1、 STDmBSI BS EN LSLB-ENGL 1778 m Lb246b7 071ib567 722 m BRITISH STANDARD I BS EN Non-destructive testing - Leak testing - Characterization of mass spectrometer leak detectors * * ui The European Standard EN 15181998 has the status of a British standard ICs 19.100 15 18: 1998 NO COPYING WITHOUT BSI PE
2、RMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW STD-BSI BS EN 15LB-ENGL 1498 = Lb24bb9 071b570 b44 = AmdNo. Date BS EN 16181998 Text affected This British Standard, having been prepared under the direction of the Engmeering Sector Board, was published under the authority of the Standards Board and com
3、es into effect on 16 August 1998 O BSI 1998 ISBN O 580 30042 O National foreword This British Standard is the English language version of EN 15181998. It supersedes BS 5914 1980 which is withdrawn. The UK participation in its preparation was entrusted to Technical Committee WEE/-%, Nondestructive te
4、sting, which has the responsibility to: - aid enquirers to understand the text* - present to the responsible European committee any enquiries on the - monitor related international and European developments and promulgate inteqretation, or proposals for change, and keep the UK interests informed; th
5、em in the UK. A list of organizations represented on this committee can be obtained on request to its secretary. Cross-references The British Standards which implement international or European publications referred to in this document may be found in the BSI Standards Catalogue under the section en
6、titied “International Stan- Correspondence Index”, or by using the “Find” facility of the BSI Standards Electronic Catalogue. A British Standard does not purport to include all the necessary provisions of a contra - producing a defmite parliai pressure of tracer gas when a specic throughput of trace
7、r gas enters the leak detector. An MSLD includes also a number of valves and pressure gauges to ensure the appropriate vacuum conditions within the system. The lealuate output can be displayed in a number of ways, for example an electrical meter, or digital displays of Merent types. In addition, a c
8、hart recorder output is usually available, which has to be used for the test procedures in this standard STD-ES1 BS EN LSLB-ENGL 1998 1b24bb 07Lb575 12b Page 5 EN 15181998 The general structure of an MSLD is described by the 5 Apparatus for metho 6.1 Leaks - separation system, - ion collector. b) Pu
9、mping system: - inlet system; - inlet he; - inlet valve; - pump valve; - test port; - vent valve; - intenial leak port. c) Sensitivity zero control. d) Display 4.2 Operating principles of MSLD 4.2.1 Direct flow leak detectors The leakage rate qx is given by the equation: where qx Sx px Qx = Px x sx
10、is the pV-throughput of tracer gas; is the intrinsic pumping speed; is the partial pressure of tracer gas in the mass spectrometer (MS). 4.2.2 Counteow leak detectors The leakrate qx is given by the equation: where qx = Px Kx sb,x For the following tests, two known leaks are required - a small trace
11、r gas leak for the test of minimum detectable leakage rate; - a large air leak for the determination of minimum detectable concentration. Both leaks have to have a specified temperature correction. For MSLD using the workmg principles indicated by 4.2.1 and 4.2.2, depending on measurement range, mor
12、e than two leaks may be necessary for determination of detection limits and sensitivity according to the working principle. 6.1.1 Small tracer gas leaks The small known leaks shall be of a size such that the total pressure in the MS is negligibly increased For the determination of sensitivity drift,
13、 the leak should produce a deflection which is not less than 50 times the smallest detectable signai. For drift measurements, as these leaks are usually of the permeation type and have an appreciable temperature coefficient, ambient temperature variation should also be taken into account. Should it
14、be necessary to have a small known leak for the determination of background signal drift (see 7.2.1), this leak has to be small enough to give a signai in the lowest decade of signai output. qx K, is the pV-throughput of tracer gas; is the compression ratio of the counterflow (see 3.1.1); 6.1.2 Larg
15、e air leak The large known leak shall be of such a size that, when ambient air is at its entrance and partial flow conditions do not apply, the pressure in the MSLD rises of the high WU pump for mer gas _. to the optimum working pressure. Such a large leak Sb,X is the speed Of the Pumping system, fo
16、r mer be a fine 1 px is the partial pressure of tracer gas in the MS. 4.3 MLSD specification The MLSD specification is described by the following list: a) Operating conditions: - optimum working pressure; - maximum working pressure; - maximum inlet pressure; - maximum gas load b) ?i.acer gas backgro
17、und signai: - background signai noise. - background signai drift; c) Non linear - minimum detectable concentration ratio. e) Resolving power. f) Display discrimination. 6.2 Leak isolation valve (see prEN 1330-8) (Refer to prEN 1330-8.) 6.3 Test vessel A test vessel is used for the determination of t
18、he inlet pumping speed of the MSLD. It is a vacuum chamber of known volume, preferably cyiindricai or spherical, typically 101. For connection to the MSLD, the test vessel shall have a flange of suitable diameter (not less than the diameter of the test port of the MSLD) and a second flange for the c
19、onnection of a calibrated leak mical arrangements are shown in Fgure 1. The test vessel shall be made entirely of metal and its inner surfaces shall conform to the requirements of high vacuum te ch no log Its leak tightness shall be better thart Pa-m3/s. O BSI 1998 Page 6 EN 16181998 I I 1s; 4 A -t.
20、 t OS D. y i I GAS INtn 0.1 D A) CYLINDRICAL TEST PORT OF LEAK DETECTOR GAS IL!E B) SPHERICAL I 0.1 o -LI .-.-. Th I OPTIONAL PRESSURE GAUGE CONNECTION Figure 1 - Vessel for determination of inlet pumping speed (see 6.3) O BSI 1998 STDoBSI BS EN 3538-ENGL 3998 W I1624669 0736577 TT9 Page 7 EN 151819
21、98 6.4 Arrangement for test 6.4.1 Auxiliarg pumping sustem The MSLD is connected to an auxiliary system as shown in Figures 2a and 2b. (Frequently, the auxiliary system is an integrai part of the MSLD.) 5.4.2 Materials The use of rubber or plastics should be kept to a minimum in the system and prefe
22、rably be restricted only to O-rings. Accordingly, the ?leak isolation vdve? shown in Figures 2a and 2b should be of all-metal construction. At least, it shall not act as a significant source of adsorbed tracer gas. 6.5 Preparation for test 6.5.1 Power supplg The MSLD shall be connected to a power su
23、pply conforming to the manufacturer?s specification (voltage, frequency, etc.). 6.6.2 Warming up The MSLD shall have been ?warmed up?, according to the manufacturer?s specifications, prior to all test procedures. 5.5.3 Aaustment The MSLD under test shall have been austed for optimw detection of trac
24、er gas in the manner specified by the manufacturer. Blanking Fiange Vent Valve irxernal Leak Port it is only the difference between the total signal and the background which is used for evaluation. In the absence of a lower mass signal, the minimum detectable concentration is determined only by the
25、minimum detectable leakage rate. In this standard the minimum detectable concentsation is defined as being equivalent to a helium peak showing no valley, but merely a shoulder on the tail of the lower mass peak This is equivalent to the evaluation of 8.2.2. Figure 3c shows this situation without any
26、 background signai for helium. 7.3.1 Background dr and noise The detennination of background drift and noise is ciwied out according to the following procedure. a) Adjust the recorder so that the zero on the recorder corresponds to the zero of the leak detector output and the fuli scale of the recor
27、der corresponds to the fuli scale of the selected decade of the MSLD output. b) Connect the iasge known leak to the test port of the MSLD. c) Admit atmospheric air (if helium is the tracer gas), or a mixhire containing p.p.m levels of tracer gas, under reference conditions, to the leak. (When atmosp
28、heric air is used, the feed line should not itself act as a source of Wer gas and preferably should be of all-metal construction.) d) Start a pump cycle or open and close the respective valves manually. e) Adjust, after the MSLD is ready for measurement, the gas flow through the leak so as to achiev
29、e the optimum upper working pressure in the instrument. Page 9 EN 15181998 f) Adjust the sensitivity control, if necessary, to the highest setting that wili give an on-scale reading on the recorder. g) Record the output for 20 min. This record is used for the determination of drift. h) Set, for dete
30、rmination of noise, the sensitivity control to the maximum setting and bring the indication to mid-scale by means of the zero control. i) Record the output again for 20 min. (If the enhanced sensitivity setting is not possible, the drift curve is taken for determination of noise.) 7.3.2 Background s
31、ignal The determination of the background signal is carried out according to the following procedure. a) With the setup as before, feed a pure gas (not containing tracer gas), preferably evaporated liquid nitrogen, to the leak detector. If this is not available, close the leak isolation valve. b) Ad
32、just the leak detector to the greatest sensitivity that will give on-scale readings. It is preferable to use an xy-recorder for the following measurement. In this case, the x-axis is connected to the scanning voltage or another equivalent operating parameter and the y-axis is connected to the record
33、er output of the MSLD. The x-axis sensitivity of the recorder has to be set so that the specified scanning voltage for the tracer gas peak is approximately mid-range. c) When the output signai has reached a steady value, showing no observable change in 1 min, scan the tracer gas peak as specified fo
34、r the instrument, if a yt-recorder is used, make sure that the scan speed is approximately constant. d) Repeat the scanning at 15 min intervals until there is no observable change over a 30 min period. The final measurement is used for determination of the background signai. 7.3.3 Sensitivity The se
35、nsitivity of the system is measured according to the following procedure: a) Close the inlet valve of the MSLD. b) Open the leak isolation valve. e) Admit atmospheric air (if helium is the tracer gas), or a mixhire containing p.p.m levels of tracer gas, under reference conditions, to the leak. d) St
36、art a pump cycle or open and close the respective valves manually e) Scan the tracer gas peak as specified for the instrument when the leak detector is ready for use and the output signal has reached a steady value, showing no observable change in 1 min. (If a yt-recorder is used, make sure that the
37、 scan speed is approximately constant.) The curve will be used to determine the sensitivity for the detection of small concentrations. O BSI 1998 increasing mass -+- Figure 3a - Identification of symbols and variables t Figure 3b - Total and background signals for He on the tail of lower mass peak (
38、produced, for example, in a reaction such as H2 + H+ + H3+) + 3 a. 4 O increasingmass Figure 3c - Signal for the minimum detectable He concentration, appearing as a shoulder on the tail of a lower mass peak Figure 3 - Interpretation of curves showing the leak detector output versus scanning voltage
39、(for Helium as tracer gas) O BSI 1998 STD-BSI BS EN 1518-ENGL 1998 1624669 0716581 42T m 7.4 Inlet pumping speed for tracer gas For the determination of the pumping speed for tracer gas, the test vessel with known volume as described in 6.3 is necessary The volume of the test vessel shall be selecte
40、d so that time constants can be evaluated from the traces on the chart recorder. For most leak detectom, this means a volume between 10 1 and 50 1. The following procedure is used. a) Connect the test vessel directly to the test port of the leak detector (if direct connection is not possible, a pipe
41、 with known conductance shail be used). b) Fit the small leak to the test vessel. There shall be a leak isolation valve referably of a-metal construction) between the leak and the vessel. c) Evacuate the vessel with the leak open and wait until the leak detector is ready for measurement and gives an
42、 indication resulting from the leak. d) Set the chart recorder to a speed of 50 cmmin or more. e) Start the recorder with the high chart speed, when the output signai has reached a steady value showing no observable change in 1 min. f) Close, at a dennite instant, the leak isolation valve on the ves
43、sel as rapidly as possible. g) Record the decrease in the resulting output until the signai is again stable at its low value (background indication). NOTE If the initial leak indication is less than 10 times the background indication, the test has to be repeated with a iarger leak. h) Mark the time
44、scale on the record. 8 Results 8.1 Minimum detectable leakage rate 8.1.1 Evaluation 0.1.1.1 Minimum detectable signai The minimum detectable signai may be determined according to the following procedure. a) Take the record of the drift and noise measurement for smallest detectable leakage rate 7.1.l
45、d) and draw a series of line segments intersecting the recorder curve at right angles to the time axis in 1 min intervals. b) Draw stsaight line approximations for each segment of the me between dacent 1 min lines. c) Determine that segment of the curve having the greatest slope. (The signal change
46、in this segment is called drift. Ifthis is less than 2% of the full scale of the recorder, determine the total change in output over the 20 min period and divide this by 20.) Page 11 EN 15181998 d) Determine the maximum deviation from the straight line approximation for each 1 min segment of the cur
47、ve, in order to determine the noise. (Any large deviation occurring no more than once in the whole length of the recorded curve shall be ignored). The noise is given by the average of the 20 deviations multiplied by 2. The minimum detectable signai is given by the sum of the drift in Imin and of the
48、 noise. Ifthe sum is less than the display resolution, the smallest resolvable indication is the minimum detectable signal. (The minimum detectable signal is nonnally given in scale divisions.) 8.1.1.2 Background signai correction ($or auxiliary WmPW swtem) This correction may be evaluated according
49、 to the following procedure. a) Subtract the background reading obtained with the leak isolation valve closed 7.1.2g) from that obtained with the leak valve open 7.1.2f) and the blanking fiange in place of the leak. The difference is termed the background signal correction (for audiary pumping system). b) If the difference is negative, it shall be taken to be zero. 8.1.1.3 Sensitivity The sensitivity is determined according to the following procedure. a) Take the reading of the small leak 7.1.3e). b) Subtract the reading with closed leak valve 7.1.2g) and
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