Metek 920, Operator'S Manual With Essential Health And Safety Requirements

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3-30 | Model 920 Multi-Gas Analyzer
Purged Analyzers
The Electronics Enclosure and its Optical Bench and Measuring Cell
Extension are continuously purged with Instrument Air to adequately
dilute any flammable gases that may have been released into these areas.
This function effectively prevents an internal explosion when the ana-
lyzer is powered up and operating under normal sampling conditions.
AMETEK analyzers that require purged enclosures in hazardous locations
use an Expo Technologies MiniPurge
®
System With eTimer to perform
this function.
The purge air supply is normally obtained from the Instrument Air supply
connected directly to the Expo MiniPurge
®
System. The required purge
air supply pressure for your analyzer is indicated on Final “As-Built”
drawings in the analyzer Documentation Package.
After the Instrument Air supply has been connected to the MiniPurge
®
system, the ALARM/PRESSURIZED indicator on the MiniPurge
®
system
(Figure 3-9) turns from RED (Alarm condition) to GREEN (Pressurized).
Next, the system’s eTimer begins its purge timing cycle, and the four
PURGE TIMING indicator LEDs will flash (YELLOW) sequentially, each
for 25 % of the total purge time (minimum 15 minutes). During this stage,
the MiniPurge
®
system will purge any flammable gases that may have
entered the Electronics Enclosure while its door was open, and then pres-
surize the enclosure. After the timing sequence is completed (LEDs off),
the pneumatic switch will send a signal to the analyzer and the analyzer
will power up (if the Purge Bypass Switch is in the “
ACTIVE ” position, if
all fuses have been engaged, and if the external explosion-proof power-
disconnect switch has been closed).
A minimum of 15 minutes is required to properly purge and pressur-
ize the analyzer Electronics Enclosure.
The Expo Technologies MiniPurge
®
System uses a Battery Pack to
power its purge timer. AMETEK recommends replacing the Battery
Pack every three years to ensure proper and safe operation of the
purging system. See “Analyzer Preventive Maintenance Schedule” in
Chapter 6 for more information.
Working with the purged enclosure open is typically limited to installa-
tion, start-up, and certain troubleshooting and maintenance procedures.
In these cases, the Purge Bypass Switch (Figure 3-10) must be in the
“
BYPASS ” position (and appropriate safety conditions must have been
met, as per company policy).
For normal analyzer operation, the Purge Bypass Switch must be in the
“
ACTIVE ” position and the key must be removed (follow company policy).
!
WARNING