Measuring and testing – Fluid pressure gauge – Diaphragm
Patent
1999-07-01
2000-09-19
Patel, Harshad
Measuring and testing
Fluid pressure gauge
Diaphragm
73724, 73708, 3612834, G01L 912, G01L 1904, H01G 700
Patent
active
061195235
DESCRIPTION:
BRIEF SUMMARY
FIELD AND BACKGROUND OF THE INVENTION
The present invention concerns a method for measuring pressure using a capacitive pressure transducer and a pressure measuring device comprising a capacitive pressure transducer according to the preamble of claim 10.
For considerable time it has been known in the art to measure the pressure of a fluid by monitoring the capacity of a capacitive pressure transducer comprising a membrane whose deformation depends on the pressure where the monitoring of the capacity involves applying an AC voltage to the capacitive pressure transducer. A description of the generic method and device can be found in: Hans-Werner Drawin: `Kondensator-Membran-Manometer fur Druckmessungen im Hoch- und Feinvakuumgebiet, unabhangig von der Gasart`, Vakuum-Technik 7/8 (1958).
However, the result of such measurement can be affected by resonance of the capacitive pressure transducer, in particular when very small pressures are being measured using very thin membranes. It has been found that a 1 torr transducer of the generic type is very sensitive to resonance. Neither a method nor a device have been known so far where erroneous readings caused by resonance were compensated for.
SUMMARY OF THE INVENTION
Capacitive pressure transducers are known from JP-A-04 104 027 and EP-A-0 194 953. The latter may also be used for measuring force or acceleration. Its properties are determined and resonance avoided during use.
The purpose of the present invention is to remove the drawbacks of the prior art and to provide a method and device for measuring pressure where the influence of resonance in the capacitive pressure transducer is compensated.
The invention is based on the concept of causing the capacitive pressure transducer to resonate, measuring the erroneous reading caused by the resonance and feeding a feedback compensation signal to the measuring element where the signal is essentially unfiltered. The device according to the invention is based on the concept of an apparatus for compensating effects of resonance comprising error detection and compensation elements whose upper barrier frequency is above the resonance frequency of the transducer, for detecting an erroneous reading of the transducer and for generating a compensation signal to be fed into the detection elements.
More specifically, the method according to the invention is characterized by what is stated in the claims.
The apparatus according to the invention is characterized by what is stated in the claims.
The invention provides considerable benefits.
The compensation is most efficient and, in the case of undistorted self-oscillation, it will eliminate the erroneous reading to 100%.
BRIEF DESCRIPTION OF THE DRAWINGS
In the following, the invention is described by means of a detailed description and exemplifying embodiments. In the annexed drawings, preferred embodiments are shown in which
FIG. 1 is a side view of the basic scheme of a capacitive pressure transducer that can be used in the invention;
FIG. 2 depicts a typical known measuring circuit for the pressure transducer of FIG. 1;
FIG. 3 is a more detailed illustration of element F1 in FIG. 2; and
FIG. 4 depicts a coupling according to the invention for electronic compensation of erroneous readings caused by resonance in a capacitive pressure transducer.
DESCRIPTION OF THE PREFERRED EMBODIMENT
An electronic circuit is described below compensating erroneous readings caused by resonance of the membrane.
The type of pressure transducers described herein are generally called capacitance manometers. In a capacitance manometer, the pressure to be measured acts on one side of the membrane, whereas its other side is under a reference pressure which is usually very low. When pressure is measured exploiting the movements of the membrane even a number of parasitic parameters are generated which in no way contribute positively to the measurement. One of these parameters comprises the natural resonance frequency of the membrane. At this frequency the membrane self-oscillates with a minimum
REFERENCES:
Puers B et al. "a capacitive pressure sensor with low impedance output and active suppression of parasitic effects", sensors and actuators, vol. A21, No. 1/03, Feb. 1, 1990, pp. 108-114, XP000149570.
Bjorkman Per
Olsson Ray
Aw-Musse Abdullahi
Balzers and Leybold Instrumentation AB
Patel Harshad
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