GE Moisture Image 1 Series, Service Manual, Page: 68 / 107

June 2003
A-6 Application of the Hygrometer (900-901D1)
Conductive Particulates
Note: Metallic particles, carbon particles and conductive liquid
droplets are typical of this category.
Since the hygrometer reading is inversely proportional to the
impedance of the sensor, a decrease in sensor impedance will cause
an increase in the meter reading. Thus, trapped conductive particles
across the sensor leads or on the sensor surface, which will decrease
the sensor impedance, will cause an erroneously high dew point
reading. The most common particulates of this type are carbon (from
furnaces), iron scale (from pipe walls) and glycol droplets (from
glycol-based dehydrators).
If the system contains conductive particulates, it is advisable to install
a Teflon® or stainless steel filter in the fluid stream.
Corrosive Particulates
Note:
Sodium chloride and sodium hydroxide particulates are
typical of this category.
Since the active sensor element is constructed of aluminum, any
material that corrodes aluminum will deleteriously affect the
operation of the moisture probe. Furthermore, a combination of this
type of particulate with water will cause pitting or severe corrosion of
the sensor element. In such instances, the sensor cannot be cleaned or
repaired and the probe must be replaced.
Obviously, the standard moisture probe can not be used in such
applications unless the complete removal of such part by adequate
filtration is assured.