Oscillators – Beat frequency
Patent
1982-01-28
1985-08-20
Laroche, Eugene R.
Oscillators
Beat frequency
331 65, 73716, 324328, 340626, H03B 2100
Patent
active
045367191
DESCRIPTION:
BRIEF SUMMARY
The present invention relates generally to an inductive pressure sensor and, more particularly, to a pressure sensor system for use with an automotive internal combustion engine.
BACKGROUND
In various measurement and regulating tasks, it is necessary to measure the pressure of a gas, either as an absolute value, or as a relative value with respect to a second pressure. Examples of such uses would be measuring the intake tube pressure of an internal combustion engine of a motor vehicles, measuring the filling level, or measuring blood pressure electrically in medical technology, among others. An induction difference pressure sensor is disclosed in Swiss Pat. No. 489,792, in which two coil devices, connected in a bridge circuit, interact in push-pull fashion with a diaphragm which is deflectable in accordance with a differential pressure. The inductance of the respective coils or coil devices varies as a function of the deflection of the diaphragm, causing a shift in the frequency of an oscillator, in which the coils are frequency-determining elements.
However, the known apparatus uses cup-shaped ferrite cores for the coils, which necessarily results in a bulky structure. Further, most prior art sensors make no particular provision for preventing the oscillator frequency from drifting due to temperature fluctuations.
THE INVENTION
Accordingly, it is an object to provide a small, temperature-compensated pressure sensor which is particularly adapted for use in an automotive internal combustion engine (I.C.E.).
Briefly, the pressure sensor of the present invention has the advantage over the prior art that particularly small sensor dimensions can be obtained, because of the flat-film form of the coil, which interacts in push-pull fashion with a diaphragm surface which is alternatively a highly conductive or a ferrite material.
By using two oscillators of identical structure, which are disposed spatially together and are thus exposed to identical temperature conditions, it is possible to mix their output signals in such a way as to compensate for temperature dependent frequency drifting of the oscillators. Thus, if one oscillator is set at a fixed frequency, it is possible to make absolute-pressure measurements and differential-pressure measurements relative to atmospheric pressure. Secondly, differential-pressure measurements between two media can be made if the two oscillators, with their respective coils and diaphragms, are exposed to different pressures.
Finally, in a particularly preferred embodiment of the invention, a particularly good compact structure, and thus a particularly good thermal coupling of the oscillators, is attained by forming the oscillators as thin-film elements, which are located on a carrier, together with the coil, which is formed on a flat spiral of film. A printed circuit board is a particularly inexpensive construction for such a sensor.
DRAWINGS
FIG. 1, a basic illustration in the form of a block circuit diagram of one form of embodiment of a pressure sensor according to the invention;
FIG. 2, the circuit diagram of an oscillator such as can be efficaciously used in the apparatus shown in FIG. 1;
FIGS. 3a and b, the front and rear, respectively, of a thin-film shield for realizing the oscillator shown in FIG. 2.
DESCRIPTION OF THE EXEMPLARY EMBODIMENT
In the exemplary embodiment of a pressure sensor according to the invention as shown in FIG. 1, its use is illustrated for measuring the intake tube pressure of an internal combustion engine of a motor vehicle. It will naturally be understood, however, that the pressure sensor shown can also be used for the other measurement tasks mentioned above solely by way of example and is in no way restricted to the illustrated exemplary embodiment.
In FIG. 1, the intake tube of an internal combustion engine of a motor vehicle is indicated by reference numeral 10. An underpressure p.sub.1 prevails in the intake tube. The intake tube 10 communicates via a line with a first pressure chamber 11, which is closed off at one side by a diaph
REFERENCES:
patent: 3756081 (1973-09-01), Young
IEEE Transactions On Microwave Theory and Techniques, MTT-16, #7, 7-1968, `Hybrid Integrated L-Band Transmitter` pp. 482-483.
Baum Helmut
Pfizenmaier Heinz
Schmidt Ewald
Strauss Franz
LaRoche Eugene R.
Pascal Robert J.
Robert & Bosch GmbH
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