MATERIALS
31
Attaining
process stability
in the flow
Correct materials and process stability are imperative for mechanical
pressure gauges for pure media to avoid compromises and combustion.
Thomas Nieswandt from WIKA explains the challenges
T
he requirements for mechanical pressure without costly time delay, dead space must be
gauges in ultra high purity applications avoided. At the moment only the so called flow
(UHP) are high. Process stability, leak through gauges with diaphragm element basis can
tightness, purity, corrosion resistance and be said to meet this claim. They are assembled
indication accuracy are the determining factors directly into the piping and passed through by the
when choosing the measuring technology for the respective medium.
respective application. However, there are two
more mutually determining features that may be Most commonly used in the industry are pressure
crucial: reduced dead space volume and, gauges with bourdon tube which are mounted onto
subsequently, a good rinsing behaviour. the pipe. During installation, commissioning and
maintenance as well as during operation temporary
During commissioning and maintenance work or concentration of dust and chip particles can occur
medium change in the mixed gas lines the in the gauge. Since the medium does not flow
indispensable rinsing of the dead space turns out to through the bourdon tube, these microparticles
be complicated and time consuming. In order to concentrate at the end of the bourdon tube. In the
ensure medium purity, e.g. gas quality 6.0 course of pressure changes these contaminations
(99,99990 %) or higher as well as reliable removal can flow back from the bourdon tube into the
of oxygen, humidity and particles from the system process pipe. Diversion of the particles involves a
October 2008
www.euroasiasemiconductor.com
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