Agilent Technologies FRG-700 User Manual page 31

Technical Information
Contamination
Gauge failures due to contamination or wear and tear as well as expendable parts
NOTE
(e.g. filament) are not covered by the warranty.
Agilent Inverted Magnetron Pirani Gauge FRG-700 and FRG-702 User Manual
Gauge contamination is influenced by the process media
used as well as by any present or new contaminants and
their respective partial pressures. Continuous operation in
-4
the range of 10 mbar ... 10
contamination as well as reduced up-time and maintenance
cycles. With constantly low pressures (p <1x10
gauge can be operated for more than one year without
cleaning.
Contamination of the gauge generally causes a deviation of
the measured values:
In the high pressure range (1< 10

pressure reading is too high (contamination of the Pirani
element). Readjustment of the Pirani measuring system.
In the low pressure range (p < 1x10

reading is usually too low (contamination of the cold
cathode system). In case of severe contamination,
instabilities can occur (layers of the measuring chamber
peel off). Contamination due to insulation layers can
even lead to a complete failure of the discharge
("Underrange" is displayed).
Contamination can to a certain extent be reduced by:
geometric protection measures (e.g. screenings,

elbows) for particles 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). It may
even be necessary to temporarily switch of the gauge while
such vapors occur.
-2
mbar can cause severe
-6
mbar), the
-3 mbar ... 0.1 mbar), the
-3 mbar), the pressure
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