6
Purge air fixture (without electronics)
7
GMP measuring probe (without electronics)
8
Temperature and pressure measurement
9
Purge air supply
ß
Pressure switch for purge air monitoring
Function
•
The device serves for continuous measurement of gas concentrations in industrial plants
•
The device is an in-situ measuring system which means measuring is done directly in the gas carrying duct
•
Measuring components: NH
3
, NH
3
+ H
2
O as well as reference values temperature and pressure
•
Measuring principle: Diode laser spectroscopy (TDLS) (laser protection class 1)
•
To maintain measuring reliability, a permanent air flow (optics purge air) protects and keeps the optics free
from soot and dust particles as well as condensate and moisture condensation
•
Ignition protection type “pressurized enclosure” is effective when using the GM700 Ex in Zone 2 potentially
explosive atmospheres. All relevant enclosures of the sender/receiver unit and connection unit connected
together via a pressure-proof metal hose are purged with a protective gas. The protective gas can be air suc‐
tioned in from the non-potentially explosive atmosphere or an inert gas.
3.7.1
Function of the pressurized enclosure
Purpose of the pressurized enclosure
The pressurized enclosure ensures Ex atmosphere cannot enter the device from out‐
side. To this purpose, the gas analyzer enclosure is filled with a protective gas. Apart
from that, it is ensured that the gas pressure inside the gas analyzer enclosure is higher
than the surrounding air pressure.
Functionality during operation
The pressurized enclosure system functions in “leakage compensation” mode: An over‐
pressure is generated in the device in relation to the atmosphere after pre-purging has
completed. If the protective gas pressure sinks below the minimum pressure set, pro‐
tective gas feed is activated until the selected overpressure is reached again.
Safety functions
If the maximum permitted overpressure is exceeded or the maximum permitted under‐
pressure underrun, the Ex control unit switches an alarm contact which must be perma‐
nently evaluated (responsibility of plant operator, see FS840 Pressurized Enclosure
Manual).
3.8
Purge air unit
•
The purge air unit must be in an Ex-free area and suction Ex-free purge air
•
The purge air unit supplies filtered ambient air to the measuring probe
•
This protects the front window of the SR-unit and the reflector in the measuring
probe against contamination and high gas temperatures
•
The purge air is blown into the gas duct through the “flange with tube”.
NOTE
Further information on the purge air unit, see Operating Instructions of the purge air
unit.
3
PRODUCT DESCRIPTION
18
O P E R A T I N G I N S T R U C T I O N S | GM700 Ex
8019532/100Q/V1-1/2018-08 | SICK
Subject to change without notice