AO2000-LS25
LASER ANALYZERS | OI/AO2000-LS25-EN REV. D
79
PROPORTIONAL and GLOBAL calibration
Line broadening compensation requires a large number of
parameters to be measured. These parameters are critical for
accuracy, but only when line broadening compensation is used.
Most of the parameters seldom or never need to be adjusted.
PROPORTIONAL calibration:
This calibrates the span of the gas concentration by adjusting
the proportionality between the peak amplitude of the
absorption line and the gas concentration. Only the proportional
calibration constant is affected by PROPORTIONAL calibration.
GLOBAL calibration:
Calibrates both the gas concentration span and line width
parameters. It is important to follow the calibration procedure
carefully and specify to the instrument the exact pressure and
temperature of the calibration cell.
The pressure (P) and temperature (T) values can be set
permanently using the service program.
However, the 4 to 20 mA inputs can also be used if these sensors
are connected to the calibration cell.
One can also use the readings of the internal sensors if these are
close to the values for the calibration cell. It is also important to
use dry gas mixed with nitrogen. For O
2
, dry air can be used.
Use GLOBAL calibration:
• If spectral properties of the laser seem to have drifted.
This can be evaluated by qualified service personnel from
readings files recorded with the device when it was
measuring on a calibration gas.
• After major device services such as replacement of laser
module, main board or receiver board.(Qualified service
personnel only!)
• After adjustment of laser parameters (laser temperature,
modulation amplitude or phase, or other laser currents).
(Qualified service personnel only!)
DO NOT use GLOBAL calibration when:
• The device is measuring on the process (with process
gas).
• The concentration of the calibration is low or the path
length of calibration cell is short such that the signal-to-
noise ratio is not good.
• If the above mentioned GLOBAL calibration conditions
are not fulfilled, but a recalibration is required, use
PROPORTIONAL calibration instead.
