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Transpector MPS Operating Manual
CAUTION
Do not operate the CDEM at temperatures above 150°C.
Permanent damage may result. Also, avoid output
currents in excess of 1 x 10
-6
amps; either decrease the
high voltage or, if possible, decrease the pressure.
Use the minimum CDEM voltage required to obtain the necessary peak amplitudes
and/or signal-to-noise ratio. Operating at higher voltages than necessary will result
in premature aging of the Electron Multiplier, requiring early replacement. As the
CDEM ages, the voltage needed to get a specific EM gain will increase.
Since EM performance depends on the condition of its interior surfaces, prevent
hydrocarbon or other contamination as follows:
Ensure diffusion-pumped vacuum systems are properly trapped to reduce oil
back-streaming.
Ensure turbomolecular pumped systems are interlocked to eliminate
mechanical pump oil back-streaming through a nonspinning turbo pump.
Electron Multiplier gain reduction from these kinds of problems can range from
50% to more than 90%. The initial gain of the EM is generally high enough to
accommodate some degradation and yet still be usable. With repeated instances
of contamination, the multiplier will eventually require replacement.
NOTE:
In addition to hydrocarbon contamination, multipliers can be adversely
affected by exposure to highly reactive chemicals. Avoid any substance
that will either cause the deposition of a surface film on the EM or etch its
surface. Avoid high levels of reactive fluorides, such as tungsten
hexafluoride, hydrogen fluoride, and nitrogen trifluoride.
