tina83e1-d (2018-12)
35
4.6
Ignition Delay
An ignition delay occurs when cold cathode gauges are switched
on. The delay time increases at low pressures and for clean,
degassed gauges it is typically:
1×10
-5
… 1×10
-2
mbar < 1
second
1×10
-7
… 1×10
-5
mbar <20
seconds
5×10
-9
… 1×10
-7
mbar < 2
minutes
<5×10
-9
mbar <20
minutes
The ignition is a statistical process. Already a small amount of
depositions on the inner surfaces can have a strong influence on
it.
MPG5xx 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 (MPG5xx)), are not covered by the warranty.
Summary of Contents for Gemini MAG500
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