to said one pair of filters.
By a preferred aspect o~ the invention, the thermopile
radiation detector also provides a pulsed reference signal in
response to radiation received through the reference filter by
the said pair of filters in another such period of time.
Preferably, the period of time during which each filter
is maintained in the radiation beam exceeds 0.5 seconds.
By one variant of the broad aspect the chopping means are
lQ arranged between said source and said filters~
By a variation thereof, the thermopile detector is of a
monolithic type.
By another variation, the apparatus is specially adapted
to analyze samples of liquid milk products.
By yet another variation, the fre~uency bands of said
filters are within the frequency range 4.5~ - 10~.
By a further variation, the source, said sample receiving
means, and said detector are aligned.
By yet another variation, the apparatus further includes
oppositely directed first and second concave mirrors, said infr-
ared radiation source being arranged in front of said first mir-
ror so as to focus the beam of radiation from said source on said
sample receiving means and said detector being arranged in front
of said second mirror so as to focus said radiation beam having
passed said sample on said detector.
By another variation, the beam directing means define bet-
ween said sample receiving means and said second mirror a radia-
tion beam diverging at an angle between 20 - ~5.
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.
By a further variant o~ this invention, the apparatus
includes temperature control means for independently controlling
the temperature of said filters.
By yet another variant, the detector provides signals
representative of the amounts of radiation energy Ec and Er
received in the periods of time in which the component filter
and the reference filter, respectively, of said pair of filters
are maintained in said radiation beam, said calculating means
being adapted to calculate a value C of the component on the
basis of the expression
(Ec/Er)/~? O
wherein ~ and ~ o are preaetermined constants.
By a variation thereof, the calculating means comprise a
variable gain amplifier, means for passing said Er signal to the
input of the amplifier, means for varying the gain of said ampli-
fier to a level at which the amplified Er signal corresponds to
a predetermined value, means for maintaining the gain of the am-
plifier substantially at said level, and means for passing said
Ec signal to the input of the amplifier while the gain thereof
is kept at said level.
By another variation, the gain maintaining means comprise
a memory connected to the output of said amplifier and to said
radiation emitting device and a switching device for disconnect-
ing said amplifier ana said memory while said Ec signal is being
passed to said amplifier.
By a further variant, the apparatus further includes fil-
ter selecting means for selecting one of a predetermined number
of combinations of said plurality of filter pairs to be used for
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measuring selected components of a sample positioned in said
sample reGeiving means, and for controlling the function of said
filter positioning means in correspondence with the selection
made.
By a variation, the filters are arranged on a rotatable
filter supporting means, said filter selecting means comprise
code markings connected to said rotatable filtex supporting means,
and code reading means arranged opposite to said code markings.
By another variation, the code markings comprise holes
defined in a disc member and said code reading means comprising
photoelectric sensors and corresponding light sources arranged
on opposite sidès of said disc member.
By yet another variation, the apparatus further includes a
mechanical locking device for locking said fil-ter supporting means
in a selected rotational position.
By yet another variation, the beam directed means define
between said sample receiving means and said second mirror a
radiation beam diverging at an angle of 20 - 45, preferably
30 _ 40
By another variant of this invention, the filters are
arranged on a filter support rotatable about an axis substantially
parallel with the longitudinal axis o said beam.
By a variation thereof, at least one of said filters is
mounted adjustably on said support so that the angle between the
axis of said support and the plane of said filter may be changed.
By another variation, one filter is mounted in an annular
holder defining a plane surface part forming an acute angle with
the plane of said filter and engaging with a corresponding plane
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surface part on said SuppoEt, said last-mentioned surface part
forming with the axis of said support an angle being substanti-
ally a complement to said acute angle, said filter being adjust-
able by turning said holder in relation to said support.
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Compared to the known liquid sample analyzing
apparatus described above the apparatus ~ccording to a.spects of this
invention is of a mechanically simple, rugged,and compact
structure. In the appara~us according to aspects o~ this inv~ntion only
one radiation beam is used, and consequently, the optical
alignment of the beam directing means of the apparatus is
sim~le and uncritical. Furthermore, the influence of the
amount of water vapour present is reduced and possible mecha-
nical distortion of the casing surrounding and protecting
the beam directing means and the apparatus parts associated
therewith will not substantially affect the measurementsof the apparatus.The thermopile radiation detector used in the
appa~atus according to the invention is a robust wide-range
detector renderiT,g at possible to determine a desired number
of different componentsof the liquid sample being measured. -
The thermopile radiation detector ispreferably of the monolithic type whereby "microphone effect"
is avoided so as to make the apparatus less sensitive to
shocks and vibrations.
~0
The apparatus according to an aspect of this invention may be used
for determining components of any type of liquid sample which
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may be analyzed by infrared spectrometry. A preferred embodiment of the
apparatus is, however, adapted to analyze samples of liquid milk products,
and in that case the frequency bands of the filters are preferably within
the frequency range 4.5 ,u - 10 ,u.
Although the apparatus according to aspects of this invention is
of the type in which one and the same radiation beam is used for generating
the component signal as well as the reference signal, that beam may be
directed along a tortuous path by means of suitable reflecting means, e.g.,
mirrors. However, it is preferred to arrange the radiation source, the
sample receiving means, and the detector so that they are aligned in order
to obtain a simplified structure. The radiation beam may then be focused
on the sample receiving means and on the detector, respectively, by means of
only two lenses or concave mirrors. In the known apparatuses described above
the radiation detector must generate several alternating component and refer-
ence signals for each component to be determined. According to an aspect
of the present invention the filter positioning means are preferably adapted
to retain each filter of a pair of filters in the single radiation beam in
a period of time exceeding 0.5 seconds and in may cases even 1.5 seconds in
order to give the thermopile detector sufficient time to detect the intensity
of the radiation passing each filter and to generate a signal in response
thereto. The calculating means of the apparatus may then be adapted to
calculate a value of the component associated with the pair of filters used
on the basis of only two such consecutive signals, namely one reference signal
and one component signal.
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It may be found necessary to retain each
filter in the radiation beam in a still ionger period of
time, for example 4.7 seconds or even more.
Due to the long residence time of each filter in
the radiation beam it is important that the conditions
of the elements of the apparatus and of the surroundings,
e.g;, temperature and moisture conditions, do not change
to any appreciable degree in the period of time in which
each pair of filters including a measuring filter and a
corresponding reference filter is placed in the radiation
beam for measurin~ f~ne cvmpvnent of a sample. In order subs~antially
~o preven.t any radiation from the chopping means fr~m influencing the de~ec-
tor these chopping means are preferably arranged between the
_ . _ ... .. . . . . ..
radiation source and the filters. The temperature of the filters
may be controlled by independent temperature control means in
order to keeEIthe optical characteristics thereof subs~ntially constant.
The detector may generate signals which are
representative of the amounts of radiation energy Ec and Er
received in the periods of time in which the component filter
and the reference filter, respectively, of a pair of filters
are positioned in the radiation beam. The value C of the
component mày then be calculated on the basis of the following
expression
-- ~ - aO
r
wherein ~ and ~O are predeterlnined constallts, e.s.,
apparatus constants determined by calibration of the appaLcltlls.
Preferably, O is an arbitrarily fixed constant wh;Lf~ ~ is
determined so as to make the expression zero when tile sanlple
is pure water.
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The appar~tus according to an aspect of thls invention
comprises a plurality of pairs of optical ilters so that
it is able to measure the content o two or more components
in a liquid sample. Ilowever, in some cases it is desired to
determine only one or some of the components which may be
measured by means of the apparatus. Therefore, in a
preferred embodiment the apparatus comprisesfilter selecting
means for selecting one of a predetermined number of combina-
tions of said plurality of filter pairs to be used for
measuring selected components of a sample positioned in th~
sample receiving means and for controlling the function of
t~ filter positioning means in correspondence with the
selection made by the user of the apparatus.
The filters may be arranged on a filter support
rotatable about an axis substantially parallel with the
longitudinal axis of the beam. It is then possible to changè
the filter position in the radiation beam merely by rotating
the filter support. One or more of the Eilters may be mounted
adjustably on the support so that the angle defined between
the axis of the support and the plane of said filter may be
changed. By changing the inclination of the filter it is
possible to change the distance traversed by the radiation
beam through the filter, and thereby the frequency band or
center wavelength of the filter may be changed slightly.
2~ In known infrared milk analyzers the radiation
beams emitted from the radiation source are restricted to
a relatively small aperture angle.
It has been found, however, that the negative influence of the
inevitable scattering of the radiation beam may be
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reduced by increasing the aperture angle. Therefore~ the beam
directing means may define between the sample receiving
means and the second mirror a radiation beam divergin~
at an angle of 20 - 45 , preferably 30 - 40 ,
According to another aspect of the invention
the apparatus for measuring components of a liquid sample
- may comprise a source of infrared radiation, transparent sample`
receiving means, means for directing one beam of ra,diation from
said source through said sample receiving means, means for
chopping said beam at a predetermined frequency and at a
position between said source and said sample receiving means, a
plurality of pairs of optical filters, each of said pairs
.being associated with a respective one of said components and
comprising a component filter for passing infrared radiation
at a narrow frequency band at which the radiation absorbing
ability of said componen-t is relatively high, and a reference
filter for passing infrared radiation at a different narrow
frequency band at which the radlation absorbing ability of
said component is low, means for successively positioning
said filters of at least one pair in said radiation beam between
' said source and said sample receiving means and for maintaining
each component.filter and each reference filter in said radia-
tion beam in a period of time comprising a plurality of cycles
of said chopping means, a radiation detector arranged so as
to receive radiation having passed said sample receiving means
and for providing a pulsed component signal in response to
radiation received through the component filter of a pair of
filters in one such period of time, and for providing a ~ se
, . : , . . .
~2322~
reference signal in response to radiation received through the
reference filter of said pair in another such period of time, and
means for calculating a value of a component on the basis of
said measuring and reference signals.
The calculating means may comprise a variable
gain amplifier, means for passing said reference si~nal to
the input of the amplifier, means for varying the gain of said
amplifier to a level at which the amplified reference siynal
correspondsto a predetermined value, means for maintaining the
gain of the amplifier substantially at said level, and means
for passing said components signal to the input o~ the ampli-
fier while the gain thereof is kept at said level. The ampli-
fied component signal will then represent the said predetermined
value multi~lied b~7 the ratio of the component signal to the
reference signal. The structure described may, for example,
be used for calculating the expression
Ec
_ ~ - a
The calculating system described
may, however, be used for calculating the ratio between any
two voltage signals.
The gain varying means may comprise a
radiation sensitive resistor, e.g., a photoresistor connected
to the input of said amplifier, and a radiation emitting device
or light source, e.~., a light emitting diode, controlled by the
output of said amplifier. The gain maintaining means
may comprise a memory connected to the output of said ampli~ier
and to said radiation emitting device, and a switchLng devi~e
which may, for example,be controlled by an elec~ronic
--10--
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` 1~23~4
control system of the apparatus, for disconnecting said
amplifier while said component signal is being passed
to said amplifier.
The invention will now be further described
with reference to the accompanying drawings, wherein
Fig. 1 is a perspective view of an embodiment
of the apparatus accor~in~ to an aspect of this invention, certain wall
parts having been removed,
Fig. 2 is a diagrammatic sectional view of an
optical unit of the apparatus shown in an enlarged scale,
Fig. 3 is a side view of a filter unit of the
apparatus, certain wall parts having been removed,
Fig. 4 is part of the filter unit shown in Fig.
3 and viewed from the opposite side,
Fig. 5 is a sectional view 5-S as indicated in
Fig. 4,
Fig. 6 is a sample flow diagram,
Fig. 7 is a ~lock diagram of the electronic
system of th~ of an aspect o~ this invention apparatus, and
Fig. 8 shows a circuit of the electronic system
more in detail.
Fig. 1 shows a milk analyzing apparatus 10 for
determining the content of one or more of the components fat,
protein, lactose, and ~ater in a milk sample~ The apparatus is
also able to determine the total content of solids and of
solids other than fat in the sample. The apparatus 10 com-
11
3Z;24
prises a sample intake unit 11, an optical unit 12, and an
electronic control unit 13.
The sample intake unit 11 includes a supporting
bracket 14 supporting a stirrer 15 which is driven by an
5~ electric motor 16. The motor 16 is energized by means of a
microswitch (not shown) which may be activated by an activating
member 17 arranged adjacent to the stirrer. The bracket 14 also
supports a pipette 18 connected to the optical unit 12 by
means of a flexible tube or hose l9, and a support 20 for
supporting a cup 21 containing a sample to be analyzed is suspen-
ded below the lower free end of the pipette 18. The vèrtical
positions of the activating member 17, the pipette 18, and
the cup support 20 may be adjusted by means of adjustin~ screws
22. A microswitch (not shown) for starting the measuring
procedure may be activated by means of an ac~ivating arm
23 arranged adjacent to the pipette 18.
The actual measurement of the sample takes place
within the optical unit 12 containing a cuvette 24 in which
the milk sample flows as a thin ~ilm between two closely spaced
transparent plates. These plates may, for example,be made from
~alcium fluoride having a spacing of 37 ~1. The temperature
of the cuvette 24 is preferably thermostatically controlled as
indicated by 24a so as to maintain the temperature at a substan-
tially constant value, for example at 40 C. The cuvette 24 com-
municates with a pipette 18 and with a discharge container 25 as
described more in detail below. The optical unit 12 also
comprises an infrared radiation source 26 fed by a stabilized
electricity supply so as to keep the energy radiated by the
infrared source substantially constant. The infrared source
may, for example,be a platinum filament moulded into a
~L2~2;~9~
porcelain tube. A concave mirror 27 reflects the
infrared radiation so as to substantially focus a
beam of radiation on the cuvette 24 as indicated in Fig.
2. The radiation source 26 and the mirror 27 are
mounted within a tubular housing 28 provided with outer
coding fins, and a blower 29 generates a flow of cooling
air for cooling the housing 28. A heat insulating plate
30,wnich may, for example, be made from polyvinyl
chloride and a tubular member 30a mounted therein
form an end wall of the housing 28 opposite to the
mirror 27 and defines an aperture 31.
The aperture angle u is preferably
relativ~ly large, for ~xan~ple 36, for reasnns described below.
The radiation beam leaving the aperture 31 passes a chopper disc
32 and a filter unit 33 and hits a second concave mirror 34
- focusing the radiation on a radiàtion detector 35 which is prefer-
ably a ther,llopile detector of the monolithic type e.g~, tllat known by th~ Trade ~a
"Ty~e S 15 Thermopile Detector" produced by Sensors .IIIC~, Michigan. The
chopper disc 32 is driven by an electric motor 36 and at con-
stant rotational speed, for example at 10 revolutions per minute.
The motor 36 may be a step motor operating at 20 steps per minute
and energized by a non-varying electricity source, for example
a generator, not shown. The chopper disc 32 is of such a shape
that the radiation beam is chopped once for each revolution
of the disc, and the time periods in which the beam is
interrupted by the chopper disc 32 are preferably of the
same duration as the time periods in which the radiation
beams passes uninterrupted.
The filter unit 33 includes a rotatable filter chan9e
wheel 3j which may be driven by an electric motor 38 Lhronc3h
a coupling 39 and gears 40. The motor 38 may, for example,
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1123Z2gL - ` ~
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be a synchroneous gear motor operating at 10 revolutions
per minute. The filter change wheel 37 is located within a
filter housing 4I the temperature of which is thermostatically
controlled as indicated by 41a so as to maintain the tempe~ature
in the filter housing 41 substantially constant. The chopped
infrared radiation beam passes through a heat filter 42 mounted
in the stationary filter housing 41 and through one of a
plurality`of optical filters mounted on the filter change
wheel 37~ The filter unit 33 further includes a filter code
device 43 for selecting the filter to be aligned with the
radiation beam as described more in detail below. The chopper
disc 32, the filter unit 33, the mirror 34, and the radiation
detector 35 are mounted within a sealed, gas-tight box or
housing 44 in which the atmosphere may be kept in a dry
condition by means of a replaceable cartridge 45 containing
silica gel or another air drying substance. ~
The filter unit 33 will now be described more in
detail with special reference to Figs. 3 - 5. The filter
change wheel 37 is provided with eight optical filters 46
arranged uniformly spaced along a circle having its center on
the axis of the wheel, The eight filters 46 comprise four
pairs of filters, each pair including a component filter
admitting a narrow band of infrared wave lengths at which
radiation absorbing ability of the component to be measured
is relatively high, and a reference filter admitting a
narrow band of wave lengths at which the radiation absorbing
ability of said compon.nt is s~lbstantially lower. The filtcrs
46 comprise a reference filter FR and a component filter FC
for measuring fat, a reference filter PR and a component
filter PC for measuring protein, a reference filter LR and
a component filter LC for measuring lactose, and a component
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.
filter WC and a reference filtèr WR for measuring water in
a milk sample. The filters for measuring fat, protein,
and lactose are preferably of the same type as those used
in ~ known luil~ sa~ple analyzer sol~ under the Y'rade Mark
"MILK0-SCAN 203" by A/S N. Foss Electric, ~iller~d, Denm~rk.
The housing 41 in which the filter change wheel 37 is rotatably
mounted is provided with supporting brackets 47 by means
of which the filter unit is connected to the bottom of
the box or housing 44 in such a position that the heat filter
42 (Fig. 2) is aligned with the radiation source 26, the
cuvette 24, and the radiation detector 35. The heat filt~Qr
~2 which is provided for protecting the filter housing from
undue heating is preferably of a type cutting off radiation
with wave lengths smaller than 4.3 ~. As indicated above the
filter housing 41 is thermostatically controlled so as to main-
tain a substantially constant temperature of the filters well
above normal ambient temperature, for example at 41 C.
For that purpose the filter housing may be made from a heat
conductive material, e.,e., aluminum, and provided with a power
transistor 48 which is controlle~ hy a thermistor 48a so as
to maintain the temperature at the desired level. In order to
allow the radiation beam emitted by the radiation source 26 to
pass through the filter unit the wall part of the filter
housing 41 opposite to the heat filter 42 defines a beam
outlet opening 49 aligned with the heat filter 42 and the cu-
vette 24.
One or more of the filters 46 and preferably the
component filter FC for measuring ~at and the component filter
WC for measuring water are adjustably mounted on the filter
change wheel 37 ~o that the incLination of the filters FC
and WC in relation to a plane normal to the axis
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of the radiation beam emitted by the radiation source 26 may
be varied, for example within the range 5 - 30. As shown
in Fig. 5 the filter FC is fastened to an annular filter
holder 50 with a flange 51 defining an abutment surface which
forms an acute angle of for example 12.S . In the mounted
position of the filter this abutment surface engages with
a corresponding oblique su~face part forming the bottom surface
of an annular recess in the filter change wheel 37 receiving
the flange 51 of the holder 50. The filter holder 50 may be
- fixed to the filter change wheel 37 by means of screws
52 or other suitable releasable fastening means. At its
upper end the filter housing 41 is provided with a removable
lid 53 having a hand grip 54. When the inclination of the filter -
FC shown in Fig. 5 is to be changed, thè lid 53 is removed,
and the filter change wheel 37 is rotated to a position
in which the filter holder 50 is accessible through the
opening provided by removal of the lid 53, When the screws 52
have been loosened the holder 50 and the filter E`C fastened
thereto may be turned till the desired oblique position has
been obtained, whereafter the holder 50 may be secured in the
new position by tightening of the screws 52. In ~ig. 5,
different positions of the holder 50 are indicated in solid
and broken lines, respectively. By changing the inclination of
the filter it is also possible to change the effective
thickness of the filter which means the transversing distance
of the radiation beam through the filter and thereby the
center wavelength.
Z3224
The filter code device 43 comprises a code disc 55 mounted on the
shaft 56 of the filter change wheel 37 outside the filter housing 41. The
code disc 55 which is of an opaque material is divided into eight sectors
corresponding to the eight filters of the filter change wheel 37, and each
sector of the code disc 55 is provided with the three first digits of a 4-
bit digital code, and each of these codes represents a corresponding one
of the filters 56. In the embodiment shown on the drawings the digital codes
are composed by throughgoing holes 57 in t~a code disc 55. The filter code
device 43 further comprises a code reading device including a fork-shaped
~0 block 58 which is preferably of a opaque material and which embraces the
code disc 55 as best shown in Fig. 2. One leg of the fork-shaped block 58
supports three light sources such as light emitting diodes 59 and the other
leg supports oppositely directed photoelectric devices such as phototransis-
tors 60. The diodes 59 and the phototransistors 60 are positioned so that
they may become aligned with the holes 57 in any sector of the code disc 55.
A mechanical locking device is adapted to lock the filter change wheel 37
in any of eight angular positions in which the light emitting diodes 59
and the phototransistors 60 register with the holes 57 of a digital code
of the code disc 55. This mechanical locking device comprises eight notches
61 which are formed in the rim portion of the filter change wheel 37 and
uniformly circumferentially spaced. A locking arm 62 having a roller 63
mounted at its free end is swingably
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mounted by means of a shaft 64 extending transversely through
the filter housing 41. An arm 65 mounted at the opposite
end of the shaft 64 carries a switch actuating spring member
66 which may actuate a microswitch 67. A spring 68 connec-
ted to the arm 65 tends to swing the arm 65 and the locking
arm 62 in a direction so as to press the roller 63 into contact
with the outer periphery of the filter change wheel 37.
~hen the wheel 37 is rotated by the motor 38 to a position
in which the roller 63 engages with one o~ the notches 61
the actuating will actuate the microswitch 67 which then
provides the fourth bit of the above mentioned digital code.
The flow of a milk sample through the apparatus
will now be described with reference to Fig. 6. The apparatus
shown in Fig. 1 is normally used in connection with a~ high
pressure pump unit 69 which may, for example, be of a known
type used in connection with the above mentioned milk sample
analyzer sold under ~he Trade ~lark "MILK0-SCAN 203" by ~/ S N .
Foss Electric, Hiller0d, Denmark. The unit 69 comprises a
high pressure pump 70 and an electrically controlled bleeder
valve 71 through which the pump cylinder is connected to
the discharge 25. The pipette 18 and the hose 19 are connected
to the high pressure pump unit 6~ throuqh a conduit 72 includin~
- a milk filter 73 and an electricaliy controlled intake valve 74.
A conduit 75 branched off from the conduit 72 includes a double
ball valve homogenizer 76 of known type, a normal one-way valve
77 and an electrically controlled by-pass valve 78. A further
conduit 79 is branched off from the conduit 75 bet~een the
18
3Z24
one-way valve 77 and the by-pass valve 78. The conduit 79
includes the cuvette 24 and a one-way valve or a back-pressure
valve 80 The conduits 75 and 79 both open into the discharge
25.
When the pump 70 is started as explained below
it will be driven through seven full strokes before it is
Stopped. During each of the suction strokes of the first
four full strokes an amount of milk sample (for example 1.5
ml) is sucked from the sample cup 21 through the pipette 18,
the hose 19, the milk filter 73, and the intake valve 74 into
the conduit 72, the valves being controlled so that the
valve 71 is closed, while the intake valve 74 is open.
During the main part of each of the pressure stroXes of said
first four full strokes the intake valve 74 is closed while
the valve 71 is open so that milk sample lS pumped through
the conduit 72 to discharge 25. However, before completion
of each of said pressure strokes the valve 71 is closed so
that part of the milk sample is pumped through the homogeni-
zer 76, the conduit 75, and the by-pass valve 78 which is open
Therefore, during the first fo~r full strokes remains of a
preceding sample are flushed out from the cond~its 72 and 75
(but not the conduit 79 and the cuvette 24) into the discharge 25.
- During each of the following two ~the fifth and
sixth) pressure strokes of the pump 70 the bleeder valve 71
remains closed so that the milk sample is pumped through the
homogenizer 76 at a high pressure, for example 90 kg/cm .
During the first part of each of the fifth and sixth pressure
strok~sthe by-pass valve 78 is open so that the major part
(for example 1.3 ml) of the homogenized milk sample pumped
in each stroke is passed to waste 25 through the conduit 75.
19
232Z~
Almost at the end of each of the fifth and sixth pressure
strokes the by-pass valve 78 is closed so that a minor part
(for example 0.2 ml) of the homogenized sample of each stroke
is flushed through the cuvette 24, the conduit 79, and the
back pressure valve 80 to waste 25, lèaving a few microliters
of clean homogenized sample in the cuvette 24 for measurement
- after completion of the sixth pressure stroke. The back
pressure valve 80 secures that a substantially constant pres-
- sure ~for example 1.5 kg/cm2 above that of the atmosphere)
is maintained during the measuring period. During the
seventh suction stroke of the pump 70 the intake valve 74
remains closed while the bleeder valve 71 is opened.
Consequently, the volume of milk sample residing in the
conduit extending between the pump 70 and the discharge
25 (for example about 1.5 ml) is sucked back into the pump
70 and during the seventh pressure stroke the bleeder
valve 71 is closed while the intake valve 7~ is opened
whereby milk sample is pumped back through the intake valve
and the milk ~ilter 73 into the sample cup 21 in order to
rinse and remove possible impurities from the filter 73.
. As indicated above , in the presently preferred
embodiment 1.5 ml of milk is removed from the sample
cup 21 during each of the first six suction strokes while
about 1.5 ml is returned to the cup 21 during the seventh
and last pressure stroke.
~lZ~
The function of the above apparatus will now
be explained more in detail with special reference to the
block diagram of the electronic sys-tem shown in Fig. 7. The
apparatus shown in Fig. 1 has a keyboard 81 with a number of
program-selecting push buttons 82 by means of
which the user of the apparatus may select a desired program,
i.e. a desired combination of components in the milk sample
to be measured, e.g., fat and protein - fat, protein,
and lactose - fat, protein, lactose, and water - fat,
protein, and total solids - fat, protein, and solids which
are not fat. The cup 21 containing the sample to be measured
may now be positioned below the stirrer 15, and by moving
the cup 21 upwardly into contact with the activating member
17 the motor 16 may be energized. When the sample has been
sufficiently stirred the sample cup 21 is moved to a position
below the pipette 18, and the cup is moved upwardly in
order to actuate the start switch activating arm 23.
Thereafter the cup may be supported by the support 20 as
shown in Fig. 1. Activation of the start switch by means of
0
the arm 23 provides a start sicnal which is supplied to a
20a
~ . . - .
~ 2~22~
memory unit in the form oE a flip-flop 83 generating an
output signal which starts a timer 84 providing an output
signal at predetermined time intervals, for example for each
4.7 secondsr corresponding to the residence time of each of the
optical filters 46 in the infrared radiation beam generated
by the source 26. The output pulses of the timer 84 control
a 4-bit decade down counter 85. The codes generated by the
counter 85 are passed to a first comparator ~6 for controlling
the electric motor 38 of the filter change wheel 37 in response
to signals received from the filter code device 43. The codes
generated by the counter 85 are also passed to a second
comparator 87 and to an operational control 88. ~he comparator
87 serves to stop the procedure when a program corresponding
- to that selected by the push buttons 82 has been passed. The
operational control 88 controls the function of various
devices of the apparatus. When the start signal has been received
the operational control 88 starts the hi~h pressure pump
70 and lights an operation in;dicating lamp 89 (Fig. 1)
indicating that the measuring procedure has started. The
comparator 86 checks whether the filter change wheel 37 is
in its starting position, i.e. in the position in which the
optical component filter WC for measuring water is in the
radiation beam emitted by the radiation source 26. If not,
the motor 38 is started in order to rotate the filter change
wheel 37 to that position. During the first two steps of
the counter 85 the milk sample is passed into the cuvette 24
as e:~plained ab~lve and the milk in the cuvette ~bta ins the
desired temperature. The temperature conditions of the milk may
be indicated by an indicating lamp 89a (Fig. 1). During t}~e ne' t
step the optical reference filter FR for measuring fat ic mG~ eCi
into the radiation beam, and a corresponding reference si~nal is
2l
,
3ZZ4
generated by the detector 35. After a time period of 4~7
seconds determined by the timer 89 the comparator 86 starts
the motor 38 to move the component filter FC for measuring
fat into the radiation beam. The detector 35 will now
generate a corresponding component signal, and these detector
signals will be processed as descri~ed below. Similarly,
reference and component filters for protein, lactose, and
water may successively be positioned in the radiation beam
in accordance with the program selected, and corresponding
signals will be generated by the detector 35.
Each detector signal is amplified by a preampli-
fier 90 arranged at the base of the detector (Fig. 2). The
preamplified detector signals corresponding -to the various
sample components are further amplified in a gain set 91 at
fixed programmed gains controlled by the operational control
88. The output of the gain set 91 is supplied to a filter
92 for selective transmission of signals at the frequency of
the chopper 32 so as to amplify the signal and remove
noise therefrom. The sinusoi~al output si~nal from the filter
92 is rec~ified in an AC/DC converter 93 which converts the
signal into a pulse DC voltage signal which is passed through
a low-pass filter or a ripple filter 94 for reducing the ripple
of the signal. The resultin~ signal from the low-pass filter
is supplied to an electronic servocircuit 95 whlch is able
to calculate the ratio of an input voltage signal to a
succeeding voltage signal, viz. a reference signal,and the
;~ccee-lirl~ corres~)ondin~ -om~onent fil~er -~s will he descrîhed
more in detail below witn Leference to Fig~ 8. lhe iynal
resulting from the calculation made in the circuit ~5 is
supplied to a first memory`which is controlle~ ~y ~ con-
trol circuit 88. As the measurement made on the various
-22-
Z3ZZ~
components have not been made with reference to a natural zero level the
output voltage is divided (multiplied by ~ of the above expression) by means
of "zero" potentiometers 98, and a fixed bias (-40) is added in a zero set
circuit 97 so as to make ~he resulting voltage zero when the sample in the
cuvette 24 is pure water. The potentiometers 98 which comprise a potentio-
meter for each of the components fat, protein, lactose, and water may be
adjusted by means of zero adjusting knobs 98a on the keyboard 81 of the
apparatus (Fig. 1). Prior to the actual measurement the knobs 98a have been
adjusted so as to obtain the measuring result zero for each of the said com-
ponents when the cuvette 24 contains pure water. The control circuit 88selects the potentiometer corresponding to the component for which a signal
is being treated.
The output signal from the memory 96 is supplied to a linearity
set circuit 99 for individual linearity control for each of the components to
be measured. The circuit 99 is controlled by the control circuit 88 and its
setting is adjustable. The circuit 99 is connectèd to a logarithmic converter
100, and the converted signal is supplied to a gain set circuit 101 having
potentiometers 102 which are adjustable by means of adjusting knobs 102a on
the keyboard 81 (Fig. 1). The selection of the respective adjusted potentio-
meters is controlled by the control circuit 88. The purpose of this lastmentioned gain setting is to obtain the same scale in the readout as the
chemical standard valves. The output of the circuit 101 is provided to a
second memory 103 including a channel for each component to be measured and
an adjusting potentiometer for intercorrela~ion of the channels. The memory
also includes an
- 23 -
~23Z24~
adjustable potentiometer constituting a dummy lactose value to be introduced
when a program including measurement o~ fat and protein, but not lactose has
been selected by the push buttons 82. The memory 103 is controlled by the
control circuit 88. The output signal from the memory 103 is added by a
sum amplifier 104 including a mineral bias potentiometer which is adjustable
by means of an adjusting knob 105 on the keyboard 81. The amplifier 104 is
controlled by the control circuit 88, and the mineral bias is inserted when
"total solias" and "total solids excluding fat" are calculated and read out.
An analog/digital converter 106 converts the signals from the amplifier 104
into digital codes and generates a read out command to a display 107 and/or
to a print out device (not shown) through an output interface circuit 108.
During calibration of the apparatus on water the signals from the
logarithmic converter 100 may be supplied directly to the A/D converter 106
via a non-caliborated xead out circuit 109 so that the result will now be in-
dependent of the adjustment of the gain set circuit 101 and of the memory
103. Various calibration modes may be selected ~by means of push buttons
82a and 82b of the keyboard 81.
The electronic servocircuit shown in Fig. 8 comprises a variable
gain amplifier 110 including a variable resistor Rl and a feedback including
a resistor R2. The circuit g5 furthermore comprises a limit sensor 111, a
switching device 112 controlled by the control circuit 88, a memory 113, and
an amplifier 114 the output of which is connected to a light emitting diode
115 controlling the variable resistor ~ hich may further comprise a
photoresistor. A constant
- 24 -
, ~ .
.~ .
. ,. :-. ., ' : - '
~'1%3ZZ4
comparation voltage U is supplied to the input of an amplifier 116 included
in the limit sensor 111.
When the input of the circuit 95 receives a reference signal UR
the switching device 112 is closed. Therefore, the variable gain of the
amplifier 110 will find a level at which the output voltage of the amplifier
is equal to the comparation voltage U. Consequently, the resulting gain of
the amplifier is
UR
This gain is maintained by the memory 113. When the following corresponding
component voltage signal Uc is supplied to the input of the circuit 95 the
switching device 112 is opened by the control circuit 88, but the memory 113
still maintains the gain of the variable amplifier 110 previously set by
the reference signal. Consequently, the signal provided at the output of
the circuit 95 will be equal to
U . G = - . U
It should be understood that the circuit 95 can be used not only in connec~
tion with the apparatus described above, but in any case where it is desired
to determine the ratio between two successive signals~ It should also be
understood that various amendments and modifications o~ the apparatus
described above could be made within the scope of the present invention. As
an example, the apparatus could be used for measuring other liquid samples
of milk and for determining any components thereof.
