Measuring and testing – Simulating operating condition – Marine
Patent
1996-05-22
1997-12-02
Chilcot, Richard
Measuring and testing
Simulating operating condition
Marine
7320422, 7320426, G01F 168
Patent
active
056938799
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention is based on a sensor carrier for a device for measuring the mass, or flow rate, of a flowing medium, as set forth hereinafter. A sensor carrier for a device is already known (German Published Patent Disclosure DE-OS 38 44 354 now U.S. Pat. No. 4,976,145), in which a so-called hot-film sensor element is placed in a flowing medium and, to measure the flow rate of the flowing medium, has a temperature-dependent sensor region composed of individual resistor layers applied to a platelike substrate and including at least one heating resistor and at least one temperature-dependent measuring resistor. For retention purposes, the hot-film sensor element is glued by its underside partly to a tongue-like support element, so that the latter element is bathed by the flowing medium on its free end in a measurement conduit. For measurement, the measuring resistor is kept at an overtemperature that is far above the temperature of the flowing medium, so that substantially because of convection, it gives off a certain amount of heat to the flowing medium as a function of the mass or flow rate of the flowing medium moving past it. The heating resistor as is known serves to maintain the constant overtemperature of the measuring resistor and is disposed in the best possible thermal contact with the measuring resistor so as to keep the temperature of the latter resistor constant. The measuring resistor has a resistance that is dependent on the temperature, so that a change in the overtemperature causes a change in its resistance, and a closed-loop control circuit connected to the measuring resistor and the heating resistor is mistuned. The closed-loop control circuit is embodied for instance as a bridgelike resistance measuring circuit that upon being mistuned by the measuring resistor varies the heating current or heating voltage of the heating resistor, so as to keep the overtemperature of the measuring resistor constant; the heating current or heating voltage of the heating resistor required for maintaining the overtemperature of the measuring resistor is a standard for the mass of the flowing medium. As may be learned from the prior art referred to at the outset, the substrate has a further resistor, which will hereinafter be called the medium temperature resistor and which is disposed on the substrate; it is thermally decoupled from the heating resistor and the measuring resistor by means of slits made by removal of material from the substrate. The medium temperature resistor has a resistance that is dependent on the temperature and is part of the closed-loop control circuit that assures that changes in the temperature of the flowing medium do not affect the measurement accuracy of the device. To attain a precise outcome of measurement, the quantity of heat output by the heating resistor should be supplied as completely as possible to the measuring resistor, or in other words without some of it being dissipated to the support element, for instance via a layer of adhesive on the sensor element.
German Published Patent Disclosure DE-OS 42 19 454 shows a sensor carrier which is intended for retaining micromechanical sensor elements in particular and which has a recess in which the sensor element is placed flush and retained by means of a layer of adhesive applied to a bottom face of the recess. It is known that micromechanical sensors of so-called micromechanical design are made by etching out a semiconductor body, for instance a silicon wafer, with a membranelike sensor region created by the etching that has at least one heating resistor and at least one temperature-dependent measuring resistor. The membranelike sensor region defines only a small area of the sensor element and has an extremely slight thickness of a few micrometers, so that only a small surface area of the sensor region needs to be heated by the heating resistor in order to react, within a short response time, to changes in the mass of the flowing medium caused by changes in the amount of heat output by the heating r
REFERENCES:
patent: 4914947 (1990-04-01), Davidson
patent: 4976145 (1990-12-01), Kienzle et al.
Lehenberger Stefan
Rilling Heinz
Chilcot Richard
Greigg Edwin E.
Greigg Ronald E.
Patel Harshad
Robert & Bosch GmbH
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