SRS Labs QMS 100 Series, Руководство пользователя

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Component Notes 5-5
Technical Reference
CDEM Handling and Care
Continuous Dynode Electron Multipliers (CDEM) have a history of high performance and dependability
in mass spectrometry applications. By following the simple recommendations described below the user
should achieve a long useful lifetime from these detectors.
Handling and mounting
•
Handling and mounting of the CDEM should only be performed in a clean vacuum fashion.
•
Work on a clean dust-free area. Avoid dust, lint and any kind of particulate matter.
•
Wear powder rubber gloves or finger cots.
•
Use properly degreased tools.
Avoid excessive shock, such as from dropping onto a hard surface (Remember that
CDEM’s are made out of glass).
Operating Temperature & Pressure
The recommended operating pressure is 3
.
10
-6
or less. The lower the pressure during any operation, the
longer the lifetime of the CDEM.
Never apply voltage to a CDEM at pressures above 10
-4
Torr.
The safe operating temperature of a CDEM is less than 100
°
C.
The bakeout temperature must be less than 300
°
C with no voltage applied across the unit.
Operating Voltage
The maximum voltage applied to any CDEM should not exceed 3500V. The SRS RGA High Voltage
power supply is limited to a 2500V output. Typical operating range is 1100-2500V. In general, the
lower the average signal current drawn from the detector and the lower the operating voltage, the longer
the lifetime that will be realized.
Initial pump-down
To best maintain the high gain and low dark current properties of electron multipliers it is very important
to follow the steps described in the CDEM Pre-conditioning section of this chapter during the initial
pump-down of the electron multiplier. The procedure serves to degas the detector and stabilize the gain.
Failure to follow the recommended steps before powering up the multiplier might result in gain
degradation by as much as a factor of ten.
Contamination
The active surface of the CDEM can be repeatedly exposed to air without degradation; however, it
should not be contaminated with dust, lint or other particles. Organic substances present in the vacuum
system tend to accumulate on the active surface of the multiplier and lead to slow performance
degradation (due to reduced secondary emission efficiency).
Oil contamination is a serious problem, and can result in catastrophic destruction of the multiplier: use