Thermo Finnigan LCQ Deca XP Plus, Hardware Manual

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Service Maintenance
_________________________________________________Replacing the Electron Multiplier
__________________ LCQ Deca XP Plus Hardware Manual _________________
5-23
5.4 Replacing the Electron Multiplier
The electron multiplier of the ion detection system includes an anode and a
cathode. See Figure 5-9. The anode and cathode have finite lifetimes. The
anode loses sensitivity over time due to contamination of its surface. The
lifetime of the cathode is decreased by: heat; electron flow (which produces
internal heat); air (which causes oxidation and arcing); and water (which
causes arcing).
The following symptoms suggest that the electron multiplier may need
replacing:
• Excessive noise in the mass spectrum
•
Inability of the multiplier gain calibration procedure to achieve a gain of
3
×
10
5
electrons per ion with an electron multiplier voltage less than or
equal to 2.5 kV
You can read the current value of the electron multiplier voltage in the Ion
Detection System dialog box, which can be reached from the Tune Plus
window by clicking on the ion detection system button.
If you are having problems with the ion detection system, you need to replace
the anode and cathode of the electron multiplier. You can replace the cathode
separately or as part of the electron multiplier assembly.
Figure 5-9. Top cover plate of vacuum manifold showing electron
multiplier
Electron
Multiplier