U.S. patent application number 12/172585 was filed with the patent office on 2008-11-13 for method for leak testing and leak testing apparatus.
Invention is credited to Martin Lehmann.
Application Number | 20080276693 12/172585 |
Document ID | / |
Family ID | 26318718 |
Filed Date | 2008-11-13 |
United States Patent
Application |
20080276693 |
Kind Code |
A1 |
Lehmann; Martin |
November 13, 2008 |
METHOD FOR LEAK TESTING AND LEAK TESTING APPARATUS
Abstract
For leak testing closed containers (9) which are filled with a
filling product containing at least one liquid component the
container is introduced in a test cavity (1) which is evacuated at
least down to vapour pressure of that liquid component. The
pressure in the surrounding of the container (9) and thus within
test cavity (1) is monitored. Monitoring is performed by a vacuum
pressure sensor (7), whereas lowering pressure surrounding the
container (9) is performed by a vacuum pump (5). Leakage is
detected by monitoring a pressure change in the surrounding of the
container which is due to evaporation of liquid emerging from a
leak and being evaporated in the low pressure surrounding.
Inventors: |
Lehmann; Martin; (Wohlen,
CH) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET, SUITE 1800
ARLINGTON
VA
22209-3873
US
|
Family ID: |
26318718 |
Appl. No.: |
12/172585 |
Filed: |
July 14, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11828495 |
Jul 26, 2007 |
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12172585 |
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11267190 |
Nov 7, 2005 |
7260981 |
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11828495 |
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10950512 |
Sep 28, 2004 |
7000456 |
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11267190 |
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10434111 |
May 9, 2003 |
6829936 |
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10950512 |
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10193914 |
Jul 15, 2002 |
6575016 |
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10434111 |
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09944407 |
Sep 4, 2001 |
6439033 |
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10193914 |
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09785261 |
Feb 20, 2001 |
6305215 |
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09944407 |
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09568288 |
May 10, 2000 |
6202477 |
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09785261 |
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09073852 |
May 7, 1998 |
6082184 |
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09568288 |
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08862993 |
May 27, 1997 |
5907093 |
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09073852 |
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Current U.S.
Class: |
73/49.3 |
Current CPC
Class: |
Y10T 29/49771 20150115;
G01M 3/04 20130101; Y10T 29/53022 20150115; G08B 21/20 20130101;
G01M 3/226 20130101; G01M 3/3263 20130101; G01M 3/22 20130101; G01M
3/3281 20130101; G01M 3/329 20130101; B65B 3/04 20130101 |
Class at
Publication: |
73/49.3 |
International
Class: |
G01M 3/32 20060101
G01M003/32 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 10, 1998 |
IB |
PCT/IB98/00039 |
Claims
1. A method for producing a closed and filled container comprising
the steps of: filling a container with a material comprising at
least one liquid component; sealingly closing said container; and
leak testing said container by: applying a pressure difference
across at least a part of the wall of the container which part is
to be tested by evacuating the surrounding of said container by
means of a pumping arrangement; exploiting loading of said pumping
arrangement by evaporation of liquid as an indicia for a leak in
said container.
2. The method of claim 1, wherein said evacuating lowers the
pressure in said surrounding toward a pressure valve which is lower
than a vapor pressure of the at least one liquid component by a
factor of at least two decades (10.sup.2).
3. The method of claim 2, wherein said container is filled with
more than one liquid component, and said vapor pressure is the
higher vapor pressure of the vapor pressures of said at least two
components.
4. The method of claim 1, wherein said testing is performed at room
temperature.
5. The method of claim 1, wherein said exploiting is performed
after the surrounding has been evacuated to a pressure value at
least according to vapor pressure of said at least one liquid
component.
6. The method of claim 1, wherein the exploiting includes
monitoring the pressure in the surrounding at first and second
points in time and utilizing a difference in the results of the
monitoring as said indicia for a leak in said container.
7. The method of claim 6, wherein said monitoring the pressure at
said first point in time results in a first pressure measuring
signal which is stored at least up to said second point in
time.
8. The method of claim 6, including the step of providing a
pressure measuring sensor in said surrounding and operationally
connecting said sensor to both inputs of a difference forming unit
at said first point in time, generating a zero offset signal
dependent from the output signal of said difference forming unit,
storing said zero offset signal and compensating zero-offset when
utilizing said difference in the results of said monitoring as said
indicia for a leak in said container.
9. The method of claim 6, including the step of providing a
pressure measuring sensor in said surrounding and comparing the
output signal of said sensor with one or more than one
predetermined signal values.
10. The method of claim 6, including storing a first measuring
signal which results from said monitoring the pressure at said
first point in time by means of an analog-to-digital converter,
which is enabled for conversion at said first point in time.
11. The method of claim 10, including reconverting the digital
output signal of said analog-to-digital converter into an analog
signal.
12. The method of claim 1, including simultaneously leak testing a
batch of filled and closed containers as one container.
13. The method of claim 1, further comprising performing an
impedance measurement at or at least adjacent to said part of said
wall in said surrounding wherein said impedance measurement is a
resistance measurement with DC and enabling or disabling further
lowering of said pressure in said surrounding by the result of said
impedance measurement.
14. The method of claim 1, including providing a test cavity with a
test chamber snugly fitting the outer shape of said container,
thereby maintaining at least at said part a residual volume to be
lowered in pressure and between said part and the wall of said test
cavity.
15. The method of claim 1, further comprising providing a test
cavity for said container, said test cavity defining a test chamber
significantly larger than the volume of said container.
16. The method of claim 1, including providing a test cavity for
said container and cleaning at least said test cavity after a
container therein has been detected as leaking.
17. The method of claim 1, including in-line testing a series of
said containers in a set of test cavities and further comprising
disabling testing in a test cavity for at least one testing cycle
if the container previously tested therein has turned out to be
leaky.
18. The method of claim 1, further comprising the step of
increasing internal pressure of said container by mechanically
biasing at least a part of its wall inwardly.
19. The method of claim 1, wherein said liquid component is water,
and including evacuating said surrounding to less than 20 mbar.
20. The method according to claim 1, wherein said pressure in said
surrounding is lowered towards a pressure value which is lower than
said vapor pressure by a factor of at least three decades
(10.sup.3).
Description
RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 11/828,495, filed Jul. 26, 2007, which is a divisional of U.S.
application Ser. No. 11/267,190, filed Nov. 7, 2005, now U.S. Pat.
No. 7,260,981 issued Aug. 28, 2007, which is a divisional of U.S.
application Ser. No. 10/950,512, filed Sep. 28, 2004, now U.S. Pat.
No. 7,000,456 issued Feb. 21, 2006, which is a divisional of U.S.
application Ser. No. 10/434,111, filed May 9, 2003, now U.S. Pat.
No. 6,829,936 which is a divisional of U.S. application Ser. No.
10/193,914, filed Jul. 15, 2002, now U.S. Pat. No. 6,575,016 which
is a divisional of U.S. application Ser. No. 09/944,407, filed Sep.
4, 2001, and now U.S. Pat. No. 6,439,033, issued Aug. 27, 2002,
which is a divisional of U.S. application Ser. No. 09/785,261,
filed Feb. 20, 2001, now U.S. Pat. No. 6,305,215, issued Oct. 23,
2001, which is a divisional of U.S. application Ser. No.
09/568,288, filed May 10, 2000, now U.S. Pat. No. 6,202,477, issued
Mar. 20, 2001, which is a divisional of U.S. application Ser. No.
09/073,852, filed May 7, 1998 (claiming priority under 35 USC
.sctn.119 to PCT/IB98/00309, filed Mar. 10, 1998 and claiming
priority to Europe 97108430.6 filed May 26, 1997), now U.S. Pat.
No. 6,082,184, issued Jul. 4, 2000, which is a continuation-in-part
application of U.S. application Ser. No. 08/862,993, filed May 27,
1997, now U.S. Pat. No. 5,907,093, issued May 25, 1999.
FIELD OF INVENTION
[0002] The present invention is generically directed on a technique
for leak testing closed and filled containers, whereby the filling
material comprises at least one liquid component.
BACKGROUND
[0003] Leak testing techniques according to which closed containers
are introduced in a test cavity which, after having sealingly been
closed, is lowered in pressure by a suctioning pump are known. If
the container is not leaking, then once a predetermined pressure
has been reached in the test cavity and thus in the surrounding of
a container to be tested; this pressure will be kept substantially
constant. If a leak is provided in an area of the container,
wherein air is entrapped, a flow of air out of the container will
lead to a rise of the surrounding pressure. If a leak is present in
the area of the container where filling good is entrapped, the
question whether such leak will lead to a significant rise of the
surrounding pressure is largely dependent on the kind of filling
good as of its viscosity, whether solid particles are present in
the filling good and, obviously, on the largeness of the leak.
[0004] Different approaches have become known to accurately detect
leaks at such product-filled containers, irrespective whether the
leak is present in an air entrapping container area or in a
container area covered with filling good. One such approach which
is the topic of the co-pending European patent application EP-A-O
791 814 and the U.S. patent application Ser. No. 08/862,993
proposes to provide an impedance measurement, specifically a
resistance measurement, just adjacent to the outer wall of the
container by means of an electrode arrangement: As soon as liquid
emerges from a leak it will contact a respective pair of impedance
measuring electrodes and lead to a significant change of impedance
measured between such electrodes.
[0005] Nevertheless, such an approach necessitates considerable
additional expenditure with respect to provision of the impedance
measuring arrangement in each test cavity, especially of a
multi-cavity in-line inspection machine and does not enable
detection of very small leaks far below of one micron and largely
independent from container shape and kind of filling good.
OBJECT OF THE INVENTION
[0006] It is a primary object of the present invention to provide a
leakage test method and apparatus, which may be applied to a very
large scale of different containers and of different filling goods,
provided at least one component thereof being liquid.
[0007] It is a further object of the present invention to provide
such method and apparatus which are rather inexpensive with respect
to electronic and further equipment, and which thus allow for very
economic testing.
[0008] It is still further an object of the present invention to
provide such method and apparatus which have a short measuring
cycle and nevertheless a very high measuring accuracy.
SUMMARY OF THE INVENTION
[0009] These objects are realised by the testing method for leak
testing at least one closed and filled container, whereby the
content of the container comprises at least one liquid component
and wherein a pressure difference is applied across at least a part
of the wall of the container which part is to be leak tested and
wherein the applied pressure difference is directed towards the
surrounding of the container and wherein further the pressure in
the surrounding of the container is monitored as a leak indicative
signal which is characterised by the fact that the pressure
difference is established by lowering the pressure in the
surrounding of the container at least to a value which accords to
the vapour pressure of the at least one liquid component of the
filling product of the container to be tested.
[0010] The present invention departs from the recognition that if a
container is leaking and liquid is drawn by the lower surrounding
pressure to its outside this will--at a constant volume of the
surrounding--lead to evaporation of the liquid as soon as the
surrounding pressure reaches its vapour pressure. This leads to a
significant change in surrounding pressure compared with the
surrounding pressure which would establish at the same measuring
conditions but with an unleaking container.
[0011] Monitoring the pressure in a test cavity containing the
container, once vapour pressure of the possibly leaking liquid is
reached reveals as being a very accurate technique for leak
testing. It has been noted that by such a technique leak detection
of containers with a very large spectrum of filling products may
accurately be performed and that leaks at present moment down to
0.02 .mu.m are accurately detectable.
[0012] Further, it has been noted that the volume of the test
cavity is uncritical, so that by the inventive technique it becomes
possible to simultaneously test batches of containers, thereby
accurately detecting if one container of such a container batch is
leaking.
[0013] As soon as the pressure surrounding a leaking container is
lowered with respect to its interior pressure, some of the liquid
is suctioned out of the container and as soon as the surrounding
pressure reaches vapour pressure it starts to evaporate. As at a
constant volume of the surrounding area of the container
evaporation of the liquid leads to increase of pressure and the
pump lowering the surrounding pressure must now remove vapour of
the liquid too, significant measurements may be done especially
after the surrounding pressure of the container becomes lower than
the said vapour pressure. Nevertheless, it is preferred to provide
pumping abilities which may evacuate the surrounding of the
container to be tested to a significantly lower value than said
vapour pressure, namely by at least two, preferably even by at
least three decades.
[0014] As a leak-significant pressure change may be detected as
soon as one of possibly several liquid components of the filling
good starts to evaporate--in the case the content of the container
contains more than one liquid component--it is recommended to
select the vapour pressure of that component of the several liquid
components which is the higher and to lower the pressure of the
surrounding of the container at least to that vapour pressure
value.
[0015] Although and as well known vapour pressure is a function of
temperature and thus it might be advantageous in some cases e.g. to
heat the surrounding of the container to a predetermined
temperature so as to settle the relevant vapour pressure for a
predetermined liquid, the inventive method and apparatus becomes
significantly less complex if the test is performed at room
temperature, and thus the vapour pressure to be at least reached is
considered at room temperature, i.e. around 20.degree. C.
[0016] Further, a very accurate leak detection becomes possible if
the surrounding pressure of the container is measured at two
subsequent points in time, whereby we understand under "point" that
interval of time necessary for accurately measuring the prevailing
pressure. Although it is absolutely possible to realise leak
detection by applying the pumping action of the evacuating pump to
the surrounding of the container and then by measuring the
resulting surrounding absolute pressure after a predetermined time
span, the said measuring of the surrounding pressure at two
specific points in time allows to use the first value measured as a
reference value and then to form the difference of the second value
measured with respect to the reference value. There is thereby
realised a pressure difference measurement instead of an absolute
pressure measurement. More specifically, the first pressure signal
which is measured at the first point in time is stored as an
electric signal, then, after having measured the second pressure
value, a difference is formed between the first value (still
stored) and the second value.
[0017] The PCT patent application No. WO94/05991 with its US
counterpart No. U.S. Pat. No. 5,239,859, assigned to the same
applicant as the present invention, describes a method and
apparatus for very accurate offset-compensated pressure difference
measurement. In a preferred mode of operating the method according
to the present invention as well as of realising the inventive
apparatus, that pressure difference measuring technique and
apparatus are used. Therefore, the WO94/05991 or the respective
U.S. Pat. No. 5,239,859 are fully incorporated by reference in this
present disclosure, although, and as will be seen most important
features are specifically described also in this present
application.
[0018] Because it is largely uncritical how big the surrounding
volume of a test cavity for the container is, with respect to the
volume of the container to be tested, the inventive method and
apparatus reveals to have a further significant advantage:
[0019] If the wall of the at least one container to be tested
withstands the pressure difference between container internal
pressure (normally ambient pressure) and lowered surrounding
pressure, such a container may simply be introduced in the test
cavity forming the surrounding, largely irrespective how big such
container is with respect to the test cavity. Nevertheless, a
highly accurate indication of leakage will inventively be gained.
Therefore, one and the same test cavity may be used for a large
number of differently sized and different-volume containers. This
results in a further advantage in that batches of more than one,
even of a multitude of containers, may be introduced in one test
cavity forming the surrounding and although one single container
occupying only a small percentage of the overall cavity volume, an
accurate leak indication will be detected if even only one of the
batch-containers is leaking into the surrounding atmosphere.
[0020] A further significant advantage of the present invention is
the following:
[0021] Sometimes the filled containers are not completely filled,
but there is some amount of air entrapped in the closed container.
If a leak is present in that area of such a container, which is
adjacent to entrapped air or gas, by lowering the surrounding
pressure, such air will be suctioned through the leak out of the
container. With the pressure of the entrapped air in the container
becoming progressively lower, there will also start vaporisation of
the liquid component within the container and such vapour will also
leave through the leak. Both, namely first the air leaving through
the leak, then vapour leaving through the leak, will enlarge the
surrounding pressure so that a leak in an entrapped air region of
the container will lead to a change in the surrounding pressure,
i.e. to rising of said pressure, as if the leak was in the liquid
content covered area of the container wall. Thus, by properly
setting a threshold value for leak detection according to the
smallest still tolerated pressure change in the surrounding, it
becomes uncritical whether such leak is present at an air-covered
container area or at a content-covered container area.
[0022] If one and the same leak at an air-entrapped area of the
container leads to a smaller pressure change in the surrounding,
than the same leak would generate if situated at a liquid-covered
container area, it is such a pressure change which will govern
setting of a threshold value to detect whether a container is leaky
or not. If, inversely, one and the same leak in a liquid-covered
area would result in a smaller pressure change in the surrounding
than such leak in an air-contacted wall area, then it is again that
smaller pressure change which governs the threshold setting for
detecting leaking/not leaking containers.
[0023] If a container under test is largely leaky, lowering of the
surrounding pressure should be stopped as soon as such leaking is
detected so as to prevent the content of the container to spoil the
interior of the test cavity or, generally spoken, the surrounding
of the container and possibly even the pumping arrangement more
than absolutely necessary. This is realised either by monitoring
whether the pumping action results in a predetermined lowering of
surrounding pressure or not or one may detect spreading of content
of the container into its surrounding by means of an impedance,
thereby preferably a DC resistance measurement in the surrounding
of the container just adjacent to the wall of the container which
is to be tested. This is realised by providing an electrode
arrangement in said adjacent surrounding and all around at least
that part of the container to be tested. As soon as filling content
of the container is suctioned to its outer wall, the electrode
arrangement will be bridged by such content, leading abruptly to an
indicative impedance change which, after having been detected, is
used to stop further pressure lowering at the surrounding of the
container.
[0024] This latter technique of rapidly detecting large leaks is
applied especially to containers where it is necessary to snugly
encapsulate them in the test cavity because their walls would not
stand the pressure difference applied. In such a case the electrode
arrangement for impedance measurement may be incorporated along the
inner wall of the test cavity, which snugly fits with the at least
one container. If such container is to be tested and therefore the
test cavity snugly fits its shape, nevertheless a continuous volume
is maintained between the outer wall of the container and the wall
of the test cavity for defining the surrounding of the container by
providing a sustaining grid or mesh inlay or preferably by
roughening the interior wall of the test cavity so that a multitude
of micro-embossments of the test cavity wall sustain the container
wall and prevent it from further outward bowing due to the applied
pressure difference. Thereby, the intercommunicating space between
such embossments defines for the surrounding space of the
container.
[0025] Once the container in a test cavity, defining for its
surrounding, has been detected as being leaky, it is probable that
such test cavity will be contaminated by some of the container's
content. Then, such cavity is cleaned after the leaky container has
been removed, be it by evacuation and/or flushing with a flushing
gas, preferably nitrogen, be it by heating or by combining these
techniques, e.g. by a heated flushing gas.
[0026] If the inventive method or apparatus is applied for in-line
testing containers and thus two or more of the inventive methods
and of the respective apparatus are operated in parallel on a set
of containers and one of such containers is detected to be leaky,
then the respective test cavity defining for its surrounding is not
anymore filled with a container at the next measuring cycle, but is
kept empty, using that cycle during which the other cavities are in
testing condition for cleaning and reconditioning the probably
contaminated cavity. Further, it is proposed in some cases to
accelerate squeezing-out of liquid, if a leak is present, by
mechanically biasing the wall of the container inwardly, thus
rising its interior pressure over atmospheric pressure.
[0027] To fulfill the object, the present invention proposes a leak
testing apparatus for leak testing at least one closed and filled
container, whereby the content of the container comprises at least
one liquid component, which comprises at least one sealingly
closable test cavity and at least one evacuation pump operationally
connected to the test cavity and further at least one pressure
sensor operationally connected to the test cavity, whereby the
evacuation pump is selected so as to be able to pump the test
cavity to at least vapour pressure of the liquid component of the
container content, approx. at room temperature and the pressure
sensor is a vacuum pressure sensor, preferably comprising at least
a Pirani sensor stage.
[0028] Preferred embodiments of the inventive method and inventive
apparatus are disclosed hereinafter. The inventive method and
apparatus may preferably be used for leak testing blisters, vials,
medical application containers, foodstuff or beverage containers,
and tanks. Thereby, it must be pointed out that besides leak
testing of smaller containers, the present invention makes it
possible to permanently monitor tightness of the tanks of huge tank
plants, as for gasoline, gases, etc., e.g., on train or street
transports, thereby generating an alarm signal as soon as a leak is
detected.
SHORT DESCRIPTION OF THE FIGURES
[0029] The present invention will now additionally be described
with the help of figures showing specific and today preferred
examples of realising the present invention. Such figures show:
[0030] FIG. 1: qualitatively the dependency of vapour pressure from
temperature of a liquid;
[0031] FIG. 2: schematically an inventive test apparatus operating
according to the inventive method;
[0032] FIG. 3: qualitatively the time course of the pressure of the
surrounding of a container to be inventively tested for explaining
the inventive method and apparatus operation;
[0033] FIG. 4: in a functional block diagram a preferred form of
realisation of an inventively operated inventive test
apparatus;
[0034] FIG. 5: as a functional block diagram a preferred form of
realisation of the evaluating electronic at an inventive apparatus
performing the inventive method;
[0035] FIG. 6: schematically batch operation of an inventive
apparatus;
[0036] FIG. 7: schematically a test cavity for testing flexible
wall containers;
[0037] FIG. 8: in a perspective view one half of a test cavity for
inventively testing three containers as a batch;
[0038] FIG. 9: schematically a double-wall tank directly used to
perform the inventive method with an inventive apparatus so as to
survey tank leakage;
[0039] FIG. 10: schematically a preferred sealing at a test cavity
of the inventive apparatus;
[0040] FIG. 11a to 11c: show the pressure courses on testing
cycles, whereat the containers or medical application blisters are
either largely or even very largely leaking (FIG. 11a), or have
only a small leak (FIG. 11b), or are to be considered unleaky (FIG.
11c). The tests are performed with test cavities according to FIG.
8 without impedance measurement and thus without electrodes 32,
34.
[0041] FIG. 12 a signal flow/functional block diagram of the
simplified preferred embodiment of an evaluation unit for operating
the inventive method at an inventive apparatus;
[0042] FIG. 13 in a pressure versus time diagram the statistical
variation of pressure courses measured at unleaky containers or at
test cavities void of any containers,
[0043] FIG. 14 in a simplified functional block/signal flow diagram
a part of the inventive apparatus operating according to preferred
mode of the inventive method, thereby forming a dynamic reference
value for leak testing by means of a subsequently updated
averaging;
[0044] FIG. 15 in a simplified signal versus time diagram
qualitatively the preferred inventive method and accordingly
operation of a preferred inventive apparatus, whereby dynamically
updated reference values are formed for leak identification;
[0045] FIG. 16 a simplified signal flow/functional block diagram
showing a further preferred mode of operation of the inventive
method and respectively of the inventive apparatus, wherein a
dynamically updated average signal is formed as the basis for a
reference value to be compared with a pressure difference signal
evaluated during container testing;
[0046] FIG. 17 in arbitrary unit over the time axis pressure
measurements at subsequently operated test cavities of an inventive
apparatus with multiple cavities to show dynamic update of an
average signal, whereon reference values for comparison are based,
leading to leakage identification;
[0047] FIG. 18 in a simplified schematic representation, a test
cavity according to the present invention, which is pivoted during
testing;
[0048] FIG. 19 the effect of pivoting the test cavity according to
FIG. 18 on the relative location of a leak with respect to filling
product;
[0049] FIG. 20 in a simplified functional diagram provision of a
calibration standard leak to calibrate the inventive apparatus as
performing the inventive method.
DETAILED DESCRIPTION OF DISCLOSED EMBODIMENTS
[0050] In FIG. 1 there is qualitatively shown the course of vapour
pressure p.sub.v(T) in the pressure versus temperature diagram. At
a predetermined temperature T.sub.x a liquid starts to evaporate
when the respective vapour pressure p.sub.vx is reached. Above the
vapour pressure course the material is liquid, below the material
is gaseous.
[0051] According to FIG. 2 an inventive apparatus comprises a test
cavity 1 with a sealingly closable cover 3. A vacuum pump 5
connected to the test cavity 1 which may be a drag pump or a
rotational piston valve pump or a diffusion pump or a turbo vacuum
pump as a turbo molecular pump. This depends on the degree of
vacuum which shall be established within cavity 1. Further, there
is provided a vacuum pressure sensor 7 as e.g. a Pirani sensor,
which measures the pressure prevailing in the test cavity 1. At
least one closed container 9, which is filled at least to some
extent with a filling product containing at least one liquid
component is introduced through opened cover 3 into the test cavity
1 which is then sealingly closed. By starting operation of vacuum
pump 5 the surrounding of container 9 and thus the intermediate
volume V of test cavity and container 9 is lowered.
[0052] According to FIG. 3 starting at ambient pressure p.sub.o the
pressure in volume V is lowered at least down to the value P.sub.v,
which accords to the vapour pressure of the liquid component within
the filling good of the container 9. It is advisable to select a
vacuum pump 5 which enables to evacuate the test cavity 1 down to a
pressure which is at least one, preferably two and even more
preferred three decades lower than the vapour pressure P.sub.v of
the liquid content of the filling product.
[0053] The test is preferably performed at room temperature, i.e.
at a temperature T of about 20.degree. C. If the liquid content is
water then the vapour pressure P.sub.v of water at room temperature
is about 20 mbar and it then is preferred to provide an evacuation
pump 5 which is able to evacuate the test cavity to about 10.sup.-2
mbar.
[0054] If the container provided in the test cavity 1 having a
relatively rigid wall 11 is not leaky, then qualitatively the
pressure in volume V will follow the course (a) according to FIG. 3
down to the more or less constant value of pressure, which may be
reached by that type of vacuum pump installed. If, on the other
hand, the container 9 is leaky as schematically shown in FIG. 2
e.g. at location 13, then a small amount 14 of liquid component of
the filling good will be drawn through the leak 13 out of the
container 9 and as soon as the pressure prevailing in the volume V
becomes P.sub.v starts to evaporate into the volume V. As
qualitatively shown in FIG. 3 this leads to a pressure versus time
course according to (b), i.e. evaporation of the liquid leads to a
pressure rise in volume V, counteracting the action of the vacuum
pump 5. The vacuum pump 5 will have to remove additionally the
vapour to finally achieve a vacuum level according to course (a).
If the leak is situated at an area of the container 9 where air is
entrapped, as in FIG. 2 at 13', then evacuation of volume V will
first lead to suctioning air out of the container, again
counteracting the operation of vacuum pump 5, then the liquid
content within container 9 will start to evaporate within the
container and vapour will be suctioned out of leak 13'. This, too,
will lead to a pressure rise in volume V, counteracting the
pressure course which would be followed if just air had to be
removed by vacuum pump 5.
[0055] By means of the vacuum sensor 7 the course of pressure in
the volume V is monitored. Experiments have shown that largely
independent of the amount of volume V in a test cavity a
significant difference of pressure according to the courses (a) and
(b) of FIG. 3 is reached after a time span T of a few seconds (one
to three seconds) and at a leak smaller than 1 micron (0.02 .mu.m),
the pressure difference between a leaky and an unleaky container
being of about one pressure decade. Measurements were performed
with water as liquid content.
[0056] Although it is absolutely possible to measure the absolute
pressure in volume V, e.g. after the time span T to detect leakage
of the container a pressure difference measurement is preferred, as
will first be explained with the help of FIG. 4.
[0057] Back to FIG. 2 the pressure sensor 7 is operationally
connected to an evaluating unit 15, whereat especially leak
indicative threshold values are preset, as schematically shown by
means of a presetting unit 17. The output of the evaluation unit 15
is a two-state signal indicating leaky or not leaky.
[0058] According to FIG. 4 the output of the vacuum sensor 7 is
input to a storage unit 19, controlled by a timing control signal
s.sub.1, as schematically shown via switch S. According to FIG. 3
this is performed at a first point in time t.sub.1. At a second
point in time, according to FIG. 3 t.sub.2, the output of the
storage unit 19 and the output of the sensor 7 are connected to
respective inputs of a difference forming unit 21, which generates
an output signal which accords with the pressure difference .DELTA.
p of FIG. 3.
[0059] A further, most preferred realisation of the evaluation
electronic is shown in FIG. 5. The output signal of sensor 7 is
input to a conversion unit 121, which comprises, as an input stage,
an analogue to digital converter 121a, followed by a digital to
analogue converter 121b. The output of the converter stage 121 is
fed to a difference amplifier unit 123, which additionally receives
directly the output signal from sensor 7. The output of the
difference amplifier unit 123, according to the difference unit 21
of FIG. 4, acts on a further amplifier unit 125, the output of
which being superimposed at 128 to its input via storage unit 127.
The input of the storage unit 127 is fed from the output of unit
125. A timer unit 129 time controls the arrangement. For storing a
first pressure value from sensor 7, according to FIG. 3 at time t1,
the timer unit 129 enables a conversion cycle at unit 121, so that
a reconverted analogue output signal el.sub.o appears at the
output. Simultaneously, the substantially same signal from sensor 7
is applied as signal el to the second input of unit 123. Thus, at
the output of unit 125, a zero signal should appear. Nevertheless,
in general a zero-offset signal will appear at the output of unit
125, which signal is stored in the storing unit 127, enabled by the
timing unit 129. At time t2 no conversion is triggered at the unit
121, so that there appears at the input of amplifier 123 directly
from sensor 7 the pressure value prevailing at t.sub.2 and, from
stage 121, the stored pressure value which was prevailing at
t.sub.1. Further, the zero offset signal which was stored in unit
127 is superimposed as a offset-compensating signal so that the
resulting signal at the output of amplifier unit 125 is zero-offset
compensated.
[0060] This allows a very accurate measurement of pressure
difference .DELTA.p according to FIG. 3.
[0061] If the container under test has a large leak, then, and
according to FIG. 3 course (c) the pressure prevailing in the
volume V of the test cavity 1 will have just from the beginning of
operating the vacuum pump 5 a different course. This may easily be
detected, e.g. by comparing at a previous point in time to the
output signal of sensor 7 with a predetermined threshold value (not
shown), and if such threshold value is not reached by the actual
pressure, the effect of the vacuum pump 5 on test cavity 1 is
disabled. This to avoid that, with a larger leak, a huge amount of
content of the container is suctioned into the test cavity and
contaminates that cavity.
[0062] As was mentioned, the proposed method accurately functions
largely independently from the volume V between test cavity 1 and
the at least one container to be tested. This allows, according to
FIG. 6, to simultaneously test batches 9' of containers 9, thereby
maintaining accuracy of detecting whether one or more than one of
the containers 9 leak. Further, the fact that detection accuracy is
not critical with respect to difference volume V leads to the
possibility of providing one test cavity 1 for a multitude of
differently shaped and different-volume containers 9 to be tested
therein.
[0063] If the wall of a container to be tested may not mechanically
withstand the pressure loading of approx. 1 bar, then, and as
schematically shown in FIG. 7, a test cavity 1' with cover 3' is
provided which snugly fits with the shape of the container 9.
Thereby, protrusions 20, as schematically shown in FIG. 7, prevent
that by effect of the evacuation the walls of the container are
firmly suctioned on to the inner wall of the test cavity and thus
make sure that there remains a volume V between container and test
cavity wall for being evacuated according to the invention. Such
protrusions 20 may be realised by a mesh or grid inlay or, and
preferably, by mechanically roughening the inner wall of the
cavity, so that micro-embossments sustain the wall of the
container, thereby leaving a continuous interspace as volume V.
[0064] As shown in dashed line in FIG. 7 it might further be
advantageous, e.g. when closing the cover 3 or 3' of the cavity, to
mechanically bias a part of the container's wall inwardly, thereby
increasing the inner pressure of the container 9 and additionally
pressing liquid component of the filling product out of a leak if
such a leak is existent. According to FIG. 9 the method and
apparatus according to the present invention may be used to monitor
huge tanks with respect to leakage. In FIG. 9 there is shown a tank
with double-wall, namely with an inner wall 23 and an outer wall
25. Testing tightness of both these walls is performed by using the
intermediate volume of the two walls, as volume V according to FIG.
2. Such a technique may be applied e.g. for tanks on road or rail
vehicles or for huge stationary tank plants, e.g. for gasoline.
[0065] In FIG. 8 there is shown one half 1a of a test cavity 1 for
applying the inventive method in an inventive apparatus on three
containers at 29 as on small plastic containers for medical
appliance. The containers may have flexible walls as the test
cavity 1 snugly fits their shape. There is further shown another
technique to rapidly detect whether one of the containers has a
large leak. There are provided impedance measurement electrodes 32
and 34 integrated in the wall of the cavity 1 and mutually
electrically isolated. They are connected to an impedance or,
preferably, resistance measuring unit 35. If by applying a vacuum
to the test cavity, preferably with a roughened interior wall,
liquid filling content is suctioned to the outside of the container
wall, this is quickly detected by an abrupt change of impedance
measured between the electrodes 32 and 34. The output of the
impedance measuring unit 35 disables (not shown) further evacuation
of the test cavity 1.
[0066] Once a test cavity has been spoiled by outpouring filling
good of a leaking container it is cleaned, either by cleaning
evacuation and/or pouring with a gas, preferably with nitrogen,
and/or by heating. In FIG. 8 there is shown a feeding line for a
flushing or cleaning gas, controllably fed from a gas tank 37 to a
contaminated test cavity 1, which gas preferably is nitrogen.
[0067] Two cavity halves, 1a according to FIG. 8 are sealingly put
one upon the other to complete a test cavity 1 according to FIG.
2.
[0068] If in-line testing of containers shall be performed, for
which the present invention is especially suited due to its short
measuring cycle, more than one, namely a set of several test
cavities is provided, e.g. on a carousel, which are automatically
loaded with containers to be tested (not shown) from a conveyor and
which perform simultaneously the described testing technique. If
one of the containers tested in such cavity is detected to be
leaky, then the respective cavity is not reloaded with a further
container afterwards, but this cavity is maintained empty during
the measuring cycle on a next set of containers. Meanwhile, the
cavity kept unloaded is cleaned, as was described, either by
evacuation and/or gas flushing and/or heating.
[0069] Obviously, there must be realised a good vacuum-tight
sealing between a cover 3 or 3' of the test cavity and the main
body of the test cavity 1 or between the two halves 1a of test
cavity according to FIG. 8. This is realised preferably by
providing at least a pair of parallel seals 28 as of concentric 0
seals and by separately pumping an intermediate space 29 between
such seals, as shown in FIG. 10. If the container to be tested
contains a filling product with more than one specific liquid
component, the vapour pressure of that component is selected for
leak detection which has the highest vapour pressure, i.e. which
component starts to evaporate at relatively highest pressure.
Thereby, viscosity has to be considered too, i.e. a component is to
be selected for defining the vapour pressure, which component is
liquid enough to penetrate smallest leaks. By evacuating the test
cavity down to a pressure which is significantly lower than the
vapour pressure of any liquid component it becomes uncritical which
vapour pressure value is to be considered.
[0070] Pressure versus time courses as measured according to the
inventive method and with an inventive apparatus, both in preferred
mode, are shown for containers with large leaks in FIG. 11a, for
small leaks in FIG. 11b and for unleaky containers in FIG. 11c.
[0071] These figures shall be discussed in connection with FIG. 12,
which shows a preferred monitoring and control unit according to
units 15, 17 of FIG. 2.
[0072] According to FIG. 11a the timing unit 201 of FIG. 12
initiates at time t.sub.10 evacuation of a test cavity 103 by means
of the pumping arrangement 105. This is shown in FIG. 12 by the
evacuation start signal EVST/t.sub.10.
[0073] After a fixed predetermined amount of time .DELTA.T of e.g.
0.75 sec. the output signal of the pressure sensor within test
cavity 103 (not shown in FIG. 12), A.sub.5, becomes compared with a
first reference signal preset at a presetting source 107, RFVGL. To
this target, comparator unit 109 is enabled by timer unit 201 at
t.sub.10+.DELTA.T.
[0074] If after time span .DELTA.T the actual monitored pressure
according to electric signal A.sub.5 of FIG. 12 has not reached the
value of RFVGL, according to course I of FIG. 11a, this means that
a very large leak VGL is present. This is detected at comparator
109 generating the output signal A.sub.109. If according to the
characteristics shown in the block 109 of FIG. 12 the output signal
of this comparator unit 109 enabled at t.sub.11=t.sub.10+.DELTA.T
is e.g still at a high level indicating presence of a VGL, this is
output at the VOL output. If the pressure prevailing in the
surrounding of the container 103 under test, i.e. in the test
cavity, has reached and crossed reference level RFVOL according to
course II of fig. ha, the VOL output signal is not generated.
[0075] As will be explained later, occurrence of the VGL signal
preferably stops the evacuation cycle because contamination of the
vacuum pump 105 may have occurred or might occur due to the very
large leak of the container under test.
[0076] As shown by the course II of FIG. 11a as VGL does not occur
evacuation continues up to a further moment of time t.sub.13. At
the time t.sub.13 the timer unit 201 disables pumping arrangement
105 and disconnects as by a valve 106 the pumping arrangement from
chamber 103. Further, timer unit 201 enables comparator unit 111,
to which a further reference value RFGL is led, generated by a
reference signal source 113. If at t.sub.13 the pressure prevailing
in the surrounding of the test cavity has not reached RFGL then
comparator unit 111 generates an output signal GL indicating that
the container under test has a large leak. Here again, and as will
be further explained later on, some reactions are taken with
respect to further operation of the testing system.
[0077] If either the signals VGL or GL are initiated by the
respective comparators 109, 111, the timer unit 201 is principally
reset because the testing has been completed and the quality of the
instantaneously tested container established has been identified.
This is schematically shown in FIG. 12 by the signal RS.sub.201. If
not reset, shortly after t.sub.13 the value A.sub.5 (t.sub.13) of
the pressure prevailing in the surrounding of the container is
stored in a holding or storing unit 117. The output of the holding
or storing unit 117 is led to one input of a difference forming
unit 119, whereas the second input of this unit 119 is connected to
the output A.sub.5 of the pressure sensor monitoring the pressure
in the surrounding of the container under test. After a presettable
test cycle time T.sub.T starting at t.sub.13, as schematically
shown by unit 121 of FIG. 12, the pressure difference DP at the
output of unit 119 is evaluated, as represented in FIG. 12 by
switching unit 123. This pressure difference DP is fed to a further
comparator unit 125 enabled at the lapse of testing time T.sub.T.
By means of a further reference value source 127 the reference
value DPREF is fed to the comparator unit 125. As will be explained
later, the value of DPREF may controllably be varied in time and/or
a reference value .phi..sub.R to which DPREF is referred to may
also controllably be varied in time.
[0078] If DP at time t.sub.13+T.sub.T is larger than the reference
value DPREF, then a signal FL is generated at unit 125, indicating
presence of a fine leak FL in the container under test. This
according to the situation as shown in FIG. 11b. If DP does not
reach DPREF, then the container is considered unleaky as none of
the signals VGL, GL and FL have been generated. This according to
FIG. 11c.
[0079] If the VGL signal is generated according to FIG. 12, the
evacuation pump 105 is immediately disconnected from any testing
chamber 103 it is connected to, be it a single chamber or be it in
an in-line processing where one pump 105 is parallel connected to a
multitude of testing chambers 103, from all such chambers. This
because at a very large leak the vacuum pump 105 could have been
contaminated by leaking content of the container. It thereby is
absolutely possible to provide for such a case a redundant pumping
arrangement which may be connected to the one or the more than one
testing chambers to continue testing, whereas the possibly
contaminated first pumping arrangement is reconditioned.
[0080] In a multiple chamber in-line testing system, as e.g. in a
carousel testing plant with a multitude of testing chambers,
occurrence of the signal GL indicating a large leak and possibly
also the occurrence of the signal FL indicating for a fine leak
leads preferably to disabling or "bypassing" that chamber with the
leaky container from further being supplied with containers to be
tested, whereas the other chambers are still operating and
performing tests on newly supplied containers. This bypass of a
testing chamber, whereat a container has been identified as heavily
or even slightly leaking, is performed so as not to influence
further testing results at that chamber which wouldn't thus be
representative anymore due to content of the leaky container having
possibly contaminated that chamber.
[0081] This bypassed chamber is reconditioned during further
testing cycles at the other chambers.
[0082] Reconditioning may be done by heating that chamber, flushing
it by a liquid and/or a gas, especially by a heater gas. Whether or
not that chamber has been properly reconditioned is checked by
having it tested as if it was filled with a container to be tested.
Thereby, the condition of proper reconditioning is indicated if 1 W
according to FIG. 12 at that empty chamber does e.g. not reach
DPREF or an appropriately set "Empty Chamber DP-REF"-value
(ECDP-REF).
[0083] Such ECDP-REV may be provided by measuring DP.sub.e at the
clean, empty test chambers and by storing these measuring values
DP.sub.e as respective reference values for testing the chambers on
proper reconditioning.
[0084] When looking to the FIG. 11a to 11b, it may by recognised
that setting the reference value RFGL and especially setting of the
reference pressure difference value DPREF may be very critical and
may largely influence accuracy of the system. Thereby, influences
as surrounding temperature, moisture of ambient air, slight
contamination of pump etc., may influence the prevailing pressure
course--and lead to false results if these critical reference
levels and especially DPREF are set for utmost accuracy.
[0085] In FIG. 13 there is quantitatively shown the pressure course
according to the courses of FIG. 11a to 11c, but measured at test
cavities void of containers. At t.sub.13 there occur statistically
distributed slightly different pressure values. Thus, before
beginning testing of containers at a multiple test cavity plant,
the unfilled, tightly closed test cavities are tested according to
FIG. 13 to establish an average (RFGL).sub.m. The value of RFGL as
used at the comparator 111 of FIG. 12 or as used according to the
FIGS. 11a to 11c is found in that an offset value .DELTA.RFGL is
added to (RFGL).sub.m. It must be pointed out that ambient
parameters as temperature, humidity of ambient air etc. may be
considered constant during the calibrating cycle performed at the
empty and conditioned test cavities and leading to the measuring
results according to FIG. 13. Nevertheless, during ongoing time as
during on-line testing, these disturbing parameters may slowly
change and may vary (RFGL).sub.m.
[0086] Every time during multiple or in-line testing, be it
subsequently with a single test cavity or consecutively with a
multitude or at least more than one test cavity, at the respective
time t.sub.13, up to which the respective container has been
identified as not heavily leaky, the actual output signal of the
pressure sensor is entered into an averaging unit 113, wherein the
last m values of actual pressure of not heavily leaky containers
are averaged. The output average result signal accords with
(RFGL).sub.m of FIG. 13, but varies in time, e.g. due to varying
ambient parameters. To the output average result A5 and according
to FIG. 13 the offset .DELTA.RFGL is added, the result of that
addition is a dynamically varying reference value RFGL, which is
applied to comparator unit 111 of FIG. 12. This dynamically varying
reference value RFGL is shown in FIG. 15, starting from an initial
setting, as e.g. found as was explained with the help measurements
at empty test cavities 103.
[0087] As may clearly be seen now from FIG. 15, the average
pressure value A5 (t.sub.13) is now the basis for also referring
DPREF to. Therefore, and as shown in FIG. 12, the difference
pressure reference value DPREF is not referred to an absolute
static value as .phi..sub.R but is referred to A5.
[0088] An even further improvement of accuracy is reached as will
now be described, which may be realised separately or additionally
to realising a dynamic RFGL and based thereon a dynamic upper limit
of DPREF. Thereby and according to FIG. 16 at the end of the time
span T.sub.T the actual pressure difference DP is led to an
averaging unit 135 whenever the output signal FL indicates that the
container under test is unleaky. The output signal of unit 135
which accords to an average pressure difference signal DP averaged
over the last m test cycles, is offset by an amount .DELTA.DP, the
result thereof being used as DPREF signal applied at unit 127 of
FIG. 12.
[0089] Looking back on FIG. 15, whereat, as discussed before, a
constant DPREF signal was applied the technique of averaging DP
results, as schematically shown with a course (DPREF).sub.t, in a
dynamically varying check value DPREF, varying according to
variations of disturbing parameters, influencing such pressure
difference.
[0090] It is clear that provision of a dynamically varying
(DPREF).sub.t signal according to that representation in FIG. 15
could be realised without providing a dynamically varying base
value A5, in referring (DPREF).sub.t to a stable, constant value
.phi..sub.R, as shown in FIG. 12 in dashed representation instead
of referring to a dynamically varying A5 value.
[0091] It is evident that preferably the evaluations of the output
signal A.sub.5 of the one or more than one test cavities is
performed digitally, i.e. after analogue to digital conversion of
the output signal of the respective sensor or sensors.
[0092] In FIG. 17 there is shown over the time axis and in
arbitrary units the actual pressure difference values DP measured
successively at a multitude of test cavities of an in-line testing
plant. According to FIG. 16 the calculated average pressure
difference DP is shown and the offset .DELTA.DP finally leading to
(DPREF).sub.t according to FIG. 15 or 16. As may clearly be seen,
the average DP and thus (DPREF).sub.t vary in time and along
successive testing, whereby pressure difference values as at A,
which are higher than the instantaneously prevailing (DPREF).sub.t,
are disregarded with respect to influencing the averaged DP, as
such measurements are due to leaky containers according to FIG.
11b.
[0093] Further, whenever the test of a container within a specific
test cavity results in a leak-indication for a predetermined number
of subsequent tests, as e.g. three times subsequently, such test
cavity is also bypassed for further testing and is considered as
contaminated or as leaky itself, thus being reconditioned. Such a
test cavity is likely to have been contaminated during succeeding
testings at leaky containers or is likely not to be tight, which
will be recognised during reconditioning and testing on proper
reconditioning too, as was described above.
[0094] Further, and as was already mentioned, for some containers
to be tested and especially for some filling products it is
advisable to heat the test cavities to a predetermined temperature
which is preferably controlled at each test cavity, e.g. by a
negative feedback temperature control. Thereby, the
temperature-dependent evaporation pressure of the filling product
is set within a predetermined pressure range. Such heating is
thereby preferably accomplished in a pre-heating cycle before the
actual testing cycle according the FIGS. 11a to 11c is
performed.
[0095] As was mentioned above, a leak in a container will be
identified irrespective of the fact whether such leak is in an area
of container's wall exposed to entrapped air within the container
or to the filling product. Nevertheless, for some filling goods as
e.g. with particulate content in liquid, there might occur
differences with respect to time a respective pressure difference
develops in the surrounding of the container under test.
[0096] Therefore, and as schematically shown in FIG. 18, it may be
advisable in some cases to provide the one or the several test
cavities 103 for the container to be tested 9 to be movable. This
is e.g. accomplished by mounting the test cavities 103 pivotable
with respect to a pivot axis A and driven via a rotational axis
140. Thereby, leads to and from the pressure sensor within such
test cavity, to and from a heating arrangement at such a test
cavity etc. may be led through the driving axis 140. The cavity 1,
103 is preferably not rotated, but is rotatably oscillated as shown
by .+-..phi. in FIG. 18. By this technique, and as schematically
shown in FIG. 19, a leak L is moved into air and into liquid
contact, so that testing will consider vaporising of liquid content
whenever it occurs, be it in the position according to FIG. 19a or
in the position according to FIG. 19b.
[0097] Proper functioning of the testing apparatus and calibration
of the evaluation unit, be it a one-chamber tester or a at
multiple-chamber testing plant as for in-line testing, is further
preferably accomplished with the help of a standard leakage
arrangement which is preferably mounted on the test plant, so that
recalibration and/or overall testing of the plant may be
accomplished whenever desired. The arrangement of such a standard
or calibration leak arrangement is shown in FIG. 20.
[0098] According to FIG. 20 there is provided in the line from a
test cavity, as 103 according to FIG. 12, to the vacuum pump 105 a
needle valve 142, which is adjustable but which preferably is
preset not variable by the user of the plant on a predetermined
leakage value. Via the needle valve 142, the line to the vacuum
pump 105 is connected to a liquid reservoir 144, which preferably
is filled with distilled water. Via a pressurising line and valve
146 the reservoir 144 may be adjustably pressurised. The needle
valve is set to such a value that no distilled water of reservoir
144 will penetrate into the connection line of chamber 103 to
vacuum pump 105, but only vapour. Nevertheless, by adjusting
pressurisation of the water within reservoir 144 via line and valve
146 a leak of different and varying extent may be simulated without
liquid penetrating and spoiling chamber and/or connection line
and/or vacuum pump. For a plant with a multitude of testing
cavities such a calibration arrangement with needle valve 142 may
centrally be provided and connected in parallel to all chambers
103, as in such a plant preferably there is provided one central
pumping arrangement 105 acting in parallel on all the chambers or
cavities provided. Alternatively such a calibration arrangement may
be provided separately for each of the chambers 103 provided.
[0099] It has been recognised that by applying the described
technique of leak testing by lowering the surrounding pressure of a
container under test below vapour pressure of a liquid component of
its content, it is mostly not necessary to additionally provide
resistance measurements, as was explained with the help of FIG. 8,
so that, at the respective test chambers, the electrode
arrangements and measurement units may be omitted, which
significantly reduces costs for the overall plant and its
complexity. The invention is especially suited for testing vials or
blisters, especially for medical appliances, in-line with their
production by checking every single vial or blister. If and as
schematically shown in FIG. 6 a multitude of containers 9 are
mechanically linked together to form a set of such of containers,
clearly such a set is considered as one container with respect to
leak testing.
[0100] With the inventive method and apparatus as for blisters the
entire testing cycle, i.e. from t.sub.10 to the end of T.sub.T
according to the FIG. 11 is performed in less than 2 sec. This
leads at an in-line plant with a multitude of test cavities, e.g.
with 24, e.g. arranged on a carousel, to a very high
throughput.
* * * * *