Measuring and testing – Volume or rate of flow – Thermal type
Patent
1996-11-08
1998-06-16
Dombroske, George M.
Measuring and testing
Volume or rate of flow
Thermal type
G01F 168
Patent
active
057654328
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a flow sensor.
BACKGROUND INFORMATION
U.S. Pat. No. 4,581,928 describes a flow sensor comprising a diaphragm, in which case, a heater and, on both sides of the heater, a temperature sensor are arranged on the diaphragm. The heater and the temperature sensors are patterned out of a resistive film. For evaluation purposes, the temperature sensors are arranged with other resistors in a measuring bridge circuit.
SUMMARY OF THE INVENTION
One of the advantages of the flow sensor according to the present invention is that an improvement in the signal from the sensor element is achieved. Only a slightly greater outlay is required for the present invention. Furthermore, the sensor element has a symmetrical form, which results in well synchronized signals from the individual temperature sensors. The outlay is especially low, since all elements are patterned out of one and the same resistive film. Therefore, manufacturing tolerances have only a slight influence on the measuring element.
The temperature sensors and the additional temperature sensors can be arranged inside one another or also side by side. Without additional expenditure, leads for the heater, the temperature sensors, and the other temperature sensors can be formed out of the resistive layer. The sensor signal is easily and precisely identifiable by configuring the temperature sensors and the additional temperature sensors in a measuring bridge. Expediently connected parallel to the interconnect resistor are adjustable resistors for adjusting (or balancing) the bridge. The adjustable resistors can be highly resistive in design to eliminate the temperature coefficient of the interconnect resistor.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a plan view of a first embodiment of the flow sensor according to the present invention.
FIG. 2 shows a second embodiment of the flow sensor.
FIG. 3 shows a third embodiment of the flow sensor.
FIG. 4 shows an equivalent circuit diagram of the measuring bridge.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 illustrates a plan view of a measuring element according to the present invention. The measuring element consists of a substrate 20, which supports a diaphragm 1. Diaphragm 1 has an especially low thermal inertia and an especially low thermal conductivity. Provided on diaphragm 1 is heater 2, temperature sensors 3 and 4, additional temperature sensors 5, 6, and an interconnect resistor 7. The diaphragm is heated by heater 2 to a predetermined temperature. When, as indicated by the arrow, fluid flows along on the top side of the diaphragm, then the diaphragm is cooled by this fluid flow. Sensors 3 and 5 situated upstream in the direction of flow are more heavily cooled than downstream sensors 4 and 6. The flow intensity can be inferred from the verification of this temperature difference.
Heater 2 is designed as a resistor element, i.e., it is warmed by an electric current flowing through it. Temperature measuring sensors 3, 4, 5 and 6 are designed as thermometer resistors, i.e., the temperature of the individual measuring elements can be determined by measuring the voltage dropping across each resistor.
Printed conductors 8 and bonding pads 31-38 are provided for contacting heater 2, temperature sensors 3, 4, and additional temperature sensors 5, 6. Wires, which establish an electrical contact with an evaluation circuit, are secured to bonding pads 31-38. The electrical signals are routed on substrate 20 through printed conductors 8.
As also described in U.S. Pat. No. 4,581,928, substrate 20 has been conceived of as a silicon substrate. To form diaphragm 1, a thin dielectric layer is applied to the top side of substrate 20, and substrate 20 is then removed underneath diaphragm 1. As also described in U.S. Pat. No. 4,581,928, this can take place through openings (or slots) in the diaphragm. Alternatively, it is also possible to etch out an opening, starting from the rear side of substrate 20 up to the diaphragm layer, and to produce diaphragm 1 in
REFERENCES:
patent: 4581928 (1986-04-01), Johnson
patent: 4651564 (1987-03-01), Johnson et al.
patent: 4696188 (1987-09-01), Higashi
patent: 4829814 (1989-05-01), Suzuki et al.
patent: 4888988 (1989-12-01), Lee et al.
patent: 5291781 (1994-03-01), Nagata et al.
Konzelmann Uwe
Lock Andreas
Artis Jewet
Dombroske George M.
Robert & Bosch GmbH
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