Evaluation of the measurement signal from a vacuum leak detector

1 . 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 τ of the vacuum leak detector, wherein the system time constant τ 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 Í(t+t 0 ) prognosed for a future time t+t 0 , based on the measured value of the buffered measuring signal I(t) and the system time constant τ, where t 0 <τ,

generating a measuring signal I(t+t 0 ) of the gas drawn from the test chamber at a time t+t 0 , using the gas detector,

forming the difference between the measuring signal I(t+t 0 ) and the prognosed measuring signal Í(t+t 0 ),

judging, whether the test object has a leakage, based on the difference formed.

2 . The method according to claim 1 , wherein a leak in the test object is considered as detected, if the difference is greater than a threshold value.

3 . The method according to claim 2 , 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.

4 . The method according to claim 1 , 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.

5 . The method according to claim 1 , wherein an error is assumed, for example in the form of an inaccurate system time constant, when the difference is smaller than zero.

6 . The method according to claim 1 , wherein the accelerated measuring signal Í(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−τ/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 Í accelerated by the factor n, which corresponds to a measuring signal compensated by the system time constant τ.

7 . The method according to claim 6 , wherein the second constant C2 is a positive real number smaller than 1 and corresponding preferably to the reciprocal 1/ n √{square root over (e)} of the n-th root of Euler's number e or including this reciprocal.

8 . The method according to claim 6 , wherein the first constant C1 is a real number greater than 1 and preferably includes or corresponds to the term 1/(1−1/ n √{square root over (e)}).

9 . The method according to claim 1 , 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.

10 . The method according to claim 1 , 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.

11 . The method according to claim 1 , wherein the accelerated signal Í(t) is calculated using the formula:

I

.

(

t

)

=

(

(

I

⁡

(

t

)

-

F

⁢

I

⁡

(

t

-

τ

n

)

e

n

)

⁢

1

(

1

-

1

e

n

)

)

12 . The method according to claim 1 , wherein the system time constant τ 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.

13 . The method according to claim 1 , wherein the vacuum time constant of the vacuum leak detector is calculated as the system time constant τ 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.

14 . The method according to claim 1 , wherein the system time constant τ 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.

15 . The method according to claim 1 , 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.

16 . A vacuum leak detector for performing the method according to claim 1 , 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 1 .

17 . The vacuum leak detector according to claim 16 , wherein the evaluation unit comprises a memory in which the process steps are stored.

18 . The vacuum leak detector according to claim 16 , wherein the evaluation unit comprises a microcontroller configured to perform the method in an automated manner.