INFICON T-Guard Leak Detection Sensor - Manual (Page 21)

Description
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3.4 Wise Technology™ Sensor
The helium detector (Wise Technology™ Sensor) consists of a closed glass
container with a measurement device for the precise determination of the pressure
inside the glass housing and a membrane chip with a large number of small quartz
windows.
The membrane is permeable only for helium; the membrane avoids all other compo-
nents of air from entering the glass housing.
The quartz membrane is heated so that the permeation for helium is sufficiently high
and fast.
Inside of the glass housing, the total pressure is measured precisely. As only helium
can enter the glass housing, the total pressure is equal to the partial pressure of
helium.
The determined total pressure inside the housing is proportional to the helium partial
pressure outside the sensor.