Measuring and testing – Vibration – Resonance – frequency – or amplitude study
Reexamination Certificate
1999-06-22
2001-12-04
Williams, Hezron (Department: 2856)
Measuring and testing
Vibration
Resonance, frequency, or amplitude study
C073S514160, C073S514180
Reexamination Certificate
active
06324910
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for measuring a physical variable and a device for measuring a physical variable.
BACKGROUND INFORMATION
Methods and devices of this type are known. These include a structure oscillating in resonance, whose swing frequency varies as a result of a change in the physical variable to be measured. The change in the oscillating frequency of the structure is detected using analytical means and results in a frequency-analog signal, from which the magnitude of the influencing physical variable to be measured can be deduced. The structure oscillating in resonance is formed by a spring-mass system, its sensitivity being dependent on the geometric dimensions of the structure oscillating in resonance. In order to analyze the shift in the natural frequency of the oscillating structure, the latter is connected as a frequency-determining element of an electronic oscillator switch. The resolution depends essentially on the signal-noise ratio of the oscillator circuit, and on the frequency measurement method used. As efforts are being made to miniaturize such measuring devices in order to make manufacturing inexpensive, it is a drawback that this entails a reduction in sensitivity or resolution.
SUMMARY OF THE INVENTION
The method according to the present invention and the device according to the present invention offer an advantage in that the measuring sensitivity can be raised even with measuring devices having a small size. Because of the fact that the structure oscillating at its resonance frequency receives an electrostatic force, which preferably acts in the direction of oscillation, it is advantageously possible to influence the sensitivity of the measuring device using the values determining the electrostatic force. Thus an operating point of the measuring device can be advantageously set using the voltage which contributes to determining the electrostatic force, which is applied between the structure oscillating in resonance and the counterstructure assigned to it. The larger the selected voltage, the closer the operating point moves to the point of mechanical instability of the measuring device.
Through the level of the voltage, which remains constant during the measuring procedure, the sensitivity of the measuring device can be set very advantageously. According to the sensitivity set using the voltage, the electrostatic force affecting the structure oscillating in resonance can be varied, using the movably mounted counterstructure, so that as a result of the constant voltage the electrostatic force is dependent solely on the change in spacing.
Because of the change in the spacing between the structure and the counterstructure, which is preferably directly proportional to the variable to be measured, a natural frequency shift of the oscillating structure can be achieved. This natural frequency shift is all the greater, for a given value of the physical variable to be measured, the closer the operating point of the measuring device is set, using the magnitude of the constant voltage, to the point of mechanical instability. Thus even very small changes in the physical variable to be measured result in a relatively high natural frequency shift (resonance frequency shift), which then can be analyzed using evaluation means. In this way even the smallest geometric shifts, that is, changes in the spacing between the structure and the counterstructure, suffice to provoke relevant frequency differences.
In a preferred embodiment of the present invention, the counterstructure giving rise to the electrostatic force is a movably mounted component of a force sensor, in particular an acceleration sensor. Preferably, the structure and the counterstructure are arranged at an angle to one sensing direction of the acceleration sensor. In this way it becomes advantageously possible to reduce a reaction of the electrostatic force on the counterstructure and to increase the overall measuring precision of the measuring device according to the present invention. Furthermore, the angular offset very advantageously makes it possible for a deflection of a seismic mass of the acceleration sensor to be demultiplied so that a more exact measurement is possible.
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Funk Karsten
Kulcke Hans-Martin
Laermer Franz
Schilp Andrea
Fayyaz Nashmiya
Kenyon & Kenyon
Robert & Bosch GmbH
Williams Hezron
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