ALARM SYSTEM UTILIZING PULSE POSITION MODULATION AND DUAL CONDUCTOR SENSOR

• US 3,848,231 A
• Filed: 07/24/1972
• Issued: 11/12/1974
• Est. Priority Date: 12/31/1970
• Status: Expired due to Term

• Current Assignee: Thomas S. Wootton
• Original Assignee: Thomas S. Wootton
• Inventors: Wootton, Thomas S.
• Primary Examiner(s): Yusko, Donald J.
• Application Number:
  US05/274,250
• Time in Patent Office: 841 Days
• Field of Search: 340/274,276,224,164,167
• US Class Current: 340/524
• CPC Class Codes: F25D 29/008 Alarm devices
• CPC Class Codes: G08B 25/10 using wireless transmission systems G08B25/009 takes precedence

Abstract

A system for transmitting, via a radio link to a central station, alarm indications at a plurality of monitored stations. Each monitored station includes a different code identification number which controls pulse position modulation of a carrier that is transmitted to the central station only in response to an alarm condition being sensed. The type of alarm condition being sensed also pulse position modulates the carrier transmitted from the peripheral station to the central station. At the central station, the carrier is received and the pulse position modulated pulses are detected and processed to provide indications of the identity of the monitored station at which the alarm condition was sensed, as well as the cause of the sensed alarm.

Claims

1. A central station for receiving from any one of several peripheral stations transmitted data indicative of the occurrence of any one of several conditions at the peripheral station, said transmitted data including repetitive identical frames of data, each of said frames including plural signals defining channels at least some of which are indicative of the identity of the transmitting station and at least one of which is indicative of the condition occurring at the transmitting station, one of the channels of each frame containing an identifiable pulse, said central station comprising, in combination common receiver means for receiving said data frames from said several peripheral stations, first means for selecting the channel of each received data frame containing said identifiable pulse, second means for determining the time duration of each channel by measuring the time interval between corresponding portions of adjacent signals of said received data, third means responsive to said first and second means for determining the identity of the transmitting peripheral station and the condition occurring at the station from the time durations of said channels, and fourth means responsive to said third means for indicating the identity of the transmitting peripheral station and the condition occurring at the station.

2. A central station according to claim 1, wherein said identifiable pulse is a pulse of time duration greater than the time duration of the pulses defining any other channel of a frame, and said first means includes means for rejecting all of said pulses of time duration less than a predetermined value.

3. A central station according to claim 1, wherein the time duration of the channel containing said identifiable signal characteristic is indicative of the condition occurring at the transmitting station, and said third means is responsive to the location of data channels relative to said identifiable signal characteristic to identify the transmitting station and the condition occurring at the station.

4. A central station according to claim 1, wherein each of said peripheral stations transmits the same predetermined number of data channels during each frame, and wherein said central station includes means for rejecting data frames having a number of channels different from said predetermined number.

5. A central station according to claim 1, wherein said second means includes a separate counting means for determining the time duration of each channel of a data frame.

6. In an alarm system, a plurality of condition sensors, each of said sensors consisting of two conductors, means responsive to opening of either one of said conductors or to shorting of one of said conductors to the other for generating a signal, and means responsive to one of said signals for initiating a radio transmission.

7. The system according to claim 6, wherein is provided latch means responsive solely to said signal for reducing said signal to zero and for maintaining said signal at zero level for a predetermined time regardless of further opening or shorting, said predetermined time being of the order of several minutes.

8. In a sensing circuit, a transistor having an emitter, a base and a collector, a first conductive tape, a second conductive tape, means connecting one of said tapes between said emitter and a ground point, a collector load for said transistor, means connecting the other of said tapes between a voltage supply point and said base, said transistor being thereby normally conductive, a capacitor connected between said collector and ground, means responsive to increase of voltage at said collector for charging said capacitor, a latch circuit responsive to the voltage acrosS said capacitor, said latch circuit being normally non-conductive and rendered conductive in response to attainment of a predetermined voltage across said capacitor, said latch circuit being connected across said capacitor when said latch circuit is conductive, and means for resetting said latch circuit operative only if said transistor is conductive.