EVALUATION OF THE MEASUREMENT SIGNAL FROM A VACUUM LEAK DETECTOR

Abstract

In a method for evaluating the measuring signal of a vacuum leak detector comprising a vacuum pump (16) and a test chamber (12) connected with the vacuum pump (16) and a gas detector (14) connected with the test chamber (12), characterized by determining the system time constant ? of the vacuum leak detector, wherein the system time constant ? is the duration of the system-related rise of the measured signal in response to a gas component escaped through a leak in the test object or the duration of the system-related drop of the measured signal in response to a gas component no longer from a leak in the test object, the following steps are provided:

generating a measuring signal I(t) of the gas drawn from the test chamber (12) at a time t, using the gas detector (14).

buffering the measured signal I(t), forming a measuring signal ?(t+t0) prognosed for a future time t>t+t0, based on the measured value of the buffered measuring signal I(t) and the system time constant ?,

generating a measuring signal I(t+t0) of the gas drawn from the test chamber (12) at a time t+t0, using the gas detector (14).

forming the difference between the measuring signal I(t+t0) an the prognosed measuring signal ?(t+t0) scaled by a constant C2,

judging, whether the test object has a leakage, based on the difference I(t+t0)?C2 ?(t+t0) formed.

(FIG. 2)

Claims

1-18. (cancelled)

19. A method for evaluating the measuring signal of a vacuum leak detector comprising a vacuum pump and a test chamber connected with the vacuum pump and a gas detector connected with the test chamber, characterized by determining the system time constant ? of the vacuum leak detector, wherein the system time constant ? is the duration of the system-related rise of the measured signal in response to a gas component escaped through a leak in the test object or the duration of the system-related drop of the measured signal in response to a gas component no longer from a leak in the test object, followed by the steps of: generating a measuring signal I(t) of the gas drawn from the test chamber at a time t, using the gas detector, buffering the measured signal I(t), forming a measuring signal ?(t+t0) prognosed for a future time t+t0, based on the measured value of the buffered measuring signal I(t) and the system time constant ?, where t0<?, generating a measuring signal I(t+t0) of the gas drawn from the test chamber at a time t+t0, using the gas detector, forming the difference between the measuring signal I(t+t0) and the prognosed measuring signal ?(t+t0), judging, whether the test object has a leakage, based on the difference formed.

20. The method according to claim 19, wherein a leak in the test object is considered as detected, if the difference is greater than a threshold value.

21. The method according to claim 19, wherein the test object is considered to be tight, when the difference is smaller than or equal to a threshold value and greater than or equal to zero.

22. The method according to claim 19, wherein an error is assumed, for example in the form of an inaccurate system time constant, when the difference is smaller than zero.

23. The method according to claim 20, wherein the threshold value is assumed to be r-times the value of a background signal of the measuring signal, where r is a rational number greater than zero and preferably greater than or equal to 5 and/or smaller than or equal to 10.

24. The method according to claim 19, wherein the accelerated measuring signal ?(t) is formed from the measuring signal I(t) by the following transformation: using a previous measuring signal I(t) of a previous time t=t??/n, where n is a rational number greater than 0, multiplying the previous measuring signal I(t) by a second constant C2, forming the difference I(t)?C2 I(t) between the measuring signal I(t) and the previous measuring signal I(t) scaled by the second constant C2, multiplying the difference I(t)?C2 I(t) by a first constant C1, to thereby obtain a measuring signal ? accelerated by the factor n, which corresponds to a measuring signal compensated by the system time constant ?.

25. The method according to claim 24, wherein the second constant C2 is a positive real number smaller than 1 and corresponding preferably to the reciprocal 1/.sup.n?{square root over (e)} of the n-th root of Euler's number e or including this reciprocal.

26. The method according to claim 24, wherein the first constant C1 is a real number greater than 1 and preferably includes or corresponds to the term 1/(1?1/.sup.n?{square root over (e)}).

27. The method according to claim 19, wherein the second constant C2 includes the n-th root of Euler's number e and preferably includes the reciprocal of the n-th root of e.

28. The method according to claim 19, wherein the second constant C2 is multiplied by a factor F, where F is a rational number <1 and is preferably between 0.9 and 0.999.

29. The method according to claim 19, wherein the accelerated signal ?(t) is calculated using the formula: $\stackrel{.}{I}\left(t\right)=\left(\left(I\left(t\right)-F\frac{I\left(t-\frac{?}{n}\right)}{\sqrt[n]{e}}\right)\frac{1}{\left(1-\frac{1}{\sqrt[n]{e}}\right)}\right)$

30. The method according to claim 19, wherein the system time constant t is determined by means of a test leak which may be an internal test leak of the vacuum leak detector or an external test leak that can be connected with the test chamber.

31. The method according to claim 19, wherein the vacuum time constant of the vacuum leak detector is calculated as the system time constant ? from the volume of the test chamber and the pipe line connecting the test chamber with the gas detector and from the suction capacity of the vacuum pump.

32. The method according to claim 19, wherein the system time constant ? is determined from that time period which elapses from the time of switching off, deactivating or removing a test leak from the vacuum leak detector to the decay of the measuring signal to a predetermined value, or which elapses from the time of switching on, activating or adding a test leak to the vacuum leak detector to the rising of the measuring signal to a predetermined value.

33. The method according to claim 19, wherein the predetermined time corresponds to the time at which the measuring signal corresponds to 1/e times the steady measuring signa of the test leak.

34. A vacuum leak detector for performing the method according to claim 19, comprising a vacuum pump, a test chamber connected with the vacuum pump and a gas detector connected with the test chamber, characterized by an evaluation unit for evaluating the measuring signal of the gas detector, wherein the evaluation unit is configured to perform the method according to claim 19.

35. The vacuum leak detector according to claim 34, wherein the evaluation unit comprises a memory in which the process steps are stored.

36. The vacuum leak detector according to claim 34, wherein the evaluation unit comprises a microcontroller configured to perform the method in an automated manner.

Description

[0072] Embodiments will be explained hereunder with reference to the Figures. In the drawings:

[0073] FIG. 1 shows a diagram with the resulting signal paths of a first embodiment,

[0074] FIG. 2 is a schematic illustration of the vacuum leak detector,

[0075] FIG. 3 shows a diagram for determining the system time constant of the system,

[0076] FIG. 4 shows another diagram for determining the system time constant,

[0077] FIG. 5 shows another diagram for determining the system time constant, and

[0078] FIG. 6 shows an example of a filtering to illustrate the accelerated signal and the system time constant.

[0079] In the embodiment of FIG. 1, the path of the upper trajectory shows the measuring signal of the gas detector and the lower trajectory shows the accelerated signal ?(t) for a volume of the test chamber and the gas-conducting connection between the test chamber and the das detector of 100 l, a suction capacity of the vacuum pump of 4 l per second and an acceleration factor (boost factor) n=1. A comparison between the path of the lower trajectory and the upper trajectory in FIG. 1 shows that the accelerated signal path ?(t) rises significantly faster than the actually measured path I(t).

[0080] FIG. 2 is a schematic illustration of the vacuum leak detector comprised of a test chamber 12, a gas detector 14 and a vacuum pump 16, the gas detector 14 being connected in a gas-conducting manner with the test chamber 12 via a gas-conduction path 18. The test chamber accommodates a test object 20 filled with a test gas. The gas detector 14 is electronically connected with an evaluation unit 22 which receives and processes the electronic measuring signal generated by the gas detector.

[0081] In another embodiment, a UL1000 with a 50 l barrels was used. As a controllable test leak, a limp valve was used in combination with a TI4-6. The data input for the filter was the leak rate signal in combination with the fixed filter, so as to be able on the one hand to avoid influences of different filtering times and on the other hand to be able to measure noise amplifications.

[0082] Various tests were performed with the limp valve being opened and closed, and the signal for different acceleration stages was examined. The signal drop and the signal rise were examined in particular, as well as the question, whether the leak rate prognosed in the filter is coherent or to what extent it differs. The filter was examined in the range between 1?10.sup.?3 and 1?10.sup.?9 mbar l/s. [0083] 1) The filter is functional. [0084] 2) The signal can be accelerated technically by a factor 32, so that a virtual suction capacity of conventional leak detectors of almost 1000 l/s can be made possible. [0085] 3) The determination of the system time constant required for the filter can be performed using the internal test leak and will take between 15 and 20 s. [0086] 4) The accelerated signal has a noise increased by the factor 1.4 x when compared to the input signal, which is consistent with the theoretical assumption. [0087] 5) However, with short spray pulses (short relative to the system time constant), the noise is increased by a factor 1,4 only as long as the acceleration factor is not to great and is proportionate to the spray time. [0088] 8) The leak rate prediction is good and the filter causes very little signal over-/underload. [0089] 9) A smoothing of the input signal adapted to the actual system time constant significantly improves upon noise without significantly impairing the system time constant. [0090] 10) The waiting time for spraying after a large leak can be shortened to about one minute for a volume of 50 l.

[0091] FIG. 3 illustrates an example for the determination of the system time constant of the leak detection system, in which the rise or fall of the logarithmic measuring signal is measured.

[0092] FIG. 4 illustrates an example for a direct determination of the system time constant, in which the time is measured that elapses until the measuring signal has fallen to a 1/e-th part.

[0093] FIG. 5 illustrates an example for the direct determination of the system time constant, in which the time is measured that passes until the measuring signal has risen to a (1-1/e)-th part.

[0094] FIG. 6 shows an example for a filtering of the measuring signal. Here, a leak is sprayed with 10.sup.?7 mbar l/s. The measuring signal I(t) is shown in blue/broken lines. The accelerated transformed signal ?(t) is shown in red. The signal time constant of the original signal I of t shown in broken lines is 17.5 seconds. In FIG. 6, from left to right, the system time constants of the transformed signal ?(t) for acceleration factors 1,75; 3,5; 5,83; 8,75; 17,5; 35: 10; 5; 3; 2; 1; 0,5 seconds.