Overview | 1-9
Functions
The Division 1 and Zone 1 versions of the IPS-4 are designed to be, and
comply with requirements for, electrical equipment in Division 1 and
Zone 1 classified hazardous areas respectively. The methods of protection
used include type “p” (pressurized), and type “d” (Flameproof enclosure).
The purge system, redundant heater control, disconnect assembly and en-
closure designs assure that the system will not ignite surrounding gases.
For this reason, any repairs must not bypass these safety considerations
and must use only recommended components.
The purge system consists of the Electronics Enclosure, a purge control-
ler, an overpressure vent, a bypass switch and power/signal disconnect
assembly. It maintains a positive pressure in the Electronics Enclosure
that prevents flammable and corrosive gases from contacting electrical
components. The oven enclosure and the seals between the enclosures are
designed to assure that the required 5x factor of safety to assure that the
sample containment system will not interfere with proper operation of
the purge system.
The disconnect assembly receives a pneumatic signal from the purge
controller when the enclosure has been adequately purged and the over-
pressure is maintained. Until these conditions are met, the relays in the
disconnect assembly break all power and signal connections between the
field and the analyzer. When the Electronics Enclosure is opened or the
pressurization gas supply is lost, the system will shut the analyzer down
and transfer a set of contacts that may be used to provide an alarm.
The bypass switch enables operation of the analyzer by applying air pres-
sure to the disconnect assembly – bypassing the purge controller. This
feature must only be used when the area is known to be safe and is being
continuously monitored (See Combustible Gas Detection protection tech-
niques in NFPA70 article 500 and 505). Figure 1-4 is a state diagram show-
ing the operation of the pressurization system and the pressure settings.
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