Title: Humidity sensor alarm unit

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Claims: What is claimed is:

1. A fail-safe humidity sensing alarm apparatus, which comprises:

an electric humidity sensor for detecting changes in humidity and having a resistance which varies in response to humidity variations;

a level detector for detecting a substantially null condition and for providing a first signal when said substantially null condition is detected and a second signal when other than a substantially null condition is detected;

a bi-stable device having a first state in response to said first signal and a second state in response to said second signal;

alarm means for providing an alarm when said bi-stable device is in said second state; and

circuit means for providing to said level detector (a) a substantially null condition when said humidity sensor detects a relative humidity which is below a predetermined threshold, (b) other than a substantially null condition when said humidity sensor detects a relative humidity which exceeds the predetermined threshold, (c) other than a substantially null condition when said humidity sensor is short-circuited, and (d) other than a substantially null condition when said humidity sensor is open-circuited.

2. A humidity sensing alarm apparatus as described in claim 1, said circuit means including first and second secondary windings of a transformer connected with the humidity sensor and an impedance device to form a bridge circuit with the level detector.

3. A humidity sensing alarm apparatus as described in claim 2, said circuit means further including a shunting resistance connected across said humidity sensor.

4. A humidity sensing alarm apparatus as described in claim 1, said bi-stable device comprising an electromagnetic relay having a plurality of relay contacts, said relay contacts being operative to close an alarm circuit when said relay is in said second state and to open said alarm circuit when said relay is in said first state.

Other info:

Inventors: Warner, Roger M. (Bethesda, MD, US)

Application Number: 724811
Filing Date: 1976-09-20
Publication_date: 1978-05-30
Assignee: Baxter Travenol Laboratories, Inc. (Deerfield, IL)
Primary Class(es): 340/507 340/602
Other Classes:
US Patent Ref:

2752586	Jun, 1956	Jordan	340/235.
2832947	Apr, 1958	Patchell	340/409.
3197699	Jul, 1965	Johansen	340/235.
3588891	Jun, 1971	Porter	340/409.
3599862	Aug, 1971	Hogan	340/235.
3771548	Nov, 1973	Rauchwerger	340/235.
3898423	Aug, 1975	Taylor	340/235.
3902040	Aug, 1975	Ikeda	340/235.
3950740	Apr, 1976	Greene	340/235.
4035787	Jul, 1977	Hornung	340/409.

Other Refs:
Primary Examiner: Habecker, Thomas B.
Assistant Examiner:
Attorney: Collins; H. W., Kinney; Richard G., Cummings; Eugene M.