DK201570808A1

DK201570808A1 - Leak detector

Info

Publication number: DK201570808A1
Application number: DKPA201570808A
Authority: DK
Inventors: Henrik Krøyer Haastrup; Sandra Lindell; Rune Bech Abrahamsen
Original assignee: Dansensor As
Priority date: 2015-12-07
Filing date: 2015-12-07
Publication date: 2017-06-26
Also published as: DK178977B1

Abstract

There is provided a leak detector for testing the leak tightness of sealed packages containing a tracer gas, comprising a test chamber for receiving a sealed pack containing a tracer gas, a vacuum device in fluid communication with the test chamber for providing a vacuum therein, and a gas sensor for detecting the presence of a tracer gas in the test chamber.

Description

LEAK DETECTOR

FI ELD OF THE I NVENTI ON

The present invention relates to a leak detector for testing the leak tightness of sealed packages containing a tracer gas, comprising a test chamber for receiving a sealed pack containing a tracer gas, a vacuum device in fluid communication with the test chamber for providing a vacuum therein, and a gas sensor for detecting the presence of a tracer gas in the test chamber.

BACKGROUND OF THE I NVENTI ON A number of principles exist for detecting leaks in supposable gastight packages containing a tracer gas. One is the pressure decay principle where the test object is physically compressed to urge the tracer gas out through possible openings. The disadvantage of this method is that it may be destructive for some types of goods and that it cannot be used for rigid packages. Another method encompass the arrangement of the test object inside a vacuum chamber which facilities the potential outflow of tracer gas from the test object. US Patent 5,373,729 discloses a leak-detection installation comprising a bellshaped cover for being lower onto a conveyor belt and a tracer gas leak detector being connected to the cover via a hose. Considerable drawbacks of this system are the time associated with performing a test and the accuracy of the tests. Removing an air sample for the cover for testing is time consuming, and the position of the opening through which tracer gas escapes from the test object influences the test results due to the fixed position of the intake to the tracer gas leak detector.

Hence, an improved leak detector would be advantageous, and in particular a more efficient and reliable leak detector would be advantageous.

OBJECT OF THE I NVENTI ON

An object of the present invention is to provide a cost effective leak detector for testing the leak tightness of test objects, such as sealed packages containing a tracer gas, in an accurate, efficient and non-destructive manner.

In particular, it may be seen as a further object of the present invention to provide a leak detector that solves the above mentioned problems of the prior art with regard to time and accuracy of the tests.

SUMMARY OF THE I NVENTI ON

Thus, the above described object and several other objects are intended to be obtained in a first aspect of the invention by providing a leak detector for testing the leak tightness of sealed packages containing a tracer gas, comprising a test chamber for receiving a sealed pack containing a tracer gas, a vacuum device in fluid communication with the test chamber and adapted for providing a vacuum therein, and a gas sensor for detecting the presence of a tracer gas in the test chamber, wherein the leak detector further comprises a ventilation device and flow pate provided inside the test chamber, the flow plate being arranged to directing an outflow of air from the ventilation device towards a periphery of the test chamber to provide circulation of the air inside the test chamber whereby an instant and uniform blending of any tracer gas escaping the sealed package inside the test chamber is achieved.

By the outflow of air from the ventilation device being directed towards the periphery of the chamber, a fast and uniform mixing of the air inside the test chamber is achieved. Hereby the leak tightness of a test object, such as sealed package, may be tested in an accurate and efficient manner. Also, the flow plate ensures that the outflow is directed all the way to the periphery of the test chamber before returning to an intake of the ventilation device. Further, the construction of the leak detector is considerable simplified compared to traditional leak detectors resulting in a smaller and more cost effective leak detector.

By the expression “leak tightness” is meant the ability of the seal package or test object to withhold a gas or fluid and prevent said fluid or gas from escaping from the sealed package or test object. I for example an outer barrier of the sealed package is punctured, the leak tightness may be very low or nonexisting.

In one aspect the ventilation device of the leak detector may be arranged in a centre of the test chamber, having a centrally located air intake and providing a radial outflow of air directed towards the periphery of the test chamber. By combining a centrally located intake and a radial outflow form the ventilation device, the uniform and fast mixing of the air inside the test chamber is ensured.

Furthermore, the test chamber may comprises a sample object area and a sensor area arranged on opposite sides of the flow plate, and the ventilation device may be adapted for simultaneously providing the necessary blending of any tracer gas escaping the sealed package inside the test chamber and for circulation of air between the sample object area and the sensor area.

Additionally, the ventilation device may comprise a rotatable fan having a plurality of fan blades arranged around the centrally located air intake and an axis of rotation of the ventilation device may be coincident with a centre axis of the test chamber. By having a rotatable fan arranged to rotate about the centre axis of the test chamber, a uniform flow of air inside the test chamber is achieved.

Also, the flow plate and an inner wall of the test chamber may define a circumferential passage arranged in the periphery of the test chamber. Further, the circumferential passage may have a substantially constant width, such as a width of 5-15 mm. By directing the outflow of air from the ventilation device through a circumferential passage of a constant relatively narrow width, the circulation and uniform blending of the air inside the test chamber is improved.

The Leak detector described above may further comprise a flow diverter for directing a sub-flow of the radial outflow from the ventilation device into the sensor area of the test chamber.

Furthermore, the flow diverter may be arranged at a distance from the rotatable fan and extending in a direction normal to at least a part of the radial outflow from the ventilation device. Further, the flow diverter may have a width of 40-70 mm. By having a flow diverter and controlling its width and distance from the rotatable fan, the flow of air into the sensor area can be controlled.

Additionally, the ventilation device may comprise a fan plate arranged between the rotatable fan and the sensor area and being adapted to guide the sub flow of air through the senor area. Hereby a sufficient flow of air past the sensor is ensure, before the sub flow is re-introduced into the test chamber.

Moreover, the gas sensor of the leak detector may be adapted for detecting the presence of C02, and the gas sensor may comprise an infrared light source arranged to irradiate the air in the sensor area, and a detector arranged to receive the reflected radiation from the infrared light source. By incorporating a gas sensor into the leak detector that analyses the air while in the test chamber, the time for conducting a leak test of a sealed package is considerable reduce. Especially, compared to detection devices wherein a test sample of air is removed from a main test chamber before being for analysed.

Further, an inlet to the vacuum device may be arranged in the sensor area of the test chamber. By arranging the inlet for the vacuum pump in the sensor area, a flow of air into the sensor area is effected immediately allowing faster detection of potential gas leaks from the sealed package.

Still further, the sensor area may be provided in a sensor chamber separate from the test chamber.

Also, the test chamber of the leak detector may be is symmetric about both a transversal plane extending in a transversal direction of the test chamber and coincident with the centre axis of the test chamber and about a longitudinal plane extending in a longitudinal direction of the test chamber and coincident with the centre axis of the test chamber. Furthermore, test chamber may be substantially rotational symmetric about its centre axis. By having a test chamber that is of great symmetry the uniform distribution, circulation and blending of air containing a possible tracer gas is improved.

Additionally, in one aspect the test chamber may be at least partially defined by a housing. Also, the housing may be a test bell having a lower opening allowing the test bell to be lower onto or arranged on top of the sealed packages to be tested. Further, the test bell may be adapted for cooperating with a planar surface, such as a conveyor belt, to define the test chamber and to ensure the gas tightness of the test chamber.

In a further aspect of the present invention there is provided a method for determining the gas tightness of the test chamber of the leak detector. This is done with a pressure gauge in the test chamber in order the measure the pressure during evacuation with the vacuum device (3). Moreover a thermopile is provided to give an output electrical potential in response to the temperature in the test chamber. The method is able to confirm if the chamber is gas tightness when both the pressure and potential is kept constant during the vacuum period. On the other hand if the chamber is not gas tight the pressure will increase in the vacuum period since the low pressure cannot be maintained. Also in that case the potential of the thermopile will decrease due to incoming C02 from the surrounding air.

BRI EF DESCRI PTI ON OF THE DRAWINGS

Figure 1 shows a schematic drawing of a leak detector according to one aspect of the invention,

Figure 2 shows a schematic drawing of another leak detector provided with a sensor area, and

Figure 3 shows a further leak detector wherein the ventilation device is arranged in a closing element for the sensor chamber.

DETAI LED DESCRI PTI ON OF THE I NVENTI ON

The leak detector according to the invention will now be described in more detail with regard to the accompanying drawings. The figures show one way of implementing the present invention and is not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

Fig. 1 shows a leak detector 1 according to one aspect of the invention, comprising a test chamber 2 in which a sealed package 11 or other kind or test object is shown for exemplary purposes. The test chamber is shown to be defined by a housing 95 in the form of a test bell cooperating with a substantially planar surface 96. However, as would be readily understood by the skilled person, the housing and the planar surface defining the test chamber may be constructed in a number of different ways without departing from the scope of the invention.

Inside the test chamber a ventilation device 5 and a flow plate 6 is provided. The ventilation device 5 is shown as a rotatable fan 56 having a plurality of fan blades 56 arranged around a centrally located air intake 51. When the ventilation device 5 is operated, air and possible tracer gas inside the test chamber is circulated as indicated by the arrows. This circulation results in the bending of the air and the tracer gas. The flow plate 6 is arranged to direct an outflow 91 of air from the ventilation device towards a periphery 21 of the test chamber adjacent an inner wall 24 of the test chamber. When the outflow 91 or air reaches the periphery of the test chamber, it is forced through a circumferential passage 25 defined between the flow plate and the inner wall 24 of the test chamber. As the outflow of air passes through the circumferential passage it is blended with the remaining air inside the test chamber and possible tracer gas before being reverted to the centrally located air intake 51.

The leak detector also comprises a vacuum device 3 for providing a vacuum inside the test chamber. In Fig. 1 the vacuum device is shown as a pump 31 fluidly communicating with the test chamber via a first valve 32 and an inlet 34. However, the vacuum device may be any type of device known to the skilled person, suitable for reducing the pressure inside the test chamber 2. A second valve 33 in fluid communication with the test chamber is provided to equalise the pressure inside the test chamber following a state of vacuum created by the vacuum device 3.

Still referring to Fig. 1, the leak detector further comprises a gas sensor 4 provided for detecting the presence of a tracer gas inside the test chamber. The gas sensor 4 may be adapted for detecting the presence or excess levels of carbon dioxide, nitrogen, hydrogen, helium, oxygen, argon or any other kind of gas used in modified atmosphere packing. The gas sensor 4 may be arranged either fully or partially inside the test chamber, or external to the test chamber with a probe or inlet provided in the test chamber for obtaining a sample of air for testing.

In one aspect the leak detector 1 may be provided with a mechanism (not shown) for lowering the test chamber 2 onto a test object 11 provided on the substantially planar surface 96. Such mechanism is readily known to the person skilled in the art, and may be constructed in a number of different ways. Further, the substantially planar surface 96 may be a conveyor belt or other means of transportation, provided as a part of a production line.

In use, the housing 95 may be lowered down onto the test object arranged on the planar surface 96. When the housing 95 engages with the planar surface 96 the test object is arranged in the gastight test chamber 2. Then a vacuum is provided in the test chamber by activating the vacuum device 3, thereby urging tracer gas out through possible openings in the test object 11. Either simultaneously with or following the activation of the vacuum device, the ventilation device is activated to circulate and blend the air and possible tracer gas inside the test chamber, as will be further described below. Simultaneously, the sensor detects the presence or excess levels of possible tracer gas escaping the test object.

Fig. 2 shows another leak detector 1 comprising a modified test chamber 2 and a vacuum device, a gas sensor and a ventilation device similar to the above described. The test chamber comprises a sample object area 22 wherein a test object 11 is to be arranged, and a sensor area 23 in which the flow of air is examined to determine the presence or possible excess levels of a tracer gas. The sample object area 22 and the sensor area 23 are arranged on opposite sides of the flow plate 6 thereby enabling the flow between the two to be controlled at least partially by controlling the ventilation device.

The leak detector shown in Fig. 2 further comprises a flow diverter 7, arranged to divert a sub-flow 92 of the radial outflow from the ventilation device into the sensor area, as indicated by the arrow 92. The sub-flow 92 is forced through the sensor area before being reintroduced into the radial outflow of the ventilation device and mixed with the remaining air inside the test chamber.

The flow diverter extends in a direction normal to the radial outflow and has a limited extension such that only a part of the outflow from the ventilation device is directed into the sensor area 23. By controlling a distance (d) between the fan 56 and the flow diverter 7 and a width of the flow diverter, the flow rate through the sensor area may be controlled. In a leak detector according to one aspect of the invention, the flow rate through the sensor area may be between 0,5 and 1,5 m/s. In another leak detector according to one aspect of the invention the flow rate may be approximately 1 m/s, resulting in the air in the sensor area being changed approximately 10 times per second.

Furthermore, a fan plate 8 is provided on a side of the rotatable fan 56 opposite the flow plate 6. The fan plate partially defines the sensor area 23 thereby ensuring the flow of air through the sensor area. Also, in the leak detector shown in Fig. 2, the inlet 34 to the vacuum device is arranged in the sensor area of the test chamber.

In a leak detector according to one aspect of the invention, the gas sensor is adapted for detecting the presence of C02 and comprises an infrared light source arranged to irradiate the air in the sensor area 23 and a detector arranged to receive the reflected radiation from the infrared light source.

The leak detector of Fig. 2 is operated in a manner similar to what has been described above in relation to the leak detector of Fig. 1.

Fig. 3 shows yet another leak detector 1 comprising a further variant of a test chamber 2 and a vacuum device, a gas sensor and a ventilation device similar to the above described. The leak detector is provided with a closing element 97 cooperating with the housing 95 to define the test chamber 2. The ventilation device 5 and the flow plate 6 are mounted on the closing element 97, and the sensor area 23 is provided in a cavity 98 in the closing element 97. Thus, following the placement of a test object 11 in the test chamber 2, the closing element 97 is arranged on top of the housing 95 to seal off the test chamber. The functionality and the further operation of the leak detector is similar to what has been described above in relation to the leak detectors of Fig. 1 and Fig. 2.

In the above different aspects of the inventions has been described with reference to the figures. As would be readily understood by the skilled person, individual features shown and described in relation to one figure, may be used in a leak detector shown in another figure. As an example, details about the sensor are primarily been disclosed in relation to the leak detector shown in Fig. 1. However, the same sensor and details about is construction and positioning may be applied in the leak detector shown in Fig. 2 and Fig. 3.

Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms “comprising” or “comprises” do not exclude other possible elements or steps. Also, the mentioning of references such as “a” or “an” etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.

Claims

CLAI MS

1. A leak detector (1) for testing the leak tightness of sealed packages containing a tracer gas, comprising A test chamber (2) for receiving a sealed pack (11) containing a tracer gas, A vacuum device (3) in fluid communication with the test chamber and adapted for providing a vacuum therein, and - A gas sensor (4) for detecting the presence of a tracer gas in the test chamber, wherein the leak detector further comprises a ventilation device (5) and flow pate (6) provided inside the test chamber, the flow plate being arranged to directing an outflow (91) of air from the ventilation device towards a periphery (21) of the test chamber to provide circulation of the air inside the test chamber whereby an instant and uniform blending of any tracer gas escaping the sealed package inside the test chamber is achieved.
2. A leak detector according to claim 1, wherein the ventilation device is arranged in a centre of the test chamber, having a centrally located air intake (51) and providing a radial outflow of air directed towards the periphery of the test chamber.
3. A leak detector according to any of the preceding claims, wherein the test chamber comprises a sample object area (22) and a sensor area (23) arranged on opposite sides of the flow plate, and wherein the ventilation device is adapted for simultaneously providing the necessary blending of any tracer gas escaping the sealed package inside the test chamber and circulation of air between the sample object area and the sensor area.
4. A leak detector according to any of the preceding claims, wherein the ventilation comprises a rotatable fan (56) having a plurality of fan blades (57) arranged around the centrally located air intake, and wherein an axis of rotation (58) of the rotatable fan is coincident with a centre axis (100) of the test chamber.
5. A leak detector according to any of the preceding claims, wherein the flow plate and an inner wall (24) of the test chamber defines a circumferential passage (25) arranged in the periphery of the test chamber.
6. A leak detector according to any of the preceding claims, further comprising a flow diverter (7) for directing a sub-flow (92) of the radial outflow from the ventilation device into the sensor area of the test chamber.
7. A leak detector according to claim 6, wherein the flow diverter is arranged at a distance (d) from the rotatable fan and extending in a direction normal to at least a part of the radial outflow from the ventilation device.
8. A leak detector according to any of claim 6 or 7, further comprising a fan plate (8) arranged between the rotatable fan and the sensor area and being adapted to guide the sub flow of air through the senor area.
9. A leak detector according to any of claim 6-8, wherein the ventilation device (5), the flow diverter (7) and the sensor area (23) are configured to provide a flow of air through the sensor area at a flow rate of 0,5 to 1,5 m/s.
10. A leak detector according to any of the preceding claims, wherein an inlet (34) to the vacuum device is arranged in the sensor area of the test chamber.
11. A method for determining the gas tightness of the test chamber of the leak detector according to any one of the claims 1-10, wherein a pressure gauge is provided in the test chamber for measuring the pressure therein, and a thermopile is provided to give an output electrical potential in response to the temperature in the test chamber, said method comprising the steps: • measuring the pressure in the test chamber during evacuation with the vacuum device (3); • measuring the potential of the thermopile; whereby gas tightness is confirmed if both the pressure and potential is kept constant during the vacuum period.