ABB ACX Commissioning Instruction page 43

Program Sequence,
Switch Over
Back-Purging
Probe Filter
Back-Purging
Probe Tube
Venting and
Switch Over
Post-Purging Period
End of the Back-Purging
Procedure
CI/ACX-EN Rev. D
continued
At first the calibration valve -Y01
separates the sample gas conditioning system and the analyzer system from the
sampling system and protects it against the back-purging pressure. 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 continuously but by two
2 sec pressure impulses alternating with a 2 sec interval each.
After this the probe tube is purged back in the same way with two pressure impulses.
A single pressure impulse of 4 sec is followed, to blow out the remaining dust from the
tube.
Next the pneumatic system is vented for 6 sec and finally the calibration valve -Y01
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. This post-purge time must be adjusted individually according to the
given conditions (see section "Adjustment of Cycle Time and Post-Purge Time",
page 46). A purge time of 150 sec 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.
1) In system version with VOC analyzer AO2000-Fidas24, the sample gas path is
blocked and unblocked with the valve -Y5 which is built-in in the PFE2 filter unit.
ACX Analyzer System Commissioning Instruction
1)
is switched over to position "Calibrate". This
1)
is
43