MAX300-RTG: Installation Manual Hardware Installation
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This option consists of an independent flameproof enclosure for user connections,
which is wired to the main enclosure.
ATEX/IECEx Category 3 (Zone 2) and Class I Div 2
This unit is intended for use in ATEX/IEC Category 3 (Zone 2) or Class I Division
2 locations. It is designed for use with group IIC or groups ABCD hazards, where
the hazardous area is non-mining (above ground) and the hazard is caused by
flammable gases or vapors.
The instrument is made suitable for hazardous locations via a purge and
pressurization technique, known as “pz” or “z” purge. This design allows purge
gas, also known as a protective gas, to be admitted into the enclosure from a safe
source. The interior of the enclosure is maintained at a pressure above
atmospheric pressure. This overpressure prevents entry of the possibly hazardous
atmosphere that surrounds the unit and allows the use of electrical devices inside
the unit while in hazardous locations. In the event that the control device senses a
failure, a failure indicator is enabled at the unit, and a failure switch contact closes,
which the user may wire to a remote indicator. The failure sensed may be due to
interruption of air flow, an air supply pressure decrease below minimum, or the
enclosure overpressure not being maintained.
The purge and pressurization system is controlled by a Control Unit (CU), a
pneumatic logic circuit, which is the heart of the system. Once the main power and
purge gas has been successfully installed on the mass spectrometer, the purge
and pressurization system can be started. When the purge gas supply is first
turned on, the purge indicator on the control unit indicates proper purge, and a
steady flow of air begins within the enclosure. After allowing purge/pressurization
gas to flow for 12 minutes, power may be connected to the unit. The purge system
allows at least 142 NL/m (5 SCFM) to flow through the enclosure at all times,
maintaining an internal pressure within the enclosure of at least 2.5 mbar (1” H2O).
If this internal pressure is not maintained, the purge indicator on the unit shows a
fault, and a dry contact switch closes, which the user may connect to a remote
alarm if desired.
Because the instrument may contain parts that may be above the ignition
temperature of the surrounding atmosphere, i.e. T4 of 135°C (T3 200°C option
available), the enclosure must not be opened even when de-energized until 5
minutes have elapsed. The delay ensures that the hot parts have cooled well below
the ignition temperature.
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