Circuit arrangement for evaluating the signal of a capacitive me

Details Circuit arrangement for evaluating the signal of a capacitive me Circuit arrangement for evaluating the signal of a capacitive me

1993-07-30

1995-04-11

Callahan, Timothy P.

Miscellaneous active electrical nonlinear devices, circuits, and

External effect

307650, 327227, 327113, G05F 110

Patent

active

054061377

ABSTRACT:
A capacitive humidity sensor circuit in which a one-shot circuit produces pulses having a pulse duration determined by the capacitance of a capacitive sensing element, the one-shot circuit being triggered by the trailing edges of pulses in a pulse train produced by a multivibrator. The multivibrator is adjustable to produce a pulse train of variable repetition rate independent of the value of the measured parameter. The pulses produced by the one-shot circuit are integrated to produce a voltage indicative of the time average value of the pulses, the voltage being supplied to an amplification and offset compensation circuit whose output signal is used to adjust the supply voltage to the multivibrator so as to effectively achieve compensation for nonlinear response of the capacitive sensing element to increasing relative humidity.

REFERENCES:
patent: 4112317 (1978-09-01), Everswick
patent: 4237420 (1980-12-01), Ebihara et al.
patent: 4282480 (1981-08-01), Fujito et al.
patent: 4287470 (1981-09-01), Fabian et al.
patent: 4330718 (1982-05-01), Kinomoto et al.
patent: 4563634 (1986-01-01), Lehle
patent: 5046859 (1991-09-01), Yamaguchi
patent: 5132631 (1992-07-01), Klopfenstein et al.
Technical note 134, "Capacitive humidity sensor for consumer applications", Philips, 7 pages.
Technical information 063, "Capacitive humidity sensor", 15 pages (20 Nov. 1980).

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