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

JUNE 27 TUESDAY MORNING
WS-18-TuM-INV6.5 LEAK DETECTION: CALIBRATIONS AND REFERENCE
FLOWS ARE REQUIRED IN EVERY TYPE OF APPLICATIONS: PRACTICAL EXAM-
PLES. A.Calcatelli, Istituto Nazionale di Ricerca Metrologica, I.N.RI.M., Turin, Italy.M.Bergoglio,
Istituto Nazionale di Ricerca Metrologica, I.N.RI.M., Turin, Italy
D. Mari, Istituto Nazionale di Ricerca Metrologica, I.N.RI.M., Turin, Italy
Several methods and related instrumentation are used for leak detection from bubble emission to the
ultrasound devices, to pressure/vacuum variation measurements (vacuum gauges, thermal conductivity
sensors), to halogen leak detectors or detectors using radioisotopes, to the more recent instruments
based on selective ion pump detection (SIPD) and finally to the application of mass spectrometry.
The most diffused methods for the leak rates lower than 10 -3 Pa m 3 /s that is based on the
application of mass spectrometry with tracer gas (generally helium) is considered (MSLD). MSLD
represents the best choice for industrial control of tightening for its good sensitivity and obtainable
speed of testing. The leak test may be performed with various methodologies (vacuum, pressure or
vacuum-pressure) and its purpose may be to localize the leaks or to quantify them.
Leak detection is considered, at European level, by the WG 6 (leak testing) of the CEN/TC 138 (Non
Destructive Testing), and worldwide level by the SC 6 “Leak detection methods” of the ISO/TC 135
(Non Destructive Testing). At European level, several standards have been published regarding terminology
as well as the choice of the method or the calibration of a leak detector and calibration of
standard leaks.
If the leak detector output must have a real meaning in term of gas flow-rate the instrument has to be
calibrated and its uncertainty must be evaluated. Therefore, the calibration of a leak detector is performed
with reference to known gas flow-rates by using the so-called standard leaks both of permeation
or geometrical type (generally capillaries) which are used to generate flow from 10 -9 Pa m 3 /s
to 10 -3 Pa m 3 /s; these standard leaks are calibrated with reference to atmospheric pressure or vacuum
against primary gas flow-meters. The I.N.RI.M. primary flowmeters are shortly described which
cover the following gas flow-rate ranges:
• 2.10 -9 Pa m3/s e 2x10 -8 Pa m 3 /s with reference to vacuum, extended uncertainty 8%
• 2x10 -8 - 3.10 -5 Pa m 3 /s with reference to vacuum, extended uncertainty from 2% to 0.5%.
• 2.10 -5 Pa m 3 /s e 1.10 -3 Pa m 3 /s with reference to atmospheric pressure, extended uncertainty 2%.
Some calibration results are presented together with the preliminary results of a bilateral comparison
which is considered as preparatory for a more wide scale comparison.
A device devoted to on line control of components which need that all the significant parameters be
well defined starting from the mass spectrometer leak detector which is characterized from metrological
point of view, that is to say essentially for what concerns linearity and repeatability of the
out-put by using reference leaks. The whole machine must be well known in its working configuration
for what concerns linearity and repeatability and the traceability chain must be made evident.
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