Servomex 07931001B, Operator'S Manual

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07931001B revision 6 © Servomex Group Limited. 2020
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absorption becomes non-linear. In this situation, further increases in absorbing gas
concentration are not correctly interpreted by the analyzer
–
effectively causing it to
under-read the real concentration. Further increases in gas concentration can lead
to the reported concentration levelling off and then falling in extreme situations.
When target gas concentrations rise to levels where optical depth saturation occur,
the analyzer will report that it has entered a saturated state and the measurement
will freeze at the last known good value. When the target gas concentration falls
back below the saturation point (taking into account hysteresis effects), the analyzer
will resume normal operation. Spectroscopic saturation events are recorded in the
status log.
Raw signal saturation.
This type of saturation is when absorption is high (>125,000 counts) and the raw
signal exceeds a certain level. When the analyzer is saturated in this way, the
measurement cannot be relied upon as the raw signal and the analyzer can no
longer respond accurately to increasing raw signal. In this situation, the analyzer will
return an (X) on the display (E flag) and status history will show ‘C29I00
SATURATION’ and ‘C35I00 STOPPED’.
Reduce DC1 and DC2 gains or check that actual concentration does not exceed
specified range.
5.5 Drift
Although there is no mechanical drift mechanism within the Laser 3 Plus Analyzer,
the TDL can experience a form of drift where the wavelength emission characteristic
can vary very slowly over time. This drift can happen whether the TDL is powered
or not such that an analyzer which has not been powered for a long period of time
can drift outside of the permitted drift window and fail to lock onto the correct line
(although the internal reference cell will ensure it will lock to an absorption line of
some description).
In these circumstances, during commissioning the signal should be checked to
ensure that the laser set point temperature is still correct for the required
wavelength. Typically, this may be required for units that have lay idle for more than
6 months.
It is not recommended that customers modify the laser set point temperature as it
can have a major impact on the measurement. Customers should contact
Servomex if they believe there is an issue with this.
Note: Locking to an incorrect absorption line can lead to inaccurate measurements as
they may have different absorption amplitudes to that selected and tuned in the
factory.