Adaptive leak testing method

Apparatus for performing leak testing on products is disclosed. Specifically, the present invention includes a method, system, and apparatus for performing an adaptive leak test on products under test.

FIELD OF THE INVENTION

The present invention relates to product testing, and more specifically to adaptive methods for testing products for leaks.

BACKGROUND AND SUMMARY

Many products are produced in an air or liquid tight manner for environmental, health, freshness, operational and/or other reasons. To meet the need for seal-tight products, test equipment has been developed to test certain types of products for leaks using air tests utilizing micro-flow sensors. For example, U.S. Pat. No. 5,861,546 to Sagi et al., the disclosure of which is expressly incorporated herein by reference, discloses a leak detection apparatus that is suitable for detecting leaks in a product having an opening to which a leak sensor and a vacuum system may be coupled to form a closed test system.

Conventional leak testing systems and methods employ procedures wherein an individual leak test lasts a predetermined amount of time. Each product under test is subjected to the same test time period, regardless of whether the product has a gross leak which is apparent immediately, a marginal leak, an insignificant leak, or no leak at all. Consequently, a given number of products require a relatively fixed period of time for testing.

The present invention provides a method by which the period of time for testing a particular product for leaks is variable and dynamically changes depending upon leak characteristics of the product in the on-going test such as the leakage flowrate and the stability of the leakage flowrate. Thus, it is possible to test a larger number of products in a given period of time as compared to conventional techniques.

These and other features of the present methods and apparatuses will become apparent and be further understood upon reading the detailed description provided below with reference to the following drawings.

DETAILED DESCRIPTION OF THE INVENTION

While the invention is susceptible to various modifications and alternative forms, exemplary embodiments thereof have been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

The present invention includes a method, system, and apparatus for performing adaptive leak testing on products. The system can be used with any type of leak testing system such as those described in U.S. Pat. No. 6,584,828 to Sagi et al., the disclosure of which is expressly incorporated herein by reference.

Additionally, embodiments of the present invention can be used by intelligent gas leak sensors (IGLS) such as those described in U.S. Pat. No. 5,861,546, the disclosure of which is expressly incorporated herein by reference.

As described above, conventional leak testing methods usually involve determining a reference pressure to apply to the product, a test time period during which the pressure will be applied to the product, and an acceptable leakage amount or limit to separate acceptable products from unacceptable or defective products. The test time period is usually fixed so that each product test takes the same amount of time. At the conclusion of the test time period, the leakage flowrate is measured and compared with the preselected acceptable leakage limit. If the actual leakage flowrate measured at the end of the test time period is greater than the acceptable leakage limit, the products fails and is classified as unacceptable. Conversely, if the actual leakage flowrate measured at the end of the test time period is less than the acceptable leakage limit, the product passes and is classified as acceptable.

The present invention involves utilizing an adaptive leak testing method which reduces the overall test time for testing a plurality of products by shortening the test period time for products that have a gross leak or an insignificant leak. In one embodiment, only the products that have a marginal leak, a leak that may make the product unacceptable, are tested for the full test time period. By shortening the test period time for products having a gross or obvious leak and products having only an insignificant leak or no leak, the overall time required to test a plurality of products is reduced.

The method of the present invention can be practiced as a computer software application that can be stored on computer readable media such as a hard-disk, CD-ROM, DVD, RAM, or a floppy disk. The software application can be installed on and the method practiced by a computer or a processor that is a component of an Intelligent Gas Leak Sensor (IGLS). The method can be used with any leak detection system configured to test products for leaks.

In one embodiment, a software application loaded on a computer is used to capture and store leak test results (signatures of leak flow vs. time), analyze those results, and develop a set of adaptive test coefficients that are downloaded to an IGLS sensor processor. Once downloaded, the computer is not required to run normal day-to-day leak testing. Once the IGLS sensor processor is programmed with the appropriate coefficients and mathematical formulas, the IGLS sensor processor performs the adaptive leak test. In alternative embodiments, the software application simulates the adaptive test using the methods and formulas described below to generate the adaptive test coefficients and design the test protocol.

One embodiment of a leak detection system10including a computer12, a pressure supply14, a leak detection processor16, a leak detection sensor18, and a test chamber20is shown inFIG. 1a. Computer12may be any conventional computing device, and is coupled to leak detection processor16. Leak detection processor16is coupled to pressure supply14, performs measurement functions and controls the leak detection sensor18. Leak detection sensor18is coupled between pressure supply14and test chamber20to detect gas flow to and from test chamber20. Test chamber20is generally operable to receive a product such as a casting or a package containing a medical product and to subject the product to a controlled pressurized environment.

It should be understood that leak testing systems having other configurations could also use the method of the present invention. For example, inFIG. 1bthe pressure source may be configured to couple directly to the product under test22, as opposed to test chamber20shown inFIG. 1a. In such an example, pressure is applied to the interior of the product. Any of a plurality of combinations of these configurations are also suitable for use with the present invention.

In the embodiment ofFIG. 1a, leak detection system10is operable to (1) obtain a measurement of the gas flow through the system10at a particular time while controlling a near constant pressure within the system10throughout a test period, (2) measure and calculate total mass, total volume, mass flow, and/or volumetric flow of the gas flow through the system10during the test period, and (3) determine whether a product being tested such as a sealed package has a leak failure based upon the calculated total mass, total volume, mass flow rate, or volumetric flow rate of the gas flow through the system10during the test period.

To perform a leak test on a product such as a medical device sealed in a plastic bag using the leak detection system10, the product to be tested is placed in the test chamber20. Leak detection processor16enables pressure source14to apply a reference pressure to test chamber20. The reference pressure is applied to the product and maintained for the test time period. Usually, the reference pressure is less than atmospheric pressure although any suitable pressure could be selected. While the reference pressure is applied by pressure source14, leak detection sensor18monitors any gas flow to or from the test chamber20. Leak detection sensor18outputs a signal indicative of an actual leakage flowrate to leak detection processor16if any gas flow is detected while the reference pressure is being applied.

Leak detection processor16records the actual leakage flowrate of any gas to or from the product while the reference pressure is applied. Based on the actual measured leakage flowrate, the predetermined coefficients, and the formulas described below, leak detection processor16stops the test dynamically if the product has a gross leak or an insignificant leak and continues the test until the full test time period has elapsed for products having marginal leaks. Leak detection processor16outputs a pass or fail signal based on the measured actual leakage flowrate, the dynamically predicted flowrates, and the set of test parameters and coefficients stored inside the leak detection processor16.

One method of the present invention can be implemented as a software application configured to be executed by computer12. The software application stores and analyzes data uploaded to computer12by leak detection processor16for a plurality of different products and performs repetitive tests to calculate leak testing coefficients which are downloaded and used by leak detection processor16during the adaptive leak testing method described herein. In another embodiment, a software application evaluates data and simulates the leak testing procedure to determine the leak testing coefficients. In yet another embodiment, the software application allows a user to select a safety factor for the product leak test. The higher the safety factor selected, the longer the average test time for testing a plurality of products. The selected safety factor is downloaded to leak detection processor16and is used in the calculations of the leak testing method.

The software application and variations thereof described above calculates the leak testing coefficients based on the user inputs and one or a combination of stored data from previous runs, simulations, experiments, knowledge in the art, research, accepted guidelines, quality assurance studies, statistical methods, etc. Based on the leak testing coefficients and mathematical models such as those described below, leak detection processor16determines whether the product has a gross leak, an insignificant leak, or a marginal leak during each test period. If a product has a leakage flowrate below the acceptable flowrate, then the product is acceptable. If a product has a leakage flowrate above the acceptable flowrate, then the product is not acceptable.

Once the leak testing coefficients are downloaded to leak detection processor16, leak detection system10can operate without computer12until a user chooses to update the coefficients, recalibrate the sensor, log data, perform system maintenance, or upload a different model optimized for a different product. Computer12can be disconnected from leak detection processor16for extended periods and reconnected when needed.

Mathematical models can be used to compute a predicted leakage flowrate of the product based on actual leakage flowrate and the rate of change of the actual leakage flowrate over time. The predicted leakage flowrate is compared to calculated upper and lower leakage flowrate values. If the predicted leakage flowrate is between the upper and lower leakage flowrate values, then the product has a marginal leak and the test continues to determine if the product has an acceptable or unacceptable leakage flowrate. If the predicted leakage flowrate is greater than the upper leakage flowrate value, then the product is classified as having a gross or obvious leak and is therefore unacceptable. If the predicted leakage flowrate is less than the lower leakage flowrate value, then the product is classified as having an insignificant leak and is therefore acceptable.

FIG. 2is a flowchart30illustrating the steps for performing one method of the adaptive leak testing which can be used with leak detection system10described above or any other suitable leak detection system. As discussed above, the leak testing coefficients and the leak test parameters are calculated by a software application loaded on a computer in step32. In step33, the leak testing coefficients and other leak test parameters are downloaded to a leak sensor processor of an IGLS. As discussed above, the leak test parameters can be determined by a software application running on computer12using information input by the user such as safety factors, test time periods, acceptable leakage limits, etc.

In step34, the test begins by applying the reference pressure to the product under test. In step36, the leak detection sensor18monitors any gas flow to or from the test chamber20while the reference pressure is maintained. In step40, the leak detection processor16calculates the predicted leakage flowrate based on the actual leakage flowrate and the rate of change of the actual leakage flowrate over time, which is the slope of a best line fit algorithm to a plot of actual leakage flowrate versus time. The predicted flowrate is then compared with upper and lower leakage flowrate values to determine if a gross leak, an insignificant leak, or a marginal leak is present. If a gross leak or an insignificant leak is detected at step40, then the test ends and the product is classified accordingly as shown in step44.

If a marginal leak is present or a determination cannot be made, then the test continues until the cumulative test time is equal to the total allowed test time selected by the user at which time the test concludes in step42. At this point, the product is determined to have a marginal leak, as shown in step46. In step48, leak detection processor16compares the actual leakage flowrate at the end of the test time period with the acceptable leakage flowrate and classifies the product as acceptable or unacceptable.

Another embodiment of a method of adaptive leak testing is shown inFIG. 3.FIG. 3shows a flowchart50including steps for performing an adaptive leak testing method which can be used with leak detection system10or any other suitable leak detection system. Generally, the method disclosed by flowchart50is implemented in the form of computer software and is performed by an IGLS, although the software can by operated by a computer to analyze data and simulate tests. In step52, the test time period, which has been specified by the user, of the leak test begins. In step54, the current flowrate F between the pressure supply and the product chamber is monitored by leak detection sensor18. In step56, if the current test time (Tcur) is equal to the end of the test time period (Tend), which indicates the end of a test cycle, then the method advances to step57. In step57, a marginal leak has been detected and the test proceeds to step58. In step58, if the actual leakage flowrate Fendat Tendis less than or equal to the acceptable leakage flowrate, Flimit, then the method proceeds to step59and outputs a pass signal indicating the product is acceptable. If Fendis greater than Flimit, then the method proceeds to step61which outputs a fail signal indicating that the product is unacceptable.

In step56, if the adaptive test period has not concluded, (i.e., Tcuris not equal to Tend), then the method proceeds to step60. In step60, the current flowrate F is stored in a first-in-first-out (FIFO) circular buffer which starts to fill up during the adaptive test period and Kslopeof F and adaptive flowrate Fadaptiveare calculated. The buffer time B (in secs) for the FIFO circular buffer determines how many sample flows will be recorded by the leak detection sensor and is calculated according to the following equation:

B=D1100×(Tend-Tstart)(1)
whereB=Buffer time in seconds.D1=Buffer time %.Tstart=Total test time before the test phase starts.Tend=Full test cycle time.

When a specified number of samples are present in the buffer, Kslopeand Fadaptiveare calculated. Kslopeis the slope of the actual readings recorded in the FIFO circular buffer. In this embodiment, Kslopeis calculated using a first order best line fit (minimum least square) method. In alternative embodiments, any other suitable method could be used to determine Kslope. Kslopeis calculated according to the following equation:

Kslope=n×Σ⁡(ti×Fi)-(Σ⁢⁢ti)×(Σ⁢⁢Fi)n×Σ⁢⁢ti2-(Σ⁢⁢ti)2(2)
whereKslope=Flowrate slope in units such as cc/(min*sec).ti=Timestamp of the measurement in sec.Fi=Flowrate measurement of the leakage flowrate in units such as cc/min.n=Buffer size for calculation.

Kslopeis then used to calculate the adaptive flowrate (Fadaptive) according to the following equation:
FAdaptive,i=Fi+α×(Tend−Tcur)×Kslope,i(3)
whereFadaptive,i=Adaptive leak flowrate in units such as cc/min.α=Alpha, signature decay factor (D5=0.1−1). 1.00 if the slope (trend) is constant, however, the trend usually becomes smaller and smaller when it gets close to the converged value. 0.8 to 1 is usually the default value.Fi=Flowrate measurement in units such as cc/min.Kslope,i=Flowrate slope in units such as cc/(min*sec).Tend=Test end time in sec.Tcur=Test current time in sec.

In step62, the adaptive flowrate variation (Fadaptive, var), the maximum adaptive flowrate (FAdaptive, Max), and the minimum adaptive flowrate (FAdaptive, Min) are calculated. The adaptive flowrate variation (Fadaptive, varis calculated according to the following equation:
Fadaptive,var=|Fadaptive,largest−Fadaptive,smallest|  (4)
whereFadaptive,var=Adaptive flowrate variation in the FIFO buffer.Fadaptive,largest=Largest adaptive flowrate in the FIFO buffer.Fadaptive,smallest=Smallest adaptive flowrate in the FIFO buffer.

The maximum adaptive flowrate (FAdaptive, Max) is calculated according to the following equation:

Fadaptive,Max=Fadaptive,last+D2*Fadaptive,var*Tend-TcurB(5)
whereFadaptive,Max=Maximum adaptive flow in the FIFO buffer.Fadaptive,last=Last adaptive flow in the FIFO buffer.Fadaptive,var=Adaptive flow variation in the FIFO buffer.Tend=Test end time in sec.Tcur=Test current time in sec.B=Buffer time in sec.D2=Safety multiplier (user defined).

The minimum adaptive flowrate (FAdaptive, Min) is calculated according to the following equation:

Fadaptive,Min=Fadaptive,last-D2*Fadaptive,var*Tend-TcurB(6)
whereFadaptive,Min=Minimum adaptive flowrate in the FIFO buffer.Fadaptive,last=Last adaptive flowrate in the FIFO buffer.Fadaptive,var=Adaptive flowrate variation in the FIFO buffer.Tend=Test end time in sec.Tcur=Test current time in sec.B=Buffer time in sec.D2=Safety multiplier (user defined).

Next, in step64, FAdaptive, Maxis compared to the upper limit of the leak rate window (Lmax). Lmaxis equal to a user specified safety multiplier (D3) multiplied by the user specified leak rate tolerance (V2) which is the acceptable leak rate. For example, Lmaxcould be set at 1.2 times the acceptable leak rate. Also in step64, FAdaptive, Minis compared to the lower limit of the leak rate window Lmin. Lminis equal to a user specified safety multiplier (D4) multiplied by the user specified leak rate tolerance (V2) which is the acceptable leak rate. For example, Lmincould be 0.8 times the acceptable leak rate. If FAdaptive, Maxis greater than Lmaxand FAdaptive, Minis greater than Lmaxa gross leak is present, as shown in step66. The product is then classified as having a gross leak which is unacceptable. If either FAdaptive, Maxor FAdaptive, Minare less than Lmax, then the method continues to step68.

At step68, FAdaptive, Maxand FAdaptive, Minare compared to Lminto determine if an insignificant leak is present. If FAdaptive, Maxand FAdaptive, Minare less than Lmin, then an insignificant leak is present, as shown in step70. In step70, the product is classified having an insignificant leak and therefore acceptable. If either FAdaptive, Maxor FAdaptive, Minare greater than Lmin, then the method loops back to step54to start the process over. The process continues to loop until the adaptive test period ends, the gross leak is detected, or an insignificant leak is detected.

Referring now toFIG. 4, a screen shot of a software application80that performs a method of analyzing data to determine leak testing parameters is shown. The software application80includes a graph display portion82, a data display portion84, and a calculation display portion86.FIG. 5(Table 1) includes descriptions of the variables in the screen shot shown inFIG. 4. Software application80can be used to analyze data captured by an IGLS and determine leak testing coefficients for a new product or update the leak testing coefficients used for a product that has already been tested.

As described in Table 1, the “Adaptive” column and the “Time” column in data display portion84are indicative of the calculated adaptive leakage flowrate (Ladaptive) at time t which is shown in the “Time” column. The “Measure” column illustrates the measured leakage flowrate (Lmeasure) which is the measured leakage flowrate at the end of the full test time period. In the embodiment shown inFIG. 4, the full test time is 75 seconds, although the user can specify any suitable test time period. In software application80, the leak test is performed on the product under test for the full test time period to compare the actual measured leakage flowrate (Lmeasure) at the end of the test time period, tend, with the predicted leakage flowrate (Ladaptive). As shown in FIG.5/Table 1, “Leak Diff” is equal to the percentage of the difference between (Lmeasure) and (Ladaptivedivided by the difference between the acceptable leakage flowrate (V2) and Lmeasure.

The pass/fail criteria for this embodiment is determined by multiplying the standard deviation of the “LeakDiff” by six and comparing the resulting percentage to 100. If six times the standard deviation is less than 100, then a pass signal is generated. In alternative embodiments, the standard deviation multiplier is user selectable. As shown in the “Average Test Time (s)” cell of portion86ofFIG. 4, the average test time for the adaptive test in this example is 43.99 seconds compared to the “Full Test Time (s)” of 75 seconds for a time savings of 31.01 seconds per test. As indicated by “Non-Leak Missed” cell, no leaks would have been undetected using the adaptive test method.

The adaptive leak testing method of the present invention can be implemented as computer software as discussed above or can be performed manually during a leak testing process. As discussed above, any suitable method for determining the parameters such as the lower and upper leakage flowrates of the adaptive leak testing method can be used.