Measuring and testing – Specific gravity or density of liquid or solid
Reexamination Certificate
2000-03-28
2003-02-04
Williams, Hezron (Department: 2856)
Measuring and testing
Specific gravity or density of liquid or solid
C073S061490, C073S064530
Reexamination Certificate
active
06513365
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method for measuring physical characteristics or physical properties of liquids including highly viscous, doughy or paste-like mediums, using an acoustic transfer system (sender—test section—receiver) with at least one test section formed from a solid surface, which can be brought at least partly into contact with the medium to be measured. In addition, a device for implementing the method is described.
Conventional methods for measuring viscosity generally require the removal of a trial quantity which is tested in a separate measuring device. Particularly common are rotation viscosimeters, falling sphere viscosimeters and capillary viscosimeters which use the shear gradient in the liquid on the basis of the relative motion of at least one solid surface to the liquid. A disadvantage of these methods, however, is that they cannot be integrated into a technical process, which means that great resources are necessary for a correct measurement. Measurements of products whose properties are subject to a rapid transitory change or whose properties can be easily distorted by the removal of the trial quantity or the transportation of the trial quantity are particularly difficult and are often encumbered with errors.
A viscosity sensor which is suitable for on-line measurements is described in EP 0 527 176 B1. It consists of a cylindrical main body of piezo-electric material which is connected to an alternating current source and which is activated to torsional vibrations in the ultrasound field (20-100 kHz). The vibration properties (e.g. frequency) of the main body are changed by the contiguous liquid and converted into correspondingly altered electric signals. By evaluating these signals conclusions can be drawn regarding the viscosity. This technical solution, however, makes high demands upon the material of the main body and requires great resources in the manufacture of suitable materials and the geometrical formation of the main body.
In addition, scientific and patent literature has revealed various acoustic methods and devices which—using surface waves—are suitable for measuring physical and/or technical dimensions (i.e. physical characteristics or physical properties) of liquids. A common factor of these methods and devices is that they are generally limited to special materials (mainly piezo-electric material, whereby sender, test section and receiver form a centralized physical entity) for the substrate of the test section and/or they rely upon defined geometric conditions (thin plates) for the sensor surface. This gives rise to disadvantages concerning the adaptability of the suggested solutions to given technical conditions (e.g. temperature, corrosivity of the medium to be measured, constructive parameters, material of the transfer section, among other things).
J. Kondoh, K. Saito, S. Shiokawa, H. Suzuki; Multichannel Shear-Horizontal Surface Acoustic wave Microsensor for Liquid Characterization; 1995 IEEE Ultrasonics Symposium, pp 445-449 disclosed the use of shear surface waves (SH-SAW→SHEAR HORIZONTAL SURFACE ACOUSTIC WAVE) for determining substance properties in liquids. In this case, it is a question of a special type of surface waves characterized by particle deflections solely parallel to the wave-guiding solid surface and perpendicular to the propagation direction. i.e. there are no deflection components of the particles arising perpendicularly to the surface. Even this type of wave requires the use of a piezo-electric material (e.g. LiTaO
3
), whereby the wave-guiding solid surface must be formed from a special crystal section.
R. M. White; Silicon Based Ultrasonic Microsensors and Micropumps; Integrated Ferroelectrics, 1995, vol. 7, pp. 353-358 describes a method for measuring viscosity using plate vibrations of a thin membrane of only a few micrometers on a silicon base. Membrane structures of this nature are, however, very sensitive particularly in relation to mechanical loads. Plate vibrations are characterized on the one hand by particle movements parallel to the surface in the propagation direction and on the other hand by particle movements perpendicular to the surface. For viscosity measurement, however, only the first-mentioned particle movements can be used.
JP 09145692 A discloses a water drop sensor for windscreens and side mirrors of vehicles or the like. The water-drop sensor consists essentially of a component (sender) generating surface waves and a component (receiver) receiving surface waves which is positioned at a distance therefrom on the surface of the body to be monitored. As soon as drops of water reach the propagation field of the surface waves between the sender and the receiver, there is a scattering of the surface waves and absorption of part of the wave energy. By means of an electronic switching circuit, an evaluation of the attenuation of the signal can be carried out. It is supposed to be possible to thereby control a windscreen wiper depending upon the quantity of water on a windscreen.
The described drop sensor can essentially only be used as a switch which triggers/does not trigger specified reactions on the basis of recognising the presence or absence of water. Due to the property of surface waves to uncouple into contiguous liquids, the measurement result—thus the degree of attenuation of the signal—depends to a large extent upon the distribution of the water on the sensed surface. Therefore, with a dormant surface, whereby upon leaving propagation paths for the surface waves the drops form local water collections, one expects a lower attenuation than with an agitated surface with the same quantity of water, whereby the drops are distributed to a more or less even layer. Should the dynamic forces working on the water drops be so great that on the surface only a liquid layer density can form which is smaller than a quarter of the wavelength of the compression wave in the liquid, then the desired attenuation effect would not come into play.
As could be shown, the measurement signal of the drop sensor is to be understood as a total value which does not allow a differentiation between the various interactions involved in its formation. Quantitative conclusions concerning concrete physical or technical dimensions, for example the viscosity of liquids, are impossible. On the other hand, with a comparatively strong, high-volume striking of the test section with water it is expected that the wave energy used is permanently almost completely uncoupled in such a way that it is not possible to obtain a measurement signal which can be analyzed quantitatively.
EP O 542 469 A1 discloses a sensor for determining the viscosity of a liquid. The sensor has a substrate forming a sensor surface (test section) which can be brought into contact with the liquid to be investigated. Acoustic energy is made available in the form of surface waves (STW) on the sensor surface. The wave components propagate predominantly within the surface itself and only have a negligibly small vertical component propagating into the liquid. Through the use of such waves, in particular horizontal shear waves, a situation is supposedly avoided where the surface waves are too strongly attenuated during their interaction with the liquid to produce a signal which can be evaluated.
U.S. Pat. No. 4,691,714 discloses a probe device for simultaneous determination of the viscosity and temperature of a liquid. This device has a plate in which volume waves propagate, which for the purpose of determining the viscosity of the liquid interact with the liquid on a first surface which can be brought into contact with the liquid, and on whose second surface—turned away from the first surface—acoustic surface waves propagate, whereby the propagation speed depends upon the temperature of the probe. As the temperature of the probe is in turn influenced by the temperature of the liquid to be investigated, the temperature of the liquid to be investigated can thereby be determined indirectly.
SUMMARY OF THE INVENTION
It is an object o
Bruetting Christian
Gallien Arnold
Kessler Michael
Klippert Uwe
Lindner Gerhard
Brose Fahrzeugteile GmbH & Co. KG Coburg
Christie Parker & Hale LLP
Miller Rose M.
Williams Hezron
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