VACUUBRAND DCP 3000 - Manual (Page 29)

page 29 of 64
Operation principle of the VSK 3000
The VSK 3000 is equipped with a capacitive pressure transducer with
ceramic diaphragm to measure the actual pressure independent of the
gas type and depending on the vacuum, i.e., absolute.
The pressure value is displayed with a resolution of 0.1 Torr (mbar) in the
pressure range from 0.1 to 795 Torr (0.1 to 1060 mbar).
Operation principle VSP 3000
The pressure transducer VSP 3000 relies on the fact that the thermal
conductivity of the residual gas in the vacuum chamber is a measure for
the gas pressure. The thermal conductivity of gases is proportional to the
pressure within a certain range and is related to the molecular mass.
The thermal conductivity of gases and vapors varies with their molecular
mass. Therefore the pressure measurement is dependent on the gas
type. The pressure transducer has been adjusted for air at the factory.
Diagram: Gas dependence of a VSP 3000
true pressure [mbar]
displayed pressure [mbar]
air
helium
argon
+
Pressure of gases with similar mass, such as O
2
or CO, can be read
off directly within the uncertainty of the measurement.
+
With gases of lower or higher mass (H
2
, He, Ar, CO
2
) it is recommend-
ed to readjust the VSP 3000 using the gas to be measured.
Notes on operation