ABB ACX Commissioning Instruction page 45

Post-Purge Time
Post-Purge Time
Duration
Guide for the
Post-Purge Time
Example
CI/ACX-EN Rev. D
The post-purge time at the end of the back-purging procedure must be such, that the
complete pneumatic system is flushed with the actual sample gas and the analyzer
gets time to take over the actual measuring value again. The needed post-purge time
depends on the respective layout of the system (i.e. the length of the sample gas line)
and will have to be adjusted individually. A post-purge time of 150 sec is factory-set.
A guide for the needed post-purge time is given in the table below. Please add the
times for the pneumatic system, the analyzer and the sample gas line.
Pneumatic system without sample gas line
plus analyzer Uras26
plus for each 10 m sample gas line I.D. = 4 mm
plus PFE2 / PFE3 with probe tube 40, length = 1 m
For an ACX analyzer system with filter unit PFE2 / PFE3 and 15 m sample gas line at
60 l/h sample gas flow the post-purge time is calculated as follows:
Post-purge time = 45 sec + 23 sec + 1.5x 8 sec + 75 sec = 155 sec
ACX Analyzer System Commissioning Instruction
Response time (3 x T , approx.) for sample gas flow
90
60 l/h 100 l/h 200 l/h
(Bypass)
45 sec 27 sec 20 sec
23 sec 20 sec 23 sec
8 sec 5 sec 2.5 sec
75 sec 45 sec 23 sec
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