ELECTRONIC ALARM SYSTEM

• US 3,725,865 A
• Filed: 05/03/1971
• Issued: 04/03/1973
• Est. Priority Date: 05/03/1971
• Status: Expired due to Term

• Current Assignee: Anthony Prince Fairchild
• Original Assignee: Anthony Prince Fairchild
• Inventors: Fairchild, Anthony Prince
• Primary Examiner(s): Yusko, Donald J.
• Application Number:
  US05/139,792
• Time in Patent Office: 701 Days
• Field of Search: 340/150,181,183,171,420,147,349,214,213,172,164
• US Class Current: 340/514
• CPC Class Codes: G08B 25/018 Sensor coding by detecting magnitude of an electrical parameter, e.g. resistance

Abstract

An electronic alarm system providing an indication of conditions existing at a number of locations with each location being equipped with a number of sensors for indicating each of a number of different types of conditions. Each sensor at a given location, when actuated, produces a step voltage output having an amplitude different from the amplitudes produced by the other sensors at that location. The step voltage output of a sensor at a given location is modulated by one signal of a dual frequency signal, the frequencies of which are peculiar to the particular sending station or location. A pulse operated reed switch is placed at the output of each sending station and permits the modulated signal to be transmitted therefrom in response to the presence of an output at one of the condition response sensors. The signal is transmitted to a central location containing a plurality of receiving stations, and the transmitted signal will actuate that receiving station which is frequency-tuned to the transmitted signal. An arrangement of Zener diode and silicon controlled rectifier detectors are used to sense the D.C. voltage level to identify the condition existing at the sending or remote station.

Claims

1. An electronic alarm system having at least one sending station and at least one receiving station, said stations being interconnected by a transmission line, said sending station comprising:

a plurality of condition responsive switch means, a plurality of voltage producing means, each of said voltage producing means being actuated by one of said condition responsive switch means, each said voltage producing means, when actuated, producing a voltage of a value differing from the voltages of the others of said voltage producing means, thereby producing an indication of which of the condition responsive switch means has been actuated, signal generating means in said sending station for producing a signal having a characteristic peculiar to that sending station and means for transmitting said voltages and said characteristic signal from said sending station over said transmission line;

said receiving station comprising;

means for receiving said transmitted voltages and said characteristic signal, a plurality of voltage detecting means, each said detecting means being responsive to a different one of the voltage values produced in said sending means to produce an output voltage indicative of the presence of said one voltage value in the received signal, thereby producing an indication at said receiving station of which of said condition responsive switch means has been activated and, signal detecting means in said receiving station for detecting the presence of said characteristic signal corresponding to said sending station and for allowing said received voltages to pass to said voltage detecting means when said characteristic signal is present.

2. The electronic alarm system defined in claim 1, wherein each said voltage producing means, when actuated, produces a step voltage of an amplitude differing from the voltage amplitudes produced by the other voltage producing means.

3. The electronic alarm system defined in claim 1, wherein said signal generating means comprises a dual frequency signal generator, and wherein said signal detecting means includes means for detecting a predetermined pair of frequencies and for allowing said received voltages to pass to said voltage detecting means when a predetermined pair of frequencies are found to be present on the received signal.

4. The electronic alarm system defined in claim 3, wherein said means for transmitting includes means for combining one of the outputs of said dual frequency signal generator with the outputs of said plurality of voltage producing means prior to transmission over said transmission line.

5. The electronic alarm system defined in claim 3 further comprising:

means , initiated at said receiving station, for transmitting a test signal from a receiving station over said transmission line to a sending station, responder means in said sending station which, responsive to receipt of said test signal, causes said dual frequency signal to be transmitted over said transmission line, and indicating means in said receiving means responsive to reception of an output from said means for detecting a predetermined pair of frequencies for indicating proper reception of said dual frequencies.

6. The electronic alarm system defined in claim 1, wherein said transmission line is a conventional telephone line.

7. The electronic alarm system defined in claim 1 wherein each said voltage detecting means in said receiving station comprises a voltage blocking means for blocking those voltages which do not exceed a predetermined level, said predetermined levels for the plurality of voltage detecting means substantially corresponding, respectively, to the voltage output values of said voltage producing means, and an output producing means, havinG a predetermined sensitivity, connected to be activated by the output of said voltage blocking means for indicating an alarm condition corresponding to said predetermined voltage level.

8. The electronic alarm system defined in claim 7 wherein each said voltage blocking means comprises a Zener diode and each said output producing means comprises a silicon controlled rectifier receiving its gating voltage from the output of said Zener diode.

9. The electronic alarm system defined in claim 1 additionally comprising:

means , initiated at said receiving station, for causing a test signal to be transmitted from said receiving station to said sending station, responder means in said sending station for transmitting a response signal responsive to said test signal, and indicating means in said receiving station for indicating proper receipt of said response signal.

10. The electronic alarm system defined in claim 8 wherein said Zener diodes have substantially equal threshold sensitivity levels.