Flame Proof Dtr/Str Enclosures - Vaisala K-PATENTS PR-23 Series Instruction Manual

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10 Indicating transmitter DTR specifications

10.5 Flame proof DTR/STR enclosures

The flame proof enclosures embedding a DTR or a STR have aluminium enclosures
with ATEX and IECEx options and with or without Isolator for hazardous Zone 1 and
2 installations.
The Ex type junction box is intended for hazardous areas where flammable gases are
present in the environment and can be ignited by an electrical spark or hot surfaces. In
these environments, all equipment manufacturers work from the assumption that it is
impossible to prevent gases from penetrating all areas. Instead the design is based on
confining the explosion by guiding the flames to follow a path long and narrow enough
to guarantee the cooling of the gases and avoiding an external explosion. This method
of protection is the oldest used to prevent explosions and remains still one of the safest
because it is based on a very simple and, therefore, unlikely fallible technology.
The EJB type junction box covers the design for ethylene gas from the gas group IIB
and hydrogen gas from the gas group IIC. The GUB type junction box covers the design
for gases from the gas group IIC. Both Ex type junction boxes have a window allowing
the user to read the DTR/STR display.