Sensor element seal for a detector

Details Sensor element seal for a detector Sensor element seal for a detector

1999-04-19

2001-05-01

Williams, Hezron (Department: 2856)

Measuring and testing

Gas analysis

Gas of combustion

C073S031050, C338S034000, C422S094000, C123S672000

Reexamination Certificate

active

06223583

ABSTRACT:

BACKGROUND INFORMATION
The present invention relates to a sensor and a seal for a sensing element of the sensor. U.S. Pat. No. 5,467,636 describes a known sensor in which a planar sensing element is immobilized in gas-tight fashion, by way of a sealing element, in a passthrough of a ceramic shaped element. The ceramic shaped element has, on the end surface facing away from the exhaust gas, a recess which surrounds the passthrough and into which a fusible glass seal is introduced. The fusible glass seal surrounds the sensing element in gas-tight fashion at this point, and creates a gas-tight connection to the ceramic shaped element. The fusible glass seal is the only sealing element which implements the seal between sensing element and ceramic shaped element.
SUMMARY OF THE INVENTION
The sensor according to the present invention, has the advantage that by way of the press-in additional seal, pre-immobilization of the sensing element in the ceramic shaped element can be accomplished during manufacture of the fusible glass seal, the pre-immobilization being also maintained during the joining process with the melting of the glass packet associated therewith. The pressed-in additional seal moreover relieves stress on the joining point between the sensing element and the fusible glass seal, both upon cooling after the joining process (because only radial stresses then act on the fusible glass seal), and when the sensor is under thermal and mechanical load, especially under vibratory load. The additional seal moreover prevents the molten glass from penetrating, during the melting process, into the front region of the sensing element which is subject to severe thermal stress when the sensor is used.
It is particularly advantageous to use as the additional seal a powder packing made of graphite or graphite-containing material, since graphite is not wetted or only partially wetted by molten glass. Powder packings made of steatite or similar ceramic materials, which preferably are presintered or precompressed so that no disruptive reactions can take place between the powder packing and fusible glass, are economical. A further embodiment of the additional seal consists in the use of ceramic films, for example made of Al
2
O
3
and/or ZrO
2
, which are introduced into the recess of the ceramic shaped element and compressed there so as to yield pre-immobilization of the sensing element in the ceramic shaped element. Lithium aluminum silicate glass or lithium barium aluminum silicate glass have proven to be advantageous glasses for the fusible glass seal.


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