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Calibration
Thermo Fisher Scientific
(typically nitrogen) purge is connected to the ballast port on the
pump. The purge flow rate is selected so that in normal operation the
oxygen content of gas passing through the pump is diluted to a level
where ignition cannot occur. A flow of 0.6 l/min is required.
A pair of flow switches is used to monitor the nitrogen flow (two
switches are required to give redundancy). In the event of loss of
flow, power to the pump is switched off, which will cause a full
vacuum system shut down to take place shortly afterwards.
Note that the pump purge shares the inert gas inlet connection with
the dry gas vent.
The flow interlock can be tested by turning off the nitrogen supply
and checking that the pump switches off. The pump should restart
when the nitrogen supply is restored. The flow switches have clear
acrylic bodies to allow easy inspection of the devices. Check that the
flow path is clean and the floats move up and down at more or less
the same time when the nitrogen flow rate is adjusted.
The calibration panels are based on safe area solenoid valve
Panels
manifolds. These are made acceptable for hazardous area use by
mounting through the wall of the Exp enclosure, such that the valve
bodies are outside the enclosure, which avoids possible leakage
inside the enclosure. The solenoid coils are inside the enclosure and
are therefore protected by the enclosure purge.
Requirements of the assembly are that:
a. The valve plunger assemblies, which contain gas and
b. Substitute parts must not be used.
c. The gasket seal between the valve manifold body and the
protrude into the enclosure, must be high integrity. The type
of valve used has a welded plunger assembly, which is a
requirement of the ATEX/IECEx certification of the system.
Testing of the integrity of the plunger assembly is carried out
in the factory where the welded assembly is tested as
'infallible'. This is a requirement of ATEX/IECEx
certification and has to be performed on each assembly prior
to fitting to an instrument or making available as a spare.
mounting plate is designed to maintain the enclosure integrity
and prevent calibration gas seeping into the enclosure in the
event of a leak on the plunger-to-manifold O-ring. Care must
be taken to correctly reassemble this gasket. It is
recommended that this gasket is replaced should it prove
necessary to strip down the assembly for maintenance
purposes.
Prima PRO & Sentinel PRO Mass Spectrometers User Guide
Hazardous Area Operation
Other Hazardous Area Considerations
A-19
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