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5
Technical Information
Description of the PHD-4
Theory of Operation
The system to be tested is filled with a mixture of helium/air.
The probe is passed over areas considered to be critical and, via a
sampling pump, the mix of gases around the areas examined is
sampled and piped towards the internal sensor.
The sensor consists of a pressure detector and of a heated quartz
capillary which is highly permeable to the molecules of helium, while
permeability for all other atmospheric gases is negligible.
While the atmospheric gases are vented to the outside, the molecules
of helium reach the pressure detector. The electric signal
proportional to the partial pressure of the helium taken from the
detector, is processed by the microprocessor of the central unit. This
permits direct readout of the concentration of helium on the display
(ref. figure below).
PHD-4 Portable Helium Detector User Manual
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