LEYBOLD LEYSPEC view Series User Manual

81 300781172_002_C0 - 01/2019 - © Leybold
Appendix
13.2.3 Detector section
The detector section collects and amplifies the ions that have passed through the
filter section. Some simplified analyzers can directly catch ions with the Faraday cup
alone to measure the ion current value. Normally, a secondary electron multiplier
tube, channeltron, ceratron, or other device is used to convert the incident ions into
electrons, amplify them by a factor of 5 or 6, and send them to the DC amplifier of
the controller.
For electronic amplification, a high voltage of about -2 kV is applied to the incident
end of the amplifier. The detector unit is arranged in the OFF-AXIS position with
respect to the centre axis of the filter section to inhibit incidence of soft X-rays
generated from the ion source section and in the filter.
13.3 Handling of quadrupole spectrometer
13.3.1 Measurement pressure range
Normally, the operating range is 0.01 Pa or less. If the spectrometer is used at a
higher pressure, the ion source filament is oxidized or burns out, causing
deterioration of the secondary electron multiplier tube. In the 10
-3
Pa range, linearity
is lost and sensitivity may lower.
To measure a high pressure gas, pump the analyzer tube section differentially using
a turbo-molecular pump, and make the measurement by feeding gas from the
system to be measured while controlling it.
13.3.2 Deterioration
It is necessary to overhaul the analyzer tube if sensitivity has lowered by a factor of
3 or more as compared with the initial period or if the waveform becomes sharp and
noise becomes noticeable. Normally, spare filaments are provided with the
instrument, but it would be more effective to disassemble/clean or replace the ion
source section rather than overhauling the analyzer tube.
If overhaul of the ion source section is not effective, replace the secondary electron
multiplier tube. Since the amplification factor of this tube is subject to gradual
decrease, it is desirable to measure sensitivity (amplification factor) periodically.
13.4 Interpretation of measurement value
Gas composition is judged from the mass number of the spectrum and is
quantitatively decided with the ion current value of the peak top of the spectrum.
Since the ion current value (A) cannot be converted directly to partial pressure (Pa),
find the sensitivity
(A/Pa) by calibrating with an ionization gauge using nitrogen gas in order to obtain
information about the pressure value.
13.4.1 Sensitivity factor
The sensitivity of a quadrupole spectrometer varies by gas species. The principal
reasons for this are:

LEYBOLD LEYSPEC view Series Specifications

General

Brand	LEYBOLD
Model	LEYSPEC view Series
Category	Measuring Instruments
Language	English