Measuring and testing – Liquid analysis or analysis of the suspension of solids in a... – Viscosity
Reexamination Certificate
1999-02-04
2001-08-07
Williams, Hezron (Department: 2856)
Measuring and testing
Liquid analysis or analysis of the suspension of solids in a...
Viscosity
C073S024050, C073S03200R
Reexamination Certificate
active
06269686
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to a sensor, in particular for measuring the density and viscosity of a medium.
BACKGROUND INFORMATION
A known sensor for measuring the density and viscosity of liquids is described in the article by Inaba et al, Sensors and Actuators A, 33 (1991), pages 163-166. In this known sensor, a bending reed is dipped into the medium, and is excited to a thermally induced vibration by irradiation with the assistance of a laser diode. The vibrational frequency is influenced by the density of the medium, and the damping of the vibration is influenced by the viscosity of the medium. Thus, the density and viscosity of the medium, which may correspond to a liquid, can be measured by measuring the vibration of the bending reed.
SUMMARY OF THE INVENTION
In contrast, the sensor of the present invention has the advantage that a particularly simple and trouble-free design is utilized. In particular, since the sensor of the present invention can be constructed to be especially small, the sensor of the present invention is also suitable for checking very small liquid or gas quantities.
By using silicon nitride, silicon oxide, metal, or mixed materials of the aforesaid, a bending reed used in the present invention is produced which is resistant to most chemical media. Therefore, such a sensor can be used for a multitude of measurable media. Furthermore, because these materials can be processed in few and well-controlled standard processes, cost-effective production in large lots is made possible. Moreover, such bending reeds can be made particularly small. Since the vibration generator is arranged on the facing-away side of a silicon substrate, the measurable medium only comes in contact with very chemically-resistant materials. Thus, vibration generators can also be used which are not so chemically resistant. The vibrations of the bending reed are detected particularly simply by a monocrystalline piezoresistive element. Such an element is also resistant to most chemical media. Alternatively, a piezoresistive thin film can also be used on the top side of the bending reed. In addition, the temperature of the measurable medium can also be ascertained by a temperature sensor on the substrate. The measured temperature can also be taken into account in calculating the density and viscosity of the measurable medium. A signal-processing circuit is advantageously integrated directly on the silicon substrate, since in this way, particularly good signal processing is achieved. The influence of parasitic variables is reduced, and the evaluating electronics can thus be more compactly, and generally also more cost-effectively produced. By appropriate feedbacks, both vibrations of maximum amplitude and of maximum speed can be attained in the zero passage.
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Flik Gottfried
Hahn Dietmar
Herrmann Falk
Kenyon & Kenyon
Politzer Jay L.
Robert & Bosch GmbH
Williams Hezron
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