Chemistry: electrical and wave energy – Apparatus – Electrolytic
Patent
1996-08-01
1997-11-25
Bell, Bruce F.
Chemistry: electrical and wave energy
Apparatus
Electrolytic
G01N 2726
Patent
active
056908008
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/DE 95/01684 filed Nov. 28, 1995.
PRIOR ART
The present invention relates to an electrochemical measuring element for determining the oxygen content of gas mixtures.
Electrochemical measuring elements have, for example, a finger-type shape where the solid electrolyte body is fastened tightly inside a metal casing. For finger-type probes, a distinction is made between potential-free and latent potential measuring elements. For latent potential measuring elements, the strip conductor of the outer electrode makes contact with the casing by means of an electrically conducting sealing ring. With the potential-free measuring elements, each electrode connection leads directly to a controller so that no electrical contact with the casing is permitted. A seal between solid electrolyte body and casing must exist in both cases. The solid electrolyte body and the strip conductor of the potential-free probe are covered with an electrically insulating layer where it fits tightly.
ADVANTAGES OF THE INVENTION
The measuring element according to the invention has the advantage that the brittle, electrically insulating layer is protected against pressure points of the metallic sealing ring. This avoids the formation of cracks in the insulating layer which would otherwise have a negative influence on the insulating effect and the mechanical stability of the insulating layer. Because of the deformability of the cover layer, the sealing ring can push into the cover layer so that a closed tight fit results. The measuring element according to the invention additionally leads to increased production safety with regard to gastightness of the sensor element and an improvement in the continuance with regard to the vibration stress for the sensor element/sealing ring arrangement. In addition, the material composition of the cover layer permits the use of commercially available materials and pastes and the use of known application techniques such as, for example, the screen printing technology.
DRAWING
The exemplary embodiments for this invention are shown in the drawing and explained in more detail in the following description. FIG. 1 is a longitudinal cut through the exhaust-gas side of a measuring element according to the invention while FIGS. 2, 3 and 4 each show an enlarged section X according to FIG. 1.
DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
The electrochemical measuring element 10 shown in FIG. 1 has a metal casing 11 with a thread 13 on the outside, used as fastening means, used to install it in a measuring gas tube that is not shown here. Casing 11 has a longitudinal borehole 18 with tight seat 19, onto which is fitted a metal sealing ring 20. A sensor element 14 with a shoulder 16, formed on a toric head 15, sits on tight seat 19 with sealing ring 20. On toric head 15 of the sensor element 14, a sealing surface 22 forms on the sensor element side between sealing ring 20 and sensor element 14. Tight seat 19 also forms a sealing surface on the casing side.
Sensor element 14 has a tube-shaped solid electrolyte body 23, the end section of which is closed on the measuring gas side. On the outside exposed to the measuring gas, a measuring electrode 25 is mounted on the solid electrolyte body 23 while a reference electrode 26, exposed to a reference gas, for example air, is mounted on the side facing toward the inside. Measuring electrode 25 is conducted via a measuring electrode strip conductor 27 to a first electrode contact 33 and the reference electrode 26 is conducted with a reference electrode strip conductor 28 to a second electrode contact 34. The electrode contacts 33, 34 are in each case located on a frontal section 36 that is formed by the open end of solid electrolyte body 23. The measuring electrode is coated with a porous protective layer 29. pieces 38 make contact with electrode connectors 41. The electrode connectors 41 lead to a connecting cable that is not shown and which, in turn, leads to a measuring and control mechanism. Furthermore, a ceramic insulating sleeve 43 i
REFERENCES:
patent: 4569748 (1986-02-01), Yamakawa et al.
patent: 5228975 (1993-07-01), Yamada et al.
Friese Karl-Hermann
Stanglmeier Frank
Bell Bruce F.
Robeert Bosch GmbH
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