40
GAA610-M
ADVANCED EMISSION GAS MONITORING SYSTEM | OI/GAA610-M-EN REV. B
9
Gas sampling with automatic back-purging
General
Filter plugging
During operation of the analyzer system the dust which is
contained in the sample gas will accumulate in the probe filter of
the gas sampling system. This is uncritical if dust concentration
is low and only requires a cleaning of the filter periodically in
longer time intervals.
But if the dust concentration is high, the dust accumulation in
the filter will cause an increasing pressure loss, and the gas feed
of the sample gas pump decreases and also the sample gas flow,
and finally the filter is blocked in an extreme case.
Pump suction increase
At first this effect can be compensated by occasional
adjustment of the sample gas flow, which increases the suction
of the sample gas pump.
The pump is strong enough, but if the fouling continues, the
needed suction for keeping up the required gas flow will increase
to such a high value, that several unfavorable effects will emerge
and can finally be accepted no longer.
Filter cleaning
If the suction exceeds a limit of about 300 mbar (accordingly the
absolute pressure falls below 700 mbar), the sampling system
filter has to be cleaned.
The filter units can be cleaned automatically by a back-purging
procedure with compressed air. This procedure is controlled by
the GAA610-M.
Components for back-purging
To carry out the automatic back-purging of the filter unit,
components are integrated in the analyzer system as follows:
• The back-purging air panel with 6 bar pressure reduction
valve, pressure regulator and 2 l buffer tank for effective
pressure pulses also with lower airflow rate
• Two solenoid valves (SOV1, SOV2)
• The gas sample probe with filter unit
• The GAA610-M control program.
Control of the back-purging procedure
The back-purging procedure is integrated into the GAA610-M
control program of the analyzer system.
The manual handling is carried out with the pushbutton ‘Back-
Flush’ on the analyzer system’s front plate.
Start of the back-purging procedure
The start of the back-purging procedure can be carried out:
• Controlled by time
• Controlled by event. If the sample gas flow is too low, a
back-purge cycle is automatically started.
• Manually controlled.
Start controlled by time
After a cycle time has run down, the back-purging procedure will
start automatically. A cycle time of 12 hours is factory-set.
Start controlled by event
A flow fault during normal measuring operation will start the
automatic back-purging procedure.
After back-purging was started by event, the procedure will run
only once.
If the procedure is finished (waiting time 30 s) and the starting
event (flow fault) is still active, the back-purging procedure will
not start again, even not controlled by time, and a status
message will be generated. However, the back-purging
procedure can be started manually after 30 minutes.
Manually controlled start
The manual start of back-purging procedure can be executed
locally by pushing the ‘Back-Flush’ pushbutton on the analyzer
system’s front plate.
