Vaisala PTB210 (analog) - Manual (Page 10)

User's Guide _______________________________________________________________________
8 ____________________________________________________________________ M210670EN-B
The PTB210 barometers incorporate the BAROCAP ® silicon
capacitive absolute pressure sensor developed by Vaisala. The sensor
features excellent hysteresis and repeatability characteristics and has
an outstanding temperature and long-term stability.
Thin film metallization
Silicon
Vacuum gap
Silicon
Glass
Silicon diaphragm
Figure 2 The BAROCAP ® Pressure Sensor
The BAROCAP ® pressure sensor consists of two layers of single
crystal silicon having a layer of glass between them. The thinner
silicon layer creates an integrated vacuum reference chamber, and
forms a pressure-sensitive silicon diaphragm. The thicker silicon layer
is the rigid base plate of the sensor, and it is clad with a glass
dielectric. Thin film metallization has been deposited to form a
capacitor electrode inside the vacuum reference chamber. The other
electrode is the pressure-sensitive silicon diaphragm.
The coefficients of thermal expansion of silicon and glass materials
used in the BAROCAP
® pressure sensor are carefully matched
together to minimize the temperature dependence, and to maximize
the long-term stability. The BAROCAP
® pressure sensor is designed
to achieve zero temperature dependence at 1000 hPa, and its long-term
stability has been maximized by thermal ageing at an elevated
temperature.