Electrical resistors – Resistance value responsive to a condition – Current and/or voltage
Patent
1990-01-10
1993-01-19
Lateef, Marvin M.
Electrical resistors
Resistance value responsive to a condition
Current and/or voltage
338 25, 338 50, 338254, 338255, 374185, H01C 710
Patent
active
051810077
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a PTC temperature sensor of the type which includes a PTC resistor connected to conductor webs disposed in a housing and also a process for producing PTC temperature sensing elements for the PTC temperature sensor.
It is generally known to use temperature sensors with temperature sensing elements containing thermally resistant resistor materials having temperature-dependent resistance values for measuring comparatively high temperatures such as prevail, for example, in exhaust gases from internal combustion engines (cf. E.D. Macklen, "Thermistors", published by Electrochemical Publications Ltd., 1979).
PTC temperature sensors utilise the continuous change in the resistance of metals or semiconductors having positive temperature coefficients with varying temperatures. The metals preferably used in PTC temperature sensors are platinum and nickel because of their high stability and reproducibility.
It is furthermore known, for example from EP-A-0,188,900 and 0,142,993 and also German Offenlegungsschrift 3,017,947 and 3,543,759, to use planar exhaust gas sensors, which can be prepared in a particularly cheap manner by ceramic film technology and screen-printing technology, to determine the .lambda.-value of gas mixtures. disadvantages of the known PTC temperature sensors are the fact that they age too rapidly during use, that their response times are too long, their method of production is too expensive and/or their dimensions are too large. The unavoidable diffusion of compounds of the gas to be measured e.g. hydrogen through highly refractory metal housings or through glass envelopes, in particular, causes undesirable changes in the resistance values. Metallic PTC resistors are put at risk at high temperatures also by oxidation in particular.
SUMMARY OF THE INVENTION
The PTC temperature sensor according to the invention has the PTC sensing element which is encapsulated hermetically with respect to the gas being measured and the ambient air in a laminated composite of ceramic films. The invention has the advantage over known PTC temperature sensors that the temperature sensing element is not subject to any aging due to the influence of varying O.sub.2 partial pressures while being cheap to manufacture, that it has a high resistance to changing the resistance characteristic in rich and lean gas mixtures, for example in motor vehicles exhaust gases at 300.degree.-1000.degree. C. and that it has a construction free from extraneous potential, is characterised by short response times owing to its low heat capacity and is suitable for incorporation in very narrow housings as a consequence of its small dimensions.
The temperature sensing element required for a PTC temperature sensor according to the invention can be produced by known laminating technology from comparatively thin ceramic films having a thickness of, in particular, 0.1 to 0.6 mm, preferably of 0.25 to 0.3 mm, which have previously been coated by known thick-film technologies with conductor webs and with thermally stable PTC resistors. In this connection, the ceramic films may be composed of an insulator ceramic such as, for example, AL.sub.2 O.sub.3, optionally with a flux added, or of another refratry ceramic, for example based on ZrO.sub.2. In the latter case, the PTC resistor and the associated conductor webs must be surrounded by insulation layers.
Various types of PTC temperature sensors can be produced, depending on the choice of the films used for producing a PTC sensing element for a PTC temperature sensor according to the invention. Preferred PTC temperature sensors which will be described in more detail below can be roughly subdivided into those having temperature sensing elements made of: AL.sub.2 O.sub.3, and
(A) Temperature sensing elements made of ceramic films based on an
insulator ceramic
Temperature sensing elements of this type are distinguished by the fact that it is possible to dispense with providing insulations between the film, on the one hand, and the PTC resistor and
REFERENCES:
patent: 4464646 (1984-08-01), Burger et al.
patent: 4489232 (1984-12-01), Wada et al.
patent: 4649364 (1987-03-01), Tanahashi et al.
Friese Karl-Hermann
Wiedenmann Hans-Martin
Lateef Marvin M.
Robert & Bosch GmbH
Striker Michael J.
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