Thermal measuring and testing – Thermal testing of a nonthermal quantity – Of fluid volume
Patent
1992-09-14
1994-07-19
Gutierrez, Diego F. F.
Thermal measuring and testing
Thermal testing of a nonthermal quantity
Of fluid volume
324694, 324696, G01N 2704, G01N 2556, G01N 2500
Patent
active
053302680
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention is concerned with an apparatus for determining the condition of a pressure transmitting fluid, in particular, for checking or monitoring the water content or the boiling temperature of a hygroscopic brake fluid. Such apparatus typically comprises an electrically heatable sensor element immersed in the fluid to be tested, a power source supplying an electric current of constant magnitude to the sensor, and a measuring device measuring the voltage drop across the sensor element to determine the temperature-dependent resistance of the sensor element. The sensor element is of a configuration and size and the heating current being at a magnitude such that heating of the sensor element over the duration of the period of measurement causes a stable cellular convection to arise in a temperature range below the boiling temperature of the fluid. The voltage drop across the sensor element is an accurate indicator of the water content of the liquid.
An apparatus of the afore-described type is disclosed by German published patent application DE 35 22 774 A1. The sensor element of the apparatus is configured and the current supply devised such that at the time of measurement, a stable cellular convection arises. This requires a heating of the sensor element to a predetermined temperature which is within a temperature range just below the boiling temperature of the fluid to be tested, it being imperative for the sensor element not to be heated to the boiling temperature of the fluid under test.
According to the referenced German application, it is suggested to form the sensor element as a hollow body having an open wall; as a hollow helix; as a perforated tube or the like to favor the formation of convection cells and of the stable cellular convection, respectively, during the measuring time. However, sensor elements of that type are relatively costly which applies, in particular, if a stationary assembly in an automotive vehicle or in each of the wheel brakes of an automotive vehicle, respectively, is desired. Moreover, the requirements placed upon the mechanical stability of the sensor element, in that case, are particularly high.
The invention is, therefore, based on the problem of providing a mechanically stable yet low-cost sensor element for use with an apparatus of the afore-mentioned type, permitting the formation of a stable cellular convection during the measuring process.
SUMMARY OF THE INVENTION
It has been discovered that this problem can surprisingly be solved by a sensor element which is in the form of a very simple linear conductor, e.g. a short length of wire which is fixed at either end in a holder to have mechanical stability. Also, the sensor element may be composed of a plurality of linear conductors of this type connected in parallel or in series
The length of wire must be geometrically configured and dimensioned such that convection cells can be formed on all linear conductors i.e., boundary layer stream caused by a stable cellular convection arises. The value of a constant electrical current is determined which when passed through the length of wire will heat the surrounding liquid in a thin layer over the wire so as to establish a boundary layer stream and steady state heat transfer by cellular convection from the wire into the liquid over a range of water content levels in the liquid. The previously determined constant magnitude of electrical current is passed through the wire extended within a liquid having an unknown water content to cause the length of electricity conductive wire to be heated to a temperature varying with the water content level in the liquid. The electrical resistance of the wire at this temperature is determined, and the results of this determination are analyzed by comparison with previously determined electrical resistance values of the length of electrically conductive wire with the constant electrical current magnitude passed therethrough for varying water content levels of the liquid, to thus enable ascertaining the
REFERENCES:
patent: 3264558 (1966-08-01), Heeps
patent: 3522530 (1970-08-01), Muller
patent: 3943767 (1976-03-01), Efferson
patent: 4558456 (1985-12-01), Bezard et al.
patent: 4805454 (1989-02-01), LeVert
patent: 5028144 (1991-07-01), Klein
patent: 5044764 (1991-09-01), Aoki et al.
Klein Hans-Christof
Krause Hans-Joachim
Lohberg Peter
May Arno
Oberdorfer Dietmar
Alfred Teves GmbH
Gutierrez Diego F. F.
Lewis J. Gordon
Seitter Robert P.
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