Agilent Technologies 9191610, User Manual

Page: 89 / 98

Technical Information
Exchange of the High Voltage Feedthrough
5
VacIon Plus 300 pumps User Manual / 87-900-103-01 (H) 89/98
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.
WARNING!
Voltages developed in the High Potter power supply are potentially lethal. Use
caution during operation and ensure correct grounding connection.