MKS Baratron 122B, Instruction Manual

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Chapter Three: Overview Sensor
27
Chapter Three: Overview
Sensor
The variable capacitance sensor, shown in Figure 6, consists of a pressure inlet tube (port)
connected to a small chamber in the sensor body. One wall of this chamber is an elastic metal
diaphragm. The back, or “reference” side of the diaphragm faces a rigidly mounted ceramic disc
containing two electrodes in a volume which is permanently evacuated and sealed. When pressure
is applied to the diaphragm, its deflection produces a change in distance between the electrodes
and diaphragm which produces corresponding changes in capacitances. The change in
capacitance of the electrode near the center of the diaphragm is always more than the capacitance
change of the outer electrode.
Figure 6: Type 122 Transducer