Mass flow sensor with rupture detection

Details Mass flow sensor with rupture detection Mass flow sensor with rupture detection

1998-08-12

2001-02-27

Fuller, Benjamin R. (Department: 2855)

Measuring and testing

Volume or rate of flow

Thermal type

Reexamination Certificate

active

06192749

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a mass flow sensor.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 4,888,988 describes a mass flow sensor which has a thin substrate on which a resistor element is arranged. The thin substrate is secured on a thick, mechanically fixed substrate. The thin substrate is configured as an electrical diaphragm, which is secured on a thick substrate made of silicon. A plurality of resistor elements are arranged on the diaphragm, but none of these resistor elements is arranged such that a rupture of the diaphragm in the stretched area could be detected.
SUMMARY OF THE INVENTION
In contrast, the mass flow sensor according to the present invention is capable of reliably detecting a rupture of the diaphragm in the stretched area of the thin substrate. Therefore, a mass flow sensor according to the present invention is capable of being diagnosed by determining whether the thin substrate, on which the resistor element is arranged, is still mechanically intact. The mass flow sensor according to the present invention can thus also be used in an environment where safety is critical, for example, in the intake manifold of an automobile.
By arranging the resistor for rupture detection in the area of great mechanical stresses, it is assured that a rupture will be immediately detected, since a rupture will develop first at these locations. In the case of an elongated stretched area, a resistor of this type for detecting a rupture is preferably arranged perpendicularly to the longitudinal direction. It is advantageous to configure the resistor for rupture detection as a thin-film resistor, preferably made of the same material as the resistor element. It is advantageous if the resistor for rupture detection and the resistor element can be configured from the same layer of material. Particularly suitable for the thin substrate are silicon oxide, silicon nitride, or a combination of these two materials, particularly if the mechanically fixed substrate is made of silicon. An example relates to a rectangular diaphragm, which is stretched on all sides by a frame-shaped fixed substrate. The resistor for rupture detection is then constituted as a meander-shaped resistor on the longitudinal sides or as a meander-shaped resistor surrounding three sides of the rectangular diaphragm.


REFERENCES:
patent: 4888988 (1989-12-01), Lee et al.
patent: 4951510 (1990-08-01), Holm-Kennedy et al.
patent: 5237867 (1993-08-01), Cook, Jr.
patent: 5321983 (1994-06-01), Nagata
patent: 5765432 (1998-06-01), Lock et al.
patent: 5936157 (1999-08-01), Yamashita

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