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Title
Sensorelement und Vorrichtung zur Messung komplexer Impedanzen sowie Verwendung der Vorrichtung
Date Issued
1999
Author(s)
Hillerich, B.
Haerle, T.
Leidl, A.
Patent No
1997-19755418
Abstract
NOVELTY - Electrodes (29) are coated with an insulating layer (27). In comparison with their spacing (S), this layer is thin (d). DETAILED DESCRIPTION - Preferred Features: The insulating layer has high chemical stability. It is silicon carbide; its thickness, 0.2 - 2 mu m, is less than a quarter of the electrode spacing. The sensor is a surface acoustic wave (SAW) device. A capacitive electrode is applied to it. The sensor element is a surface acoustic wave sensor with interdigital electrodes on the substrate. One of the interdigital electrodes forms a measurement electrode pair. The measurement equipment includes analysis circuitry. Further variables are measured. The analysis unit is an oscillator circuit. The analysis unit voltage source produces two oscillatory signals of the same frequency. A current source controlled by one of them, produces an oscillatory current signal. An amplifier measures the signal dropped across the impedance to be measured, and is suitable to produce a c orresponding oscillating voltage signal. A mixer takes this signal, combining it with the second of the two source signals cited with 0 deg. or 90 deg. phase shift, so that real and imaginary parts of the impedance can be determined. The amplifier has connections for positive and negative supply voltages supplied via a series resistance with connections to a voltage stabilizer and the amplifier output. Sensor line screening and buffer amplification are described. A signal switch changes over between individual sensors. USE - To analyze fluid properties, determine aging of lubricating oils, measure ground moisture, measure ion concentrations, measure water content in fluids of low dielectric constant, measure water in alcohol or oils and vice versa, measure water content in braking fluids, determine milk composition, determine a hardening point of concrete, determine contamination of ground with oil or acids, identify acids and alkalis in water and to determine their concentration. ADV A NTAGE - The principal feature of the new sensor is the coating protecting it from its environment. This coating is sufficiently thin in relation to electrode spacing, for reliable complex impedance measurements to be taken with sufficient accuracy. The coating protects against highly corrosive media. Additional unspecified measurements may be taken, possibilities include mechanical properties at various frequencies. DESCRIPTION OF DRAWING(S) - The drawing shows an arrangement of electrodes in the sensor element. coating thickness d electrode spacing S thin silicon carbide insulating layer 27 electrodes 29
Language
de
Patenprio
DE 1997-19755418 A: 19971212