Penning vacuum meter

Details Penning vacuum meter Penning vacuum meter

1999-10-14

2001-09-04

Metjahic, Safet (Department: 2858)

Electricity: measuring and testing

Using ionization effects

For monitoring pressure

C324S463000, C324S466000, C313S311000

Reexamination Certificate

active

06285192

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a Penning vacuum meter comprising a cathode and an anode.
A Penning vacuum meter is a cold cathode vacuum meter, the operation of which is based on a cold discharge. It comprises a tube with two non-heated electrodes, cathode and anode, between which a discharge is ignited and maintained by means of a DC voltage (about 2 kV during operation), whereby said discharge is maintained in a steady state also at very low pressures. This is attained by making the path for the electrons so long with the aid of a magnetic field, that their collision rate with the gas molecules is sufficiently high in order to form the required quantity of charge carriers to maintain the discharge.
In the tubes of Penning vacuum meters, the cathode material is disintegrated by the ions which are accelerated in the direction of the cathode, particularly so in connection with coating processes involving heavy noble gases (argon, xenon) being performed in the pressure range between 10
−4
and 10
−2
mbar. The disintegrated cathode material forms on the walls of the measurement tube a conductive layer.
Generally, stainless steel is employed as the material for the cathode. Owing to the cathode disintegration process described (“sputtering”) the service life of the cathode is limited. Moreover, disintegrated stainless steel cathode material is magnetic. Parts coming loose from the formed layers are capable of aligning themselves in the magnetic field thereby causing short circuits. In addition, parts of the measuring cell, which actually should be electrically isolating (ceramic feedthroughs) may become electrically conducting. These disadvantages result in an unstable readout or extinguishing of the discharge and thus in a failure of the measurement tube. Even so, the Penning vacuum meter is employed very often, since it is cost-effective and insensitive to air inrushes and vibrations.
SUMMARY OF THE INVENTION
It is the task of the present invention to substantially remove the detrimental effects which occur owing to the disintegration effect described.
This task is solved by employing titanium as the material for the cathode. Owing to the lower sputtering yield, sputtering of the cathode material is only slight when using titanium. Thus the service life of the cathode is improved and coating with conductive metal is reduced. The sputter products are non-magnetic so that they may no longer cause the described short circuits in the magnetic field. Therefore, Penning vacuum meters with titanium cathodes will provide a stable readout over a long time even in coating processes. Surprisingly, the ignition characteristic is also improved.


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