Supervised wireless security system

• US 4,523,184 A
• Filed: 09/30/1982
• Issued: 06/11/1985
• Est. Priority Date: 09/30/1982
• Status: Expired due to Fees

• Current Assignee: Pacific Microelectronics Corporation
• Original Assignee: Sentrol Incorporated (Carrier Global Corporation)
• Inventors: Abel, William E.
• Primary Examiner(s): Crosland, Donnie L.
• Application Number:
  US06/429,116
• Time in Patent Office: 985 Days
• Field of Search: 340/539, 340/500, 340/506, 340/536, 340/531, 340/533, 340/534, 340/825.2, 340/825.21, 340/825.44, 340/825.49, 340/825.47, 340/825.45, 340/345, 340/34 6, 455/9, 455/38, 455/51, 455/53, 455/56, 455/65
• US Class Current: 340/539.16
• CPC Class Codes: G08B 25/007 Details of data content structure of message packets; data protocols
• CPC Class Codes: G08B 25/10 using wireless transmission systems G08B25/009 takes precedence

Abstract

Apparatus and method for communication by use of a single FM radio frequency, from a plurality of transmitters to a central receiver in a security alarm system or similar system. A transmitter'"'"'s radio frequency signal is modulated in wide frequency swings to transmit digitally encoded address, subaddress, and sensor status information in a very brief format. A transmission is provided periodically from each transmitter, but a very low duty cycle is used to avoid interference among the transmitters. A transmitter frequency sweep provides the receiver an opportunity to lock onto a transmission before data is transmitted. Thereafter the receiver automatically tracks the rapidly varying frequency of the transmitted signal. Address and subaddress data identify each transmission and a maintenance warning ir provided by the receiver-decoder unit to identify any transmitter which fails to report within a predetermined time. Each significant sensor status change initiates a transmission from the related transmitter. Low duty cycle and low transmitter power requirements provide long transmitter battery life.

Claims

1. A security monitoring system, comprising:

(a) sensor means for detecting an observable event;

(b) a transmitter including means for responding to said sensor;

(c) a radio frequency oscillator included in said transmitter and having a nominal oscillation frequency and an actual oscillation frequency;

(d) modulator means associated with said oscillator for varying said actual instantaneous oscillation frequency;

(e) encoder means associated with said transmitter and responsive to said sensor for causing said modulator to vary said actual oscillation frequency by a predetermined frequency shift in accordance with a digital code pattern including a sensor status code;

(f) a receiver having a radio frequency band-pass filter tuned to said nominal frequency, said band-pass filter having a radio frequency bandwidth extending at least said predetermined frequency shift on each side of said nominal frequency;

(g) automatic frequency tracking circuit means for tuning said receiver to follow radio frequency signals produced by said transmitter while said modulator varies said transmitter actual oscillation frequency by said predetermined frequency shift in accordance with said digital code pattern;

(h) detector means included in said receiver and responsive to the changes of said actual oscillation frequency for detecting said digital code pattern and providing an electrical signal corresponding thereto;

(i) decoder means for receiving and decoding said electrical signal; and

(j) wherein said transmitter includes lock-on pulse generator means connected controllingly to said modulator for sweeping said actual oscillation frequency through a range of frequencies including said nominal frequency during each transmission, at a lower rate of change of actual oscillation frequency than the rate at which said encoder means causes said modulator to vary said actual oscillation frequency, before said encoder means causes said modulator to vary said actual oscillation frequency.

2. A transmitter for use in a wireless security monitoring system, comprising;

(a) a radio frequency oscillator having an actual frequency within a predetermined frequency range of a first predetermined frequency;

(b) encoder means for producing a pulse train including digitally coded address and sensor data;

(c) modulator means interconnecting said encoder means and said radio frequency oscillator for modulating said actual frequency in response to said pulse train to produce a frequency-modulated output signal;

(d) multivibrator means connected to said encoder means for periodically initiating transmission of said output signal;

(e) sensor-responsive means connected to said encoder means for initiating transmission of said output signal in response to detection of a predetermined event by a sensor; and

(f) voltage ramp generating means connected to said modulator means for causing said actual frequency to sweep through said first predetermined frequency at a predetermined rate of change of frequency before said encoder means produces said pulse train.

3. A wireless security monitoring system, comprising:

(a) sensor means for detecting an observable event;

(b) a battery powered transmitter including means for responding to said sensor means;

(c) a radio frequency oscillator included in said transmitter and having a nominal oscillation frequency and an actual oscillation frequency;

(d) modulator means associated with said oscillator for varying said actual oscillation frequency;

(e) encoder means associated with said transmitter and responsive to said sensor means for causing said modulator to vary said actual oscillation frequency by a predetermined frequency shift in accordance with a digital code pattern including a sensor status code, wherein said predetermined frequency shift is at least as great as the maximum expected difference between said actual oscillation frequency and said nominal oscillation frequency;

(f) a receiver having a radio frequency band-pass filter tuned to said nominal frequency, said band-pass filter having a radio frequency bandwidth extending at least said predetermined frequency shift plus said maximum expected difference on each side of said nominal frequency;

(g) detector means included in said receiver and responsive to the changes of said actual oscillation frequency for detecting said digital code pattern and providing an electrical signal corresponding thereto;

(h) decoder means for receiving and decoding said electrical signal; and

(i) wherein said transmitter includes pulse generating means for producing at least one pulse varying from the actual oscillation frequency by a frequency at least as great as the maximum expected difference between the nominal oscillation frequency and the actual oscillation frequency, and said receiver means including lock-on means responsive to said pulse for locking said receiver to said actual oscillation frequency prior to the detection of said digital code pattern by said detector means.

4. The security monitoring system of claim 3 wherein said transmitter includes timing means for periodically enabling said transmitter to transmit a coded message and wherein the ratio of the time that said transmitter is enabled to the time that it is disabled lies in the range of 1:

100 to 1;

14,000.

5. The security monitoring system of claim 4 wherein said coded message comprises a channel address code identifying said transmitter and a sensor status code conveying data detected by said sensor means.