Sensor Balancing; Helpful Hints For Operating The Unit - GE Optica Operator's Manual

Chapter 3. Operation

3.8 Sensor Balancing

During normal operation, the sensor mirror surface may become partially obscured with salts or other contaminants
from the sample gas. The balance indicator displayed on the screen shows whether the system is operating near the
center of its normal range, or has been forced away from the center by mirror contamination. In general, it is
recommended to start with an
indicator is displayed after an
(described in detail in "The PACER Cycle" on page 6). In most applications, it is desirable to perform a balance
operation periodically to maintain optimum performance. The interval and type of balance are configurable as
described in the Optica programming chapters.
If the Service indicator is displayed after a balance operation, the sensor may need to be adjusted (see "Minor
Maintenance of Sensor Optics" on page 75).

3.9 Helpful Hints For Operating the Unit

Time response: At dew points above 0°C, the system stabilizes within a few minutes at a consistent dew layer. The
status Control is displayed when the system is stable and readings are valid.
When the system is operating at low frost points (below –40°C), extra care may be required when interpreting readings
because of the longer response times of the system. Time response depends on a number of factors including dew/frost
point, slew rate, upstream filtering, and flow rate.
•
As the dew/frost point becomes lower, water molecules in the air sample become scarcer, and it takes longer to
condense a frost layer on the mirror thick enough to establish an equilibrium condition.
•
Mirror temperature slew rate depends on dew point and depression (the temperature difference between the
mirror and the sensor body); at higher dew points and moderate depressions, it is typically 1.5°C/second. At
lower dew points and/or larger depressions, the slew rate is slower.
•
Flow rate affects response by determining the rate at which water vapor is supplied or carried off.
There is, of course, a trade-off between response time, control system stability, and sensitivity to contamination.
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balance cycle provided relatively clean gases are being used. If the Service status
AUTO
cycle, the mirror is likely still dirty and may require use of a
AUTO
cycle
PACER
Optica™ Operator's Manual