Vaisala DM500 - Manual (Page 25)

Chapter 3 ______________________________________________________ Functional Description
VAISALA _______________________________________________________________________ 23
Contamination and Chemical
Resistance
The DM500 operates reliably even with substantial particulate
contamination on the sensing element. Analysis of frequency and
impedance makes it possible to distinguish between frost and dew and
to give warning of hygroscopic contaminants on the detector.
Use of a quartz wafer as a sensor substrate results in excellent
resistance to aggressive chemicals. Wetted parts inside the DMP501
dewpoint sensing unit are limited to stainless steel, silicone, tantalum,
quartz, Vectra® (Liquid Crystal Polyester).
Vectra and silicone parts as well as those optional components that
have water-absorbing materials are located downstream from the
active area of the sensor thus not disturbing the measurement
especially in low dewpoints.