B2 - Schoonover, Inc.

SKY TM Capacitance Diaphragm Gauge
Vacuum Gauges
A) Vacuum connection
Stainless Steel, AlSl316L (18% Cr, 10% Ni, 3% Mo, 69% Fe)
B) Protective chamber
Stainless Steel, AlSl316L (18% Cr, 10% Ni, 3% Mo, 69% Fe)
C) Plasma shield
Stainless Steel, AlSl316L (18% Cr, 10% Ni, 3% Mo, 69% Fe)
D) Metal-ceramic connection
Vacon 70 (28% Ni, 23% Co, 49% Fe)
and Braze, Ti, Ag, Cu
E) Measurement chamber
F) Reference chamber
G) Diaphragm
Al 2
O 3
³ 99.9% for 0.1 Ð 10 Torr
Al 2
O 3
³ 99.5% for 100 Ð 1000 Torr
H) Electrode
Gold
I) Glass ceramic solder
J) Sensor housings
Al 2
O 3
³ 99.5%
Better Mechanical Stability
The construction of the measuring cell is based on a symmetry principle.
The diaphragm is bonded to the lower and upper sensor housing with the
same material under the same process. Unwanted asymmetric tension of
the diaphragm is avoided. Another benefit of such a relatively large bond is
the good thermal contact between the housings and the diaphragm.
Thanks to this construction the sensor has excellent mechanical and thermal
stability. Even frequent pressure changes and overpressures cannot alter
such a cell. The measuring results are consistent and remain excellent over
much longer periods of operation than with metal ones.
Better Temperature Stability
Aluminum oxide ceramic has a significantly lower thermal expansion
coefficient than the metals traditionally used. Conventional CDGs are
constructed of a combination of ceramic parts and a metal diaphragm.
The different thermal expansion of these materials can cause tension on the
diaphragm resulting in a distorted pressure reading. The sensor of a
SKYª CDG consists only of aluminum oxide ceramic. Because of this the
span coefficient of a temperature compensated SKY CDG (CDG025) is
improved over a conventional CDG by a factor of four. That of a temperature
controlled gauge (CDG045) by a factor of two.
High Corrosion Resistance
Aluminum oxide ceramic is highly corrosion resistant. ThatÕs why the
SKY CDGs are particularly useful under corrosive process conditions
and deliver reliable measurement values much longer than conventional
(metal diaphragm) CDGs. Corrosive process gases can impair or
damage metal membranes to the point where accuracy and
repeatability are adversely effected or the gauge ultimately fails.
B6
B6.7