GB2493009A

GB2493009A - Seal integrity detector for sealed packages

Info

Publication number: GB2493009A
Application number: GB1112552.3A
Authority: GB
Inventors: Malcolm Robert Snowball
Original assignee: PACKTESTER Ltd
Current assignee: PACKTESTER LIMITED
Priority date: 2011-07-21
Filing date: 2011-07-21
Publication date: 2013-01-23
Also published as: WO2013011329A3; WO2013011329A2; GB201112552D0

Abstract

The apparatus is provided for detecting leaks in sealed packages 1which contains a detectable signature gas (such as helium or neon or a mixture). The apparatus comprises a package contact surface 3, an arrangement (a ram) 2 for subjecting sealed packages on a production line sequentially to compression between the contact surface 3 and the ram 2 to promote signature gas leakage, and a gas detector comprising circuitry coupled to electrodes 4 located about expected leakage points of a sealed package. The circuitry applies a voltage across the electrodes to detect a change in electrical characteristics indicative of signature gas leakage from the sealed package. The defective package can be segregated mechanically from the production process for further work/processing. Alternatively, or additionally, the apparatus comprises a gas detector 5 (figure 12) comprising multiple probes arranged in communication with respective ducts to detect a change in local gas characteristics indicative of signature gas leakage from the sealed package. A further invention aspect relates a sealed package containing a perishable product and a signature gas with an electrical breakdown voltage lower than atmospheric air.

Description

Seal Integrity Detector for Sealed Packages The present invention relates to a seal integrity detector for sealed packaging, a method of detecting sea! integrity in sealed packaging and sealed packaging for S use with the seal integrity detector.

Flexible packaging material such as that made of polymer or polymer derivatives has been widely used for packaging in the food industry. These materials can be manufactured in almost any size and shape which is highly beneficial to package manufacturing, However, these materials pose certain problems. As they are light and flexible, they are more prone to puncturing, sUcing and other problems than conventional metallic or glass packaging material.

One of the most prevalent problems in the food packaging industry effecting food sheff life and food safety is detective package seals or defective packaging material. Problems in the defective package seals may be due to wrinkles in the packaging material, improper sealing temperatures, contamination of the seal with extraneous material, absence of adhesive and variability of the sealant thickness.

As a result of these factors, the flexible packaging manufacturing process is not completely reliable. Most perishable foods are packed in a modified atmosphere to slow down the reproduction of spotge and pathogenic micro-organisms.

Generally the food is placed in the package and then gas flushed with an atmosphere which is usually oxygen depleted (low oxygen, high nitrogen and carbon dioxide), then sealed to hold the modified atmosphere inside the package.

If the seal is defective (not tightly sealed) the modified atmosphere escapes through the defect by natural dispersion rendering the food unprotected with the inevitable consequence that the food prematurely spoils and is no longer it for human consumption.

At present up to 4% of sealed packages can have defective seals creating a large amount of food waste, large expense to food manufacturers and poses a serious risk to human health.

There is a great need for an automatic seal integrity detection device which wili autornaticaUy detect leaky" packages as they are being processed and which will then automaticafly segregate them for reprocessing.

Patent publication No. CA2037185 discloses a leak detecting device for S packaging having a plastic cover. Before sealing the cover, a modiFied atmosphere containing Helium is introduced into the package. The package is placed under a hood. Air within the hood is moved through a pipe when a pre deterniined amount of pressure is applied to the packaging. A Helium sensor is placed within the pipe to detect any Helium leaks from the packaging. A drawback of this type of device is that the sampling time of Helium sensors is too long for efficient testing of food packaging on a production line. Another drawback of this type of device is the dispersion of the gases from the packaging's modified atmosphere within the hood may slow sampling time and reduce sensitivity of the Helium detector.

It is an object of the present invention to overcome, or at least mitigate, these drawbacks by providing an apparatus which may detect leaks in sealed packages quickly, and with a high degree of sensitMty, and which may avoid disruption to the production line by removing defective sealed packages swiftly and reliably.

Accordingly, the present invention there is provided an apparatus for detecting leaks in sealed packages containing a detectable signature gas, the apparatus comprising: a package contact surface; an arrangement for subjecting sealed packages on a production line sequentially to compression between the contact surface and the arrangement to promote signature gas leakage; and a gas detector comprising circuitry coupled to electrodes located about expected leakage points of a sealed package, wherein the circuitry applies a voltage across the electrodes to detect a change in electrica.l characteristics indicative of signature gas leakage from the sealed package.

Preferably, the apparatus comprises multiple electrodes in order to increase the sensitivity of the gas detector.

Preferably, the gas detector comprises a multiplicity of ducts in communication with expected leakage points of a sealed package and wherein the electrodes are arranged in communication with respective ducts. The ducts may channel any leak of signature gas into a relatively small space to increase the concentration of signature gas for the electrodes to detect. This helps increase the sensitivity of the gas detector.

Preferably, the electrodes are located at opposite ends of all or some of the ducts. This may channel any teak of signature gas to directly between two electrodes. This helps increase the sensitivity of the gas detector.

Accordingly, the present invention there is also provided an apparatus for detecting leaks in sealed packages containing a detectable signature gas, the apparatus comprising: a package contact surface; an arrangement for subjecting sealed packages on a production fine sequentially to compression between the contact surface and the arrangement to promote signature gas leakage; a multiplicity of ducts in communication with expected leakage points of a sealed package; and a gas detector comprising multiple probes arranged in communication with respective ducts to detect a change in local gas characteristics indicative of signature gas leakage from the sealed package. The ducts may channel any leak of signature gas into a relatively small space to increase the concentration of signature gas for the probes to detect. This may increase the sensitivity of the gas detector.

Preferably, the probes are located at opposite ends of all or some of the ducts.

This may channel any leak of signature gas directly between two probes. This helps increase the sensitivity of the gas detector.

Preferably, the multiplicity of ducts comprises at least five ducts. More preferably, the multiplicity of ducts comprises at least ten ducts. Still more preferably, the multiplicity of ducts comprises a mesh of ducts. A greater number of ducts helps to gather a leak of signature gas and channel it, in an increased concentration, towards electrodes or probes of the gas detector. This helps increase the sensitivity of the gas detector. It may also make the apparatus less susceptible to external atmospheric air movement which could otherwise influence the detection of signature gas.

Preferably, the probes are electrodes and the gas detector comprises circuitry coupled to the electrodes, wherein the circuitry applies a voltage across the electrodes to detect a change in electrical characteristics indicative of signature gas leakage from the sealed package.

Preferably, the package contact surface is an insulator which provides support for some or all of the electrodes, This may improve stability of the electrodes. It helps S maintain space between the electrodes without need for a separate spacer. Also, this arrangement enables some, or all, of the electrodes to abut the sealed packaging when it is compressed against the package contact surface thereby putting the electrodes in dose proximity with likely location of any leaks. The electrodes can be directly applied to the insulator surface.

Preferably, the package contact surface is linearly translatable to follow sealed packages on a production line sequentially. The signature gas detection can occur without interrupting the production line or removal of the sealed packages from the production line.

Preferably, the seated package subjected to compression is substantially surrounded by electrodes, This arrangement is beneficial for seated packages where the expected leakage points can vary significantly from one package to the next.

Preferably, the circuitry applies a series of increasing voltages across the electrodes to detect the change in electrical characteristics indicative of a signature gas leakage from the sealed package. Preferably, the series of increasing voltages across the electrodes is a sweeping voltage increase. As an alternative to voltage across the electrodes being switched on as a high voltage pulse, it may be switched on as a sweeping voltage increasing steadily from zero to a high voltage over a very short time. Commercially available electronic circuitry can instantaneously measure changes in resistance and I or impedance across the electrodes which occurs as voltage rises and before electric discharge occurs. The rate of resistance or impedance change, as shown by a classic electrical breakdown curve, varies according to the nature of gas present between the electrodes. For example, the signature curve of a noble gas will be distinctly different to that of atmospheric air or other gases. Rather than detecting for the occurrence of electrical discharge at a point voltage, an electronic circuitry using a sweeping voltage may detect the shape of the electricS breakdown curve and comparing it with what is expected for atmospheric air. Any deviation from what is expected, or an electrical breakdown curve resembling the signature gas, indicates a leak in the sealed packaging. This may improve reliable detection.

Preferably, the circuitry memorises rate of change of resistance and / or impedance across the electrodes detected during each sweeping voltage increase. The electronic circuitry may compare rate of change of resistance and I or impedance across the electrodes detected during successive sweeping voltages. The electronic circuitry may compensate for any gradual variation in atmospheric conditions and maintain reliable signature gas detection.

Preferably, the circuitry applies an alternating voltage across the electrodes to detect the change in electrical characteristics indicative of a signature gas leakage from the sealed package. The alternating voltage can overlay a sweeping increase in voltage offset.

Preferably, voltages applied by the circuitry across the electrodes lie within a range of OV to 3000V per millimetre of gap between the electrodes.

Preferably, the electrodes are sufficiently spaced apart to provoke electrical breakdown when the circuitry applies peak voltage in the presence of the signature gas and not when the circuitry applies peak voltage in the presence of atmospheric air. This provides that a leak of signature gas will be detected and false leak indications are eliminated, or at least reduced to a negligible amount.

Preferably, some or all of the electrodes are clad with insulating materiaL An alternating high voltage applied across the electrodes has a peak voltage which is not high enough to ionise the atmospheric air between the electrodes. However, in the presence of the signature gas, which has a significantly lower electrical breakdown voltage than atmospheric air, the signature gas leaks into the gaps between electrodes and breaks down to create a low impedance path between the electrodes and strike cold plasma. This results in a current drain from the circuitry which detects a defective package. As there Es no arc and hence no metallic erosion in this process, the electrodes may be any convenient metal The cold plasma is so short lived there is no appreciable heating of the electrodes.

Preferably1 the electrodes are arranged to be shockproof. This can be done by shielding the live electrode away from external interference, 5., Preferably, the apparatus is ventilated with fresh atmospheric air after each sequential sealed package is subjected to the predetermined pressure. The signature gas used in the apparatus should only found in air in trace quantities so that it is much easier for the gas detector to detect. Ventilation of the apparatus S may help keep the signature gas at trace quantity in the surrounding air.

Preferably, the package contact surface is roughened to provide micro-channels for escape of any signature gas leaking from a part of the sealed package in abutment with the package contact surface.

Accordingly, the present invention there is also provided a method of detecting leaks in sealed packages containing a detectable signature gas using the above apparatus, wherein the method comprises the steps of: a) presenting the sealed package to the package contact surface; b) compressing the package and detecting for signature gas with the gas detector: c) releasing the sealed package to the production line if no signature gas detected or isolating the sealed package from the production line if signature gas detected; and d) preparing to return to step (a) for the next sequential sealed package on the production line.

A signature gas is introduced into the package along with the modified atmosphere at the gas flushing stage. Preferably, the signature gas is a non-reactive noble type so that it does not impart any taste or smell to the foodstuff in the package. Preferably, the noble gas is lighter than the modified atmosphere so that when the package is held with its seal at the top of the package the signature gas substantially congregates around the seal. Preferably, the signature gas is not explosive. Preferably, the signature gas constitutes a very small percentage in atmospheric air and therefore makes it easier to detect. Preferably, the signature gas is Helium, Neon or some other suitable gas or gas mixture.

The internal pressure of the sealed package is then increased by mechanical compression or some other suitable means to put the seal under pressure and expose any weakness in the seal by encouraging the package to leak signature gas from any defective seal or material portions. Preferably, the amount of compression is chosen not to produce any permanent distortion to the package.

Accordingly, the present invention there is also provided a sealed package containing a perishable product and a gas modified with respect to atmospheric air to include a signature gas with an electrical breakdown voltage lower than atmospheric air. The perishable product can be food or any other product which may deteriorate more rapidly outside the seated package or if the sealed package is damaged.

Preferably, the percentage of signature gas in the modified gas is no less than 0.01 percent. Preferably, the percentage of signature gas in the modified gas is no more than ten percent.

Preferably, the signature gas is a noble gas or a mixture of noble gases. For a gas to be used in contact with food products it must be nonreactive, stable and must not impart any taste or odour to the foodstuff. Ideal gases are the noble gases which meet these criteria exactly and are suitable for use in the modified atmosphere inside packaging. it would aLso be helpful it the gas was lighter than air for food packages that are sealed at the top.

Noble Gasses of interest Helium one of the lightest of the noble gases (density 0.1785 Kg/rn3 compared with air at 1.204 Kg/rn3) and totally non-reactive. Paschen curves for gases show that Helium has an electrical breakdown voltage at one atmosphere of approximately 84v per millimetre compared to air which is approximately 3kv per millimetre. Helium is breathed by humans when mixed with oxygen.

Neon lighter than air with a density of 0.8999 Kg/rn3, but with a density nearest air amongst the noble gases, and totaily non-reactive with an electrical breakdown voltage at one atmosphere of approximately lOGy per millimetre.

Neon is breathed by humans when mixed with oxygen in some medical procedures.

Krypton much heavier than air with a density of 3.37 Kg/m3 and is totally non-reactive, It has a lower electrical breakdown voltage than Helium and Neon however its high density is unsuitable for applications where a single seat is at the top of the package.

Xenon -the heaviest of the noble gases at 5.584 Kg/rn3 and is totally non-reactive. It has a lower electrical breakdown voltage than Helium and Neon however its high density is unsuitable for appcaUons where a single seal is at the top of the package.

Argon Heavier than aft with a density of 1.783 Kg/rn3 and is totally non-reactive.

It has a slightly higher electrical breakdown voltage than Helium (approximately S 86v per mulimetre) however its high density is unsuitable applications where a single seal is at the top of the package, although would be a good candidate for pillow packs or bags.

Preferably, the signature gas is a mixture of noble gases having a density comparable to atmospheric air. In the case of packages which are sealed at both ends, like, for example, "pillowcase" sealed packages, the use two or more noble gases of mixed density (some more dense than atrnospheric air and some less dense) may provide a signature gas spread evenly about the package, and its seals, in any orientation.

Embodiments of the invention will now be described with reference to the accompanying drawings: Figure IA shows a schematic diagram of a d.c. discharge between parallel plate electrodes in a low-pressure environment.

Figure 1 B shows a graph of the voltage -current characteristic for the type of d.c.

discharge of Figure 1k Figure 2 shows a Paschen curve with the electrical breakdown voltage of air.

Figure 3 shows Paschen curves with the electrical breakdown voltages of Air, Xenon, Argon and Neon.

Figure 4 shows Paschen curves with the electrical breakdown voltages of Argon, Neon, Nitrogen, Helium and Hydrogen.

Figure 5 shows part sectioned view of a package with a leakage detector electrodes according to embodiment I of the present invention.

Figure 6 shows part sectioned view of a package with leakage detector electrodes according to embodiment 2 of the present invention.

Figure 7 shows part sectioned view of a package with leakage detector electrodes according to embodiment 3 and 4 of the present invention.

Figure 8 shows part sectioned view of a package wfth leakage detector electrodes according to embodiment 5 of the present invention.

Figure 9 shows part sectioned view of a package with leakage detector electrodes according to embodiment B of the present invention.

Figure 10 shows part sectioned view of a package with leakage detector electrodes in pseudo parael plate configuration according to embodiment 7 of the present invention.

Figure 11 shows part sectioned view of a package with leakage detector electrodes in a small stacked gap configuration according to embodiment 8 and 9 of the present invention.

Figure 12 shows part sectioned view of a package with leakage detector without electrodes according to embodiment 10 of the present invention.

is Figure 13 shows part sectioned view of a package with leakage detector arrangement with one rotating electrode and one fixed electrode according to embodiment 11 of the present invention.

Figure 14 shows part sectioned view of a package with leakage detector arrangement with both electrodes rotating according to embodiment 12 of the present invention.

When a gas is passed between two electrodes which have a voltage apped across them, as shown in Figure IA, and the voltage is higher than the gas's electrical breakdown voltage the gas ionizes and becomes a low impedance path which generally leads to a rapid rise in current between the electrodes as shown in Figure lB. This rapid rise in current is very fast and is easily and rapidly detected by electronic circuits. The values shown on the current scale of Figure 16 are only illustrative and the exact values depend on the details of the discharge configuration. A d.c. electrical discharge operates at the crossing point of the voltage -current characteristic and the load-line, which is determined by the external circuit. As a result of the linear-tog scales of the graph, the load-line appears as a curved tine.

Friedilch Paschen worked on the elechical breakdown voltages of various gases.

His work shows that different gases have different electrical breakdown voltages and that these electrical breakdown voltages also vary depending on gas pressure. Figures 2 10 4 are Paschen curves showing the electrical breakdown voltage (Vbr) as a function of pressure for a given space between the electrodes (pd) for different gases. For example, Torr cm is the pressure in Torr for an electrode gap of 1 cm. Figures 3 and 4, in particular show that the electrical breakdown voltages of the noble gases are generally much lower than the electrical breakdown voltages of air and the main constltuents of gases of air.

In the food production environment it is important that the detection process is carried out quickly. The present invention aims to carry out detection in less than one second to fit in with manufacturing process speeds.

Any escaping signature gas is detected by a suitable detector technology which may be of one of the following commercially available electrical circuitry: a thermal conductivity detector or using a Galvanic technique; a system based on corona discharge detection; a system based on plasma discharge detection; a.

system based on dielectric impedance detection; a system based on change of resistance or impedance detection.

Referring to Figure 5 there is shown a first embodiment of a leakage detector arrangement according to the present invention.

1 -Tray type sealed package to be tested 2 Ram to squeeze the sealed package 3 -Detector head arrangement -An insulator with strip electrodes which are wired in pairs to a high voltage supply, one being at earth or Ov potential and the other being at the high voltage potential. The electrodes can be electroplated or sputtered onto the inside surface of a moulded or thermo-formed insulator and then chemically etched to form the electrode array. Preferably the insulator is rigid, preferably the insulator has a high melting point, preferably the insulator is ceramic or glass.

-

4 Electrode -Conductive, preferably metal, preferably the metal is resistant to electrical arcing; preferably the metal is Tungsten or a Tungsten aUoy or some other suitable metal.

5-Electrical contact connected to earth and/or the common of the power supply.

6-Electrical contact connected to the high voltage supply.

The signature gas is introduced into the package at the package sealing stage, preferably the signature gas is a non-reactive gas, preferably the signature gas is lighter than air, preferably the signature gas has a lower electrical breakdown voltage than air, preferably the signature gas is Helium or Neon.

Because the signature gas is lighter than air the signature gas naturally migrates to the top of the tray type package it surrounds the seat so in the vicinity of the seal there is a high concentration of the signature gas.

The package is elevated into the detector head 3 by the ram 2. The detector head 3 is rigidly [ixed and being of rigid construction it presents a substantiafly solid Is structure for the package I to be pressed against. The ram 2 squeezes the package to a pre-set pressure against the detector head to stress the seal; just before the seal becomes pressure stressed the power is switched on and a high voltage potential is applied via contacts S & 6 between the electrode pairs 4. If the seal is imperfect the signature gas leaks out as the seal as it is being stressed, and into the detector head and hence the electrodes. The electrode pairs 4 are positioned such that the high voltage between the electrode pairs 4 is not high enough to strike an arc between the electrodes 4 in aft, but because Helium or Neon have an electrical breakdown voltage significantly lower than air when they leak into the gap between the electrodes they break down and cause substantially a short circuit.

The short circuit produces an arc between the electrodes 4 causing a current pulse as the power supply discharges through the short circuit and this currant pulse is detected electronically to alert that the package is defective. The defective package once alerted can be segregated mechanically from the production process for further rework.

-:11-Referring to Figure 6 there is shown a second embodiment of a leakage detector arrangement according to the present invention.

Figure 8 shows the same configuration as figure 5 except that the electrodes are coated with an insulating material 7 converting them to insulated coplanar electrodes. The electrodes are attached to an alternating high voltage. The peak voltage of the alternating high voltage is not high enough to strike a plasma between the electrodes 4 in air, hut because the signature gas (Helium or Neon) has a breakdown voltage significantly lower than air when it leaks into the gap between the electrodes it break down and substantially create a low impedance path between the electrodes. Theretore when the signature gas leaks into the electrode pairs 4 cold plasma is struck between the electrodes resulting in a current drain from the power supply. This current drain is detected electronically to alert that the package is defective.

As there is no arc and hence no metallic erosion in this process the electrodes can be any convenient metal and because the plasma is so short lived there is no appreciable heating of the electrodes.

Referring to Figure 7 there is shown a third embodiment of a leakage detector arrangement according to the present invention.

1 -High voltage electrode -comprising a perforated plate or wire mesh formed into the "top hat? section, sized to cover the package to be tested. Preferably the metal is resistant to electrical arcing; preferably the metal is Tungsten or a Tungsten alloy or some other suitable arc resistant metal. Preferably the open area of the high voltage electrode I is made as large as practicable without compromising rigidity.

2 -Common or earthed electrode -comprising a perforated plate or wire mesh formed into the "top hat' section, sized to fit inside the high voltage electrode I and to cover the package to be tested. , preferably the metal is resistant to electrical arcing; preferably the metal is Tungsten or a Tungsten alloy or some other suitable arc resistant metaL. Preferably the open area is made as large as practicable without compromising rigidity.

3 -Support plate -comprising a perforated plate made from an insulating material which provides backing support to the electrode arrangement. Preferably -12 -the materia' is substantially rigid. Preferably the material is plastic. Preferably the material is one of the thermo-set piastics or cloth re-enforced thermo-set plastics.

4 -Support spacer -to maintain a constant spacing between the electrodes a number of support spacers are placed between the two electrodes which also provide additional support when the package is pushed against the electrodes.

The support spacer is an insulator.

Electrode fixing plate An insulating plate to fix the electrodes into place.

6 -Body To provide the main structural support for the electrodes I & 2 and the top 9. The body must be an insulator. Preferably the material is plastic, preferably the material is food grade, preferably the material is substantially rigid, preferably the material is PETG copolyester.

7 -High voltage supply -Electrical contact connected to the high voltage supply.

8 -Electrical contact connected to earth an War the common of the power supply.

9.. Top -to provide the cavity 20 and support the piston 21 material food grade metal. Preferably the metal is stainless steel.

-Piston cylinder material stainless steel.

11 Piston body material stainless steel.

12 --Piston OB rings.

13 -Piston shaft-Material stainless steel.

14-Shaft Bush-Preferably an oil impregnated scintered bearing.

Piston cap screw on and made from Brass.

16 -Top seal -together with bottom seal 17 makes the cavity 20 air tight.

Preferably the material is Silicon Rubber or fluoroelastomer material.

17 -Bottom seal -Preferably the material is Silicon Rubber or fluoroelastomer material.

18-Holes--Perforations-holes or slots.

19 -Suction inlet After each test the suction inlet which is connected to a suction source is switched on to purge the cavity 20 of any signature gas.

-Cavity 21 Top sealed package to be tested.

S 22-Ram The signature gas is introduced into the package at the package seaHng stage, preferably the signature gas is a non-reactive gas, preferably the signature gas is lighter than air, preferably the signature gas has a lower breakdown voltage than air, preferably the signature gas is Helium or Neon.

Because the signature gas is tighter than air the signature gas naturafly migrates to the top of the tray type package it surrounds the seal so in the vicinity of the seal there is a high concentration of the signature gas.

The package 21 is elevated into the electrode array I & 2 by the ram 22. The electrode array 1 & 2 is rigidly supported by the support plate 3 and being of rigid construction the combination presents a substantially sohd structure for the package 21 to be pressed against. The ram 22 squeezes the package to a pre set pressure against the electrode array 1 & 2 to stress the seal; just before the seal becomes pressure stressed the power is switched on and a high voltage potential is applied via contacts 7& 6 and hence between the electrode pairs 1 & 2. At the same time the piston 11 is moved a set distance to substantially displace a volume of air which is equivalent to the volume of air occupied in the holes 18 in the support plate 3. This encourages any signature gas to enter the electrode array 1 & 2if the seal is imperfect the signature gas leaks out as the seal is being stressed into the electrode array. The electrodes in the electrode array 1 & 2 are positioned such that the high voltage between the electrodes is not high enough to strike an arc between the electrodes 1 & 2 in air, but because Helium or Neon have an electrical breakdown voltage significantly lower than air when they leak into the gap between the electrodes they break down and cause substantially a short circuit, The short circuit produces an arc between the electrodes 1 & 2 causing a current pulse as the power supply discharges through the short circuit and this currant -14-pulse is detected electronicaUy to alert that the package is defective. The defective package once alerted can be segregated mechanicafly from the production process for further rework.

At the end of each test the suction inlet is switched on and fresh air is drawn in from the ambient air surrounding the electrode array to remove or purge any signature gas from the cavity 20 and the electrode array I & 2.

The process described in this embodiment is unaffected neither by metal or metal coated packaging materials or is it affected by moisture or debris in the top of the package.

A fourth embodiment is discussed with reference to Figure 7.

The third embodiment can be made to operate as a cold plasma detection system by providing an insulation fayer between the electrodes 1 & 2 (Figure 7). In the case of the electrodes being electroplated or sputtered they can be coated with an insulating layer on one or both electrodes in sheet form or by being radio frequency sputtered to form an insulation I Urn.

The electrodes I & 2 are attached to an alternating high voltage. The peak voltage of the alternating high voltage is not high enough to strike a cold plasma between the electrodes I & 2 in air! but because the signature gas (Helium or Neon) have electrical breakdown voltages significantly lower than air when they leak into the gap between the electrodes they break down and substantially create a low impedance path between the electrodes.

Therefore when the signature gas leaks into the electrode pairs 1, 2 cold plasma is struck between the electrodes resulting in a current drain from the power supply. This current drain is detected electronically to alert that the package is defective.

As there is no arc and hence no metallic erosion in this process the electrodes can be any convenient metal and because the plasma is short lived there is no appreciable heating of the electrodes.

The process described in this embodiment is unaffected by metal or metalised packaging materials or is it affected by moisture or debris in the top of the package. -15-

Referring to Figure 8 there is shown a fifth embodiment of a leakage detector arrangement according to the present invention.

I -High Voltage electrode comprising an insulating plate 5 formed into a "top hat" section, sized to cover the package 15 to be tested. The insulating plate 5 is S coated with a metafit layer on both sides to provide electrodes 1 & 2. Preferably the metal is resistant to electrical arcing; preferably the metal is Tungsten or a Tungsten aUoy or some other suitable arc resistant metal. The plate complete with electrodes is perforated such that there is free passage for gas to pass between the electrodes through the holes or slots IS and out the other side.

Preferably the open area in the electrode array is made as large as practicable without compromising rigidity.

2 Common or earthed electrode -The bottom electrode on I 3 Top seal -Preferably the material is Silicon Rubber or fluoroelastomer material 4 -Bottom seal -together with "O rings 17 makes the cavity 20 air tight.

Preferably the material is Silicon Rubber or fluoroelastomer material -Insulating plate comprising a perforated plate made from an insulating material which provides support to the electrodes I & 2. Preferably the material is substantially rigid. Preferably the material is plastic. Preferably the material is one of the therrno-set plastics or cloth re-enforced thermo-set plastics. Preferably the material is glass or ceramic.

6-Body -To provide the main structural support for the electrodes 1 & 2 and the top 9 -must be an insulator. Preferably the material is plastic, preferably the material is food grade, preferably the material is substantially rigid, preferably the material is PEIG copolyester.

7 -High voltage supply Electrical contact connected to the high voltage supply.

8 ---Electrical contact connected to earth and/or the common of the power supply.

9-Top to provide the cavity 19 and support the piston assembly -material food grade metal. Preferably the metal is stainless steel.

10 -Piston body-material stainless steel. -16-

11 -Piston shaft -Material stainless steeL 12-Shaft Bush Preferably an oil impregnated scintered bearing.

13 Electrode base plate -Insulator fixed to the Body 6 to position and supports the electrode assembly.

14-Bush tube -stainless steel tube to support the piston assembly.

15-Tray type sealed package to be tested.

16 -Ram to squeeze the sealed package.

17 -"0" rings -Providing a gas tight seal with the waH of the body 6 and the cavity 19.

18-Slots or holes -Pierced through the electrodes I & 2 and the insulating plate 19 Cavity the cavity above the electrode assembly.

-Cavity -the cavity above the piston, 21 Suction inlet connected to a suction source.

The signature gas is introduced into the package 15 at the package sealing stage, preferably the signature gas is a none reactive gas, preferably the signature gas is lighter than air, preferably the signature gas has a lower electrical breakdown voltage than air, preferably the signature gas is Helium or Neon.

Because the signature gas is lighter than air the signature gas naturally migrates to the top of the tray type package it surrounds the seal so in the vicinity of the seal there is a high concentration of the signature gas.

The package 15 is elevated into the electrode assembly I & 2 by the ram 16. The electrode assembly 1 & 2 being of rigid construction and presents a substantiafly solid structure for the package 15 to be pressed against. The ram 16 squeezes the package to a pre"set pressure against the electrode assembly I & 2 to stress the seal; just before the seal becomes pressure stressed the power is switched on and a high voltage potential is applied via contacts 7& 8 and hence between the electrodes I & 2. At the same time the piston body 10 is moved a set distance to substantially displace a volume of air which is equivalent to the volume of air occupied in the holes 18 in the electrode assembly. This encourages any signature gas expelled under pressure to enter the electrode assembly I & 2. If S the seal is imperfect the signature gas leaks out as the seal is being stressed and into the electrode assembly. The thickness of the insulating plate 5 in the electrode assembly I & 2 are chosen such that the high voltage between the electrodes is not high enough to strike an arc between the electrodes I & 2 in air, but because Helium or Neon have an electrical breakdown voltage significantly lower than air when they leak into the gap between the electrodes they break down and cause substantially a short circuit.

The short circuit produces an arc between the electrodes 1 & 2 causing a current pulse as the power supply discharges through the short circuit and this currant pulse is detected electronically to alert that the package is defective. The defective package once alerted can be segregated mechanically from the production process for further rework.

At the end of each test the suction inlet 21 is switched on and fresh air is drawn in from the ambient air surrounding the electrode array to remove or purge any signature gas from the cavity 19 and the electrode array 1 & 2.

In this embodiment if the bottom electrode 2 is earthed the system becomes substantially shock proof and hence very operator friendly.

The process described in this embodiment is unaffected by metal or metalised packaging materials nor is it affected by moisture or debris in the top of the package.

Referring to Figure 9 there is shown a sixth embodiment of a leakage detector arrangement according to the present invention.

The fifth embodiment can be made to operate as a cold plasma detection system by providing an insulation layer to cover and completely encapsulate the electrodes 1 & 2 (Figure 9). In the case of the electrodes being electroplated or sputtered they can be coated with an insulating layer on one or both electrodes by spray coating, electrophoresis, powder coating etc., or by being radio frequency sputtered to provide an insulation layer. -18-

The electrodes I & 2 are attached to an alternating high voltage via connections 7 & 8. The peak voltage of the alternating high voltage is not high enough to strike a cold plasma between the electrodes I & 2 in air, but because the signature gas (Helium or Neon) have electrical breakdown voltages significantly lower than air when they leak into the gap between the electrodes they break down and substantially create a low impedance path between the electrodes.

Therefore when the signature gas leaks into the electrodes 1 & 2 cold plasma is struck between the electrodes resulting in a current drain from the power supply.

This current drain is detected electronically to alert that the package is defective.

As there is no arc and hence no metaflic erosion in this process the electrodes can be any convenient metal and because the plasma is short lived there is no appreciable heating of the electrodes.

In this embodiment if the bottom electrode 2 is earthS the system becomes substantially shock proof and hence very operator friendly.

Referring to Figure 10 there is shown a seventh embodiment of a leakage detector arrangement according to the present invention.

The process works on other packaging configurations such as "pillowcase packaging" and straight forward plastic bags, which are made using a "form, fill and seal" machine.

Figure 10 shows the process to test this type of packaging.

1 Top electrode assembly High Voltage electrode 5 & earthed or common electrode 6 comprising an insulating plate 8 formed into a "top hat" section, sized to cover the package 3 to be tested. The insulating plate 8 is coated with a metallic layer on both sides to provide electrodes 5 & 6, Preferably the metal is resistant to electrical arcing; preferably the metal is Tungsten or a Tungsten alloy or some other suitable arc resistant metal. The plate complete with electrodes is perforated such that there is free passage for gas to pass between the electrodes -19 -.

through the holes or slots 18 and out the other side. Preferably the open area is made as large as practicable without compromising rigidity.

2 Bottom electrode assembly -High Voltage electrode 6 & earthed or common electrode 5 --comprising an insulating plate 5 formed into a lop hat" section, S sized to cover the body of the package 3 to be tested but not its sealed ends.

The insulating plate 5 is coated with a metallic layer on both sides to provide electrodes I & 2. Preferably the metal is resistant to elecifical arcing; preferably the metal is Tungsten or a Tungsten alloy or some other suitable arc resistant metal, The plate complete with electrodes is perforated such that there is free passage for gas to pass between the electrodes through the holes or slots 18 and out the other side. Preferably the open area is made as large as practicable without compromising rigidity.

3 Pillow package or plastic bag to be tested.

4 End seals.

5 -High voltage electrode on electrode assembly I and earthed or common electrode on electrode assembly 2.

6 Earthed or common electrode on electrode assembly I and High voltage electrode on electrode assembly 2.

7 Holes or perforations through both sides of the electrode assemblies; electrode insulating plate -electrode.

B -Insulating plate.

The signature gas is introduced into the package 3 at the package sealing stage.

Preferably the signature gas is a non-reactive gas. Preferably the signature gas is close to the density of air, Preferably the signature gas has a lower electrical breakdown voltage than air. Preferably the signature gas is Argon or any other suitable gas mixture comprising one or more noble gases formulated to be a similar density to air and which, due to its similar density to air, will substantially distribute itself equally around the inside of the package 3.

The package 3 is elevated into the electrode assembly 1 by the electrode assembly 2. The electrode assembly 1& 2 are of rigid construction and presents a substantiafly solid structure for the package 3 to be pressed against. The electrode assembly 2 squeezes the package to a pre-set pressure against the electrode assembly I & 2 to stress the seals at both ends of the package and in the case of the pillow pack its centre seam; just before the seal becomes S pressure stressed the power is switched on and a high voltage potential is applied via contacts 9 (earth or common) & 10 (high voltage) and hence between the electrodes 5 & 6. If any of the seals are imperfect or there is a pinhole in the packaging material the signature gas leaks out as the seal is being stressed and into one of the electrode assemblies. The thickness of the insulating plate 8 in the electrode assembly I & 2 is chosen such that the high voltage between the electrodes is not high enough to strike an arc between the electrodes 1 & 2 in air, but because an argon/air mixture has an electrical breakdown voltage significantly lower than air on its own when it leaks into the gap between the electrodes it break down and causes substantially a short circuit.

is The short circuit produces an arc between the electrodes 5 & 6 causing a current pulse as the power supply discharges through the short circuit and this currant pulse is detected electronically to alert that the package is defective. The defective package once alerted can be segregated mechanically from the production process for further rework.

The process described in this embodiment is unaffected by metal or metalised packaging materials and because the electrode assembly is fully encapsulated it is very safe for process operators.

This system is unaffected by moisture or debris in the surface of the package This process can be converted to a cold plasma detection technology as described in the fifth embodiment, Referring to Figure 11 there is shown an eighth embodiment of a leakage detector arrangement according to the present invention.

1 -Electrode -Conductive, connected to the high voltage potential, preferably metal, preferably the metal is resistant to electrical arcing; preferably the metal is Tungsten or a Tungsten alloy or some other suitable metal. Formed into a rod with a small hole through the centre.

2 -Electrode -Conductive, connected to earth and/or the common of the power supply. Preferably metal, preferably the metal is resistant to electrical arcing; preferably the metal is Tungsten or a Tungsten aHoy or some other suitable metaL Formed into a rod with a small hole through the centre.

S 3 Insulator.-formed into a rod with a small hole through the centre. Preferably the material is a rigid insulating material, preferably the material is plastic, ceramic or glass.

4 -. Support insulator -formed into a rod with a small hole through the centre and made with a screw thread 16 on one end. Preferably the material is a rigid insulating material, preferably the material is plastic, ceramic or glass.

-High voltage electric contact connected to the high potential of the power supply.

6-Electrical contact connected to earth and/or the common of the power supply.

7 -Sam pflng hole -small hole drled through the wall of the top plate 8 providing is a conduit from the sampling cavity 17 to the sampling electrode assembly 18 via support insulator 4. Preferably the hole is conical in nature so it becomes substantially self-cleaning every time the clamp plate 10 returns to the production conveyor.

8 -Top plate -Clamped rigidly in position to provide a robust structure for the package 12 to be pushed against by the ram 13 9 -"0" ring provides a seal against the vertical wall of the clamp plate 10 together with the resilient seal 11 to make the sampling cavity 17 gas tight.

Clamp plate provides the means to lift the package 12 up to the top plates and provide the gas tight seal.

11 -Resilient seal -forms a seal around the package 12 rim or upper wall when the clamp plate 10 is in position. Preferably the material is resilient in nature.

preferably the material is plastic, preferably the material hardness is less than 40 Shore, preferably the material is of the closed cell foam type, preferably the material is foamed fluoroelastomer material or Silicone rubber.

12 -Package-The sealed package to be tested.

-22 - 13 -Ram to provide the mechanical compression to put the package seal under stress.

14 -Electrode outer tube -made from an insulating material, preferably the material is substantiafly rigid, preferably the material is plastic or ceramic or glass.

15-Bottom surface of the top plate 8 and the top surface of the clamp plate 10 are roughened to provide a path for the signature gas to enter the sampling cavity 17. The ideal process for this is to first sand blast the surfaces and then to electrolytically de-plate (Electropole) the sand blast area which rounds the peaks on the surfaces, In this way when the package is compressed by the ram against the surface of the top plate there is no damage to the surface of the package.

16-Screw thread on the support insulator 4.

17-Sampling cavity.

18-Electrode assembly.

The signature gas is introduced into the package 12 at the package seaftng stage, preferably the signature gas is a non-reactive gas, preferably the signature gas is Hghter than air, preferably the signature gas has a lower electrical breakdown voltage than air, preferably the signature gas is Helium or Neon.

The package 12 is elevated into the top plate B by the clamp plate 10. The top plate being of rigid construction presents a substantially solid structure for the package 12 to be pressed against. The clamp plate continues its upward motion until stopped by the bottom face of the top plate, In this position the NO" rings 9 have sealed against the vertical wall of the top plate and the resilient seal forms a seal around the rim or upper wall of the package 12 hence making the sampling cavity 17 gas tight. The rani 13 squeezes the package to a pre-set pressure against the top plate 8 to stress the seal; just before the seal becomes pressure stressed the power is switched on and a high voltage potential is applied via contacts 5 & 6 and hence between the electrodes I & 2. If the seal is imperfect the signature gas leaks out as the seal is being stressed into the space between -23 - (he top plate 8 and the surface of the package and using the roughened surface of the top plate as a conduit moves to the sampng cavity 17. As the ram holds its pressure any leaking gas is forced into the sampling hole 7 and rite the electrode array I & 2. The Gap between the electrodes is chosen such that the high voltage S between the electrodes is not high enough to strike an arc between the electrodes I & 2 in air, but because the signature gas (Heum or Neon) have electrical breakdown voltages significantly lower than aft and when they leak into the gap between the electrodes they break down causing substantiafly a short circuit.

The short circuit produces an arc between the electrodes 1 & 2 causing a current pulse as the power supply discharges through the short circuit and this currant pulse is detected electronicafly to alert that the package is defective. The defective package once alerted can be segregated mechanically from the production process for further rework.

The action of the clamp plate returning the package to the production line conveyor i.e. a fast downward motion automaticay purges the top plate and electrode assembly of any residual signature gas. If any additional purging is required a suction inlet can be fitted as described in previous embodiments.

Whilst only one electrode assembly is shown for clarity in practice there would be a plurality of electrode assemblies 18 around the wall of the top plate 8 or indeed across the entire surface of the top plate 8, Referring to Figure 11 there is shown a ninth embodiment of a leakage detector arrangement according to the present invention.

The eighth embodiment can be made to operate as a cold plasma detection system by providing an insulation to cover and completely encapsulate the electrodes I & 2 in Figure II. The electrodes being coated with an insulating layer on one or both electrodes by spray coating, electrophoresis, powder coaUng etc., or by being radio frequency sputtered to provide an insulating layer.

The electrodes 1 & 2 are attached to an alternating high voltage via connections & 6. The peak voltage of the alternating high voltage is not high enough to strike a cold plasma between the electrodes 1 & 2 in air, but because the signature gas (Helium or Neon) have electhcal breakdown voltages significantly S lower than air when they leak into the gap between the electrodes they break down and substantially create a low impedance path between the electrodes.

Referring to Figure 12 there is shown a tenth embodiment of a leakage detector arrangement according to the present invention.

Is This shows the same configuration as embodiment S except that it works without electrodes to detect the signature gas. Instead of an electrode assembly an inlet 2 and an outlet I are fitted through the vertical wall of the top plate 8 and connected to a gas detector 5 via tubes 3 & 4. The gas detector continually samples via its inlet port 6 and outlet port 7 by drawing air from sampling cavity 17 through the gas detector 5 where it is monitored for traces of the signature gas then out and back into the sampling cavity 17 via outlet 1.

The gas detector which will be a commercially available type is set to detect the signature gas above a pre-set minimum level. If a defective package leaks signature gas into the sampling cavity 17 it is detected by the gas detector 5 and compared with the preset minimum value. If the signature gas is more than the minimum value it signals that the package is defective.

The defective package once alerted can be segregated mechanically from the production process for further rework.

Referring to Figure 13 there is shown an eleventh embodiment of a leakage detector arrangement according to the present invention.

1 Sealed package to be tested -25 - 2-Drive roVer 3 Tensioning rofler 4 High voltage electrode -comprising an insulating plate 5 formed into an inverted U" shape section covering the belt 8 and overlapping its sides. The S electrode 4 is sized to cover the package 15 to be tested. The insulating plate 5 is coated with a metaflic layer on its top side to provide the high voltage electrode.

The high voltage electrode is connected to the high voltage via connectionl3, Preferably the metallic layer is resistant to electrical arcing; preferably the metal is Tungsten or a Tungsten alloy or some other suitable arc resistant metal. The plate complete with electrode is perforated such that there is free passage for gas to pass between the electrode through the holes or slots 6 and out the other side.

Preferably the open area is made as large as practicable without compromising rigidity.

Insulating plate -comprising a perforated plate made from an insulating IS material which provides support to the electrodes 4. Preferably the material is substantially rigid enough to act as a solid pressure plate for the perforated belt 8.

Preferably the insulator material is plastic. Preferably the material is one of the thermo-set plastics or cloth re-enforced thermo-set plastics.

6 -Holes in the insulator and electrode 7 -Holes in the perforated belt 8.

8 Perforated belt At least the inside surface of the belt is conductive.

Preferably the material is reasonably flexible, preferably the belt is hard wearing, preferably the belt is seamless, preferably the belt is made from metal, metalised plastic, metalised reinforced rubber or reinforced conductive plastic or rubber, preferably the belt is made from woven wire.

9-Top electrode assembly 10-Pressure wheel 11 -Divider -the divider produces a moving top hat section as it traverses through the "U" section top electrode assembly 9 therefore substantially containing the signature gas to aVow it to permeate into the top electrode assembly 9.

12 Earth or common connection -either of the roers 2 or 3 can be earthed or connected to common which Ml hold the conductive perforated belt 8 at earth or common potentiaL 13 High voltage connection Connects the top electrode with the high voltage supply The signature gas is introduced into the package 1 at the package sealing stage, preferably the signature gas is a nonreactive gas, preferably for this application the signature gas is Ughter than air, preferably the signature gas has a lower electdcal breakdown voltage than air, preferably the signature gas is Helium or Neon.

The sealed package I is synchronised and presented to the rotating perforated belt 8 by in4eed conveyor 15 such that it moves into the perforated belt S between divisions 11. It passes between the top electrode assembly 9 and the pressure wheel 10 which squeezes the package to a pre-set pressure against the perforated belt 8 and the top electrode assembly top 8 to stress the seal; just before the seal becomes pressure stressed the power is switched on and a high voltage potential is applied via contacts 12 & I 3and hence between the perforated belt S and the top electrode. If the seal is imperfect the signature gas leaks out as the seal is being stressed into the space between the perforated belt 8 and the surface of the package. As the pressure wheel 10 holds the internal pressure of the package 1 substantially constant any leaking gas is forced through the holes 7 in the perforated belt 8 and into the holes 6 in the top electrode assembly 9. The thickness of the insulating plate 5 and the thickness of the perforated belt 9 is chosen such that the high voltage between the top electrode 4 and the perforated belt 8 is not high enough to strike an arc between the electrode and belt in air, but because the signature gas (Helium or Neon) have electrical breakdown voltages significantly lower than air and when they -27 leak into the gap between the top electrode 4 and belt 8 they break down causing substantially a short circuit.

The short circuit produces an arc between the electrodes 1 & 2 causing a current pulse as the power supply discharges through the short circuit and this currant S pulse is detected electronicay to alert that the package is defective. The defective package once alerted can be segregated mechanicaDy from the production process for further rework.

The detection system for this embodiment can be converted to cold plasma detection by providing an insulation layer around one or both electrodes as explained in previous embodiments.

Referring to Figure 14 there is shown a twelfth embodiment of a leakage detector arrangement according to the present invention, 1 -Sealed package to be tested 2 -Drive rofler 3-Tensioning rofler 4 -High voltage electrode -comprising a conductive layer formed on one side oF a perforated belt 9. The high voltage electrode is connected to the high voltage via connectionl3 and high voltage roVer 15.

-Insulating layer -comprising the body of the perforated belt 9 which may be reinforced to improve strength and maintain dimensional stability 6-Holes in the perforated belt 9 7-Suction head.

B -Earth or common electrode -comprising a conductive layer formed on the other side of a perforated belt 9. The earth or common electrode is connected to the earth or the power supply common via connection 12 and earth or common roller 14. The earth or common electrode surface is roughened to provide micro-channels for escape of any signature gas leaking from a part of the sealed package I in abutment with the earth or common electrode surface.

9 Perforated belt -Both surfaces of the perforated belt are conductive and the body of the belt is an insulator. Preferably the body of the perforated belt material is reasonably flexible, preferably it is hard wearing, preferably it is seamless, preferably the body of the belt is made from rubber or plastic preferably the body S of the belt is made from reinforced plastic or rubber. Preferably the conductive surface is a material which is reasonably flexible, preferably the surface is hard wearing, preferably the surface is seamless, preferably the surface is made from metal, metafised plastic, metalised reinforced rubber or reinforced conductive plastic or rubber, conductive plastic or rubber, preferably the surface is made from woven wire.

10-Pressure wheel 11 -Suction inlet -provides suction to the suction head 7 in order to clear the environment in and around the holes 6 of the perforated belt 9, 12--Earth or common connection -Connects the earth or common rollerl4 and ir hence the earth or common electrode S to the earth or common of the power supply.

13 -High voltage connection Connects the high voltage roflerl5 and hence the high voltage electrode 4 to the high voltage of the power supply.

14-Earth or common rofler conductive preferably metal or conductive plastic or conductive rubber.

High voltage roller -conductive -preferably metal or conductive plastic or conductive rubber.

16 -Nip roller -The roller or roller assembly must be insulated and robust enough to provide a nip to the package I in conjunction with the pressure wheel 10. Two or more nip rollers 16 at spaced intervals along the perforated belt 9 may be employed to evenly spread pressure appfled to the package 1.

17-Package guide to support and guide the package as it is being pressurized by the nip roller 16 and the pressure wheel 10 The signature gas is introduced into the package 1 at the package sealing stage, preferably the signature gas is a non-reactive gas, preferably for this application the signature gas is fighter than air, preferably the signature gas has a lower electrical breakdown voltage than air, preferably the signature gas is Hefium or Neon.

Because the signature gas is lighter than air the signature gas naturally migrates to the top of the tray type package it surrounds the seal so in the vicinity of the sea! there is a high concentration of the signature gas.

The sealed package 1 is synchronised and presented to the rotating perforated belt 9 by in4eed conveyor 15 (not shown) and shute 17 such that it moves into the perforated belt 9. It passes between the perforated belt 9 and the pressure wheel 10 and the nip roller 16 which squeezes the package to a pre-set pressure against the perforated belt B and nip roller 16 to stress the seal; just before the seal becomes pressure stressed the power is switched on and a high voltage potential is appUed via contacts 14 & 15 and hence between the electrodes 4 & B. If the seal is imperfect the signature gas leaks out as the seal is being stressed into the space between the perforated belt 9 and the surface of the package. As the pressure wheel 10 holds the internal pressure of the package I substantially at constant pressure, any leaking gas is forced through the holes 6 in the perforated belt 9 and into the space between the electrodes (holes 6). The thickness of the perforated belt 9 is chosen such that the high voltage between the top electrode 4 and the perforated belt 8 is not high enough to strike an arc between the electrode and belt in air, but because the signature gas (Helium or Neon) have electrical breakdown voltages significantly lower than air and when they leak into the gap between the top electrode 4 and belt 8 they break down causing substantially a short circuit.

The short circuit produces an arc between the electrodes 4 & 5 causing a current pulse as the power supply discharges through the short circuit and this currant pulse is detected electronically to alert that the package is defective. The defective package once alerted can be segregated mechanically from the production process for further rework.

The detection system for this embodiment can be converted to cold plasma detection as explained in previous embodiments. -30

Claims

<claim-text>Claims 1. An apparatus for detecting leaks in sealed packages containing a detectable signature gas, the apparatus comprising: a package contact surface; s an arrangement for subjecting sealed packages on a production line sequentiafly to compression between the contact surface and the arrangement to promote signature gas leakage; and a gas detector comprising circuitry coupled to electrodes located about expected leakage points of a sealed package, wherein the circuitry applies a voltage across the electrodes to detect a change in electrical characteristics indicative of &gnature gas leakage from the sealed package.</claim-text> <claim-text>2. An apparatus as claimed in claim 1, wherein the apparatus comprises multiple electrodes.</claim-text> <claim-text>3. An apparatus as claimed in either one of claims 1 or 2, wherein the gas detector comprises a multiplicity of ducts in conimunication with expected leakage points of a sealed package and wherein the electrodes are arranged in communication with respective ducts.</claim-text> <claim-text>4. An apparatus as claimed in claim 3, wherein the electrodes are located at opposite ends of aD or some of the ducts.</claim-text> <claim-text>$ An apparatus for detecting leaks in sealed packages containing a detectable signature gas, the apparatus comprising: a package contact surface; an arrangement for subjecting sealed packages from a production line sequentially to compression between the contact surface and the arrangement to promote signature gas leakage; a multiplicity of ducts in communication with expected leakage points of a sealed package; and a gas detector comprising multiple probes arranged in communication with respective ducts to detect a change in local gas characteristics indicative of signature gas leakage tram the sealed package.</claim-text> <claim-text>6. An apparatus as claimed in claim 5, wherein the probes are located at S opposite ends of all or some of the ducts.</claim-text> <claim-text>7. An apparatus as claimed in any one of claims 3 to 6, wherein the multipflcity of ducts comprises at least five ducts.</claim-text> <claim-text>8. An apparatus as claimed in any one of claims 3 to 6, wherein the multiplicity of ducts comprises at least ten ducts.</claim-text> <claim-text>9. An apparatus as claimed in any one of claims 3 to 6, wherein the multiplicity of ducts comprises a mesh of ducts.</claim-text> <claim-text>10. An apparatus as claimed in either one of claims 5 or 6 or any one of claims 7 to 9 when appended to either one of claims 5 or 6, wherein the probes are electrodes and the gas detector comprises circuitry coupled to the electrodes, wherein the circuitry applies a voltage across the electrodes to detect a change in electrical characteristics indicative of signature gas leakage from the sealed package.</claim-text> <claim-text>11. An apparatus as claimed in any one of claims 1 to 4 or 10, wherein the package contact surface is an insulator which provides support for some or all of the electrodes.</claim-text> <claim-text>12. An apparatus as claimed in claim Ii, wherein the package contact surface is linearly translatable to follow sealed packages on a production line sequentially.</claim-text> <claim-text>13. An apparatus as claimed in either one of claims 11 or 12, wherein the sealed package subjected to compression is substantially surrounded by electrodes.</claim-text> <claim-text>14. An apparatus as claimed in any one of claims ito 4 and 10 to 13, wherein the circuitry applies a series of increasing voltages across the electrodes to detect the change in electrical characteristics indicative of a signature gas leakage from the sealed package. 32 -</claim-text> <claim-text>15. An apparatus as claimed in claim 14, wherein the series of increasing voltages across the electrodes is a sweeping voltage increase.</claim-text> <claim-text>16. An apparatus as claimed in claimed in claim 15, wherein the circuitry memorises rate of change of resistance and / or impedance across the electrodes S detected during each sweeping voltage increase.</claim-text> <claim-text>17. An apparatus as claimed in any one of claims ito 4 and 10 to 18, wherein the circuitry applies an alternating voltage across the electrodes to detect the change in electrical characteristics indicative of a signature gas leakage from the sealed package.</claim-text> <claim-text>18, An apparatus as claimed in any one of claims ito 4 and 10 to 17, wherein voltages applied by the circuitry across the electrodes lie within a range of OV to 3000V per millimetre of gap between the electrodes, 19. An apparatus as claimed in claim 18, wherein the electrodes are sufficiently spaced apart to provoke electrical breakdown when the circuitry applies peak voltage in the presence of the signature gas and not when the circuitry applies peak voltage in the presence of atmospheric air.20. An apparatus as claimed in any one of claims ito 4 and 10 to 19, wherein some or all of the electrodes is or are clad with insulating material.21. An apparatus as claimed in any one of claims ito 4 and 10 to 20, wherein the electrodes are arranged to be shock-proof.22. An apparatus as claimed in any one of the previous claims, wherein the apparatus is ventilated with fresh atmospheric air after each sequential sealed package is subjected to compression.23. An apparatus as claimed in any one of the previous claims, wherein the package contact surface is roughened.24. A method of detecting leaks in sealed packages containing a detectable signature gas using the apparatus as claimed in any one of the previous claims, wherein the method comprises the steps of: a) presenting the sealed package to the package contact surface; 33 -b) compressing the package and detecting for signature gas with the gas detector; c) releasing the sealed package to the production fine if no signature gas detected or isolating the sealed package from the production fine if signature gas S detected; and d) preparing to return to step (a) for the next sequential sealed package on the production line, 25. A sealed package containing a perishable product and a gas modified with respect to atmospheric air to include a signature gas with an electrical breakdown voltage lower than atmospheric air.26. A sealed package as claimed in claim 25, whereki the percentage of signature gas in the modified gas is no less than 0Th percent.27. A sealed package as claimed in either one of claims 25 or 26, wherein the percentage of signature gas in the modified gas is no more than ten percent.28. A sealed package as claimed in any one of claims 25 to 27, wherein the signature gas is a noble gas or a mixture of noble gases.29. A sealed package as claimed in any one of claims 25 to 28, wherein the signature gas is a mixture of noble gases having a density comparable to atmospheric air.30. An apparatus for detecting leaks in sealed packages containing a detectable signature gas substantiafly as hereinbefore described with reference to Figures 5, 6, 7, 8, 9, 10, 11, 12, 13 or 14 of the drawings.-34 -</claim-text>