Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
1999-06-08
2001-01-30
Chapman, John E. (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
C310S329000, C310S334000, C073S652000
Reexamination Certificate
active
06178820
ABSTRACT:
The invention relates to a sensor for measuring acceleration and sound pressure, the sensor separately comprising means for measuring the acceleration of a surface and means for measuring the sound pressure affecting the surface.
Extremely accurate values of the magnitudes of the acceleration and the pressure affecting a surface are needed e.g. in an application which actively attenuates sound and oscillation caused by nose. Said values are needed for controlling the means, i.e. actuators, generating counter-oscillation. Since the signals to be measured are wave-formed, completely reliable measurement results are extremely difficult to obtain, since a phase difference can be present at the time of measurement in two different measurements, the phase difference excessively interfering with the final result.
German Publication No. 4,342,169 discloses an electromechanical transformer operating as e.g. a microphone. Said transformer comprises a film for emitting a signal which is proportional to the sound pressure and/or surface acceleration. However, the transformer cannot be used in accurate sound attenuation applications since the sound pressure and acceleration signals cannot be distinguished one from the other.
It is the object of the present invention to provide a sensor for measuring acceleration and sound pressure accurately and reliably.
The sensor of the invention is characterized in that the means for measuring the acceleration and the means for measuring the sound pressure are arranged substantially concentrically and substantially in the same plane.
An essential idea of the invention is that the means for measuring acceleration and the means for measuring sound pressure are arranged concentrically in the same plane. The idea of a preferred embodiment in that the means for measuring pressure is circular and the means for measuring acceleration is arranged in the middle of said circle. The pressure sensor is most preferably formed of pressure-sensitive film having flat gas bubbles and a metal coating on at least one side, a permanent electric charge being formed in the film, the sensor emitting an electric signal proportional to the pressure. Furthermore, the acceleration sensor is preferably made of similar material by adding a mass on top of it and arranging the acceleration sensor in such a way that pressure changes do not affect it, but the movement of the surface to be measured causes the mass disposed upon the material to emit a signal.
It is an advantage of the invention that one of the measuring means, arranged concentrically in the same plane, measures pressure and the other measures acceleration from the same place at the same time, whereby no error caused by a phase error can affect the measurement result, i.e. the measurement is reliable and accurate. When the same material is mainly used in the acceleration and pressure measurement sensors, the sensor production technique becomes easy. By arranging the acceleration sensor such that a mass is placed on the pressure-sensitive film, the resulting acceleration sensor is not substantially affected by lateral movements.
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Kirjavainen Kari
Lekkala Jukka
Nyk{umlaut over (a)}nen Hannu
Uosukainen Seppo
Chapman John E.
VTT
Young & Thompson
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