The Pacer Cycle - GE Optica Operator's Manual

Chapter 1. Features and Capabilities

1.6 The PACER Cycle

GE Measurement & Control has developed and patented a compensation technique called
Automatic Contaminant Error Reduction) that is very effective in reducing the Raoult Effect error associated with
soluble contaminants, particularly for near-ambient dew points. The Optica is equipped with the
balance as found on earlier models. The user can choose which self-cleaning and balancing routine to run
AUTO
depending on the severity of the contamination.
The cycle, diagrammed in Figure 3 below, begins with a coalescence period, during which the mirror is cooled
PACER
well below the dew point of the sample gas, condensing out a large amount of water.
Prevailing
Dew Point
This excess water easily dissolves any water-soluble contaminants. The mirror is then heated. During the heating
phase, the large puddles of water gradually evaporate, carrying increasingly heavy concentrations of salts as the
puddles become smaller. Finally, when all the puddles have evaporated, dry "islands" of crystallized salt are left on the
mirror. The area between the islands (80-85% of the mirror surface) is now clean and shiny, whereas before the
cycle it may have been completely covered. The total amount of contamination has not been reduced, but instead,
redistributed as shown in Figure 4 below, with more clean mirror surface available for dew formation. The reflected
light signal is then electronically balanced against the reference.
6
Mirror Cools
and Coalesces
(30 sec)
Figure 3: A Typical PACER Cycle
Before
PACER Cycle
Figure 4: Results of the PACER Cycle
Data is Sampled
and Held
(3 min)
Mirror Heats
To Dry State
(90 sec)
After
PACER Cycle
(Programmable
PACER
cycle as well as
PACER
Optical System
Automatically
Adjusts for
Correct
Reflectance
(5 sec)
Mirror Returns
To Dew Point
(60 sec)
Optica™ Operator's Manual
PACER