Mirror Flooding; Sample Line Maintenance; Pressure Effects - GE OptiSonde User Manual

October 2007
Minimizing the Effects of
Contaminants

Mirror Flooding

Sample Line Maintenance

Pressure Effects

3-8
The following steps are suggested for maintaining optimum
performance:
•
PACER
Use the feature to reduce the effect of contaminants on the
unit's performance (see The PACER Cycle on page E-4).
•
Reduce the gas flow rate to reduce the rate of accumulation of
contaminants on the mirror.
•
Clean the mirror according to the recommended optics cleaning
procedure (see Minor Maintenance of Sensor Optics on page 5-1).
To determine the proper cleaning interval for a given set of
conditions, take a dew point reading before and after the cleaning.
Any appreciable shift indicates that under these conditions, the
mirror should be cleaned more often.
If there is an abrupt transition from dry to moist conditions
(particularly when accompanied by a transition from cold to warm
temperatures), the mirror may accumulate an overload of moisture. It
then may take several minutes before the sensor dries out and valid
readings can be obtained. The drying process can be accelerated by
heating the sensor.
Contaminated sample lines slow the unit's response time and can
cause erroneous readings, usually on the high side. Clean the sample
lines as often as necessary. To determine the required cleaning
frequency, take dew point readings before and after cleaning the lines,
sensor cavity, and mirror. If the two readings differ appreciably, the
sampling lines should be cleaned more often. To reduce the rate of
contamination, reduce flow and/or install a filter upstream.
If the pressure of the gas is increased or reduced from atmospheric
pressure, but the mixing ratio (moisture content) stays constant, the
dew point is correspondingly increased or decreased. The OptiSonde
displays the dew/frost point at the pressure to which it has been
programmed. The sensor location and hookup arrangement can
influence the pressure.
The dew point change due to pressure change can be calculated by
using psychrometric equations. Appendix C contains basic data for
these calculations.
Operation