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

JUNE 26 MONDAY AFTERNOON
WS-18-MoA-OR 5 DYNAMIC EXPANSION SYSTEM AT CEM. C.Matilla;
N.Medina; S.Ruiz. Spanish Centre of Metrology (CEM).
The Spanish Metrology Centre has an orifice-flow primary pressure standard. In this kind of pressure
standard a known flow of gas passes through an orifice of calculated conductance creating a pressure
gradient between both sides of the orifice. The known flow of gas is generated by a precision flowmeter
which can work using the constant volume method or the constant pressure method. Since its
construction the system has suffered several modifications in order to improve its results which will
be described as follows.
The first flowmeter was manually operated. That is the reason why it could basically be used with
the constant volume method. Nowadays it has been completely automatised
and it uses the constant pressure method, which is much more accurate. Data acquisition software
has been designed to monitor all the parts of the system involved. Some parts of the flowmeter have
been correctly isolated by means of aluminium walls to stabilise their temperature.
The first vacuum pump connected to the vacuum chamber was a 300l/s turbomolecular pump. At
present it has been replaced by a 700 l/s turbomolecular pump which allows the system to be closer
to ideal conditions as well as to obtain an appropriate base pressure more easily.
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