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Capacitance Humidity Sensor

Published online by Cambridge University Press:  15 February 2011

Andrew R.K. Ralston ,
Paul E. Thoma ,
Carl F. Klein  and
Denice D. Denton
Andrew R.K. Ralston
Affiliation:
University of Wisconsin-Madison, Materials Science Program, Department of Electrical and Computer Engineering and Department of Chemistry, 1415 Johnson Drive, Madison, WI 53706
Paul E. Thoma
Affiliation:
Johnson Controls, Inc., Central Research, P.O. Box 591, Milwaukee, WI 53201-0591
Carl F. Klein
Affiliation:
Johnson Controls, Inc., Central Research, P.O. Box 591, Milwaukee, WI 53201-0591
Denice D. Denton
Affiliation:
University of Wisconsin-Madison, Materials Science Program, Department of Electrical and Computer Engineering and Department of Chemistry, 1415 Johnson Drive, Madison, WI 53706
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Abstract

A capacitance relative humidity (RH) sensor is described that has a design, construction, and material composition that result in an inexpensive and robust sensor. This sensor has a multilayer, free-standing film construction. It consists of a humidity sensitive polyimide (PI) dielectric core and conductive layers consisting of carbon filled polysulfone on each side of the polyirnide film to form a capacitor. The polyimide used is a BPDA-ODA type, and replaces a PMDA-ODA type polyimide used in a previous version of this sensor. The BPDA-ODA sensor has a nominal capacitance of 200 pF and a nominal sensitivity of 13% at 100% RH. The characteristics of this humidity sensor are discussed and compared to the characteristics of the PMDA-ODA type sensor. Characteristics considered include the PI film moisture uptake and water vapor transmission, and the sensors' sensitivity to relative humidity, frequency response, and aging at 85°C/85% RH. The dual-state sorption model and free volume calculations are used to demonstrate that observed differences in the film are due to differences in chemical composition between the films.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 382: Symposium G – Structure and Properties of Multilayered Thin Films , 1995 , 469
Copyright
Copyright © Materials Research Society 1995

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References

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