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5
Technical Information
Basic Unit Data and Specification
Protection Level 1 (Enabled in Factory):
The backflow valve fitted in series with the sampling line is activated
preventing further pumping of the gases rich in helium and, at the
same time, "purging" the entire sampling line with helium-free
atmospheric gases (sucked in from the exhaust point or in a helium-
free environment using a dedicated line - see note).
Functioning of the backflow valve is showed in the figure below.
Restricting delivery of helium to the sensor, this protection extends
its lifetime, also guaranteeing maximum sensitivity.
As it restricts the amount of helium conveyed to the sensor, tripping
of the backflow device shortens waiting times between one
measurement and the next (zeroing time).
82/140
Probe
2
1
Backflow
1
valve
P
Sensor
PHD-4 Portable Helium Detector User Manual / 87-900-120-01 (F )
Outlet
1
> Normal operation
2
> Protection mode
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