Electricity: measuring and testing – Using ionization effects – For monitoring pressure
Patent
1997-06-10
1999-07-13
Brown, Glenn W.
Electricity: measuring and testing
Using ionization effects
For monitoring pressure
324459, 250299, 250382, G01L 2130, G01N 2762
Patent
active
059231726
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a Penning type gauge head with an electrode system comprising an anode and a cathode disposed in the magnetic field of a permanent magnet, as well as with an ignition aid for the electrode system.
Penning type gauge heads of this type are installed in ionization vacuum gauges. They comprise two unheated electrodes (cathode and anode) between which, by means of a DC voltage of the order of magnitude of 2 kV, a cold discharge is ignited and maintained. With the aid of a magnetic field the path of the electrons is extended so that their impact rates with gas molecules is sufficiently large in order to form the required number of charge carriers for maintaining the discharge even at very low pressures. The positive and the negative charge carriers migrate to the corresponding electrodes and form the pressure-dependent discharge current which is displayed on a measuring scale. Of disadvantage in vacuum gauges of this type is that the discharge cannot always be ignited.
From DE-OS 30 47 744 a gauge head of the above described type is known. To attain a reliable ignition it is suggested to provide, apart from the measuring system comprising unheated electrodes, a glow cathode in addition. This measure is expensive since the supply of a sufficiently large current to the glow cathode is required. An additional current supply device as well as a separate current lead-in are required.
From EU-A-271 769 a gauge head of the type relevant here is known, which, apart from the measuring system (main measuring system), comprises a further Penning system with cathode and anode (ignition system). Its dimensions are significantly smaller than the dimensions of the main system. The production of an ignition system of this type is also expensive. Moreover, tests have found that the ignition of the measuring system is not always ensured. The gauge head known from EU-A-271 769 was therefore never introduced on the market.
SUMMARY OF THE INVENTION
The present invention is based on the objective of equipping a gauge head of the above cited type with a reliable ignition aid of simple structure.
According to the invention, this objective is accomplished by attaching at least one metal strip on the anode, whose free end extends in the direction toward the cathode. Due to the high electric field strength in the region of the free end of the metal strip, gas ions are detached which impinge on the cathode and generate their secondary electrons. These cause a rapid and reliable ignition of the electrode system.
A preferred embodiment of the present invention has been found by the selection of the longitudinal direction of the metal strip such that it is not parallel to the magnetic lines but rather intersects the magnetic lines. The ignition could be further increased significantly through this measure.
Further advantages and details of the invention will be explained in further detail in conjunction with an embodiment example depicted in FIGS. 1 and 2.
DETAILED DESCRIPTION OF THE INVENTION
The Penning type gauge head 1 shown schematically in FIGS. 1 and 2 comprises a vacuum-tight housing 2 which simultaneously forms the cathode.
The housing 2 is equipped with a flange 3 with which the gauge head is connected to a receptacle in which the pressure is to be measured and/or monitored.
Within the volume 4 formed by the housing, respectively the cathode, 2 is disposed the annular anode 5 whose axis is denoted by 6. With the aid of the anode voltage feed 7 the anode 5 is mounted in the electrode volume 4. The anode voltage feed is at a positive high-voltage potential (approximately 2 kV). During the operation of the gauge head the discharge is maintained between the anode 5 and the grounded housing 2.
Anode 5 and cathode, respectively housing, 2 are disposed in a magnetic field generated by magnets 8 and 9. One north pole and one south pole each are facing the housing 2 so that the magnetic lines of the magnetic field extend approximately parallel to the anode axis 6.
The ignition aid
REFERENCES:
patent: 2643342 (1953-06-01), Simpson
patent: 2758232 (1956-08-01), Fox
patent: 4847564 (1989-07-01), Limp
patent: 5568053 (1996-10-01), Drubetsky et al.
Brown Glenn W.
Leybold Aktiengesellschaft
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