ABB GAA330-M Operating Instructions Manual page 48

48
Switch over
Back-purging probe filter
Back-purging probe tube
Venting and switch over
Post-purging period
End of the back-purging procedure
GAA330-M EMISSION MONITORING SYSTEM
At first the calibration valve -Y01 is switched over to position "Calibrate".
This separates the sample gas conditioning system and the analyzer system
from the sampling system and protects it against the back-purging pres-
sure. At the same time the status "Maintenance mode" is activated and all
analog outputs and limits are set on hold. The display reports "Purge back is
active".
The back-purging procedure continues with the back-purging of the probe
filter. To increase the cleaning effect, the compressed air is applied not con-
tinuously but by two 2 s pressure impulses alternating with a 2 s interval
each.
After this the probe tube is purged back in the same way with two pressure
impulses. A single pressure impulse of 4 s is followed, to blow out the re-
maining dust from the tube.
Next the pneumatic system is vented for 6 s and finally the calibration valve
-Y01 is switched back from position "Calibrate" to position "Measure". This
venting time removes an internal remaining pressure which might be still
present in the pneumatic system and so avoids a damage of the analyzer's
measuring cell.
The calibration valve switch back to position "Measure" will not finish the
back-purging procedure, because first the actual sample gas must flow
through the pneumatic system to purge it, and the analyzer must adjust to
the new actual measuring value. A purge time of 150 s is factory-set.
The back-purging procedure is not finished until the purge time has expired.
Now the analog outputs and limits are set free again and they will take over
the actual values. The message "Purge back active" in the display as well as
the status signal "Maintenance mode" will vanish.
| OI/GAA330-M-EN REV. C