Sensing Physics
Vacuum measurement instruments utilize the change in electrical capacitance between a flexible metal diaphragm and a fixed electrode to determine absolute pressure. A capacitance diaphragm gauge provides a reading that is independent of gas composition. This sensor operates by detecting the sub-micrometer deflection of the metal plate as pressure varies.
The measurement stops being effective once the pressure exceeds the mechanical limit of the diaphragm tension.
Electrode Geometry
Fixed ceramic or glass substrates support the stationary plate in a capacitance diaphragm gauge. High resolution depends on the initial gap width between the surfaces. A smaller gap increases sensitivity but reduces the maximum pressure range.
Thermal Stability
Heating the sensor head to a constant temperature prevents the condensation of process gases on the internal surfaces. Because a capacitance diaphragm gauge depends on physical dimensions, thermal expansion of the housing would otherwise induce measurable zero drift. Most units include an internal heating element and an insulation jacket.
Calibration Standard
Primary laboratories use a dead weight tester or a spinning rotor gauge to verify the accuracy of these instruments. Users check a capacitance diaphragm gauge against these references annually to confirm that the tension in the metal has not relaxed. This verification happens at a controlled ambient temperature.
