High-Potting - Agilent Technologies VacIon Plus 800 Manual Del Usuario

Technical Information

High-potting

A constant pump current when no vacuum leak exists is often caused by field
emission currents which prevent the use of the pump current as a UHV pressure
indicator. To reduce this field emission current, "high-potting" should be performed.
"High-potting" is the term used to describe the application of higher than normal
operating voltage
(8 kV AC, max. 50 mA) for the purpose of burning off "whiskers" (sharp edges) on
the pump cathode.
High-potting should be done under vacuum and preferably without pump magnets
installed (to reduce the drawn current).
High-potting must be done carefully and in voltage steps since uncontrolled arcing
inside the pump can cause permanent damage. Therefore slowly increase the
applied voltage and watch the current meter for indication of arcing inside the
pump as whiskers are burned away. If arcing occurs wait at this voltage until the
current is stable again. Then slowly increase voltage again in steps up to a
maximum voltage. The maximum voltage may be applied to the pump for a period
of about 15 seconds. This should effectively remove any "whiskers" or sharp edges
on the pump cathode.
Voltages developed in the high-potter power supply are potentially lethal.
WARNING
Use caution during operation and ensure the correct grounding.
232 Agilent VacIon Plus 800 User Manual