Abstract:
A reference leakage device for a leak sniffer detector that is equipped with a sniffing tip and a control unit. The reference leakage device includes a gas reservoir and a constriction wherefrom there is released a specific amount of test gas, at least during calibration. A sensor is located in the constriction for detecting the approach of the sniffing tip wherein the device further is capable of transmitting signals to control unit of the leak detector.

Description:
FIELD OF THE INVENTION 
   The invention concerns a reference leakage device for a leak sniffer apparatus. 
   BACKGROUND OF THE INVENTION 
   Many systems and products in industry and research are subject to high requirements regarding their leaktightness. These requirements depend on the type of leak, the leak rate or size of the leak which leak detection method is applied, respectively, which leak detection instrument is employed. 
   In the instance of test samples or subassemblies manufactured in the refrigerating industry, automotive industry or other industries, the method of sniffer leak detection is frequently employed. This method requires that the test sample or subassembly contains a test gas, preferably at an overpressure. Frequently, helium is employed as the test gas which before sealing off is introduced into the hollow spaces which are to be analysed for the presence of leaks. It is also known to employ gases present in any case within the test samples or subassemblies as the test gas, for example, SF6 or halogen gases in the refrigerating industry. 
   The test sample which is to be analyzed for the presence of leaks is scanned with the aid of the suction intake (tip) of a sniffer gun, which takes in test gas flowing out of a possibly present leak and which supplies said lest gas to a test gas detector. The test gas detector may be accommodated together with other components in an instrument to which the sniffer gun is connected, among other things, by means of a hose. Provided the detector is sufficiently small (for example, an infrared gas analyser), it may also be accommodated in the sniffer gun itself, thereby significantly reducing the response time. 
   Test gas leak detection instruments need to be calibrated frequently. To this end, it is known to employ reference leakage devices exhibiting a defined leak. Reference leakage devices for these purposes comprise a gas reservoir and a constriction having a known conductance. For the purpose of calibrating a leak detection instrument equipped with a sniffer gun, commonly the sniffer tip is located in the vicinity of the constriction and the leak rate indication is aligned. From the German patent application publications 27 02 002, 32 43 752 and 199 63 073, reference leakage devices of this kind are known. 
   Reference leakage devices shall exhibit, on the one hand, a constant gas flow over a period of time which is as long as possible (significantly longer than one year). On the other hand, if they are to be accommodated within the enclosure of a leak detection instrument, they need to be sufficiently small in size. This requires that the test gas be present under a high-pressure (8 bar and more) within the reference leakage device. Reference leakage devices of this kind are temperature sensitive. This applies in particular when the test gas assumes the liquid state at the pressures stated. For safety reasons, a maximum temperature must not be exceeded. Installing, for reasons of operational convenience, a reference leakage device of this kind within a leak detection instrument containing heat producing components is problematic, frequently even impossible. 
   During the calibration process employing an external reference leakage device it is required in the instance of the leak detectors employed to date, to start the calibration through a menu entry and confirm the process of “Sniff leak”/“Sniff air”. This is rather cumbersome and contradicts the idea of an instrument which is easy to operate. This applies above all to—frequently unskilled—persons who need to analyse items moving on a conveyor as to the presence of leaks using a sniffer gun. They cannot bother themselves as to an operation-wise cumbersome and therefore time-consuming calibration process. 
   SUMMARY OF THE INVENTION 
   It is the task of the present invention to design an external reference leakage device, i.e. a reference leakage device separated from a leak detection instrument, such that said reference leakage device allows simplified operation of the leak detection instrument while performing the calibration.c 
   This task is solved by the present invention through the characterising features of the patent claims. Through these measures it is achieved, by only locating the sniffer tip in the vicinity of the constriction of the reference leakage device, that the calibration of the leak detection instrument separately from the reference leakage device can be performed. 
   This task is solved by the present invention. Through these measures it is achieved, by only locating the sniffer tip in the vicinity of the constriction of the reference leakage device, that the calibration of the leak detection instrument separately from the reference leakage device can be preformed 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further advantages and details of the present invention shall be explained with reference to the examples of embodiments depicted schematically in the drawing figures in which: 
       FIG. 1  depicts a sniffer leak detection instrument with components built in therein, 
       FIG. 2  depicts a sectional view through an example of an embodiment for a separate reference leakage device in accordance with the present invention and 
       FIGS. 3(   a ) and  3 ( b ) depict flowcharts for the implementation of a calibration process according to the known art ( FIG. 3(   a )) and with the aid of a reference leakage device ( FIG. 3(   b )) in accordance with the present invention. 
   

   DETAILED DESCRIPTION 
   The leak detection instrument  1  depicted in  FIG. 1  is equipped with a housing  2 , in which there are located instrument components. Presented by way of blocks are, for example, a vacuum pump  3 , a power supply unit  4 , a gas detector  5 , and a control unit  6 . Located exterior with respect to the housing is the sniffer gun  7  with its intake point (tip)  8 . Said sniffer gun is connected through a hose  9  to the gas detector  5 . In the instance of the gas detector  5  being accommodated within the sniffer gun  7 , said sniffer gun is connected through signal lines to the control unit. All instrument components are accommodated within housing  2 . The housing  2  itself is equipped in the area of the bottom section  11  and in the upper section with cooling air entry openings  12 , respectively louvres  13 . Since at least some of the instrument components generate heat, a cooling air flow due to the thermal conditions is effected. Should this flow be inadequate, an additional fan may be provided supporting the cooling air flow. 
     FIG. 2  depicts an example of an embodiment for a reference leakage device  14  in accordance with the present invention. The device is equipped with a housing  15 , in which the actual reference leakage device  20  is removably accommodated—in a manner not specifically detailed. The actual reference leakage device  20  exhibits a pipe connection  21  opening out through the housing  15  to the outside. The pipe connection  21  forms a commonly constantly open connection between the constriction, details of which are described below, of the actual reference leakage device  20  and an aperture  22  suited for introducing the sniffer tip  8 . This arrangement allows the leak detection instrument  1  to be calibrated at any time. 
   The actual reference leakage device  20  is equipped with an internal pressure vessel  31  with the gas reservoir. This is a common commercially available pressurised dispenser which contains the desired test gas in the liquid state. The pressure in filled cartridges of this type is very temperature dependent. It may commonly not exceed 8 bar (test pressure 12 bar). The maximum temperature to which pressurised dispensers of this type may commonly be exposed, is restricted to 50° C. 
   In order to employ, even so, from time to time pressure vessels of this kind also at higher ambient temperatures as a gas reservoir for reference leakage devices, a second outer housing  32  is provided. It consists, for example, of steel and is designed for significantly higher pressures than 8 (respectively 12) bar. It exhibits in the area of one face side the constriction  33  designed by way of a diaphragm  34 . There then follows the already mentioned pipe connection  21 . In the area of the other face side a releasable cap  35 , preferably suited for screwing off, is provided. It allows to seal off the housing  32  being separable from the cap. Located between its face side opening and the cap  35 , is a sealing ring  36 . After removing the cap  35 , the inside of the housing  32  is accessible for inserting or removing the pressure vessel  31 . 
   In the area of the face side opposing the cap  35 , the housing  32  is equipped with a flange  37  projecting towards the inside. Said flange carries on its side facing the pipe connection  21 , the diaphragm  34 . The pressure vessel  31  inserted into the housing  32  is supported by the side of the flange  37  facing the cap  35 . 
   In the instance of the example of an embodiment depicted in  FIG. 2 , the pressure vessel  31  is equipped with a ball valve  38  being located in one of its face sides. The pressure vessel  31  is inserted into the housing  32  such that the valve  38  faces in the cap  35 . The cap  35  is equipped with a pin  39  assigned to the valve  38 , the length of said pin being so selected that it opens the valve  38  when the cap  35  is completely screwed on. If a pressure vessel without valve  38  is employed, a spike is provided instead of the pin  39 , said a spike providing an opening in the pressure vessel  31  upon closing the cap  35 . After closing the cap, either the valve  38  is open, or the opening provided by the spike is present so that test gas flows into the housing  32 . Decisive for the temperature burden is then no longer pressure vessel  31 , but the housing  32  instead. 
   If it is required to exchange the pressure vessel  31 , the actual reference leakage device  20  is taken out of the housing  15  of the reference leakage device  14 . Thereafter the housing  32  is opened by unscrewing the cap  35 . The rim of the cap  35  is equipped in the vicinity of its upper side with a small bore  40 . Said bore allows the pressure to be equalised between the inside of the housing  32  and the surroundings before finally unscrewing the cap  35 . 
   The special advantage of the reference leakage device in accordance with the present invention is that the pressure resistant housing  32  does not have to be exchanged. It may, with respect to its stability, be designed in accordance with the desired requirements. Only during transportation and storage of the pressure vessel  31  need the relatively low ambient temperatures be taken into account. Also the constriction (diaphragm  34 ) itself does not belong to a disposable product. This offers the advantage that the leak rate of the reference leakage device does not change upon changing the gas reservoir. 
   In accordance with the present invention the actual reference leakage device  20  of the reference leakage device is equipped with a sensor  42  which senses the presence of a sniffer tip  8  in the pipe connection  21 . The sensor  42  may be implemented by way of a Reed contact, for example, or a similar contact. In the instance of the example of the embodiment depicted, the sensor is implemented by way of a light barrier. For this, the pipe connection  21  is equipped with two openings opposing each other, to which a light source  43  (a light emitting diode, for example) and a component  44  which is sensitive to light (a photodiode, for example) are assigned. 
   Between the sensor  42  and the leak detection instrument  1  there must exist a link, allowing feeding of the sensor signals to the control unit  6  of the leak detection instrument  1 . Presented are connectors  46 ,  47  at the housings  2 , respectively  15  as well as a wire link  48 . It is especially advantageous when there exists a wireless link, for example, a transmitter in the reference leakage device  14  and a receiver in the leak detection instrument  1 , whereby transmitter and receiver are not specifically depicted. This link allows, using only one reference leakage device, the calibration of several leak detection instruments placed at different locations. 
   It is especially expedient to equip the actual reference leakage device  20  in the vicinity of its constriction with a temperature sensor  51  and to transmit through the link between the actual reference leakage device  20  and the leak detection instrument  1 —either wireless or through a wire link—also the signals of the temperature sensor  51  to the control unit  6 . These measures allow taking into account the temperature dependent permeability of the constriction  33  of the actual reference leakage device  20  during the calibration of the leak rate indication. In particular, in the instance of reference leakage devices equipped with a diaphragm as the constriction this is of significance, since the permeability of the diaphragm is exponentially temperature dependent. Now in order to attain a reliable calibration of the leak detection instrument, the temperature dependence of the reference leakage device is compensated by a correction curve saved in the software of the instrument (control unit  6 ). The temperature is measured in the area in which the actual reference leakage device is located. 
   Expediently the actual reference leakage device  20  is equipped, besides the temperature sensor  51 , also with an EEPROM. In  FIG. 2 , the EEPROM is depicted schematically and designated as  52 . If in the EEPROM production date, filling quantity as well as leak rate have been saved, it is thereby possible to provide an estimate as to the point of time when the reservoir will have emptied itself, and when for this reason the actual reference leakage device  20  needs to be exchanged. If the EEPROM  52  is also linked to the control unit  6 , this point of time may be indicated on the display of the leak detector. 
     FIGS. 3(   a ) and  3 ( b ) depict flow charts for the implementation of the calibration process employing instruments according to the state-of-the-art  FIG. 3(   a ) and with the aid of a reference leakage device in accordance with the present invention  FIG. 3(   b ). From the comparison of the flow charts, the simplification of the calibration process due to the present invention is apparent.