Alarm circuit for detecting overheated condition

• US 4,278,970 A
• Filed: 05/02/1979
• Issued: 07/14/1981
• Est. Priority Date: 05/02/1979
• Status: Expired due to Term

• Current Assignee: Joseph B. Loughlin, Michael Streczyn
• Original Assignee: Joseph B. Loughlin, Michael Streczyn
• Inventors: Streczyn, Michael, Loughlin, Joseph B.
• Primary Examiner(s): Swann, III, Glen R.
• Application Number:
  US06/035,321
• Time in Patent Office: 804 Days
• Field of Search: 340/599, 340/573, 340/598, 340/664, 340/584, 340/595, 340/635, 307/117, 307/257, 337/298, 337/14, 73/362 SC, 73/362 AR, 128/736
• US Class Current: 340/599
• CPC Class Codes: A61B 5/01 Measuring temperature of body parts ; Diagnostic temperature sensing, e.g. for malignant or inflamed tissue clinical contact thermometers G01K13/20
• CPC Class Codes: G01K 3/005 Circuits arrangements for indicating a predetermined temperature fire detection G08B17/00
• CPC Class Codes: G01R 17/105 for measuring impedance or resistance
• CPC Class Codes: G01R 19/16576 comparing DC or AC voltage with one threshold G01R19/16514, G01R19/16519, G01R19/16528, G01R19/16533 and G01R19/1659 take precedence
• CPC Class Codes: G08B 17/06 Electric actuation of the alarm, e.g. using a thermally-operated switch

Abstract

An alarm circuit for detection of an overheated condition comprises a bridge rectifier or a battery to provide a d.c. input, and a detector bridge including a thermistor and Zener diode in adjacent arms. The diode is set to operate along that portion of the thermistor response curve which is slowly changing. Hence, the Zener diode will be activated if the thermistor detects at the very onset of an overheated condition. Bridge unbalance is fed to an operational amplifier which activates a transistor to turn on an alarm such as an audio indicator, LED, telemetry system, etc. The alarm circuit has application for detection of a line overload, as a monitoring device for patients and for persons undergoing physical activity such as joggers and the like. By sounding an early alarm, overheating in a line wire caused by say, an overheated appliance, can be corrected with a consequent energy saving and minimizing damage to the appliance.

Claims

1. A detecting circuit for an overheated condition, comprising:

(a.) a d.c. powered bridge circuit having a detector thermistor in a bridge arm, the bridge being fed by the d.c. source;

(b.) thermistor response detector in an adjacent bridge arm, the detector being set for a response to thermistor changes in about the 300°

K.-400°

K. range;

(c.) a two state comparator amplifier for activation by the thermistor response detector;

(d.) an on-off switch activated by the amplifier; and

,

(e.) output signal means for the circuit connected to the on-off switch, whereby a bridge unbalance due to thermistor changes caused by an overload will activate the thermistor response detector, thereby activating the on-off switch and then turn on the output signal means.

2. The detecting circuit of claim 1 in which the comparator is an operational amplifier and the on-off switch is a transistor.

3. The circuit of claim 1, adapted for detection of an overheated body condition.

4. The circuit of claim 1 adapted for detection of an overheated line wire.

5. The circuit of claim 1, in which the thermistor response detector is a thermistor.

6. The circuit of claim 1, in which the detector is a Zener diode.

7. The apparatus of claim 1, comprising a plug board mounting for the circuit.

9. The method of claim 6 in which the comparator is an operational amplifier and the on-off switch is a transitor.

8. A method for signalling an overheated body condition, comprising:

(a.) detecting skin temperature with a thermistor in one arm of a d.c. powered bridge circuit;

(b.) providing a thermistor response detector in an adjacent opposing arm of the bridge circuit, the detector being set for a response to thermistor changes in the 300°

K.-400°

K. range;

(c.) feeding bridge unbalance signals from the detector to a two state comparator amplifier;

(d.) activating an on-off switch fed by the comparator when the bridge is unbalanced; and

,

(e.) turning on an output signal from the on-off switch, when the switch is activated.

10. The method of claim 8 in which a thermistor is the detector.

11. The method of claim 8, in which the detector is a Zener diode.