Thyracont VSH87D, Operating Instructions Manual, Page: 44 / 64

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4.3 Degas
Deposition or adsorbed gas molecules on the electrodes of the hot cathode sensor
may lead to increased degassing in ultrahigh vacuum or even cause instabilities of
the measurement signal. In such cases it is appropriate to clean the anode of the
sensor from such deposited material and adsorbed gas molecules by degassing.
This is done at pressures below 2.0x10
-6
mbar by ohmic heating of the anode to
temperatures around 800
◦
C.
Degas Control by Pushbutton
The degas function can be activated directly at the transducer by means of the
pushbutton, see operating scheme in section 4.2.
To do this first remove the rubber cap above the »Adj« pushbutton (1), then press
the button several times by means of a small screwdriver or similar tool (2) un-
til the status LED starts flashing quickly in red color. After 3 s the degas process
starts, signalized by a slowly flashing red status LED. The degas procedure will
end automatically after approx. 3 minutes, but can be stopped anytime by a further
keypress. Finally insert the rubber cap again.
Degas Control by External Voltage Signal
Degas can be started simply by connecting pin 9 (see section 3.3.2) to a defined
voltage level for a short moment (min. 20 ms). Depending on the setting of software
parameter »Digital Logic« (DL) the degas procedure starts, as soon as pin 9 is
a) connected to GND for a short moment (parameter set to 0, active low, default
setting) or
b) connected to 3 ... 24 VDC for a short moment (parameter set to 1, active
high).
VSH-RS485-200116