INFICON Gemini ATM to Ultra-High Vacuum Gauge - Manual (Page 33)

tina83e1-a (2014-02) 33
The optimum measuring configuration for the particular pressure
range, in which measurement is performed, is used:
10 -3 mbar
10 -2 mbar
1000 mbar
1×10 -9 mbar
Cold cathode Pirani
• The Pirani measuring circuit is always on
• The cold cathode measuring circuit is controlled by the Pirani
circuit and is activated only at pressures p < 1×10
-2
mbar
As long as the cold cathode measuring circuit has not ignited,
the measuring value of the Pirani is output as measuring signal.
4.5 Gas Type Dependence
The measurement value is gas dependent. The pressure reading
applies to dry air, O
2
, CO and N
2
. For other gases, it has to be
corrected:
• (MAG50x →  18)
• (MPG50x →  20).
If the gauge is operated with an INFICON controller, a calibration
factor for correction of the actual reading can be applied (→
 of
the corresponding controller).
4.6 Ignition Delay
An ignition delay occurs when cold cathode gauges are switched
on. The delay time increases at low pressures and is typically:
1Ч10
-5
… 1Ч10
-2
mbar < 1 second
1Ч10
-7
… 1Ч10
-5
mbar <20 seconds
5Ч10
-9
… 1Ч10
-7
mbar < 2 minutes
<5×10
-9
mbar <20 minutes