TESTO 6681 Instruction Manual page 74

testo 6610
74
- 2.1 Specifications
2.1.1.2 The Testo humidity sensor
With the Testo humidity sensor, which has been in successful use and
continually improved for more than twenty years, the focus has from the very
beginning been on both accuracy parameters, namely measuring uncertainty
and long-term stability.
The capacitive humidity sensor is in principle a plate capacitor consisting of
two electrically conductive plates (electrodes (1) and (2), see diagram below)
opposite each other.
A humidity-sensitive polymer (5) serves as the dielectric. The special feature
lies in the perfect way the individual layers are matched to each other. This is
evident particularly in the top electrode, which has to perform two tasks that,
at first glance, appear contradictory: it must be completely permeable to the
water vapour that is to be fed into the polymer dielectric, but at the same time
it must be impervious, smooth and repellent to condensate, oil and dirt in
order to protect the sensor.
The humidity sensor cannot be exchanged by the customer.
The humidity sensor may not be damaged or touched.
Contamination and damage lead to an impairment of the
measurement and the measuring accuracy.
1 Cover electrode
2 Bottom electrode
3 Substrate
(Ceramic substrate for
mechanical protection)
4 Connections
(protected against corrosion)
5 Dielectric layer