Capacitative-type humidity sensing element and system, and method of manufacture

US4752855A · kind A · utility

Assignee

• Robert Bosch GmbH · DE

Inventors

• Horst Fedter · Bühlertal, DE
• Werner Grunwald · Gerlingen, DE
• Peter Nolting · Bühl, DE
• Claudio De La Prieta · Stuttgart, DE
• Kurt Schmid · Ditzingen, DE

Key dates

• Filing date: Mar 17, 1987
• Grant date: Jun 21, 1988
• Expiry date: Mar 17, 2007

Classification

• Technology area (CPC G): Physics
• CPC primary: G01N27/225
• WIPO field: Measurement
• WIPO sector: Instruments

Abstract

A humidity sensor, and particularly a sensor which can distinguish between low humidity values, for example below 60% humidity, and high humidity values, for example 90% humidity and thereover, and change the capacitance between output electrodes (5, 6) is formed by applying interdigited comb electrodes (1, 2) on a substrate (8) and applying over the substrate a ceramic mass formed of BaRuO.sub.3, V.sub.2 O.sub.5 and Na.sub.2 WO.sub.4, with a weight relationship of (1.+-.0.4):(1.+-.0.4):(0.6.+-.0.2) preferably 1:1:0.6. The sensor is made by first making a powder of the components, mixing it with a glass paste and, if necessary, a thinner, and applying the resulting paste by thick-film technology to a ceramic substrate on which the electrodes have been applied, and then firing the substrate at a temperature of between 550.degree. C. to 850.degree. C. The sensor is particularly sensitive in humidity ranges above 60% relative humidity and is especially suitable to sense fogging of the inside of a windshield of an automotive vehicle.