Wüest M. 51 Wykes M. 82 Yamaguchi M. 17 Ybarra G. 129 Yubero F ...

JUNE 27 TUESDAY MORNING
WS-18-TuM-OR.7 HEALIUM LEAKS TRACEBILITY AT CZECH METROLOGY
INSTITUTE (CMI). Dominik Prazak. Czech Metrology Institute, Okruzni 31, 638 00, Brno,
Czech Republic. Jiri Tesar. Czech Metrology Institute, Okruzni 31, 638 00, Brno, Czech Republic.
Petr Repa. Charles University Prague, V Holesovickach 2, 180 00, Prague 8, Czech Republic.
Ladislav Peksa. Charles University Prague, V Holesovickach 2, 180 00, Prague 8, Czech Republic.
Tomas Gronych. Charles University Prague, V Holesovickach 2, 180 00, Prague 8, Czech Republic.
Martin Vicar. Czech Metrology Institute, Okruzni 31, 638 00, Brno, Czech Republic.
The tightness of vacuum systems has very high and increasing importance in contemporary research,
industry and safety of work. Its consequence is continuous and growing demand for the calibration
services in this field.
Mass spectrometers as helium leak detectors are traditionally used for accurate measurement of vacuum
leaks. The critical point of their accuracy is their low long-term stability. It is necessary to calibrate
them with very short recalibration periods utilizing the secondary helium leak standards. But,
of course, these secondary standards need the traceability to the standards of higher order. Until recently,
CMI has used the services of other national metrological laboratories, but this system has
been becoming more and more insufficient.
So there has been decided to build our own primary standard of vacuum leaks in the framework of
United vacuum laboratory of CMI and Charles University – Prague. The recently finished high vacuum
standard based on continuous expansion has been chosen as the base leading to the reduction of
costs. That implies use of constant pressure - variable volume flow meter and comparative measurement
method. Its preliminary range is 3 . 10 -7 - 7 . 10 -4 Pa . m 3. s -1 with uncertainty less than 0.5 %, but we
study the possibilities of its extending. First of all it is needed in the lower range limit.
The paper will describe the problems that have occurred during construction (flow meter based on
bellows, its compression mechanism and measurement, reproducibility of its volume, pressure and
temperature stabilization and measurement, parasitic effects), the method of traceability and the attainable
uncertainties.
[1] ŘEPA, P., TESAŘ, J., GRONYCH, T., PEKSA, L., WILD, J.: Analyses of gas composition in
vacuum systems by mass spectrometry. Journal of Mass Spectrometry. 2002 (37), p. 1287-1291.
[2] PEKSA, L., GRONYCH, T., ŘEPA, P., TESAŘ, J.: Measuremet of the pressure differences in a
large chamber where the pressure is generated dynamically. Vacuum. 2002 (67), p. 333-338.
[3] PEKSA, L., ŘEPA, P., GRONYCH, T., TESAŘ, J., PRAŽÁK, D.: Uncertainty analysis of the
high vacuum part of the dynamic flow standard. Vacuum. 2004 (76), p. 477-489.
69