POINT SOURCE DISCRIMINATOR THERMAL ALARM

• US 3,812,483 A
• Filed: 05/26/1972
• Issued: 05/21/1974
• Est. Priority Date: 05/26/1972
• Status: Expired due to Term

• Current Assignee: Howard T. Graves
• Original Assignee: Howard T. Graves
• Inventors: Graves, Howard T.
• Primary Examiner(s): Caldwell, John W.
• Assistant Examiner(s): Swann, III, Glen R.
• Application Number:
  US05/257,222
• Time in Patent Office: 725 Days
• Field of Search: 340/258D,258R 178/DIG.38,DIG.33,DIG.8
• US Class Current: 340/527
• CPC Class Codes: G08B 13/19 using infrared-radiation detection systems G08B13/194 takes precedence
• CPC Class Codes: Y10S 250/01 Passive intrusion detectors

Abstract

An alarm system is provided for a scanning type far infrared system. The video signal is processed by a gated pulse blanking system which permits automatic surveillance of one or more windows within the scene displayed. Any significant change within the selected window triggers an audible or visible alarm.

Claims

1. An alarm circuit for an infrared viewer utilizing a cathode ray tube (CRT) display with first and second terminals, respectively, for periodic linear horizontal and vertical sweep signals and a third terminal for an intensity modulation or video signal derived from an infrared detector comprising, at least one horizontal window pulse forming circuit means having an input coupled to said first terminal to generate a pulse of controlled width and having a controlled delay relative to the beginning of each of said periodic horizontal sweep signals, at least one vertical window pulse forming circuit means having an input coupled to said second terminal to generate a pulse of controlled width and having a controlled delay relative to the beginning of each of said periodic vertical sweep signals, an AND gate having at least first and second inputs respectively coupled to the outputs of each of said horizontal and vertical window pulse forming means, a gated amplifier having a first gate signal input coupled to the output of said AND gate and a second amplifier input coupled to said third terminal on the CRT display and a detector means coupled to the output of said gated amplifier to actuate an alarm device when the average signal output from said gated amplifier exceeds a preset threshold.

2. An alarm circuit according to claim 1 wherein at least one tandem control means is connected between a horizontal and a vertical window pulse forming circuit to vary said delay in each circuit simultaneously.

3. An alarm circuit according to claim 1 wherein a sound generating alarm is connected to the output of said detector means.

4. An alarm circuit according to claim 1 wherein a light source alarm is connected to the output of said detector means.

5. An alarm circuit according to claim 1 wherein said horizontal and vertical window pulse forming means each comprise:

a first differentiating network;

a first half wave rectifier;

a first monostable multivibrator;

a second differentiating network;

a second half wave rectifier; and

a second monostable multivibrator, the above being serially connected in the order named.

6. An alarm circuit according to claim 5 wherein said first and second monostable multivibrators include a variable resistance to control the pulse width generated.

7. An alarm circuit according to claim 6 wherein said variable resistance means are two rotatable potentiometers ganged to directly track one another.

8. An alarm circuit according to claim 6 wherein said variable resistance means are two rotatable potentiometers ganged to track one another in an inverse relationship.

9. An alarm circuit according to claim 6 wherein said variable resistance means are two push-pull potentiometers coupled to a joy stick control whereby the potentiometers may be varied in direct, inverse or independent relationships.

10. An alarm circuit according to claim 1 wherein:

said AND gate includes a plurality of pairs of inputs;

a like plurality of said horizontal window pulse forming circuits all having a common input; and

a like plurality of said vertical window pulse forming circuits all having a common input, the output of each of said window pulse forming circuIts being connected to a different one of said inputs to said AND gate.