Leak testing

Abstract

There is provided a method of leak testing a component using an optical fluid analyser, the component positioned within a vessel, the vessel defining a chamber and the component defining an internal volume, the chamber and internal volume together defining a test volume, the method comprising reducing the pressure of a fluid in the test volume, injecting a tracer fluid into the test volume, while reducing the pressure of the fluid in the test volume and while injecting the tracer fluid into the test volume, using the optical fluid analyser to measure an amount of the tracer fluid exiting the test volume to obtain a tracer fluid signal, and determining a leak rate of the component based on the tracer fluid signal obtained while injecting the tracer fluid into the test volume.

Description

[0001] Leak testing

[0002] Field of Invention

[0003] The present invention relates to a leak test method, and to a leak testing apparatus.

[0004] Background

[0005] Components which, in use, will contain liquid or gas and cannot be permitted to leak may be subject to leak testing in order to assess the integrity of the components. Components from a large variety of applications may be subject to leak testing, for example refrigeration and air conditioning equipment and automotive parts, such as gasoline tanks.

[0006] Helium leak testing is one method of detecting small leaks. Helium is often in short supply on a global scale due to its use in a wide number of applications. Therefore, users of helium leak testing apparatus are vulnerable to the fluctuations in supply of helium.

[0007] The present invention seeks to obviate, or at least mitigate, one or more problems associated with known leak testing methods and apparatus, whether identified herein or otherwise.

[0008] Summary

[0009] In a first aspect of the invention, there is provided a method of leak testing a component using an optical fluid analyser, the component positioned within a vessel, the vessel defining a chamber and the component defining an internal volume, the chamber and internal volume together defining a test volume, the method comprising, reducing the pressure of a fluid in the test volume, injecting a tracer fluid into the test volume, while reducing the pressure of the fluid in the test volume and while injecting the tracer fluid into the test volume, using the optical fluid analyser to measure an amount of the tracer fluid exiting the test volume to obtain a tracer fluid signal and, determining a leak rate of the component based on the tracer fluid signal obtained while injecting the tracer fluid into the test volume.

[0010] The tracer fluid may be supplied to the test volume once a predetermined amount of time has elapsed since reduction of the pressure of the fluid in the test volume started. The

[0011] 69414738-1 tracer fluid may be supplied to the test volume once the pressure of the fluid in the test volume falls below a predetermined threshold value.

[0012] The tracer fluid may be injected into the internal volume of the component, and the tracer fluid exiting the test volume may be tracer fluid exiting the chamber of the vessel. Alternatively, the tracer fluid may be injected into the chamber of the vessel, and the tracer fluid exiting the test volume may be tracer fluid exiting the internal volume of the component.

[0013] Reducing the pressure of the fluid in the test volume and injecting the tracer fluid into the test volume may be distinct phases. For example, injecting the tracer fluid into the test volume may take place subsequent to reducing the pressure of the fluid in the test volume. That is, the pressure of the fluid in the test volume may be reduced first, and then tracer fluid may be injected into the test volume.

[0014] Since the method uses an optical fluid analyser, the method can be carried out with a large variety of different tracer fluids (e.g. not using Helium). Therefore, the method is more versatile than conventional methods. Conventional methods typically employ mass spectrometers to detect for the presence of a leak. Mass spectrometers are able to monitor for the presence of only a small number of fluids. This is undesirable because a particular tracer fluid may at times be in short supply either on a local or global scale. Since the present method can be carried out with a large variety of different tracer fluids, if a particular tracer fluid is in short supply, a different tracer fluid can be used to carry out the method.

[0015] The amount of the tracer fluid exiting the test volume is also referred herein to tracer fluid abundance measurements.

[0016] The method may further comprise positioning the component within the vessel.

[0017] The method may further comprise comparing the leak rate of the component to a predetermined threshold value. The method may further comprise determining, based on comparing the leak rate of the component to the predetermined threshold value, that the component passes or fails a leak test.

[0018] 69414738-1 The method may further comprise, while the pressure of the fluid in the test volume is being reduced, determining a plurality of offset values, the plurality of offset values each being equal to a difference between the measured amount of the tracer fluid exiting the test volume at a given time and a datum value, and using at least one of the plurality of offset values to obtain the tracer fluid signal.

[0019] The plurality of offset values may be determined at a predetermined time interval, such as 0.1 seconds (e.g. at each 0.1 second interval a measurement of the amount of tracer fluid exiting the test volume is obtained and the datum value subtracted to obtain the offset value for that given time). Upon commencement of the method, background tracer fluid may be present in the system used to carry out the method. Here and throughout this document, background tracer fluid may be understood to refer to tracer fluid originating from, for example, previously conducted leak test cycles and / or atmospheric tracer fluid. At least some background tracer fluid may be present in the system upon injection of the tracer fluid. Therefore, a component of the measured amount of the tracer fluid exiting the test volume (e.g. tracer fluid abundance measurements) obtained using the optical fluid analyser will be as a result of the background tracer fluid. It is not possible to distinguish between the background tracer fluid and the tracer fluid that has leaked through the component. This is undesirable because the tracer fluid signal will not accurately reflect the leak rate of the component.

[0020] Using at least one of the plurality of offset values to obtain the tracer fluid signal may comprise subtracting a final offset value from the measured amount of the tracer fluid exiting the test volume, or may comprise using the at least one of the plurality of offset values to generate a model for predicting offset values, and subtracting predicted offset values from the measured amount of tracer fluid exiting the test volume. In this way, the obtained tracer fluid signal may be thought of as a corrected measure of the amount of tracer fluid exiting the test volume, the correction removing the background tracer fluid abundance.

[0021] Using the at least one of the plurality of offset values to obtain the tracer fluid signal may comprise contemporaneously subtracting the offset values from the measured amount of the tracer fluid exiting the test volume. For example, in cases where there is no leak in the component, each determined offset value may be subtracted from each corresponding measured amount of tracer fluid exiting the test volume.

[0022] 69414738-1 Using the at least one of the plurality of offset values to obtain the tracer fluid signal may comprise subtracting the at least one of the plurality of offset values from the measured amount of the tracer fluid exiting the test volume to obtain the tracer fluid signal.

[0023] The at least one of the plurality of offset values may be a final offset value. The final offset value may be the final offset determined based on the final measurement taken prior to injecting the tracer fluid into the test volume. Alternatively, the final offset value may be the final offset determined prior to the value of the offset rising (e.g. the final offset being the lowest value offset calculated). Advantageously, by using the final offset value prior to injection of the tracer fluid, the determined leak rate of the component is more accurate as compared to if an earlier offset value were used. This is because the final offset value is the closest value to the amount of background tracer fluid present just prior to injection of the tracer fluid.

[0024] The method may further comprise determining, based on at least a portion of the plurality of offset values, a predicted offset function, the predicted offset function for outputting a predicted offset value.

[0025] The predicted offset value predicts a difference between background tracer fluid abundance and the datum value, e.g. is a prediction of the offset value. The predicted offset function is a mathematical model that predicts future offset values based on previous offset values.

[0026] The at least a portion of the plurality of offset values may be all of the plurality of offset values determined based on each measured amount of the tracer fluid exiting the test volume, or may only include some of the plurality of offset values, such as the first 10, 20, 50, or any other number, offset values determined. As described herein, it can be advantageous to only use a portion of the plurality of offset values as those values not used can be used to test the accuracy of the predicted offset function.

[0027] Using the at least one of the plurality of offset values to obtain the tracer fluid signal may comprise using at least one predicted offset value output by the predicted offset function to obtain the tracer fluid signal.

[0028] 69414738-1 That is, instead of using one of the determined plurality of offset values (such as the final offset value) to obtain the tracer fluid signal, one or more predicted offset values may be used instead to obtain the tracer fluid signal.

[0029] Removing all of the background tracer fluid during a leak test is generally not feasible in mass production environments. This is because the time taken to remove all of the background tracer fluid would slow down the production line resulting in a bottleneck, which is undesirable. Therefore, instead, the pressure of the fluid in the test volume is typically reduced for a predetermined amount of time, or to a predetermined pressure, before the tracer fluid is injected into the test volume. Upon injection of the tracer fluid into the test volume, a component of the tracer fluid signal comprises the remaining background tracer fluid, and a component of the tracer fluid signal comprises the injected tracer fluid that has leaked through the component. However, following injection, the two sources of tracer fluid (the background tracer fluid and the injected tracer fluid that has leaked through the component) cannot be distinguished in the tracer fluid signal. Furthermore, it is often the case that the amount of background tracer fluid present in the test volume continues to reduce following injection of the tracer fluid into the test volume.

[0030] Therefore, obtaining the tracer fluid signal using the at least one of the plurality of offset values to obtain the tracer fluid signal (either directly by subtracting a determined offset value from the obtained measurements, or indirectly by generating a predicted offset function which output is subtracted from the obtained measurements) leads to more accurate results.

[0031] The predicted offset function may comprise a sum of exponentials.

[0032] Determining the predicted offset function may comprise performing an iterative optimization loop to determine values of one or more parameters of the predicted offset function.

[0033] That is, the parameters of the predicted offset function may be iteratively updated until the predicted offset function models (e.g. fits) the determined offset while the pressure of the fluid in the test volume is being reduced.

[0034] 69414738-1 The one or more parameters of the predicted offset function may be initialised as random values prior to performing the iterative optimization loop.

[0035] During the iterative optimization loop, the output of the predicted offset function at each iteration can be compared to the measured data (e.g. the determined offset calculated based on the measured amount of the tracer fluid exiting the test volume). The comparison can be used to iteratively update the parameters. The iterative optimization loop can continue until any suitable criteria has been met. Once the suitable criteria has been met the iterative optimization loop can be halted and the final values for the one or more parameters can be obtained.

[0036] Using the at least one predicted offset value output by the predicted offset function to obtain the tracer fluid signal may comprise subtracting the at least one predicted offset value from the measured amount of tracer fluid exiting the test volume to obtain the tracer fluid signal.

[0037] The predicted offset value may be subtracted from the amount of tracer fluid exiting the test volume measured while the tracer fluid is being injected into the test volume. Subtracting the predicted offset value from the measured amount of tracer fluid exiting the test volume may comprise subtracting one or more predicted offset values output by the predicted offset function for given points in time from corresponding measured amounts of tracer fluid exiting the test volume measured at those given points in time.

[0038] The method may further comprise, prior to injection of the tracer fluid, comparing one or more predicted offset values output by the predicted offset function to at least a second portion of the determined plurality of offset values and determining, based on the comparison, whether the predicted offset values are within a predetermined error range of the at least a second portion of the determined plurality of offset values.

[0039] Prior to injection of the tracer fluid, the tracer fluid signal accounts for only background tracer fluid. Therefore, prior to injection of the tracer fluid, the abundance of background tracer fluid is known. Advantageously, comparing the predicted offset values of the predicted offset function to the determined at least a second portion of the determined plurality of offset values allows an assessment of the accuracy of the predicted offset function to take place. This allows action to be taken if the predicted offset values of the

[0040] 69414738-1 predicted offset function are not within the predetermined error range, preventing an inaccurate leak test from taking place. The predicted offset values of the predicted offset function used in the comparison are values output by the function at times which correspond to times at which each amount of the tracer fluid exiting the test volume is measured, said measurements used to determine the at least a second portion of the plurality of offset values.

[0041] The at least a second portion of the plurality of offset values may be obtained after the portion of offset values used to determine the predicted offset function. That is, the plurality of offset values may comprise a first set of values and a second set of values. The first set of values may be measured in a first time period and the second set of values may be measured in a second time period. The first time period may be prior to the second time period. Both the first and second time period may be within the period in which the pressure is being reduced in the test volume. The first set of values may be used to determine the predicted offset function. The second set of values may be used to determine the accuracy of the predicted offset function.

[0042] The method may further comprise, if the one or more predicted offset values of the predicted offset function are within the predetermined error range, using at least one predicted offset value output by the predicted offset function to obtain the tracer fluid signal, or if the one or more predicted offset values of the predicted offset function are not within the predetermined error range, using the at least one of the determined plurality of offset values to obtain the tracer fluid signal.

[0043] Advantageously, this improves the accuracy of the determined leak rate of the component. This is because the method allows a determination of the optimal steps to be followed during the leak test that will yield the more accurate results. For example, either the predicted offset function is used to subtract predicted offset values from the measured amount of tracer fluid exiting the test volume during the injecting of the tracer fluid into the test volume or at least one of the plurality of offset (such as the final measured offset value) is subtracted from the measured amount of tracer fluid exiting the test volume during the injecting of the tracer fluid into the test volume.

[0044] 69414738-1 The predetermined error may be 10%. Advantageously, this error range optimises the method such that the more accurate offset subtraction is performed, thereby improving the accuracy of the determined leak rate.

[0045] The datum value may be at least zero and up to 1 E-9 mbarm3 / s.

[0046] The datum value is a reference value. The reference value may represent a value which is too low to be achieved. The datum value may equal zero. Alternatively, the datum value may be greater than zero, such as up to 1 E-9 mbarm3 / s. For example, while a leak testing apparatus may be able to measure down to 1 E-9 mbarm3 / s or lower, it may not be practical (or feasible) to measure down to 1 E-9 mbarm3 / s or lower during the cycle time of the leak test. Therefore, the datum value may be set at any suitable value that cannot be achieved during the present set up and cycle time of the leak testing apparatus.

[0047] The tracer fluid may be nitrogen. Leak testing is typically conducted using helium as the tracer fluid. Supply of helium is inconsistent, and shortages can lead to machine downtime. Nitrogen is a highly abundant gas, and does not suffer from the same shortages as helium. Therefore, where the tracer fluid is nitrogen, the likelihood of downtime is advantageously reduced, thereby making the method is more efficient.

[0048] The optical fluid analyser device may be a plasma spectroscopy device.

[0049] Injecting the tracer fluid to the test volume may comprise injecting the tracer fluid to the internal cavity of the component or to the chamber.

[0050] In a second aspect of the present invention, there is provided a leak testing apparatus for leak testing a component that defines an internal volume, the apparatus comprising, a vessel that defines a chamber, wherein, in use, the chamber and the internal volume of the component together define a test volume, and wherein the vessel comprises a tracer fluid inlet for injecting tracer fluid into the test volume, an optical fluid analyser, a pumping system that is configured to reduce the pressure of the fluid in the test volume, and to pump fluid from the test volume through the optical fluid analyser such that the optical fluid analyser measures an amount of tracer fluid exiting the test volume and a controller configured to carry out the method of the first, third and fourth aspects of the

[0051] 69414738-1 present invention. It will be appreciated that optional features of, for example, the first aspect may be used in conjunction with the apparatus of the second aspect.

[0052] The leak testing apparatus may further comprise a tracer fluid source that is connected to the tracer fluid inlet.

[0053] The tracer fluid may be nitrogen.

[0054] The optical fluid analyser may be a plasma spectroscopy device.

[0055] In a third aspect of the present invention, there is provided a method of leak testing a component, the method comprising, positioning the component within a vessel, the vessel defining a chamber and the component defining an internal volume, the chamber and internal volume together defining a test volume, reducing the pressure of a fluid in the test volume, injecting a tracer fluid into the test volume, while reducing the pressure of the fluid in the test volume and while injecting the tracer fluid into the test volume, using a fluid detection device to measure an amount of the tracer fluid exiting the test volume to obtain a tracer fluid signal, determining, based on the measured amount of tracer fluid exiting the test volume obtained while the pressure of the fluid in the test volume is being reduced, a predicted offset function, the predicted offset function for predicting a difference between background tracer fluid abundance and a datum value, subtracting an output of the predicted offset function from the measured amount of tracer fluid exiting the test volume obtained while injecting the tracer fluid into the test volume, to obtain a predicted leak signal, determining a leak rate of the component based on the predicted leak signal and comparing the leak rate of the component to a predetermined threshold value.

[0056] In a fourth aspect of the present invention there is provided a computer implemented method of leak testing a component, the component provided within a vessel, the vessel defining a chamber and the component defining an internal volume, the chamber and internal volume together defining a test volume the method comprising, measuring an amount of tracer fluid exiting the test volume while reducing the pressure, the amount of tracer fluid indicative of a background tracer fluid abundance within the test volume, generating, based on measuring the amount of tracer fluid exiting the test volume, a model configured to predict the amount of tracer fluid exiting the test volume due to the

[0057] 69414738-1 background tracer fluid abundance, measuring an amount of tracer fluid exiting the test volume while injecting tracer fluid into the test volume, determining, based on the model, a correction to the measured amount of tracer fluid exiting the test volume while injecting tracer fluid into the test volume, determining a leak rate of the component based on the corrected measured amount of tracer fluid exiting the test volume.

[0058] Generating the model may comprise generating a predicted offset function, such as the predicted offset function described herein.

[0059] Optional features of the first aspect of the present invention may be used in conjunction with the fourth aspect. While an optical fluid analyser has been described for measuring an amount of the tracer fluid exiting the test volume in conjunction with the first aspect, it will be appreciated that in other aspects, such as the third aspect any suitable fluid detection device may be used.

[0060] In a fifth aspect of the present invention, there is provided a computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the method of the first, third and fourth aspects of the present invention.

[0061] Brief Description of the Figures

[0062] Embodiments of the present invention will now be described with reference to the accompanying drawings, in which:

[0063] Figure 1 schematically depicts a leak test system in accordance with an embodiment of the present invention;

[0064] Figures 2a and 2b depict example plots of a tracer fluid signal;

[0065] Figure 3 depicts a graph of a tracer fluid signal obtained according to an embodiment of the present invention;

[0066] Figure 4 depicts a graph of a tracer fluid signal obtained according to a further embodiment of the present invention;

[0067] Figure 5 is a schematic representation of a controller of the leak test system shown in Figure 1 ; and

[0068] Figure 6 is a flow chart according to an embodiment of the present invention.

[0069] 69414738-1 Detailed Description

[0070] Figure 1 schematically depicts a leak testing apparatus 2 in accordance with an embodiment of the present invention. The leak testing apparatus 2 comprises a vessel 4. In use, the vessel 4 receives a component 6 that is to be leak tested. The leak testing apparatus 2 can be used to assess whether the component 6 has a leak, and to assess the severity of the leak. It will be appreciated that a leak may result in fluid leaking into and / or out of a component.

[0071] The vessel 4 defines a chamber 8. The chamber 8 is the internal volume that is defined by the vessel 4. The vessel 4 may be any suitable vessel that allows the chamber 8 to be sealed from the external environment. It will, however, be appreciated that the chamber 8 may be in fluid communication with the external environment via one or more components of the leak testing apparatus 2. The component 6 comprises an internal volume 10. When the component 6 is placed in the vessel 4, the chamber 8 and the internal volume 10 of the component together define a test volume 12.

[0072] The leak testing apparatus 2 further comprises a first vacuum pump 14. The first vacuum pump 14 is able to reduce the pressure of fluid in the internal volume 10 of the component 6. The term ‘vacuum pump’ may be understood to refer to any pump that is suitable to reduce the pressure of fluid in the internal volume 10 of the component 6. The first vacuum pump 14 may for example be a centrifugal pump, a rotary vane pump, a scroll pump or a diaphragm pump. An inlet of the first vacuum pump 14 is connected to the internal volume of the component 6. An outlet (not shown in Figure 1 due to the schematic representation of the leak testing apparatus 2) of the first vacuum pump 14 is in fluid communication with an external volume (not shown in Figure 1). The external volume may be a vessel or container, or may be the external environment. When the first vacuum pump 14 is operating, fluid is pumped from the internal volume 10 of the component 6 to the external volume. This reduces the pressure of fluid in the internal volume 10 of the component 6.

[0073] The leak testing apparatus 2 further comprises a second vacuum pump 16. The second vacuum pump 16 is able to reduce the pressure of fluid in the chamber 8. The first vacuum pump 14 and the second vacuum pump 16 form a part of a pumping system. The pumping system is able to reduce the pressure of the fluid in the test volume 12. The second vacuum pump 16 may for example be a centrifugal pump, a rotary vane

[0074] 69414738-1 pump, a scroll pump or a diaphragm pump. An inlet of the second vacuum pump 16 is connected to the chamber 8. An outlet (not shown in Figure 1 due to the schematic representation of the leak testing apparatus 2) of the second vacuum pump 16 is in fluid communication with an external volume (not shown in Figure 1). The external volume may be a vessel or container, or may be the external environment. When the second vacuum pump 16 is operating, fluid is pumped from the chamber 8 to the external volume. This reduces the pressure of fluid in the chamber 6.

[0075] The vessel 4 comprises a tracer fluid inlet 18. The leak testing apparatus 2 further comprises a tracer fluid vessel 20. The tracer fluid vessel 20 contains a tracer fluid. The fluid contained in the tracer fluid vessel 20 is pressurised. The tracer fluid that is contained within the tracer fluid vessel 20 may be any suitable fluid. The tracer fluid may be a tracer gas. The tracer gas may be, for example, nitrogen or helium. An outlet 19 of the tracer fluid vessel 20 is connected to the tracer fluid inlet 18. In the depicted embodiment, the internal volume 10 of the component 6 is connected to the tracer fluid inlet 18 such that, in use, tracer fluid is supplied to the internal volume 10 of the component 6.

[0076] The leak testing apparatus 2 further comprises a fluid detection device 22. The fluid detection device 22 may be an optical fluid analyser, such as a plasma spectroscopy device. The fluid detection device 22 is able to monitor, and measure the abundance of, a fluid flowing through the fluid detection device for the presence of one or more fluids. Optical fluid analysers are highly versatile in that they are able to detect the presence of, and determine the abundance of, a number of difference fluids. The type of fluid(s) detected by the fluid detection device 22 may be a gas or a vapour. An inlet 23 of the fluid detection device 22 is in fluid communication with the chambers. In use, the vacuum pump 16 draws fluid to the inlet of the fluid detection device 22. In some, non-depicted, embodiments, a third vacuum pump may be provided with the sole purpose of drawing fluid through the fluid detection device. Where the third vacuum pump is provided, the third vacuum pump and the vacuum pump 16 may draw fluid to the inlet of the fluid detection device 22. The third vacuum pump may be a component part of the fluid detection device 22 or may be separate to the fluid detection device 22. Where the third vacuum pump is provided, the fluid detection device 22 may be said to be differentially pumped.

[0077] 69414738-1 In some, non-depicted, embodiments, the component 6 need not be connected to the tracer fluid inlet 18. Instead, the tracer fluid may be supplied to the chamber 8 via the tracer fluid inlet 18. Where the tracer fluid is supplied to chamber via the tracer fluid inlet, the inlet of the fluid detection device 22 may be in (direct) fluid communication with the internal volume 10 of the component 6. Whether the fluid detection device 22 is in (direct) fluid communication with the chamber 8 or with the internal volume 10 of the component 6 may depend upon, for example, the conditions that the component 6 will be subject to when in use. If, in use, the pressure of the fluid in the internal volume 10 of the component 6 is less than the pressure of the fluid surrounding the component 6, the component 6 may be undergo a leak test with the fluid detection device 22 in fluid communication with the internal volume 10 of the component 6, and the tracer fluid may be supplied to the chamber 8. If, in use, the pressure of the fluid in the internal volume 10 of the component 6 is greater than the pressure of the fluid surrounding the component 6, the component 6 may be undergo a leak test with the fluid detection device 22 in fluid communication with the chamber 8, and the tracer fluid may be supplied to the internal volume 10 of the component 6.

[0078] The leak testing apparatus 2 further comprises a controller 24. The components of the leak testing apparatus, including the first vacuum pump 14, the second vacuum pump 16, the tracer fluid source 20, and the fluid detection device 22, are able to communicate with the controller 24. Furthermore, the components of the leak testing apparatus including the first vacuum pump 14, the second vacuum pump 16, the tracer fluid source 20, and the fluid detection device 22, are able to be controlled by the controller 24.

[0079] The leak testing apparatus 2 conducts a leak test operation in two main phases: a pressure reduction phase and a leak detection phase. Throughout the leak test, the controller 24 receives a plurality of tracer fluid abundance measurements from the fluid detection device 22 at periodic intervals. The measurements may be taken by the fluid detection device 22 and sent to the controller 24 at any suitable interval. In a specific example, the measurements may be taken approximately every 0.1s. The controller 24 then generates a tracer fluid signal based upon the measurements that it received from the fluid detection device 22.

[0080] In the pressure reduction phase, the first vacuum pump 14 and the second vacuum pump 16 are operated to reduce the pressure of the fluid in the test volume 12. Once the

[0081] 69414738-1 pressure of the fluid in the internal volume 10 of the component 6 reaches a first predetermined value and the pressure of the fluid in the chamber 8 reaches a second predetermined value and is stable, the tracer fluid is injected into the test volume 12 (i.e., into the chamber 8 or into the internal volume 10 of the component 6). To stabilise the pressure of the fluid in the chamber 8, a purge fluid, such as argon, may be injected into the chamber once the pressure of the fluid in the chamber 8 reaches the second predetermined value. The purge fluid may be provided to the chamber 8 from a purge fluid source via a purge fluid inlet (not shown in the Figures). The pressure reduction phase ends when the pressure of the fluid in the internal volume 10 of the component 6 reaches the first predetermined value and the pressure of the fluid in the chamber 8 reaches the second predetermined value and is stable.

[0082] During the pressure reduction phase, tracer fluid is not supplied from the tracer fluid source 20 to the test volume 12. During the pressure reduction phase, the fluid detection device 22 is operated to measure an amount of tracer fluid exiting the test volume 12. The measurements of the tracer fluid obtained using the fluid detection device 22 are sent to the controller 24 which the controller 24 uses to generate a tracer fluid signal. Although no tracer fluid is supplied from the tracer fluid source 20 to the test volume 12 during the pressure reduction phase, background tracer fluid is present in the apparatus. Throughout this document, background tracer fluid may be understood to refer to tracer fluid present in the system that originates from, for example, previously conducted leak test cycles and / or atmospheric tracer fluid, and not from the tracer fluid source 20 being used for a current leak test. Where the component 6 does not have a leak, the tracer fluid exiting the test volume 12 during the pressure reduction phase will originate from the chamber 8 only. That is to say, the tracer fluid exiting the test volume 12 during the pressure reduction phase will not include any tracer fluid present in the internal volume 10 of the component 6. Where the component 6 does have a leak, during the pressure reduction phase, the tracer fluid that is present in the internal volume 10 of the component 6 will pass through the component 6 and into the chamber 8. From the chamber 8, the tracer fluid will pass through and be detected by the fluid detection device 22. Therefore, where the component does have a leak, the tracer fluid present in the internal volume 10 of the component 6 will contribute towards the background tracer fluid present in the test volume 12.

[0083] 69414738-1 Once the pressure of the fluid in the test volume 12 reaches the predetermined values described above, the tracer fluid is injected into the test volume 12 (i.e., into the chamber 8 or into the internal volume 10 of the component 6). The leak detection phase is considered to have started upon injection of the tracer fluid into the test volume 12. During the leak detection phase, fluid is drawn from the test volume 12 by and through the fluid detection device 22 by the second vacuum pump 16 (and the third vacuum pump, where provided). This allows the fluid detection device 22 to continue to measure the amount of tracer fluid exiting the test volume 12. Again, the measurements obtained by the fluid detection device 22 are sent to the controller 24, which the controller 24 uses to generate a tracer fluid signal. The first vacuum pump 14 is not active in the leak detection phase.

[0084] As discussed above, the pressure reduction phase seeks to remove fluid from the test volume 12. At least some of the fluid that is removed during the pressure reduction phase is background tracer fluid. Conventionally, the tracer fluid is injected into the test volume 12 from the tracer fluid vessel 20 once the pressure of the fluid in the test volume 12 reaches a predetermined value. As discussed above, different predetermined pressure values may be used for different parts of the test volume 12. The predetermine pressure value is conventionally non-zero. Therefore, it is usually the case that, when the tracer fluid is injected into the test volume 12, the tracer fluid abundance measurements are non-zero. This is as a result of the background tracer fluid present in the leak testing apparatus 2 as described above. The abundance of background tracer fluid in the test volume 12 is usually non-zero when the tracer fluid is injected from the tracer fluid vessel 20 into the test volume 12. This is because it is not feasible in a production environment to wait until all of the background tracer fluid has been removed from the test volume 12. This is due to the time that would be required to remove all of the background tracer fluid from the test volume 12, which would result in a bottleneck in the production line.

[0085] Figure 2a shows an example plot of tracer fluid abundance measurements from a leak test. The graph of Figure 2a plots two separate tracer fluid abundance measurements - a background signal 26 and component leak signal 28. The background signal 26 accounts for only background tracer fluid detected during the leak test, and the component leak signal 28 accounts for only tracer fluid that has passed through the component 6. In practice, it is not possible to distinguish between the two sources of tracer fluid during the leak detection phase 34, but the background signal 26 has been

[0086] 69414738-1 included in the plot to demonstrate the effect of background tracer fluid on the tracer fluid signal. Therefore, in practice, the measured leak rate is dependent on the sum of the background signal 26 and the component leak signal 28. The graph also includes a reject set point 32. The reject set point 32 is used to determine whether a component 6 is awarded a pass or fail following the leak test. If the tracer fluid signal exceeds the reject set point 32, then the component is awarded a fail, and if the tracer fluid signal stays below the reject set point 32 throughout the leak test, then the component is awarded a pass.

[0087] As can be seen, during the pressure reduction phase 30, the background signal 26 reduces as the first and second vacuum pumps 14, 16 remove fluid from the test volume 12. Once the pressure of the fluid in the test volume 12 reaches a predetermined value, the tracer fluid is injected into the test volume 12. The leak detection phase commences upon injection of the tracer fluid into the test volume 12. Shortly after injection of the tracer fluid, the tracer fluid passes through (i.e., leaks through) the component 6. The abundance of tracer fluid passing through the component 6 is measured by the fluid detection device 22, and the measurements are sent to the controller 24 that generates a component leak signal 28 based on the measurements. The amount of fluid passing through the component is depicted as the component leak signal 28. A further amount of time is allowed to pass before the test ends. The controller 24 then determines a leak rate of the component 8 based on the final value, or maximum value, of the component leak signal 28. As can be seen, the component leak signal 28 remains below the reject set point 32 throughout the leak test. However, in practice, the tracer fluid abundance measured by the fluid detection device 22 would include both the component leak signal 28 and the background signal 26. In the graph shown in Figure 2a, the sum of these signals 26, 28 would result in the measured tracer fluid abundance rising above the reject set point 32. This is undesirable because, based on the component leak signal 28, the component leak signal does not rise above the reject set point 32 and so the component is acceptable from a leak test perspective.

[0088] Figure 2b shows a further example plot of tracer fluid abundance measurements from a leak test. Again, the graph plots two separate tracer fluid abundance measurements - a background signal 26 and a component leak signal 28. The graph also include a reject set point 32. In this graph, the background signal 26 has not fallen below the reject set point 32 upon the component leak signal 28 increase, whereas the component leak

[0089] 69414738-1 signal 28 does not rise above the reject set point 32. However, since the fluid detection device 22 and controller 24 cannot distinguish between the sources of tracer fluid, the component 6 is rejected based upon the results of this leak test operation. Rejection of components based upon the background tracer fluid is undesirable because it results in wastage of components that should have passed the leak test.

[0090] Figure 3 shows an example plot of a tracer fluid signal 36 obtained by a leak test according to an embodiment of the present invention. As with Figures 2a, 2b the leak test from which the graph of Figure 3 was obtained also includes a pressure reduction phase 30 and a leak detection phase 34. The tracer fluid signal 36 may be obtained using the leak testing apparatus 2. The graph of Figure 3 shows a single tracer fluid signal 36, which is plotted as a solid line. For illustration purposes, the tracer fluid signal 36 has a first part 36a, second part 36b and a third part 36c. The first part 36a, occurring between time period T1 , corresponds to measurements made during the pressure reduction phase 30, and indicates the background tracer fluid abundance (e.g. the background signal 26). The second part 36b, occurring between time period T2, also corresponds to measurements made during the pressure reduction phase 30, but where the background tracer fluid abundance measurements have been corrected to remove the background, as described below. The third part 36, occurring between time period T3, corresponds to measurements made during the leak detection phase 34, and indicates a corrected component leak signal (e.g. a measured component leak signal 28 that has been corrected to remove the background). The graph of Figure 3 also shows the background signal 26 for reference, plotted as a dashed line. Again, it is not possible for the fluid detection device 22 to distinguish between the sources of tracer fluid (such as when operating in the leak detection phase 34), but the background signal 26 has been shown for reference.

[0091] Throughout the leak test, the controller 24 receives a number of tracer fluid abundance measurements from the fluid detection device 22 at periodic intervals. The measurements may be taken by the fluid detection device 22 and sent to the controller 24 approximately once every 0.1s, or any other suitable time interval. The controller 24 then generates a tracer fluid signal 36 based upon the measurements received from the fluid detection device 22.

[0092] 69414738-1 As describe above, the tracer fluid is injected from the tracer fluid vessel 20 to the test volume 12 following elapse of a predetermined amount of time following initiation of the pressure reduction phase 30, or upon the pressure of the fluid in the test volume 12 reaching a predetermined value (or reaching the first and second predetermined values for the component 6 and chamber 8 as described above).

[0093] In this embodiment, during the pressure reduction phase 30, the controller24 determines a plurality of offset values O. Each offset value of the plurality of offset values O is equal to a difference between the values of the tracer fluid abundance measurements and a datum value D at a given time. The plurality of offset values comprises a first offset value Oi. The first offset value Oi is determined once the tracer fluid signal 36 falls below a predetermined value. The plurality of offset values O are determined at periodic intervals. The plurality of offset values may be determined at intervals corresponding to the intervals that the controller 24 receives the tracer fluid abundance measurements from the fluid detection device 22. Alternatively, the plurality of offset values may be determined at intervals greater than the intervals that the controller 24 receives the tracer fluid abundance measurements from the fluid detection device 22.

[0094] The datum value D is any suitable reference value. For example, the datum value D may be zero mbarm3 / s, or may be a non-zero value such as 1 E-9 mbarm3 / s. The datum value may be representative of a background tracer fluid abundance that cannot feasibly be detected during the pressure reduction phase. The controller 24 contemporaneously subtracts the plurality of offset values O from the values of the tracer fluid abundance measurements. That is to say, the controller 24 subtracts each offset value determined at a given time from each corresponding value of the tracer fluid abundance measurement at that given time. As can be seen from Figure 3, the first offset value Oi is subtracted from the value of the tracer fluid abundance measurement (e.g. subtracted from the background signal 26) at a time corresponding to when the first offset value Oi is determined, correcting the background tracer fluid abundance to value D. Following the subtraction of each measured value of the tracer fluid abundance measurement by its corresponding offset, and while no tracer fluid is being injected into the test volume, the tracer fluid signal 36 is equal to D (as shown in the second part 36b of the tracer fluid signal 36). For illustration, the dotted curved line in time period T2 indicates the measured tracer fluid abundance as read from the fluid detection device 22, which has

[0095] 69414738-1 not been corrected with the offset values. The dotted vertical lines within time period T2 illustrate the value of the calculated offsets.

[0096] The plurality of offset values comprises a final offset value OF. The final offset value OF can be determined in a number of ways. In a specific example, the final offset value OF is defined as the last offset value that is determined prior to their being an increase in the value of the offset. The value of the offset gradually reduces with time during the pressure reduction phase 30, but will increase if, during the leak detection phase 34, there is a leak in the component 6 as the measured tracer fluid abundance will rise. In this way the last offset value OF has the lowest value of all offset values. If there is no leak in the component 6, then the last offset value OF will be the last value recorded in the leak test. In the example shown in Figure 3, the third part 36c of the tracer fluid signal 36 begins to rise as soon as the leak detection phase 34 begins (indicating that the component 6 has a leak).

[0097] Once a final offset value OF has been determined, the final offset value OF may be subtracted from the tracer fluid abundance measurements obtained for the remainder of the leak test operation (e.g. during time period T3), to obtain the third part 36c of the tracer fluid signal 36. That is to say, the final offset value OF is subtracted from each value of the tracer fluid abundance measurement for the entirety of the leak detection phase 34 (e.g. during time period T3). Of course, if the offset value had not begun to rise as soon as the leak detection phase 34 had started, but had instead started to rise sometime later within the leak detection phase 34, the final offset value will have been identified during the leak detection phase 34, and those measurements recorded after identification of the rise in offset value may have been amended by subtracting the final offset value. Subtracting the final offset value OF from subsequent tracer fluid abundance measurements effectively removes the background from those subsequent measurements, leading to a more accurate result.

[0098] While it has been described that the final offset value is determined prior to their being an increase in the value of a given offset, alternatively, the final offset value may instead simply be determined to be the last offset value prior to the start of the leak detection phase 34. Selecting a final offset value OF in this way would represent the most accurate background tracer fluid abundance known prior to commencement of the leak detection phase 34, since prior to commencement of the leak detection phase 34 the only tracer

[0099] 69414738-1 fluid detected by the fluid detection device 22 is background tracer fluid. That is to say, prior to commencement of the leak detection phase 34, the background signal 26 is the measured tracer fluid abundance. Therefore, by subtracting the final offset value OF from the tracer fluid abundance measurements to obtain tracer fluid signal 36, the accuracy of the leak rate determined using the tracer fluid signal 36 is improved. That is, as compared to if no offset were subtracted from the tracer fluid abundance measurements, or if an earlier offset value were subtracted from the tracer fluid abundance measurements. Where an increase in the tracer fluid abundance measurements is not detected, the final offset value OF may be determined upon completion of the leak test. An increase may not be detected where the component 6 does not have any leaks. Where no increase in the offset values are detected, the plurality of offset values are contemporaneously subtracted from the tracer fluid abundance measurements, leading to a tracer fluid signal equal to D (such as that shown in part 36b).

[0100] Although subtracting the final offset value OF from the tracer fluid signal 36 improves the accuracy of the leak rate determined, the accuracy of the leak rate determined is dependent upon the nature of the background signal 26 during the pressure reduction phase 30. In particular, the accuracy of the leak rate determined is dependent upon the nature of the background signal 26 when the final offset value OF is determined. As can be seen from Figure 3, the background signal 26 is falling when the final offset value OF is determined. The background signal 26 continues to fall during the leak detection phase 34 before stabilising part-way through the leak detection phase 34. Therefore, the final offset value OF is greater than the values of the background signal 26 throughout the leak detection phase 34. Since the final offset value OF is greater than the values of the background signal 26 during the leak detection phase 34, the tracer fluid signal 36 (e.g. part 36c) is reduced, by virtue of the subtraction of the final offset value OF, by a greater amount than is necessary to account for the background tracer fluid. This leads to the determined leak rate of the component 6, which is determined based upon the tracer fluid signal 36, being smaller than the actual leak rate of the component 6. This is undesirable because the component 6 may be awarded a pass based on the results of the test, but the component 6 may have a leak rate that would result in it being awarded a fail.

[0101] Where the background signal 26 is stable upon commencement of the leak detection phase 34, the final offset value OF is representative of the values of the background

[0102] 69414738-1 signal 26 throughout the leak detection phase 34. Therefore, where the background signal is stable upon commencement of the leak detection phase 34, the above issues do not occur.

[0103] Figure 4 shows a further example plot of a tracer fluid signal 36 obtained by a leak test operation in accordance with an embodiment of the present invention. The tracer fluid signal 36 may be obtained using the leak testing apparatus 2. As with the leak test operation of Figure 3, during time period T2 the leak testing operation of Figure 4 also determines a plurality of offset values O, which may include a first offset value Oi and a final offset value OF. The plurality of offset values O are determined in the same manner as for the leak test of Figure 3, and are subtracted from the tracer fluid abundance measurements during time period T2 contemporaneously to obtain tracer fluid signal 36 (e.g. second part 36b).

[0104] In the leak test operation that results in the graph of Figure 4, the controller 24 determines a model that can be used to predict future offset values based on previously determined offset values. In the following example, the model is a predicted offset function. The predicted offset function is determined based on the tracer fluid abundance measurements obtained during the pressure reduction phase 30. The predicted offset function predicts, for a given time during the leak test, a difference (e.g. offset value) between the background tracer fluid abundance and the datum value D. As noted above, during the pressure reduction phase 30, the tracer fluid abundance measurements corresponds to the background tracer fluid abundance, since no tracer fluid is being injected into the test volume 12. Advantageously, the predicted offset function can be used to predict offset values during the leak detection phase 34, where, as discussed above, it is not possible to distinguish between the sources of tracer fluid present in the test volume 12. Therefore, by predicting the difference between the background tracer fluid abundance and the datum value D for the duration of the leak test (or at least during the leak detection phase 34), and subtracting that difference throughout the test, the accuracy of the tracer fluid signal with respect to the actual leak rate of the component 8 is improved. The vertical dotted lines during time period T3 (e.g. during the leak detection phase 34) in Figure 4 represent predicted offset values at those time points.

[0105] Where a predicted offset function is determined, the leak test may follow the steps discussed in relation to Figure 3 prior to injection of the tracer fluid. Therefore, where a

[0106] 69414738-1 predicted offset function is determined, a plurality of offset values O may be determined prior to injection of the tracer fluid. The initial offset value Oi may be determined and subtracted from the tracer fluid abundance measurements once the tracer fluid abundance measurements falls below a predetermined value (e.g. the start of time period T2). The plurality of offset values O may then be determined periodically (e.g., every 0.1s) until the tracer fluid is injected into the test volume 12. Once the tracer fluid is injected into the test volume 12, the predicted offset function may be used to generate values of the predicted offset, and these predicted offset values may be subtracted from the tracer fluid abundance measurements to obtain the tracer fluid signal 36 (e.g. the third part 36c during time period T3).

[0107] The predicted offset function may comprise any suitable mathematical model for modelling data. In a specific example, the predicted offset function comprises a sum of exponentials, although other methods, such as Fourier, polynomial or LaPlace series, may be used. The method used may be chosen based on, for example, the available computing resources and the accuracy required. In the present case, it has been found that due to the logarithmic nature of the measured data during the pressure reduction phase 30, a sum of exponentials with two or three constant parameters provides a good approximation. The predicted offset function models the offset as a function of time (the offset being the background tracer fluid abundance minus the datum value D). Given that D is a constant, the predicted offset function also models the background tracer fluid abundance measured by the fluid detection device 22.

[0108] The predicted offset function comprises a number of parameters, the values of which need to be determined in order for the predicted offset function to model the background tracer fluid abundance. The values of the parameters of the predicted offset function may be determined based on measured data. That is known data obtained during the pressure reduction phase 30 can be used to determine the values of the parameters of the predicted offset function. The known data may include the tracer fluid abundance measurements taken during the pressure reduction phase 30 (e.g. measured offset values). For example, during the pressure reduction phase 30 a first set of measurements (such as the first ten, twenty, thirty, etc. measurements) of the tracer fluid abundance measurements (or of the offset) may be used to determine the parameters of the model. That is, the predicted offset function may be fit to the measured first set of measurements. In a specific example an iterative optimization loop may be used to

[0109] 69414738-1 determine the values of the parameters. The controller 24 may carry out the iterative optimization loop. An example iterative optimization loop may comprise the following steps:

[0110] 1. Declare a set of input variables. In a specific example, the input variables may be: timeVector, measuredValue, and numExponentials, where the timeVector are the time values, the measuredValue is the real world measured value at each of the number of time values, and numExponentials is the number of exponentials in the sum. For example, the timeVector may be [0, 0.1 , 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9] where each entry is a value indicating a time in seconds. The measuredValue may be [Oo, Oi, O2, O3, O4, O5, Oe, O7, Os, Og], where each value Onis a measured offset value at time tn. So for example, at time to = 0, the measured value is Oo, at time ti=0.1 the measured value is O1, at time t2=0.2 the measured value is O2, etc. The number of exponentials may be any suitable number. In a specific example, the number of exponentials may be two or three. The number of exponentials may be chosen based on, for example, the available computational resources, and the expected accuracy and / or precision required. As will be well understood by the skilled person, a larger number of exponential may fit the data better, but will be more computationally expensive to execute.

[0111] 2. Initialize the parameter values of the predicted offset function. The parameters can comprise, for example, amplitude and timeConstant. The initial parameter values can initially be set to be random. An example of predicted offset function, having two exponential terms may be given by A*eA(b*t) + C*eA(d*t), where A and C are constant coefficients (amplitude) that represent the magnitude of that term in the solution. The terms b and d are the time constants of the exponential terms and t is the independent variable time. Depending on the value of the each term's time constant, that term will contribute more or less to the value of the prediction. While the parameters are constants in this example, the parameters could also vary as a function of time.

[0112] 3. Begin the iterative optimization loop, which comprises: a. For each iteration, calculate the value of the predicted offset function at each time point using the current set of values for the parameters.

[0113] 69414738-1 b. Calculate the difference between the value of the predicted offset function (e.g. an extrapolated value obtained from the predicted offset function) and a measured value at each time point to obtain a residual value. That is, each estimated value for the offset is compared against its corresponding measured value, where the difference between each corresponding value provides a residual value. c. Calculate the Jacobian matrix by computing the partial derivatives of the predicted offset function with respect to each parameter. d. Calculate a parameter update vector using the Jacobian matrix and the residual values. An example of calculating the parameter update value is given in the code listed below, which corresponds to a simplified Gauss-Newton algorithm in that it iteratively optimizes the parameter estimates using the pseudoinverse of the Jacobian matrix, but varies in that it does not linearize the least squares cost function. e. Update the current set of values for the parameters based on the parameter update vector. For example, the parameter update vector may be added to the current set of values for the parameters to obtain updated values for the parameters. f. Calculate a cost function. The cost function may be calculated using the sum of squared residuals. That is, the cost function may be the output of using the method of least squares. The cost function represents the magnitude of the sum of the error between the model prediction and the measured values. g. Determine convergence. Convergence may be determined by checking a convergence criterion. If the cost function is below a specified tolerance level, the optimization loop is terminated. The tolerance level may be specified as an input parameter. When the cost (sum of errors) is less than the tolerance, then the parameter update loop will stop. The loop may also stop if a maximum number of iterations is reached before the convergence criteria. In this case, the optimization loop may be run again.

[0114] 69414738-1 Following completion of the iterative optimization loop described above, the values of the parameters will have been updated from an initial set of parameter values (which could be random) to a final set of parameters values. The predicted offset function can now be used to predict future values of the offset using the final set of parameter values.

[0115] Following completion of the iterative optimization loop, it can be advantageous to carry out a validation phase to test the predicted offset function with its final set of parameters. One way of testing the predicted offset function is to obtain further measured values of the offset (e.g. a second set of measurements) at time periods during the pressure reduction phase 30, and to compare these measured values to predicted values using the predicted offset function. For example, continuing from the example above where ten values are obtained and used to optimize the parameters of the predicted offset function, the measured offset may further be determined at times t = 1 second, tn = 1.1 second and ti2 = 1.2 seconds, the values being Ow, On , Ow respectively (three values are described here for illustration, however it will be appreciated that any suitable number of values may be recorded). The values [O10, On , O12] can be obtained while the iterative optimization loop is being carried out. During the validation phase, the predicted offset function can be used to predict offset values at times tw, tn and tw, and these predicted offset values can be compared to the measured values, Ow, On Ow.

[0116] The difference between the predicted values and the measured values at each time point can be determined to obtain the residual for each time period. The residuals can be used to calculate a measure of error, such as a percent error. The residuals, such as a percent error, can be used to determine whether or not to use the predicted offset function. For example, prior to injection of the tracer fluid, the controller 24 may compare the values of the predicted offset function to the plurality of offset values [Ow, On , Ow]. This allows the controller 24 to determine whether the values of the predicted offset function are within a predetermined error range of the plurality of offset values [Ow, On , Ow]. The values of the predicted offset function may be considered to be within the predetermined error range of the plurality of offset values where each value of the predicted offset function is within 10% of the corresponding offset value of the plurality of offset values. Since offset values [Ow, On , Ow] are determining using tracer fluid abundance measurements taken during the pressure reduction phase 30, offset values [Ow, On , O12] are known to be a true reflection of the background tracer fluid abundance during the pressure reduction phase 30. Therefore, by comparing the values of the

[0117] 69414738-1 predicted offset function to offset values [O10, On, O12] , the controller 24 can determine how close the values of the predicted offset function are to the background tracer fluid abundance. Although this comparison only takes place during the pressure reduction phase 30, it can be inferred that the accuracy of the values of the predicted offset function is the same or similar for the leak testing phase 34.

[0118] If the values of the predicted offset function are within the predetermined error range of the offset values [O10, On, O12], then, upon commencement of the leak detection phase 34, the controller 24 generates the tracer fluid signal 36 (e.g. third part 36c during time period T3) by subtracting the values of the predicted offset function from the tracer fluid abundance measurements at each time point. That is, when using the predicted offset function during the leak detection phase 34, the controller 24 generates the values of the predicted offset function periodically and subtracted from the tracer fluid abundance measurements. The predicted offset function may generate offset values in the same intervals as the intervals in which the tracer fluid abundance measurements are taken by the fluid detection device 22. The predicted offsets are highlighted in Figure 4 as vertical dotted lines within time period T3.

[0119] If the values of the predicted offset function are not within the predetermined error range of the plurality of offset values O, then, upon commencement of the leak detection phase 34, the controller 24 generates the tracer fluid signal 36 (e.g. third part 36c during time period T3) by subtracting the final offset value OF from the tracer fluid abundance measurements as described with respect to Figure 3. This approach allows the controller 24 to determine which method of accounting for the background tracer fluid is more accurate, and use the more accurate method during the leak detection phase 34.

[0120] An example of code in structured text for carrying out an iterative optimization loop as described above is provided below. The predicted offset function in the following case is a sum of exponentials. The example is merely for illustrative purposes and can of course be implemented in any suitable programming language.

[0121] PROGRAM SumOfExponentials

[0122] VARJNPUT timeVector : ARRAY[*] OF REAL; / / Input time vector measuredValue : ARRAY[*] OF REAL; / / Input measured value vector numExponentials : INT; / / Number of exponentials to use in the model function

[0123] END_VAR

[0124] VARJDUTPUT parameters : ARRAY[1 ..4*10] OF REAL; / / Array to hold the parameter estimates

[0125] 69414738-1 extrapolatedValue : ARRAY[*] OF REAL; / / Extrapolated value vector difference : ARRAY[*] OF REAL; / / Difference between extrapolated and measured values percentError : REAL; / / Percentage error between extrapolated and measured values converged : BOOL; / / Flag to indicate if convergence has been achieved

[0126] END_VAR

[0127] VAR i, j : INT; / / Loop counters modelValue : REAL; / / Value of the model function at current time point residual : ARRAY[*] OF REAL; / / Array to hold the residuals at each time point jacobian : ARRAY[1 ..4*10, *] OF REAL; / / Jacobian matrix update : ARRAY[1 ..4*10] OF REAL; / / Parameter update vector cost : REAL; / / Cost function iteration : INT := 0; / / Iteration counter maxiterations : INT := 100; / / Maximum number of iterations tolerance : REAL := 1e-6; / / Tolerance for convergence

[0128] END_VAR

[0129] / / Initialize parameter estimates to random values

[0130] FOR i := 1 TO 4*numExponentials DO parameters[i] := RANDOM(0.0, 1.0);

[0131] END_FOR

[0132] / / Allocate memory for output vectors

[0133] SET_LENGTH(extrapolatedValue, LENGTH(timeVector));

[0134] SET_LENGTH(difference, LENGTH(timeVector));

[0135] / / Main optimization loop

[0136] REPEAT iteration := iteration + 1 ; / / Increment iteration counter

[0137] / / Calculate model function and residuals at each time point

[0138] FOR j := 1 TO LENGTH(timeVector) DO modelValue := 0.0;

[0139] FOR i := 1 TO numExponentials DO modelValue := modelValue + parameters[(i-1)*4+1] * EXP(parameters[(i-1)*4+2] * timeVector[j]) + parameters[(i-1)*4+3] * EXP(parameters[(i-1)*4+4] * timeVector[j]);

[0140] END_FOR residual[j] := measuredValue[j] - modelValue;

[0141] END_FOR

[0142] / / Calculate Jacobian matrix

[0143] FOR j := 1 TO LENGTH(timeVector) DO

[0144] FOR i := 1 TO numExponentials DO jacobian[(i-1)*4+1 , j] := EXP(parameters[(i-1)*4+2] * timeVector[j]); jacobian[(i-1)*4+2, j] := parameters[(i-1)*4+1] * timeVector[j] * EXP(parameters[(i-1)*4+2]

[0145] * timeVector[j]); jacobian[(i-1)*4+3, j] := EXP(parameters[(i-1)*4+4] * timeVector[j]); jacobian[(i-1)*4+4, j] := parameters[(i-1)*4+3] * timeVector[j] * EXP(parameters[(i-1)*4+4]

[0146] * timeVector[j]);

[0147] END_FOR

[0148] END_FOR

[0149] / / Calculate parameter update vector update := INV(jacobian * TRANSPOSE(jacobian)) * (jacobian * TRANSPOSE(residual));

[0150] / / Update the current set of parameter estimates

[0151] FOR i := 1 TO numExponentials DO parameters[(i-1)*4+1] := parameters[(i-1)*4+1] + update[(i-1)*4+1];

[0152] 69414738-1 parameters[(i-1)*4+2] := parameters[(i-1)*4+2] + update[(i-1)*4+2]; parameters[(i-1)*4+3] := parameters[(i-1)*4+3] + update[(i-1)*4+3]; parameters[(i-1)*4+4] := parameters[(i-1)*4+4] + update[(i-1)*4+4];

[0153] END_FOR

[0154] / / Calculate the cost function cost := 0.0;

[0155] FOR j := 1 TO LENGTH(timeVector) DO modelValue := 0.0;

[0156] FOR i := 1 TO numExponentials DO modelValue := modelValue + parameters[(i-1)*4+1] * EXP(parameters[(i-1)*4+2] timeVector[j]) + parameters[(i-1)*4+3] * EXP(parameters[(i-1)*4+4] * timeVector[j]);

[0157] END_FOR difference!]]:=measuredValue[j] - modelValue; cost := cost + difference!]] * difference!]];

[0158] END_FOR cost := 0.5 * cost I LENGTH(timeVector);

[0159] / / Check for convergence

[0160] IF ABS(cost) < tolerance THEN converged := TRUE;

[0161] END_IF

[0162] UNTIL converged OR iteration >= maxiterations;

[0163] An example of code in structured text for determining whether the predicted offset function outputs values within the predetermined error range is as follows:

[0164] PROGRAM DataCollectionAndProcessing

[0165] VARJNPUT sampleTime : REAL := 0.1 ; / / Sample time in seconds numSamples : INT := 100; / / Number of samples to collect numExponentials : INT := 3; / / Number of exponentials to use in the model

[0166] END_VAR

[0167] VARJDUTPUT timeVector : ARRAY[1 ..numSamples] OF REAL; / / Time vector for measured data measuredValue : ARRAY[1 ..numSamples] OF REAL; / / Measured value vector extrapolatedValue : ARRAY[1 ..numSamples] OF REAL; / / Extrapolated value vector difference : ARRAY[1 ..numSamples] OF REAL; / / Difference between extrapolated and measured values percentError : REAL; / / Percentage error between extrapolated and measured values errorFlag : BOOL; / / Flag to indicate if error exceeds threshold

[0168] END_VAR

[0169] VAR i, j : INT; / / Loop counters a, b, c, d : REAL; / / Parameter estimates from SumOfExponentials program END_VAR

[0170] / / Collect and preprocess data

[0171] FOR i := 1 TO numSamples DO

[0172] / / Collect and preprocess data from sensors timeVector[i] := i * sampleTime; measuredValue[i] := PREPROCESS_DATA(GetSensorValueO);

[0173] END_FOR

[0174] 69414738-1 / / Call SumOfExponentials program to estimate model parameters and extrapolate values SumOfExponentials(timeVector := timeVector, measuredValue := measuredValue, numExponentials := numExponentials, parameters := [a, b, c, d, a, b, c, d, a, b, c, d], extrapolatedValue := extrapolatedValue, difference := difference, percentError := percentError);

[0175] / / Check if error exceeds threshold and set error flag accordingly

[0176] IF percentError > 10.0 THEN errorFlag := TRUE;

[0177] ELSE errorFlag := FALSE;

[0178] ENDJF

[0179] The controller 24 may comprise any suitable hardware suitable for processing data. A schematic representation of a controller 24 is shown in Figure 5. The controller 24 comprises a processor 24a which is configured to read and execute instructions stored in a volatile memory 24b which may take the form of a random access memory. The volatile memory 24b stores instructions for execution by the processor 24a and data used by those instructions. For example, in use, the measured data acquired by the fluid detection device 22 may be stored in the volatile memory 24b.

[0180] The controller 24 further comprises non-volatile memory 24c, which could be in the form of a hard disc drive. The data acquired by the fluid detection device 22 may be stored in the non-volatile memory 24c. The predicted offset function may be stored in the volatile memory 24b, and / or stored in the non-volatile memory 24c. The controller 24 further comprises an I / O interface 24d suitable for connecting with external devices, such as the fluid detection device 22. Other external devices may include a display output, such as a monitor. The display may, for example, display a representation of the data generated by the controller 24, such as the offset values described above. Alternatively or additionally, separate input devices may be connected to the I / O interface 24d, such as a mouse and / or keyboard. A network interface 24f allows the controller 24 to be connected to an appropriate computer network so as to receive and transmit data from and to other computing devices. The processor 24a, volatile memory 24b, non-volatile memory 24c, I / O interface 24d, and network interface 24f, are connected together by a bus 24g.

[0181] The controller 24 may be provided on a single PCB, or may be distributed over multiple electronic devices. The controller 24 shown in Figure 5 is purely illustrative, and it will be appreciated that not all features shown will be required.

[0182] 69414738-1 Actions of the controller 24, such as generating the predicted offset function may occur elsewhere, such as at another location, e.g. a server in the cloud.

[0183] Figure 6 shows a flow chart of an example method of leak testing a component using an optical fluid analyser according to the present disclosure. The method may be used with the leak testing apparatus 2 described herein. The component is positioned within the vessel, the vessel defining a chamber and the component defining an internal volume, the chamber and internal volume together defining a test volume. This arrangement is described in more detail above.

[0184] At Step S1 , pressure of a fluid in the test volume is reduced. For example, this step can correspond to the pressure reduction phase 30 described herein.

[0185] At Step S2, a tracer fluid is injected into the test volume. For example, this step can correspond to the leak detection phase 34 described herein.

[0186] At Step S3, and while reducing the pressure of the fluid in the test volume and while injecting the tracer fluid into the test volume, using the optical fluid analyser to measure an amount of the tracer fluid exiting the test volume to obtain a tracer fluid signal. For example, the optical fluid analyser is used during both the pressure reduction phase 30 and the leak detection phase 34 to measure the amount of the tracer fluid exiting the test volume. The measured amount may be further processed to obtain the tracer fluid signal. For example, as described herein, the background tracer fluid abundance may be taken into account to correct the measured amount of tracer fluid exiting the test volume to obtain the tracer fluid signal.

[0187] At Step S4, a leak rate of the component is determined based on the tracer fluid signal obtained while injecting the tracer fluid into the test volume. For example, the tracer fluid signal determined during the leak detection phase 34 may be used to determine a leak rate of the component.

[0188] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to

[0189] 69414738-1 one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.

[0190] 69414738-1

Claims

CLAIMS:

1. A method of leak testing a component using an optical fluid analyser, the component positioned within a vessel, the vessel defining a chamber and the component defining an internal volume, the chamber and internal volume together defining a test volume, the method comprising: reducing the pressure of a fluid in the test volume; injecting a tracer fluid into the test volume; while reducing the pressure of the fluid in the test volume and while injecting the tracer fluid into the test volume, using the optical fluid analyser to measure an amount of the tracer fluid exiting the test volume to obtain a tracer fluid signal; and determining a leak rate of the component based on the tracer fluid signal obtained while injecting the tracer fluid into the test volume.

2. The method of claim 1 , further comprising: while the pressure of the fluid in the test volume is being reduced, determining a plurality of offset values, the plurality of offset values each being equal to a difference between the measured amount of the tracer fluid exiting the test volume at a given time and a datum value; and using at least one of the plurality of offset values to obtain the tracer fluid signal.

3. The method of claim 2, wherein using the at least one of the plurality of offset values to obtain the tracer fluid signal comprises: subtracting the at least one of the plurality of offset values from the measured amount of the tracer fluid exiting the test volume to obtain the tracer fluid signal.

4. The method of any of claims 2 or 3, further comprising: determining, based on at least a portion of the plurality of offset values, a predicted offset function, the predicted offset function for outputting a predicted offset value.

5. The method of claim 4, wherein using the at least one of the plurality of offset values to obtain the tracer fluid signal comprises using at least one predicted offset value output by the predicted offset function to obtain the tracer fluid signal.69414738-16. The method of claims 4 or 5, wherein the predicted offset function comprises a sum of exponentials.

7. The method of claims 4, 5 or 6, wherein determining the predicted offset function comprises performing an iterative optimization loop to determine values of one or more parameters of the predicted offset function.

8. The method of any of claims 5, 6 or 7, wherein using the at least one predicted offset value output by the predicted offset function to obtain the tracer fluid signal comprises subtracting the at least one predicted offset value from the measured amount of tracer fluid exiting the test volume to obtain the tracer fluid signal.

9. The method of any of claims 4 to 8, further comprising, prior to injection of the tracer fluid, comparing one or more predicted offset values output by the predicted offset function to at least a second portion of the determined plurality of offset values; and determining, based on the comparison, whether the predicted offset values are within a predetermined error range of the at least a second portion of the determined plurality of offset values.

10. The method of claim 9, wherein: if the one or more predicted offset values of the predicted offset function are within the predetermined error range, using at least one predicted offset value output by the predicted offset function to obtain the tracer fluid signal; or if the one or more predicted offset values of the predicted offset function are not within the predetermined error range, using the at least one of the determined plurality of offset values to obtain the tracer fluid signal.11 . The method of claim 9 or 10, wherein the predetermined error is 10%.

12. The method of any of claims 2 to 11 , wherein the datum value is at least zero and up to 1 E-9 mbarm3 / s.

13. The method of any preceding claim, wherein the tracer fluid is nitrogen.69414738-114. The method of any preceding claim, wherein the optical fluid analyser device is a plasma spectroscopy device.

15. The method of any preceding claim, wherein supplying the tracer fluid to the test volume comprises supplying the tracer fluid to the internal cavity of the component or to the chamber.

16. A leak testing apparatus for leak testing a component that defines an internal volume, the apparatus comprising: a vessel that defines a chamber, wherein, in use, the chamber and the internal volume of the component together define a test volume, and wherein the vessel comprises a tracer fluid inlet for injecting tracer fluid into the test volume; an optical fluid analyser; a pumping system that is configured to reduce the pressure of the fluid in the test volume, and to pump fluid from the test volume through the optical fluid analyser such that the optical fluid analyser measures an amount of tracer fluid exiting the test volume; a controller configured to carry out the method of any preceding claim.

17. The leak testing apparatus of claim 16, further comprising a tracer fluid source that is connected to the tracer fluid inlet.

18. The leak testing apparatus of claim 16 or 17, wherein the tracer fluid is nitrogen.

19. The leak testing apparatus of any of claims 14 to 18, wherein the optical fluid analyser is a plasma spectroscopy device.

20. A method of leak testing a component, the method comprising: positioning the component within a vessel, the vessel defining a chamber and the component defining an internal volume, the chamber and internal volume together defining a test volume; reducing the pressure of a fluid in the test volume; injecting a tracer fluid into the test volume; while reducing the pressure of the fluid in the test volume and while injecting the tracer fluid into the test volume, using a fluid detection device to measure an amount of the tracer fluid exiting the test volume to obtain a tracer fluid signal;69414738-1determining, based on the measured amount of tracer fluid exiting the test volume obtained while the pressure of the fluid in the test volume is being reduced, a predicted offset function, the predicted offset function for predicting a difference between background tracer fluid abundance and a datum value; subtracting an output of the predicted offset function from the measured amount of tracer fluid exiting the test volume obtained while injecting the tracer fluid into the test volume, to obtain a predicted leak signal; determining a leak rate of the component based on the predicted leak signal; and comparing the leak rate of the component to a predetermined threshold value.

21. A computer implemented method of leak testing a component, the component provided within a vessel, the vessel defining a chamber and the component defining an internal volume, the chamber and internal volume together defining a test volume the method comprising: measuring an amount of tracer fluid exiting the test volume while reducing the pressure, the amount of tracer fluid indicative of a background tracer fluid abundance within the test volume; generating, based on measuring the amount of tracer fluid exiting the test volume, a model configured to predict the amount of tracer fluid exiting the test volume due to the background tracer fluid abundance; measuring an amount of tracer fluid exiting the test volume while injecting tracer fluid into the test volume; determining, based on the model, a correction to the measured amount of tracer fluid exiting the test volume while injecting tracer fluid into the test volume; determining a leak rate of the component based on the corrected measured amount of tracer fluid exiting the test volume.

22. A computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the method of any of claims 1 to 15 and 20 to 21.69414738-1

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