Abstract:
The invention relates to a film leak detector with two films ( 5, 6 ) each stretched in a frame ( 3, 4 ); in order to attain a simple and stable structuring, it is proposed that each of the frames ( 3, 4 ) is comprised of two synthetic material subframes between which the particular film ( 5, 6 ) is fastened.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a film leak detector with two films each stretched in a frame. Film leak detectors of this type are known from DE-A-196 42 099. 
     The present invention is based on the task of structuring a film leak detector of the known type simply and stably as well as improving it with respect to its operation. 
     This task is solved through the measures listed in the patent claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Advantages and details of the invention will be explained in conjunction with embodiment examples represented in the Figures. Therein depict: 
     FIG. 1 schematically a film leak detector according to the invention including its circuit diagram, 
     FIG. 2 a partial section through the frame in which the films are stretched, and further details in elevation as well as 
     FIG. 3 a section through a detachable connection of a connection port, fastened on a film, with a line extending further. 
    
    
     DESCRIPTION OF THE INVENTION 
     FIG. 1 shows schematically a film leak detector  1  with its two frames  3  and  4  connected across an articulation  2  as well as films  5  and  6  stretched therein. The frames  3  and  4  are circular. The lower frame is stayed on the margin.  7  of a plate-form bottom  8 , preferably comprising steel. Spunbonded web sections  9  disposed on the films  5 ,  6  ensure the formation of a contiguous test chamber with the test sample emplaced. The fundamental structure of a film leak detector of this type for the remainder is known from DE-A-196 42 099. 
     The lower frame  4  is equipped with several bores, not shown in detail, which terminate in the interior of the test chamber, which is formed by the two films  5 ,  6  with the test sample emplaced. Connected to these bores are line sections  10 , which communicate across a common Line  11  with a valve  12  with a forevacuum pump  13 . Upstream with respect to the valve  12  are additionally connected to the line  11  a pressure meter  14  and a venting valve  15 . 
     The lower film  6  is equipped approximately in its center with a line connection  18 , which is succeeded by line section  19 , filter  20  and line  21  with valve  22 . The line  21  is also equipped with a pressure meter  23  and with a venting valve  24 . 
     The section of line  21 , disposed between the connection of the pressure meter  23  and the valve  22 , communicates across two parallel lines  26  and  27  with a line  28 , which extends between the test gas detector  29  and a second forevacuum pump  30 . In line  26  is disposed a choke valve  32 . Line  27  is equipped with a valve  33 . 
     The forevacuum pump  13  is usefully a single-stage “pump”, the forevacuum pump  30  is developed as a two-stage “pump”. Pump  30  is equipped with a gas ballast device. With valve  31  open, air (or also inert gas) streams into pump  30 . 
     In the test gas detector  29  is disposed a turbomolecular vacuum pump  35 , whose outlet communicates with line  28 . To the inlet of the turbomolecular vacuum pump is connected a mass spectrometer  36 . In addition, a pressure meter  37  is a component of the leak detector  29 , which measures the pressure in line  28 . 
     Downstream with respect to the valves  12  and  22 , the two lines  11  and.  28  communicate across a line  38  into which the line  21  also terminates. In this line  38  between the termination of line  21  and line  28  are disposed valves  41  and  42 . In the section of line  38  disposed between valves  41  and  42  terminates a line  44 , which is connected with a coupling  45 . The coupling  45  serves for establishing the connection of line  44  with the sniffing line  47  of a sniffer  48 . The sniffing probe, denoted by  51 , of the sniffer  48  comprises a handle  52  and a sniffing tip  53 . 
     For depositing the sniffing probe a holder  54  is provided. Such is either fastened on the film leak detector  1  or developed as a separate stand. It comprises a void  55  which, when the probe  51  is deposited, contains the sniffing tip. In addition is provided a sealing ring  56  which seals the void  55  against the handle  52  when the probe  51  is deposited. Succeeding void  55  is a line  57 , which communicates across a coupling  58  with an underpressure switch  59  accommodated in the housing of the film leak detector  1 . As sniffing line  47  serves in known manner a capillary “tube” (diameter approximately 0.5 mm). This applies also to the line  57 , in order for the underpressure generated by the sniffing tip  53  in chamber  55  to exert its effect rapidly on the underpressure switch  59 . 
     In the film leak detector according to FIG. 1 the leak detector cycle proceeds automatically. To control the process flow, a control center is provided which is only depicted as a block  61 . With it are connected all meters and all structural components to be controlled. This applies also to a switch which is actuated with the closing of the test chamber. In the embodiment example depicted this switch is a proximity switch, which comprises a metal pin  62  provided on frame  3  and a sensor  63  disposed on frame  4 . The sensor  62  is connected with the control center  2 . Other switches, be they operated electrically, mechanically or optically, can be applied for this purpose. 
     For the sake of clarity, the great number of electric connection leads between the control center  61  and the structural parts are not depicted. Connected with the control center are also two signal lights  64 ,  65 , of which one lights up green if a test sample is detected to be impermeable and the other red if a test sample is detected to be permeable. 
     In the operationally ready film leak detector  1 , if the test chamber—as depicted in FIG.  1 —is opened or if the upper frame  3  is raised from the lower frame  4 , all valves—except for valve  41 —are closed. After the test sample is placed onto the lower film  6  and after the upper frame  3  is placed onto the lower frame  4 , the proximity switch  62 ,  63  initiates a leak detection process. For this purpose, first a check takes place of whether or not an increased helium background is in the system, which could falsify leakage measurements. This takes place with the aid of the mass spectrometer  36 . If it reports too high a background, valve  31  is opened and pump  30  is operated with gas ballast until the helium background has assumed a harmless value. 
     As a rule, an increased helium background is not present such that with the closing of the test chamber, the leak detection cycle proper also starts. First, valves  12  and  22  are opened. This causes the extremely rapid evacuation of the volume between the films  5  and  6 . Outside of the regions in which the spunbonded fabric sections  9  are disposed, the films  5 ,  6 , directly in contact with one another, form the sealing of the test chamber. 
     Of significance is that in the first evacuation phase only valves  12  and  22  are opened. It occurs only in this first phase that the wall/packaging of the test sample to be tested for leaks suffers a defect, for example could burst. Since in this phase connections between the test chamber and the leak detector are closed, there is no danger of helium pollution or contamination due to the product penetrating out of the test sample. 
     At a pressure of a few hundred mbar (100 to 300 mbar) the choke valve  32  is opened. It is dimensioned such that the necessary forevacuum pressure of the turbomolecular vacuum pump  35  does not assume impermissibly high values. With the opening of the choke valve  32  the gross leak detection starts. If helium flows through the choke valve  32 , it reaches the mass spectrometer  36  in counterflow through the turbomolecular pump  35 . If helium is being registered, the test sample is permeable; the leak detection cycle is terminated. 
     In the event helium is not yet being registered, the evacuation process is continued. If the pressure reaches a value, measured with apparatus  23 , which is of the order of magnitude of the forevacuum pressure of the turbomolecular pump  35 , valves  12 ,  22  and  32  are closed and valve  33  is opened. The phase of the sensitive leak detection starts. This is terminated if either test gas is being registered, thus the test sample is permeable, or after a specific length of time. Either a fixed time interval is preset or the test is carried out until the pressure (measured with apparatus  23 ) falls below a certain value. If test gas is not registered within this time, the result allows the conclusion that the test sample is impermeable. 
     During the sensitive leak detection phase, only lines  19 ,  21  and  27  represent the connection between the test chamber and the leak detector  29 . Bursting of the test sample no longer needs to be anticipated. Between lines  19  and  21 , for the remainder, is disposed the particle filter  20 , which keeps any impurities away from leak detector  29 . 
     Termination of the leak detection cycle takes place in such manner that all previously open valves—except for valve  41 —are closed and valves  15 ,  24  are opened. The test chamber is vented and the upper frame  3  can be raised from the lower frame  4 . It is useful if the two frames  3 ,  4 , articulated with one another, in the proximity of the articulation  2  are under the effect of a (not shown) spring device whose force acts continuously in the direction of opening. Its force should be such that the vacuum generated during the leak detection keeps the test chamber closed and that frame  3  assumes its open position after the venting process. 
     If during the leak test it is found that a test sample is permeable, it is of interest to the user to locate the site of the leak. For this purpose the film leak detector according to the invention is equipped with a sniffer  48 . It is connected with its sniffing line  47  to line  44  across the coupling  45 . 
     As long as the sniffer  48  is not in use, it is deposited in a holder  54 . This holder  54  is equipped with the means  55  to  59  already described, with the aid of which the control center  61  can detect whether or not probe  51  is deposited in holder  54 . Other means, be they mechanically, electrically or inductively actuated switches, can also be used for this purpose. 
     As long as probe  51  is in holder  54 , valve  41  is kept open, as has already been described. Thereby the sniffer is continuously in standby. Only when it is removed from its holder  54 , does valve  41  close and valve  42  open. The gas stream penetrating sniffer  48  thereby reaches line  28  and is maintained by pump  30 . In this state, sniffing leak detection is possible. If helium is picked up by the sniffing tip  53 , it reaches the mass spectrometer  36  in counterflow through the turbomolecular pump  35 . 
     The control center  61  is programmed such that switching the sniffer  48  from standby to leak detection operation (switching over valves  41  and  42 ) does not occur as long as the proximity switch  62 ,  63  is closed. The simultaneous leak detection leading to error measurements via the film leak detector  1  and via the sniffer  48  is consequently excluded. 
     Of interest to the visitor in the quantitative leak detection as a rule is the leakage rate of a detected leak, measured in mbar1/sec. 
     In the inspection of test samples produced in high production numbers, however, it is also of interest to measure the concentration of the test gas in the test sample. This can take place thereby that the sniffing tip  53  is inserted into the test sample or that the test sample is provided with a defined leak and in the film leak detector  1  a leak detection cycle is carried out. The control center is therefore developed such that on a (not shown) display the leakage rate as well as also the concentration can be read. 
     FIG. 2 shows the structure of frames  3  and  4 . Each comprises an outer ring  71  or  72  and an inner ring  73 ,  74 . Between the pairs of rings are fastened, preferably adhered, the films  5 ,  6 . Each of the inner rings is disposed in recesses  75 ,  76 , corresponding to one another. The recesses are disposed such that the outer rings  71 ,  72  in their regions facing the test chamber directly oppose one another and thereby determine the planes of the stretched films  5 ,  6 . In the outer region the inner rings  73 ,  74  directly oppose one another. Between them is disposed a lip seal  77 . Films  5 ,  6  extend through the angular gap between the particular ring pairs and are thus adhered or screw-connected all-over. 
     In FIG. 2 is also evident that the films  5 ,  6  form a test chamber  80  when a test sample  79  is placed between them. The spunbonded fabric sections  9  ensure the formation of a contiguous test chamber  80 . 
     Ring  72  of the lower frame  4  is stayed on margin  7  of the plate-form bottom  8  and is adhered to it (adhesion layer  78 ). Associated with the upper frame  3  is a support, which is formed by a steel profile  81  encompassing the frame  3  from the outside and partially from above. Frame  3  is fastened on steel profile  81  so as to float in the axial direction such that, after it is lowered, it comes to rest uniformly on the entire periphery of frame  4 . Through the evacuation of the test chamber  80 , additionally, a pressing force is generated. In the axial direction the steel profile  81  extends downwardly beyond frame  3  and, in the last phase of the lowering movement, forms a guidance. A trim ring  85  serves for covering the steel ring  81 . 
     FIG. 2 shows further that the depicted film leak detector is equipped with an encompassing handle  82 . On it is fastened the holder  54  for the sniffer  48 . In holder  54  is disposed the means, already described in connection with FIG. 2, which indicates whether or not probe  51  of the sniffer  48  is deposited on holder  54 . Between holder  54  and the housing  86  extends the capillary hose  57  which is inserted into the coupling  58 . 
     FIG. 3 shows the transition between the connection port  18  and the line section  19  extending further. Both are comprised of synthetic material, preferably polyamide. The line section  19  is developed as a corrugated tube and, together with sealing rings  83 ,  84 , encompasses the connection port  18 .