INFICON Gemini ATM to Ultra-High Vacuum Gauge - Manual (Page 34)

34 tina83e1-a (2014-02)
MPG50x only
As long as the cold cathode measuring circuit has not ignited,
the measuring value of the Pirani is output as measuring signal.
The status output (= 0 V) indicates the Pirani-only operation.
If the high voltage is activated at a pressure p < 3×10
-9
,
the gauge cannot recognize whether the cold cathode
system has ignited.
Once flanged on, permanently leave the gauge in the
operating mode irrespective of the pressure range. Like
this, the ignition delay of the cold cathode measuring
circuit is always negligible (<1 s), and thermal stabilizing
effects are minimized.
4.7 Contamination
Gauge failures due to contamination or wear and tear, as well as
expendable parts (e.g. ionization chamber, ignition aid, Pirani
filament (MPG50x)), are not covered by the warranty.
Gauge contamination is influenced by the process media used
as well as any existing or new contaminants and their respective
partial pressures. Continuous operation in the range of
10
-4
mbar ... 10
-2
mbar can cause severe contamination as well
as reduced up-time.
Contamination of the gauge generally causes a deviation of the
measured values:
• MPG50x only: In the high pressure range
(1×10
-3
mbar … 0.1 mbar), the pressure reading is too high
(contamination of the Pirani element). Readjustment of the
Pirani
→  38.
• In the low pressure range (p < 1×10 -3
mbar), the pressure in-
dication is usually too low (as a consequence of the contami-
nation of the cold cathode system). In case of severe contami-
nation, instabilities can occur (layers of the measuring cham-
ber peel off). Contamination due to isolating layers can even
lead to a complete failure of the discharge.