Note: Descriptions are shown in the official language in which they were submitted.
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Sampler and Method of Dispensing and Cooling a Fluid
FIELD OF THE INVENTION
This invention relates to a sampler and to a method of
dispensing and cooling a fluid.
BACKGROUND OF THE INVENTION
Fluids of different origins and applications often have to
be monitored for their chemobiological condition, which is
determined, among other things, by substances being
entrained in the fluid. To monitor aqueous fluids,
particularly in drinking water treatment or wastewater
purification plants, representative fluid samples have to
be taken at sampling locations in a spatial and temporal
distribution, and examined. The volume of such fluid
samples generally ranges between approximately 10 ml and
500 ml.
The samples are commonly taken and dispensed by means of a
sampler. U.S. Patents 3,795,347, 3,880,011, 4,415,011, and
5,587,926, for example, disclose a sampler for dispensing a
sample of a fluid withdrawn at a sampling location, said
sampler comprising:
-a vessel assembly
-- with a tubular intake vessel for conducting a moving
fluid, and
. -- with a storage vessel for storing the fluid sample.
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Samplers of the kind described generally include a suitable
pumping deviate, particularly a pumping device controlled by
control electronics, by means of which the fluid is caused
to flow into the vessel assembly. In many cases, a vacuum
pump or a displacement pump, particularly a peristaltic
pump acting mechanically on the intake vessel, is used, as
described, for example, in U.S. Patent 3,880,011,
4,077,263, 4,660,607, or 5,587,926.
Furthermore, the vessel assembly of the sampler may include
a metering vessel for metering a volume of the fluid
sample.
Moreover, the sampler commonly comprises a single cabinet
in which the vessel assembly, the pumping device, and
electronic units may be mounted.
Because of the entrained substances, particularly because
of bacteria, but also because of particular chemical
compounds, metabolic processes take place in the fluid,
which constantly change the chemobiological condition of
the fluid. The change in the chemobiological condition of
the fluid per unit time is commonly referred to as the
activity of the fluid. The activity is temperature-
dependent and increases with increasing fluid~temperature
and particularly also with an increasing temperature of the
fluid sample.
The quality of the monitoring is determined, inter alia, by
how closely the chemobiological condition of the fluid
sample at the time of examination corresponds with the
chemobiological condition of the fluid at the sampling
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instant. In many cases, however, considerable time elapses
between the sampling and the examination of the sample.
Therefore, the fluid samples are metered and stored in
suitable storage vessels, e.g., in sample bottles.
If the fluid sample is to represent the chemobiological
condition existing in the fluid at the sampling instant as
precisely as possible, the activity of the fluid sample,
averaged over the period between sampling and examination,
must be minimized. Therefore, as shown in U.S. Patent
5,587,926 or in PCT international publication number
WO-A 90 14 586 published November 29, 1990, for example, the
fluid samples are usually cooled to a constant storage
temperature of, e.g., 4°C (=277 K), at which a permissible
activity is not exceeded.
To cool the fluid samples, the storage vessels are stored at
an appropriate temperature in a cold-storage room, which, as
proposed in U.S. Patent 5,587,926, for example, may be
provided directly in the sampler cabinet, and the fluid
samples taken by the sampler are dispensed from the sampling
location practically directly into the storage vessels,
where they are cooled.
It has turned out, however, that with this method, the
cooling rates, particularly at a fluid temperature at the
sampling location of above 15°C, may be too low, so that the
activity of the fluid sample until the time of examination
may be too great. For example, at a fluid temperature of
16°C and for a volume of the fluid sample of 500 ml, an
average cooling rate of 1 K/h, and thus a cooling time until
attainment of the storage temperature of 12 h, was measured.
Because of the excessive-activity of
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the fluid sample, during the dispensing and cooling, the
chemobiological condition of the fluid sample may change
considerably from the chernobiological condition at the
sampling instant.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a
sampler for dispensing and cooling such a fluid sample with
which the cooling time, and thus the activity of the fluid
sample, can be reduced.
A further object of the invention is to provide a method of
dispensing and cooling such a fluid sample whereby the
cooling time is reduced.
To attain the first-mentioned object, the invention
provides a sampler for dispensing and cooling a sample, to
be stored at a predeterminable storage temperature, of a
fluid withdrawn at a sampling location and having an
instantaneous sampling temperature greater than the storage
temperature, said sampler comprising:
-a vessel assembly of a predeterminable volume with
-- an internal temperature averaged over the volume,
-- a tubular intake vessel for conducting the withdrawn
fluid, and
-a storage vessel for storing the fluid sample; and
-a cooling assembly, thermally coupled to the vessel
assembly, for setting the internal temperature of the
vessel assembly and comprising
-- a first cooling volume, encompassing at least the
storage vessel and having a predeterminable first
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cooling temperature, for cooling the fluid sample to the
storage temperature, and
-- a second cooling volume, jacketing the vessel assembly
at least in sections and having a predeterminable second
5 cooling temperature, for cooling the withdrawn fluid
sample to a temperature below the sampling temperature.
Furthermore, the invention consists in a method of
dispensing and cooling a sample, to be stored at a
predeterminable storage temperature, of a fluid withdrawn
at a sampling location and having an instantaneous sampling
temperature greater than the storage temperature, by means
of a sampler comprising:
-a vessel assembly of a predeterminable volume with
-- an internal temperature averaged over the volume,
-- a tubular intake vessel for conducting the withdrawn
fluid, and
-- a storage vessel for storing the fluid sample; and
-a cooling assembly, thermally coupled to the vessel
assembly, for setting the internal temperature of the
vessel assembly and comprising
-- a first cooling volume, encompassing at least the
storage vessel and having a predeterminable first
cooling temperature, for cooling the fluid sample to the
storage temperature,
-the internal temperature of the vessel assembly prior to
the dispensing, an initial internal temperature of the
vessel assembly, being lower than the sampling
temperature,
-the first cooling temperature being set at the storage
temperature after the storing of the fluid sample,
said method comprising the steps of:
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-lowering the internal temperature of the vessel assembly
by means of the cooling assembly to a temperature lower
than the initial internal. temperature of the vessel
assembly;
-letting the withdrawn fluid flow through the intake
vessel; and
-letting a partial volume of the withdrawn fluid, which
serves as the fluid sample, flow into the storage vessel.
In a first embodiment of the sampler according to the
invention, the second cooling volume is encompassed at
least in part by the first cooling volume.
In a second embodiment of the sampler according to the
invention, the vessel assembly comprises a metering vessel
closable temporarily at the outlet end for metering the
fluid sample.
In a third embodiment of the sampler according to the
invention, the vessel assembly comprises a distributing
vessel for dispensing the fluid sample into the storage
vessel.
In a fourth embodiment of the sampler according to the
invention, the cooling assembly comprises a first cooling
element, disposed at the intake vessel, for setting an
internal temperature of the intake vessel.
In a fifth embodiment of the sampler according to the
invention, the the cooling assembly comprises a second
cooling element, disposed at the metering vessel, for
setting an internal temperature of the metering vessel.
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Iru a sixtto ernbodimerut of t:~~e sampler accur~iing to the
invention, the cooling assembly comprises a third cooling
element, disposed at the distributing vessel, for setting
an internal temperature of the storage assembly.
In a se~Jenth embodiment of the sampler according to the
invention, the cooling assembly comprises a fourth cooling
element, disposed at the storage vessel, for setting the
internal temperature of the storage vessel.
In an eighth embodiment of the sampler according to the
invention, the first cooling element is a flow cooler.
In a ninth embodirr~ent of the sampler according to the
invention, the metering vessel is disposed within the first
cooling volume.
In a tenth embodiment of the sampler according to the
invention, the metering vessel is partially encompassed by
the first cooling volume.
In an eleventh embodiment of the sampler according to the
invention, the fluid is drinking water or wastewater.
In a first embodiment of the method according to the
invention, the internal temperature of the vessel assembly
is set at the lower temperature by lowering the first
cooling temperature temporarily to a first temperature
below the storage temperature.
In a second embodiment of the method according to the
invention, a cooling assembly with a second cooling volume
encompassing the vessel assembly at least in sections and
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having a predeterminable second cooling temperature is used
to cool the withdrawn fluid to a temperature below the
sampling temperature, and, before fluid is allowed to flow
into the storage vessel, the lower internal temperature of
the vessel assembly is lowered to a second temperature below
the storage temperature by temporarily setting the second
cooling temperature.
In a third embodiment of the method according to
the invention, the fluid sample is taken from a aqueous
fluid.
A basic idea of the method according to the
invention is to reduce the activity of the withdrawn fluid,
and thus of the fluid sample, already during the dispensing
process and to reach a required minimum of the activity in
the shortest possible time. This is achieved in the
invention by cooling a fluid-conducting volume of the vessel
assembly priar to the dispensing process by means of a
suitable cooling assembly. This coolable volume may extend
over the total internal volume of the vessel assembly, so
that the cooling of the fluid begins immediately upon its
entry into the vessel assembly, or comprise only part of the
total internal volume.
According to a broad aspect of the invention,
there is provided a sampler for dispensing and cooling a
sample of a fluid withdrawn at a sampling location, said
sample to be stored at a selectable storage temperature,
said fluid having an instantaneous sampling temperature
greater than the storage temperature, said sampler
comprising: a vessel assembly of a predetermined volume,
said vessel assembly including a displacement pump having a
tubular intake vessel for conducting the withdrawn fluid and
a storage vessel for storing the fluid sample; and a cooling
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assembly thermally coupled to the vessel assembly, said
cooling assembly including a first cooling volume being
operable to cool the fluid sample to the storage
temperature, and a second cooling valume being operable to
cool the withdrawn fluid to a temperature below the sampling
temperature; wherein at least the storage vessel is disposed
in said first. cooling volume, and wherein the vessel
assembly is disposed at least partially in said second
cooling volume.
According to another aspect of the invention,
there is provided a method of dispensing and cooling a
sample of a fluid withdrawn at a sampling location by means
of a sampler, said sample to be stored at a selectable
storage temperature value, said fluid having a sampling
temperature value greater than the storage temperature
value, said sampler comprising a vessel assembly of a
predetermined volume with a displacement pump having a
tubular intake vessel for conducting the withdrawn fluid,
said sampler further comprising a storage vessel for storing
the fluid sample, said vessel assembly having an internal
temperature, wherein prior to the dispensing, said internal
temperature of the vessel assembly has an initial internal
temperature value which is lower than the sampling
temperature value; and said sampler further comprising a
cooling assembly thermally coupled to the vessel assembly
for adjusting said internal temperature of the vessel
assembly, said cooling assembly comprising at least a first
cooling volume having a first cooling temperature, said
first cooling temperature being set at the storage
temperature value at least after the storing of the fluid
sample, said method comprising steps of: lowering the
internal temperature of the vessel assembly by means of the
cooling assembly to a temperature value, which is lower than
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the initial internal temperature value of the vessel
assembly; letting the withdrawn fluid flow through the
intake vessel; and letting a partial volume of the withdrawn
fluid flow into the storage vessel to obtain the fluid
sample.
According to a further aspect of the invention,
there is provided a sampler for dispensing and cooling a
sample of a liquid withdrawn at a sampling location, said
liquid having a sampling temperaturE, said sample to be
stored at a storage temperature having a preselected
temperature value lower than a temperature value of said
sampling temperature, said sampler comprising: a vessel
assembly with a displacement pump having a tubular intake
vessel for conducting the withdrawn liquid and a storage
vessel for storing the liquid sample, said vessel assembly
having a changeable internal temperature; and a cooling
assembly for adjusting the internal temperature of the
vessel assembly, said cooling assembly being thermally
coupled to the vessel assembly at least in sections and said
cooling assembly including a first cooling unit for cooling
the fluid sample to the temperature value of the storage
temperature, said first cooling unit being thermally coupled
at least to said storage vessel, and said cooling assembly
further including a second cooling unit for cooling off the
withdrawn fluid to a temperature value lower than the
temperature value of the sampling temperature, said second
cooling unit being at least partially in contact to the
vessel assembly.
According to a further aspect of the invention,
there is provided a method of dispensing and cooling off a
sample of a liquid by means of a sampler, said sampler
comprising a vessel assembly being operable to conduct and
to store said sample, said vessel assembly comprising a
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displacement pump having an intake vessel, said method
comprising steps of: adjusting an internal temperature of
the vessel assembly to an initial mean temperature value;
lowering the internal temperature of: the vessel assembly to
a mean temperature value lower than the initial mean
temperature value; using said displacement pump to withdraw
liquid at a sampling location, said sampling location having
a liquid temperature value higher than the initial mean
temperature value; letting the withdrawn liquid flow through
said intake vessel of said displacement pump; obtaining said
sample from said withdrawn liquid by letting flow a partial
volume of the withdrawn liquid into a storage vessel of said
vessel assembly, said storage vessel having a variable
storage vessel temperature; and adjusting said storage
vessel temperature for storing said sample at a storage
temperature value lower than said liquid sampling
temperature value of the sampling location; wherein said
step of lowering the internal temperature of the vessel
assembly includes adjusting the storage vessel temperature
to a temperature value lower than the storage temperature
value.
According to a further aspect of the invention,
there is provided a method of dispensing and cooling off a
sample of a .Liquid by means of a sampler, said sampler
comprising a vessel assembly being operable to conduct and
to store said sample, said vessel assembly comprising a
displacement pump, said method comprising steps of:
adjusting an internal temperature of the vessel assembly to
an initial mean temperature value; lowering the internal
temperature of the vessel assembly to a mean temperature
value lower than the initial mean temperature value; using
said displacement pump to withdraw liquid at a sampling
location, said sampling location having a liquid temperature
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value higher than the initial mean temperature value;
letting the withdrawn liquid flow through an intake vessel
of said displacement pump; obtaining said sample from said
withdrawn liquid by letting flow a partial volume of the
withdrawn liquid into a storage vessel of said vessel
assembly; adjusting a storage vessel temperature of said
storage vessel for storing the sample at a storage
temperature value lower than said liquid sampling
temperature value of the sampling location; and raising the
internal temperature of the vessel assembly to a mean
temperature value about equal to the initial mean
temperature value.
One: advantage of the invention is that the
activity of the fluid sample can be reduced very quickly,
particularly also at higher fluid temperatures at the
sampling location. Another advantage of the method is that
it can also be applied to existing vessel assemblies.
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DETAILED DESCRIPTION OF THE PREFERED EMBODIMENTS
While the invention is susceptible to various modifications
and alternative forms, exemplary embodiments thereof have
been shown by way of example in the drawings and will be
described in detail. It should be understood, however, that
there is no intent to limit the invention to the particular
forms disclosed, but on the contrary, the intention is to
cover all modifications, equivalents, and alternatives
falling within the spirit and scope of the invention as
defined by appended claims.
The invention and further advantages will now be explained
in more detail with reference to the accompanying drawings,
which show embodiments of the invention.
Fig. 1 schematically shows a first embodiment of a
sampler;
Fig. 2 schematically shows a second embodiment of a
sampler; and
Fig. 3 shows temperature-time characteristics in the
sampler of Fig. 1 or 2, which are set using the
method of the invention. .
Figs. 1 and 2 each show schematically a sampler for
withdrawing a fluid, particularly an aqueous fluid, at a
sampling location 1 and for metering, dispensing, and
storing a sample of the fluid. The sampler comprises a
vessel assembly 2 of a predeterminable volume which serves
to conduct the withdrawn fluid and hold the fluid sample,
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and which is disposed, at least in part, in a cabinet 10,
particularly in a single cabinet.
The sampler may be both a stationary sampler and a
5 transportable sampler.
Vessel assembly 2 comprises at least one intake vessel 21
for withdrawing and conducting the fluid and, at least
during operation, a storage vessel 24 for storing the fluid
10 sample.
Intake vessel 21 is tubular in shape and has an inlet-side
first end and an outlet-side second end. Preferably, intake
vessel 21 is implemented, at least in sections, as a
flexible tube, particularly a tube of elastic material. The
materials commonly used for such intake vessels in
samplers, such as polyethylene and, if necessary, glass,
can be used.
In a preferred embodiment of the invention, vessel assembly
2 further comprises a distributing vessel 23 for dispensing
the metered fluid sample into storage vessel 24.
Distributing vessel 23, like intake vessel 21, is tubular
in shape, and preferably elastically deformable in
sections. It is shaped and dimensioned so that a fluid
flowing through its outlet-side end can be dispensed into
storage vessel 24 through an inlet opening of the latter.
If distributing vessel 23 has only a single outlet-side end
as shown in Figs. 1 and 2, but several fluid samples are to
be dispensed in succession, distributing vessel 23 is
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preferably arranged to swivel such treat a fluid flowing
through the second end can be dispensed into further
storage vessels, which are spatially separated from storage
vessel 24. Distributing vessel 23 may also have two or more
outlet-side ends and be so designed that if two or more
storage vessels have to be filled, each of them is assigned
one of the outlet-side ends so that the fluid flowing
through the ends can be dispensed into the respective
storage vessel.
If distributing vessel 23 is connected directly to intake
vessel 21, it may also be implemented by an end-side
section of distributing vessel 21 which can be swiveled in
a suitable manner to the respective storage vessel to be
filled, as is proposed in U.S. Patent 4,415,011, for
example.
In a further preferred embodiment of the invention, vessel
assembly 2, as shown in Fig. 2, comprises a metering vessel
22 for receiving a partial volume of the fluid and for
metering the fluid sample from the partial volume. For this
purpose, intake vessel 21 has its second end connected to a
first inlet/outlet opening of metering vessel 22, which is
preferably located at a highest point of metering vessel 22
or in the vicinity thereof; if necessary, the~inlet/outlet
opening may also be located at a lower point of metering
vessel 22, for example.
Metering vessel 22, as is usual with such metering vessels,
has a tubular inlet/outlet piece 221 of predeterminable
length, which starts at the inlet/outlet opening and one
end of which extends into the volume of the metering
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vessel, if the predeterminable length of inlet/outlet piece
a~'1 is not variable during operation of the sampler, the
inlet/outlet piece will advantageously be implemented by an
outlet-side section of intake vessel 21 which extends
perpendicularly from above into the volume of metering
vessel 22.
Metering vessel 22 is preferably made of glass; it may also
be of any of the other materials commonly used for such
metering vessels, such as polyethylene.
In this embodiment of the invention shown in Fig. 2,
distributing vessel 23 has an inlet-side first end
connected to a temporarily closable outlet opening of
metering vessel 22. The outlet opening is preferably
located at a lowest point of metering vessel 22; if
necessary, it may also be at any other point of metering
vessel 22.
As shown in Fig. 2, in this embodiment of the invention,
the sampler further comprises a shutoff arrangement 4 which
serves to temporarily close sections of vessel assembly 2,
particularly metering vessel 22, in a pressure-tight
manner.
To temporarily close the inlet/outlet opening of metering
vessel 22, a first shutoff element 41 of shutoff
arrangement 4 is provided at this opening or at intake
vessel 21. To temporarily close the outlet opening of
metering vessel 22, a second shutoff element 42 of shutoff
arrangement 4 is provided at this outlet opening or at
distributing vessel 23. Shutoff elements 41, 42 may be
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conventional manually, electromechanically, or
pneumatically operated valves or slide valves, see U.S.
Patent 3,795,397 or 3,880,011. If a distributing vessel 23
is used which is elastic at least in sections, the shutoff
element may also be designed as a pinch clamp, see U.S.
Patent 4,077,263.
The fluid to be sampled with the sampler is a fluid,
particularly drinking water or wastewater, that is to be
tested, at a location remote from sampling location l, for
its chemical and/or biological properties, particularly for
entrained substances or bacteria. Such fluids exhibit a
temperature-dependent activity which may cause these
chemobiological properties to change after the sampling.
The higher an instantaneous temperature value of the fluid,
the greater the activity of the fluid. Accordingly, the
higher the temperature TFQ of the fluid sample, the greater
the activity of the sample. Therefore, the fluid, after
being withdrawn at an instantaneous temperature T1, is
stored at a predeterminable low storage temperature TL,
particularly at a constant temperature. This storage
temperature TL is chosen so that the resulting activity is
reduced to the point where it does not change the fluid
sample in an undue manner.
As a rule, the fluid is withdrawn at a relatively high
temperature T1, e.g., at 288 K (Kelvin), at which the fluid
may exhibit a correspondingly great activity. This, in
turn, necessitates cooling the fluid sample as rapidly as
possible, i.e., a cooling phase Ota between the beginning
of the withdrawal and the attainment of the storage
temperature TL should be minimized.
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The sampler therefore comprises a cooling assembly 3,
thermally coupled to vessel assembly 2, for cooling the
fluid. "Thermally coupled" means that temperature
differences temporarily existing between cooling assembly 3
and vessel assembly 2, particularly a volume of vessel
assembly 2, can be nearly equalized, particularly with a
slight delay and nearly completely.
In operation, cooling assembly 3 encloses a first cooling
volume 31, which has a predeterminable, spatially averaged
first cooling temperature T31 and encompasses at least
storage vessel 24. Cooling volume 31 is formed by the
volume of a cold-storage room, as shown in Figs. 1 and 2.
The cold-storage room is preferably provided directly in
cabinet 10, and can thus be designed as a transportable
cooltainer or as a stationary cooling chamber.
Cooling volume 31 is surrounded by an outer enclosure,
particularly by a double-walled enclosure. The enclosure
serves both to thermally insulate the cooling volume and,
as part of cabinet 10, to provide a supporting structure
for vessel assembly 2. It is therefore preferably made, on
the one hand, of thermally insulating material, such as
polyurethane foam, and, on the other hand, of~mechanically
strong construction material, such as high-grade steel or
polyethylene.
As shown in Fig. 2, cooling volume 31 may be so designed as
to also encompass metering vessel 22, if present, and/or
part of intake vessel 21. Furthermore, cooling volume 31 is
preferably designed in such a way that besides storage
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vessel 24, further storage vessels can be simultaneously
accommodated therein.
At the beginning of a withdrawal of fluid, the first end of
intake vessel 21 is connected with sampling location l, for
example by being immersed in the fluid, so as to
communicate therewith, as shown in Figs. 1 and 2. Sampling
location 1 may be located in any suitable partial volume of
the fluid to be sampled.
At a first instant t1, the fluid is caused to flow into
intake vessel 21, which communicates with sampling location
1, and carried onward therein so that, if vessel assembly 2
comprises metering vessel 22, which is connected to intake
vessel 22, the fluid reaches the metering vessel at a
second instant t2.
As shown schematically in Figs. 1 and 2, the withdrawal of
fluid is accomplished by immersing intake vessel 21 in the
fluid being conducted in, e.g., an open channel, and by
drawing fluid off against the force of gravity; however,
the fluid may also be drawn off from a suitable sampling
location 1 in the direction of the force of gravity, or
from a pipe or tank.
To withdraw the fluid from sampling location 1, therefore,
samplers of the kind described have a pressure source 5,
which is connected to vessel assembly 2 and serves to
generate a static pressure of predeterminable magnitude in
a volume of vessel assembly 2, particularly in the volume
of intake vessel 21 and of metering vessel 22, if present,
see also U.S. Patent 3,795,347, 3,880,011, 4,077,263, or
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5,587,926. Accordingly, pressure source 5 may, for
instance, be a vacuum pump, particularly a diaphragm or
piston pump, or a displacement pump, particularly a
peristaltic pump. Since in vessel assemblies of this kind
with a pressure source 5 in the form of a vacuum pump,
there are virtually no moving parts that are in direct
contact with the fluid, such vessel assemblies are
generally almost nonwearing, and thus require little
maintenance. By contrast, such vessel assemblies with a
pressure source 5 in the form a displacement pump are
subject to higher mechanical loading and thus require more
maintenance, but such a vessel assembly is simpler in
construction and, consequently, less expensive.
To withdraw the fluid, a first pressure difference is
generated in the volume between the inlet-side and outlet-
side ends of intake vessel 21 to draw the fluid into intake
vessel 21.
To accomplish this in the sampler according to the
embodiment of Fig. l, intake vessel 21 is set, section by
section, into fluid-conveying displacement motions by means
of pressure source 5. The fluid sample is then metered by
conveying a partial volume beyond a dead volume remaining
during this process in intake vessel 21 and transferring it
as the fluid sample directly to storage vessel 24, as shown
in U.S. Patent 4,660,607, for example.
In the sampler according to the embodiment of Fig. 2, with
the inlet/outlet opening open and the outlet opening
closed, the static pressure in the volume of metering
vessel 22 is first reduced by means of pressure source 5 at
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least to the point that the fluid flowing against the force
of gravity into intake vessel 21 reaches at least a maximum
?.evel of intake vessel 21, see also U.S. Patent 4,077,263.
The fluid is then allowed to flow into metering vessel 22
W ntil the latter is filled with the partial fluid volume.
This partial fluid volume is commonly chosen so that a
predeterminable first level above the end of inlet/outlet
piece 221 is reached in metering vessel 22. After the
partial fluid volume has been filled into metering vessel
22, a second pressure difference is generated in the volume
of vessel assembly 2 between the end of inlet/outlet piece
221 and the first end of intake vessel 21, such that part
of the partial fluid volume will flow back through
inlet/outlet piece 221 into intake vessel 21 and from there
to sampling location 1. The flowing back of the fluid
continues until a second level reaches the end of
inlet/outlet piece 221, so that metering vessel 22 contains
only a residual fluid volume, which serves as a fluid
sample. The second pressure difference can be generated,
for example, by increasing the static pressure in metering
vessel 22 by means of pressure source 5 at least to the
point that the fluid subsequently flowing against the force
of gravity into inlet/outlet piece 221 and into intake
vessel 21 reaches at least the maximum level of intake
vessel 21. If, as shown in Fig. 2, the end of~inlet/outlet
piece 221 is at a higher level than a fluid level at
sampling location l, so that a level difference exists
between the two, the second pressure difference will
preferably be generated by effecting an equalization of the
static pressures of sampling location 1 and metering vessel
22. If sampling location 1 is open toward the atmosphere,
this can be accomplished by simply supplying metering
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vessel 22 with air, for example. The resulting pressure
difference is then determined essentially by the level
difference between the end of inlet/outlet piece 221 and
the fluid level. Now that metering vessel 22 holds
virtually only the fluid sample, the outlet opening is
opened at a third instant tj, and the residual fluid volume
is dispensed to storage vessel 24 by means of distributing
vessel 23.
After attainment of the essentially constant storage
temperature TL of, e.g., 277 K at an instant t9, the fluid
sample in storage vessel 24 is stored. The storage
temperature TL is not higher than a maximum permissible
storage temperature of the fluid, but at least equal to a
minimum permissible storage temperature of the fluid. If
different fluids are contained in cooling volume 31, the
maximum permissible storage temperature will be equal to
the lowest of the respective maximum permissible storage
temperatures of the fluids and the minimum permissible
storage temperature will be equal to the highest of the
respective minimum permissible storage temperatures.
Analogously, the cooling temperature T31 of cooling volume
31, particularly with fluids contained therein, is set to a
value not greater than the maximum permissible storage
temperature, and thus to a value which is virtually always
lower than that of the ambient temperature of cooling
volume 31. The cooling temperature T31, as is commonly done
in such cold-storage rooms, is set by means of an active
heat sink 311, such as a heat pump or a Pettier element,
which is thermally coupled with the cooling volume. This
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cau be done using any of the temperature control or
regulation methods fam.i.Liar tc those sk.il:led in the art.
To implement the control and/or regulation processes
necessary for the operation of the sampler, particularly
for the withdrawal of fluid and for cooling the fluid
sample, the sampler comprises a suitable control circuit 6,
which is also housed in cabinet 10. Control circuit 6 is
preferably supplied from an external power supply,
particularly with an alternating voltage in the 230-V
range. Furthermore, particularly if the sampler is
transportable as mentioned above, control circuit 6 may
also be powered from an on-board supply system of a
transport vehicle, from a storage battery which is also
mounted in the sampler cabinet, and/or from a solar-cell
array. Control circuit 6 may also comprise suitable input/
output interfaces, particularly also for manual operation.
In the following, further steps of the method will be
explained. During operation of the sampler, an
instantaneous internal-temperature distribution with a
spatially averaged internal temperature T2 exists in the
volume of vessel assembly 2, particularly at and in the
walls thereof, at any point in time. Due to heat transfer
or heat conduction and due to convection in vESSel assembly
2, the value of the internal temperature T2 of the vessel
assembly is also dependent on the value of the cooling
temperature T31.
At an initial instant to prior to the withdrawal of fluid,
the cooling temperature T3~ is set at the storage
temperature TL of the fluid, as shown in Fig. 3. Thus, at
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the intial instant to, there exists an initial internal-
temperature distribution with a corresponding average
initial internal temperature of the vessel assembly which
is lower than the sampling temperature T1.
Since, as shown in Figs. 1 and 2, cooling volume 31
encompasses only parts of vessel assembly 2, the internal-
temperature distribution of the latter, particularly if
intake vessel 21 and metering vessel 22 are not or only
partially thermally insulated outside cooling volume 31, is
influenced correspondingly by an external ambient-
temperature distribution.
The further the cooling volume 31 extends over vessel
assembly 2 and/or the lower the cooling temperature T3i.
averaged over the cooling phase Ota, is set, the smaller a
corresponding ratio TZ,ota/TL of the internal temperature
Ota of the vessel assembly, averaged over the cooling phase
Vita, to the storage temperature TL will be. The cooling
phase Ota follows from the time difference t9 - t1, which
lasts from the beginning of the withdrawal of fluid at the
instant t1 until the instant t9, at which the fluid sample
has reached the storage temperature TL.
The smaller this temperature ratio T2,oca/TL, the greater a
cooling rate of the fluid in vessel assembly 2, also
averaged over the cooling phase Ota. An increase in the
cooling rate shortens the time required for the fluid
sample to reach the storage temperature TL, and thus the
cooling phase Ota.
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According to the method of the invention, therefore, prior
t;. the withdrawal of fluid the internal temperature of the
vessel assembly is reduced from the initial internal
temperature, which is of the order of 1 K to 5 K, for
example, to a lower internal temperature, averaged over
vessel assembly 2_, particularly to a temperature which is
lower at the instant t~, see Fig. 3. If necessary, the
initial internal temperature of the vessel assembly may
also be lowered by more than 5 K.
In a preferred embodiment of the method according to the
invention, the cooling temperature T31 is temporarily
lowered, by means of active heat sink 311, from the storage
temperature TL to a temperature of, e.g., 273 K ( - 0 °C).
This results in a corresponding change in the internal-
temperature distribution in vessel assembly 2.
During or after the lowering of the cooling temperature
T31, the fluid is caused to flow into the vessel assembly 2
in the manner described. Because of the lower internal
temperature existing within vessel assembly 2, the fluid
sample is cooled to a temperature below the sampling
temperature T1. This is effected essentially by heat
transfer or by heat conduction in the wall of vessel
assembly 2. The cooling of the fluid sample thus begins
with its entry into the portion of vessel assembly 2
encompassed by cooling volume 31, and continues,
particularly in storage vessel 24, until the fluid sample
has taken on the set cooling temperature T31. Since,
however, the storage temperature TL to be set for the fluid
sample is to be higher than the lowered cooling temperature
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T;1, the latter is remised after a certain time,
particularly to the value set at instant t;.
The lowering and rer_aising of the first cooling temperature
T_,i, and thus the cooling of the fluid sample within vessel
assembly 2, particularly within storage vessel 24, may be
accomplished by use of regulating and/or timing devices.
The corresponding regulating and/or control variables can
be determined by suitable calibration measurements. The
method according to the invention can be implemented in the
manner familiar to those skilled in the art using suitable
program codes, for example, which are implemented and
executed in a microcomputer of control circuit 6. The
control signals necessary to carry out the method, e.g.,
control signals for pressure source 5 or heat sink 311, are
provided by control circuit 6 as shown schematically in
Fig. l, and may be generated, for example, by signal output
cards controlled by the microcomputer.
During the cooling phase Vita, the cooling temperature T31,
if necessary, may also be set to a value below 273 K.
However, the temperature should only be lowered to the
point that neither unduly high cooling rates are reached in
the fluid nor fluid samples already stored in cooling
volume 31 are unduly undercooled. Therefore, the lowering
and remising of the cooling temperature T31 must, if
necessary, be modified by setting the cooling temperature
T31 during the cooling phase 4ta to intermediate values
higher than the lower cooling temperature. The intermediate
temperature values can be determined by suitable
calibration.
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If necessary, particularly if the cooling temperature T3i
is to be regulated, a suitable measurement signal
representative of the cooling temperature T31 and/or of the
internal temperature of the vessel assembly must be
generated in the manner familiar to those skilled in the
art. This can be done, for example, using a temperature
sensor 7 disposed within cooling volume 31, such as a
resistance thermometer or a thermocouple, which is
connected, e.g., via a signal input card, to control
circuit 6, particularly to the aforementioned
microcomputer, see also U.S. Patent 5,587,926.
In a further embodiment of the sampler according to the
invention, cooling assembly 3 comprises a second cooling
volume 32, which encloses vessel assembly 2 at least in
part and has a predeterminable, spatially averaged second
cooling temperature T32. This second cooling volume 32 is
formed at least within sections of the wall of vessel
assembly 2 and in the volume of vessel assembly 2 enclosed
thereby.
Cooling volume 32 serves, on the one hand, to further
extend the coolable volume of vessel assembly 2 in the
direction of fluid-sampling location 1. On the other hand,
it serves to selectively influence the internal-temperature
distribution in vessel assembly 2, and thus to more finely
and accurately set the internal temperature TZ of the
vessel assembly during the cooling phase Vita.
As shown in Figs. 1 and 2, cooling volume 32 is formed by a
first cooling element 321 at intake vessel 21 for setting
the internal temperature of the intake vessel, a second
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cooling element 322 at metering vessel 22 for setting the
internal temperature of the metering vessel, a third
cooling element 323 at distributing vessel 23 for setting
the internal temperature of the distributing vessel, and a
fourth cooling element 324 at storage vessel 24 for setting
the internal temperature of storage vessel, so that it is
divided into corresponding partial cooling volumes. As
illustrated in Fig. 1 by the example of cooling element
321, the necessary control signals are also provided by
control circuit 6.
For the cooling elements, particularly for cooling element
321, suitable heat pumps can be used. In a preferred
embodiment of the invention, cooling element 321 is
designed as a flow cooler. It is also possible to use
Pettier elements in cooling elements 321, 322, 323, 324.
If necessary, cooling volume 32, as shown in Fig. l, may
also be formed by only three, two, or one of these cooling
elements 321, 322, 323, 324, particularly if cooling volume
32 is preferably encompassed at least in part by cooling
volume 31, as shown.
The advantage of this embodiment of the invention is that
existing samplers can be easily retrofitted with such
cooling elements.
In a further embodiment of the method of the invention,
prior to the withdrawal of fluid, the internal temperature
T2 of the vessel assembly is temporarily lowered by means
of one or more of cooling elements 321, 322, 323, 324 to a
value of, e.g., 273 K, so that the internal temperature T2
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is lower than the initial internal temperature of the
vessel assembly, particularly at instant t;.
During or after the lowering of the cooling temperature
T-;~, the fluid is again allowed to flow into vessel
assembly 2 and thereby cooled to a temperature below the
sampling temperature T1. In this embodiment of the
invention, the above-described method in which the first
cooling temperature T31 is lowered may, of course, be used
as well.
Prior to the withdrawal of fluid, particularly if two or
mcre successive dispensing operations are performed,
fluidic residues are usually removed from vessel assembly
2. This is accomplished in the embodiment of Fig. 2 by
generating a static overpressure in the volume of metering
vessel 22 and of the connected intake vessel 21 by means of
pressure source 5, with the outlet opening of metering
vessel 22 closed and the inlet/outlet opening open. Due to
this overpressure, residues in intake vessel 21 will be
forced out through the first end of the intake vessel. If
necessary, by closing the inlet/outlet opening with the
outlet opening open, and generating an overpressure in the
volume of metering vessel 22, the metering vessel itself
and the connected distributing vessel 23 can be freed from
fluidic residues; the latter can then be drained through
the second end of distributing vessel 23 into a suitable
vessel of the sampler or out of the sampler. In the
embodiment of Fig. 1, fluidic residues can be removed from
vessel assembly 2 by simply operating pressure source 5,
which is implemented as a displacement pump, reversely,
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i.e., in the direction opposite to that during the
withdrawal of fluid.
While the invention has been illustrated and described in
detail in the drawing and foregoing description, such
illustration and description is to be considered as
exemplary and not restrictive in character, it being
understood that only exemplary embodiments have been shown
and described and that all changes and modifications that
come within the spirit of the invention are desired to
protected.
