ABB AO2000-LS25, Manual

Page: 81 / 88

AO2000-LS25
LASER ANALYZERS | OI/AO2000-LS25-EN REV. D 81
Span and zero check with internal sealed span cell
Note that this option also includes zero check functionality.
Span and zero checks may be carried out with the device
installed on the process. The receiver unit includes a small sealed
gas cell containing the gas to be measured. This cell is moved
into the laser optical path by a compact servomotor.
The span and zero mode is initiated by input through digital
communication, see
Mode on page 53.
The instrument calculates and stores the absorption signal for
the gas concentration measured in normal mode just before the
span check.
This absorption signal is continuously subtracted from the
measured signal during span check operation.
The resulting signal, therefore, corresponds to the signal from
the internal cell providing that the signal from the process
remains stable during span procedure (typically 15 seconds).
The ambient temperature and pressure recorded with the
internal temperature and pressure sensors located inside the
receiver unit is used to calculate the concentration of the span
gas.
By default the internal span cell is calibrated to give a 75 to 80 %
of full-scale reading.
(Alternative calibration is possible, contact ABB or your local
distributor.)
14 Decommissioning
Temporary shutdown
1. Switch off the power supply.
2. Switch off the purging gas supply.
NOTICE
Damage to the gas analyzer
Damage to the gas analyzer in high temperature applications
due to lack of purging gas.
• In high temperature applications, the purging gas supply
must remain on so as to further cool the gas analyzer.
• Alternatively, disassemble the transmitter unit / receiver
unit from the purging flanges.
Recommissioning
Refer to Commissioning on page 46. Check the transmission
during recommissioning and clean the optical windows in
accordance with
Cleaning of optical windows on page 75 if
necessary.
For operation in potentially explosive atmospheres, also notice
the instructions in
Use in potentially explosive atmospheres in
accordance with ATEX and IECEx on page 7 ff. und Use in
hazardous areas in accordance with CSA on page 22 ff..