BG 5153 BEN / D (2017-07) IKR 261
13
4 Operation
As soon as the required voltage is applied, the measuring signal is available
between pins 2 and 3. (
→
Appendix B for the relationship between the measuring
signal and the pressure).
The green lamp on the gauge
indicates the operating state:
Supply voltage present.
No supply voltage.
Caution
Turn on the gauge only at pressures <10
-2
hPa to prevent excessive
contamination.
If you are using a Pfeiffer Vacuum measurement unit for Compact
Gauges with at least two gauge connections, the cold cathode gauge
can be controlled, for example, by a Pirani gauge.
The measuring signal depends on the type of gas being measured. The curves are
accurate for dry air, N
2
, O
2
and CO. They can be mathematically converted for
other gases (
→
Appendix C).
If you are using a Pfeiffer Vacuum measurement unit for Compact Gauges, you
can enter a calibration factor to correct the measurement value displayed (
→
of
that measurement unit).
An ignition delay occurs whe
n
cold cathode gauges are switched on. The delay
time increases at low pressures and for clean, degassed gauges it is typically:
10
-7
hPa
≈
0.1 minute
10
-8
hPa
≈
1 minute
2×10
-9
hPa
≈
5 minutes
The ignition is a statistical process. Already a small amount of depositions on the
inner surfaces can have a strong influence on it.
Gauge failures due to contamination are not covered by the warranty.
Gauge contamination is influenced by the process media used as well as any
present or new contaminants and their respective partial pressures. Continuous
operation in the range of 10
-4
hPa ... 10
-2
hPa can cause severe contamination as
well as reduced up-time and maintenance cycles. With constantly low pressures (p
< 1×10
-6
hPa), the gauge can be operated for more than one year without cleaning
(cleaning the gauge
→
17).
In general, contamination of the gauge leads to deviations of the measured values:
•
In the low pressure range (p < 1×10
-3
hPa), the pressure indication is usually
too low (as a consequence of the contamination of the cold cathode system). In
case of severe contamination, instabilities can occur (as layers of the
measuring chamber 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 protections (e.g. screenings, elbows) against 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 (e.g. of the
cold cathode measurement system). It may even be necessary to temporarily
switch of the gauge while vapors occur.
Gas type dependence
Ignition delay
Contamination
