Measuring and testing – Fluid pressure gauge – Electrical
Patent
1996-06-19
1998-07-07
Chilcot, Richard
Measuring and testing
Fluid pressure gauge
Electrical
G01L 900
Patent
active
057772339
DESCRIPTION:
BRIEF SUMMARY
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a national stage application of PCT/DE94/01482 filed 14 Dec. 1994 and based upon German National Application P 43 43 575.0 of 21 Dec. 1993 under the International Convention.
1. Field of the Invention
The invention relates to a gas-friction vacuum meter or indicator with a gas-friction sensor rotating about a fixed axis of rotation. The gas-friction sensor is supported contactlessly and magnetically for rotation within an evacuatable measurement chamber. The magnetic field that is required for this is formed rotationally symmetrical with respect to the rotation axis of the gas-friction sensor and is controllable. The measurement chamber is spatially connected for the pressure measurement with the vacuum chamber whose vacuum is to be measured.
2. Background of the Invention
Gas-friction vacuum meters with magnetically supported rotatable gas-friction sensors are known, see for example German patent 33 34 750 C2. For a vacuum measurement in this pressure measuring device, the braking of the sensor rotation caused by the impingement of molecules on the gas-friction sensor is determined. The braking per unit time is lower to the degree that the pressure is lower, i.e. to the extent that measured vacuum is better. In German patent 34 31 517, a gas-friction vacuum meter is described whose pressure measurement value is temperature correlated, to correct, at a vacuum measurement above a pressure of 0.1 mbar, the gas friction which is influenced by the viscosity. The construction of this gas-friction vacuum meter has required heretofore that the measurement chamber axis, which corresponds to the rotation axis of the gas-friction sensor, be vertically aligned as exactly as possible exactly if inaccuracies in the indication of the measured vacuum were to be avoided.
OBJECT OF THE INVENTION
The object of the invention is, without increased structural cost, to permit a measurement chamber axis to deviate from the horizontal and to compensate for the measurement errors resulting therefrom.
SUMMARY OF THE INVENTION
This object is attained according to the invention in a gas-friction vacuum meter which comprises a gas-friction sensor rotating about a fixed axis of rotation within an evacuatable measuring chamber connected with the evacuated space, whose vacuum is to be measured. The sensor is supported contactlessly, so as to be rotatably by means of a magnetic field which is rotationably symmetrical with reference to the rotation axis. According to the invention the rotation axis deviates from the vertical and preferably has a horizontal orientation. A measuring device is provided for measuring the inclination of the rotation axis with respect to the vertical and has an output signal which serves for the correction of the indicated pressure value, whereby the correction value is determined depending on at least one previously tested eddy-current-conditioned braking value of the gas-friction sensor for a certain inclination angle.
With the aid of the inclination measuring device the true orientation of the rotation axis, with respect to the vertical, is determined and the output signal of the measuring device is fed to a computer unit for correction of false measured values, which are based upon the given position of the axis. The computer displays the pressure measurement which corresponds to the rotation braking of the gas-friction sensor as a result of the instantaneously effective vacuum. The correction magnitude given by the computer unit is based upon the proportionality between the square of the sine of the angle between the vertical and the given orientation of the rotation axis on the one hand and on the other hand, the eddy-current-conditioned braking, determined by the rotation axis, of the gas-friction sensor, the eddy-current braking being additional to the braking as a consequence of the pressure-dependent molecular friction in the vacuum chamber. One can obtain for a known angle the eddy-current induced braking experimentally at high vacuum
REFERENCES:
patent: 4395914 (1983-08-01), Fremerey et al.
patent: 4619144 (1986-10-01), Fremerey et al.
Hirata et al.; Effect of Measuring Conditions on the Accuracy of a Spinning Rotor Gauge; Journal of Vacuum Science and Technology; pp. 1724-1727, 1986 .
Fremerey Johan K.
Lindenau Bernd
Witthauer Klaus
Chilcot Richard
Dubno Herbert
Felber Joseph L.
Forschungszentrum Julich GmbH
RWD-Datentechnik GmbH
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