GE Optica, Operator'S Manual

Page: 104 / 150

January 2006
7-4 Maintenance
Field Replacement of
Sensor Mirrors
One advantage of using a GE Infrastructure Sensing chilled mirror
dew point sensor is that the mirror is user-replaceable. The sensor
does not have to be returned to the factory for replacement of the
reflective surface, unless that is desired.
A mirror may require replacement for any of the following reasons:
The mirror is constructed of silver/rhodium plated copper. Copper
provides excellent thermal conductivity to the platinum thermometer.
However, some gas constituents, such as sulfur dioxide (SO2) may
react with the copper and eventually pit the surface or form a copper
sulfate coating.
The reflective surface may be gradually abraded by sharp dirt
particles in the gas being measured.
The mirror surface may be accidentally scratched or gouged during
use or cleaning.
If the sensor mirror has reacted with a corrosive material in the gas
sample, such as an acid or sulfur compound, it should be replaced
with a solid platinum mirror to remove any possibility of copper
corrosion.
In extreme cases, a solid platinum mirror can make possible a
successful application of chilled mirror technology. For example,
measurements in tobacco factories and malting houses have
drastically improved after this change, since both locations have
sample gas constituents that attack copper.
In addition, fine scratches can be buffed out of a solid platinum
surface, restoring the mirror to new condition, since it is of solid
construction.