36 tina83e1-d (2018-12)
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:
• MPG5xx 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 → 39.
• 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.
Contamination can to a certain extent be reduced by:
• geometric protection (e.g. screenings, elbows) against parti-
cles that spread rectilinearly
• mounting the flange of the gauge at a place where the partial
pressure of the pollutants is particularly low.
Special precautions are required for vapors deposited under
plasma (of the cold cathode measuring system). While vapors
occur it may even be necessary
• to temporarily switch of the gauge
• to temporarily seal off of the gauge from the vacuum chamber
using a valve.
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