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9.8.Filament Activation
（
GI-N8 Only
）
9.8.1.Actuating conditions
When the filament of a nude gauge (WIN-N type) is replaced, the filament is activated
to activate the oxide coated on the filament.
(If the filament is supplied as mounted on the sensor head, this step is not required because it
has been factory treated.)
9.8.2.Operation
Install the sensor head to the pumping system and make sure using another vacuum
gauge that the pressure is within the measured pressure on the gauge.
Select Act_2 in the setting mode.
After selecting Act_2, turn ON the filament switch on the front panel. Activation will
end about 30 minutes later and the filament will be turned OFF automatically.
The FIL lamp at upper right of the front panel blinks during activation.
Upon completion of activation, the setting is automatically corrected to Act_1 (invalid).
9.8.3.What is filament activation?
The standard sensor head for this gauge uses a tungsten wire filament (hot cathode).
Tungsten is an excellent material for filaments and is widely used in a variety of
applications, including vacuum gauge sensor heads.
However, tungsten is subject to rapid wear in oxygen or water vapor at a high
temperature.
Therefore, if the vacuum gauge is used in a place where the partial pressure of oxygen
or water vapor is high, the filament life will be extremely shorter than with nitrogen or
inert gas though the measured pressure is the same.
The work coefficient
φ
of an oxide-coated filament is lower than that of a pure tungsten
wire. Therefore, power to be supplied to the filament to obtain the same emission
current is smaller. This means that the heat generated by the filament is smaller.
Lower filament temperature is not only desirable in terms of longer life, but also
reduces outgassing by heating and disturbance to others when pressure in an ultrahigh
pressure region is measured.
Summary of Contents for GI-M2
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