Servomex 07931001B, Operator'S Manual

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07931001B revision 6 © Servomex Group Limited. 2020
151
7.6 Purge connections
Note: Purge connections are listed in section 2.6.3.
Alignment / purging assemblies
Make sure the purge gas pressure is above that of the process being
monitored to avoid exposure to hazardous gases leaking from the
process.
Make sure that the flange purges are connected and operational before
you connect the transmitter and receiver units to the process. If you do
not do this, the Laser 3 Plus optics could be damaged by the hot
process.
Hint: Servomex recommend that the purge gas is supplied using flexible piping to
minimise strain on the alignment assembly.
The instrument windows are kept clean by setting up a positive flow of air through
the alignment / purging flanges and into the stack. This purging prevents particles
settling on the optical windows and contaminating them.
Use non-hazardous gas for purging. The purge gas must be dry and clean. Specific
gas selected is application dependent.
Hint: For Fixed pipe installations a typical flow rate is between 20 and 30l min
-1
. For
all other configurations, set an initial purge flow in the flange to approximately 1/10
of the gas velocity in the duct.
After you have completed the installation, optimize the purge flow for your specific
application.
Note: Purge flows that are too low may cause blockage or contamination of the 07931
series Laser.
Note: Purge flows that are too high may cause dilution of the measurement gas.
If in doubt, please contact Servomex or local representative for further advice
Note: The air quality should conform to the standard set by ISO 8573.1, Class 2-3:
particles down to 1 micron should be removed, including coalesced liquid water
and oil, and a maximum allowed remaining oil aerosol content of 0.5 mg/m
3
(4.99423685 × 10-4 oz/cubic foot) at 21 °C (70 °F) (instrument air).
Note: Some instruments require nitrogen purging grade 3.0 or higher, for example, O
2
instruments for temperatures below 500 °C (932 °F).
If in doubt, please contact Servomex or local representative for further advice