Abstract:
An apparatus and method for simulating a package pressure burst condition for calibrating a package pressure burst detector, where the package pressure burst detector is connected to a pressure tank, and the detector applies an air flow into the tank to gradually increase the tank pressure, and the tank has an output relief conduit connected to a pressure relief valve via a pressure switch, wherein the pressure relief valve is activated for a predetermined time when the pressure switch detects a preset pressure in the tank.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to instruments for testing sealed packages for burst strength; more particularly, the invention relates to an apparatus for calibrating such an instrument, to ensure that the instrument provides accurate and repeatable measurements. 
     One such instrument which may be used for flexible and rigid package testing is manufactured by the assignee of the present invention, under the designation SKYE Model 2000 a . The SKYE Model 2000 a  is a microprocessor-controlled package test system that gives a measurement of package integrity and seal strength. The instrument may be used with a needle apparatus for puncturing the package to enable the instrument to selectively pressurize the interior volume to a predetermined amount, and to monitor the interior volume pressure, to determine whether the package can maintain a certain pressure without leaking, or to determine the actual burst pressure. 
     When the instrument is used for pressure burst testing of a package, a needle is first sealably penetrated into the package, and an air tube from the instrument is connected to the needle. The computer processor which is part of the instrument is set to gradually increase the air pressure inside the package, while monitoring the internal pressure. When the pressure rises to a value to cause the package to burst, the sudden drop in package internal pressure is monitored and recorded. 
     Burst testing is normally done by periodically removing a package from the assembly line, using some statistical sampling procedure, and using the instrument to ascertain whether the packages produced on the assembly line statistically meet the design requirements for the packages. 
     A problem in using such instruments can occur when more than one instrument is used for testing the same type of package on an assembly line, for even though each particular instrument produces accurate and repeatable measurement results, it is difficult to ensure that two or more different instruments will test to exactly the same absolute burst pressure value, because of variations between instruments and test set-ups. Likewise, when an instrument is used on many different days for the same package type testing, it is difficult to ensure that all packages tested on different days are being stressed to the same absolute pressure levels. What is needed is a test or calibration device which can be connected to any of a number of package burst detector instruments to ensure that all instruments are set to the same test conditions. The present invention meets this need, and provides a device for calibration of any test instrument to the same set of test conditions as any other similar test instrument. 
     SUMMARY OF THE INVENTION 
     The present invention comprises a device for calibrating a burst pressure detector for measuring burst pressure of packages, the device including a pressure container capable of being pressurized to predetermined pressures by the burst pressure detector via an input pressure port. A second port to the pressure container is connected to a pressure relief solenoid valve via an electrical pressure switch, which may be preset to any desirable burst pressure, which itself is electrically connected to a timer relay. When the pressure in the pressure container reaches the preset value of the pressure switch, the switch activates the timer and the timer activates the pressure relief solenoid valve, which vents the pressure from the pressure container to atmosphere. The timer continues to vent the pressure for the preset time of the timer, and then deactivates the pressure relief solenoid. A further port on the pressure container is connectable to a pressure sensor in the burst pressure detector, to enable the detector to monitor and record the burst pressure. 
     It is a principal object and advantage of the present invention to provide a calibration apparatus for the proper setup of package burst detectors. 
     It is another object and advantage of the present invention to provide a calibration and setup device to ensure that a plurality of package burst detectors can produce consistent and repeatable measurements. 
    
    
     These and other advantages and objects of the invention will become apparent from the appended specification and claims, and with reference to the drawings, in which: 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows an isometric view of the present invention, connected for testing a commercially available leak/burst tester; 
     FIG. 2 shows a block diagram of the setup for using the invention in conjunction with a burst detector; 
     FIG. 3 shows a functional block diagram of the package burst tester with which the invention is used; and 
     FIG. 4 shows a diagram of the electrically activated control box of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawing figures, In the figures, like reference characters refer to the same or functionally similar parts of the respective devices illustrated in each of the figures. 
     FIG. 1 shows an isometric view of the invention connected to a commercially available leak/burst tester  60 . A pressure tank  10  serves to simulate a package volume of a predetermined size, and is preferably made from a rigid material which does not significantly expand when pressurized to the degree required by the test and simulation process. Tank  10  has a closed top and bottom end, with a number of fixtures connected to and penetrating through the top surface. A pressure safety valve  20  is provided to provide a pressure release when and if the tank  10  becomes overpressurized; the safety valve  20  has an internal spring-loaded valve which opens at a predetermined excess pressure. An outlet fitting  29  is connected to a pressure switch  30 , which provides an electrical signal over conductor  31  whenever a predetermined pressure exists inside tank  10 . 
     The apparatus  50  for penetrating into tank  10  is mounted to the top end of pressure tank  10 . The penetrating apparatus  50  is a conventional apparatus associated with a particular leak/burst detector, and is characterized by a mounting bracket  52  and a hollow needle  54 , used for penetrating a package to be tested. Mounting bracket  52  is attached to the top of pressure tank  10  by a rigid post  56 , which is affixed to the top cover of the tank  10 . The illustration of apparatus  50  in FIG. 1 is intended to be representative of any of a number of conventional penetrating fixtures which may be used for this purpose, for penetrating a package and monitoring the pressure inside the package. In such cases, the penetrating apparatus has a lower projecting hollow needle, associated with a seal membrane  55  which is affixed to the outside surface of the package, and the needle is inserted through the seal membrane  55 . In the present case, the seal membrane is affixed over an opening through the top cover of pressure tank  10 , to permit the insertion of the needle into the interior of pressure tank  10 . 
     An air passage exists between the needle and an interior chamber in the penetrating fixture  50 . This interior chamber is connected to an outlet port to which hoses  12  and  13  are connected. Air hose  12  is attached to an air flow outlet port  62  on leak/burst detector  60  (see FIG. 3) and air hose  13  is attached to a sensor port  64  on the leak/burst detector (see FIG.  3 ). Referring to FIG. 3, the leak/burst pressure detector  60  typically has an internal valve  65  to control the flow of air from an external source to the penetrating apparatus  50 . An internal electronic circuit board  61  controls the various valves, and also registers the pressures detected by pressure sensor  63 . 
     A conventional power entry module  65 , such as an AC voltage receptacle, receives input power from a wall socket or the like. This power is connected to a conventional 24-volt DC power supply  66  and to a conventional 5-volt DC power supply  67 , each of which supply requisite DC voltage to the electrical circuits in electronic circuit board  61 . 
     A control box  15  (see FIG. 1) is connected to a source of AC power via wire  17 , and is connected to pressure tank  10  by a vent air hose  11 , and is connected to pressure switch  30  by conductor  31 . Control box  15  also has an on/off switch  22  and a power indicator light  16 , as well as a “ready” indicator light  42  which will be explained more fully hereinafter. Control box  15  contains the components illustrated in FIG.  4 . 
     Referring to FIG. 4, the AC power line  17  is connected to a fuse  21 , and then to on/off switch  22 , before being connected to the various electrical components. 
     The air vent hose  11  is connected to an inlet port  24  of a solenoid valve  25 ; solenoid valve  25  has an outlet port  26  which is vented to atmosphere. Solenoid valve  25  is electrically operated, via a signal over line  27 , which is connected to a timer relay  40 . Timer relay  40  is in turn activated by a signal over line  31  from pressure switch  30 . A “ready” indicator lamp  42  is connected to timer relay  40  to provide a visual indication when the timer relay is turned off. 
     FIG. 2 shows a block diagram of the package burst pressure simulator connected to a typical and representative leak/pressure decay detector  60 , of the type commonly used for purposes of testing packages for burst pressures. An air supply is connected to detector  60 , and an air line  12  is connected to the pressure tank  10  for feeding pressurized air to the tank, and an air line  13  is used for monitoring the pressure inside the tank. 
     In operation, the systems are first connected together, as shown in FIG.  1 . The control box  15  is turned on with the on/off switch  22 , which in turn activates both the power indicator light  16  and the ready indicator light  42 . The leak/burst pressure tester  60  is activated, and it begins to pressurize the tank  10 . 
     When the pressure inside tank  10  equals that which has been selected for the pressure switch  30  setting, the pressure switch contacts close, and the “ready” light  42  goes out. The timer relay  40  becomes activated, which opens the pressure relief solenoid valve  25 , and the pressure inside the tank is relieved to atmosphere. 
     When the timer cycle ends, the pressure relief solenoid valve  25  closes and the “ready” light again turns on, thus readying the simulator for another test. 
     During the time the tank  10  is being pressurized, the internal tank pressure is monitored by the detector  60 , and is recorded. At the instant the pressure inside tank  10  is relieved, sensor  63  detects this change, and the pressure at that instant is also recorded, to provide a record of the simulated burst pressure created by the apparatus. This value may be compared to the known pressure setting for pressure switch  30 , and the internal circuits of detector  60  can be readjusted if necessary, to calibrate the reading of detector  60  with the known “burst” pressure set by pressure switch  30 . 
     The present invention may be embodied in other forms without departing from the spirit or essential attributes thereof; and it is, therefore, desired that the present embodiment be considered in all respects as illustrative and not restrictive, reference being made to the appended claims rather than to the foregoing description to indicate the scope of the invention.