GB2245398A

GB2245398A - Detector and signalling system

Info

Publication number: GB2245398A
Application number: GB9013752A
Authority: GB
Inventors: Julien Glazer
Original assignee: GLAZERTRON Ltd
Current assignee: GLAZERTRON Ltd
Priority date: 1990-06-20
Filing date: 1990-06-20
Publication date: 1992-01-02
Also published as: GB9013752D0

Abstract

A detector and signalling system comprises a detector, preferably a passive infra-red detector, connected to a mains power supply, a transmitter for generating an oscillating signal in response to an output from the detector and for injecting the signal into the mains power supply, and a receiver connected to the mains power supply at a location remote from the detector and arranged to detect the oscillating signal and to provide an output control signal in response thereto. The system avoids the need for separate signalling wiring, simplifying installation.

Description

Detector and Signaling System This invention relates to a detector and signalling system, preferably of the type incorporating a passive infra-red detector.

Passive infra-red detectors are used, for example, in building security to detect the presence of a person and to cause a light to be switched on and/or an alarm to sound.

In the installation of such detectors, particularly in a large building, the wiring necessary to connect the detector to, for example, a central alarm system may be extensive and therefore costly. The present invention permits the detector to send a signal using existing electric mains wiring.

Accordingly, the invention provides a detector and signalling system, comprising a detector, preferably a passive infra-red detector, connected to a mains power supply, a transmitter for generating an oscillating signal in response to an output from the detector and for injecting the signal into the mains power supply, and a receiver connected to the mains power supply at a location remote from the detector and arranged to detect the oscillating signal and to provide an output control signal in response thereto.

Preferably the receiver is arranged to provide an output control signal in response to detection of a predetermined number of cycles of the oscillating signal, for example 30, thereby providing isolation from mains fluctuation. The output signal may be used to control a relay switching alarms or lighting, for example. Preferably the relay is associated with a time-delay so that the alarm and/or lights continue to operate for a period after the output from the detector ceases.

The system of the invention is such that the transmitter may derive its operating power from the existing power supply of the detector, for example the passive infra-red device. The signal, which is at a frequency in the approved range of 125 to 150 kHz may be kept at a very low level and the period of the transmission may be kept very short, for example less than 1 second.

Reference is made to the drawings, in which: Figure 1 is a circuit diagram of a transmitter in a system according to a preferred embodiment of the invention; and Figure 2 is a circuit diagram of the receiver for use with the transmitter illustrated in Figure 1.

Referring to Figure 1, the transmitter has DC power connections P1 and P2 and an input signal connection S which may be connected respectively to the power supply connections and the output signal connection of a passive infra-red detector, for example of known type. Receipt of a signal at S causes npn transistor Q3 to switch, thereby causing an oscillator circuit comprising components Q1, R1, C1, I1 and R2, to operate for a period which can be extended by the value of capacitor C4. The oscillator produces a good quality sine wave, avoiding the possibility of spurious emissions at other frequencies. These oscillations are injected into the mains supply LN via inductance I2. The signal induced is at a level of about 200 mV and at a frequency of between 125 and 150 kHz, for example about 140 kHz. The period of transmission can be less than 1 second.

Referring now to Figure 2, the signal on the mains LN is sensed via inductor I3 which has approximately 130 turns on the larger winding and 20 to 25 turns on the smaller winding, depending upon the chosen operating frequency. The detector stage, comprising transistor Q4 and capacitors C8 and C9 and associated components, is arranged so that capacitor C9 is charged up stepwise via capacitor C8.

Resistor R7 controls the number of cycles required to charge capacitor C9 up to the required level at which a comparator Z1 provides an output which in turn switches on transistor Q5, providing a control signal, which can then be used to operate a relay, for example, a timed relay operating an alarm, switching on a light or other functions as desired.

The tuned amplifier in the receiver provides a dynamic range better than 10:1 and can thus accommodate the range of signal input typically found on different electric circuits in a typical house. The receiver requires at least 30 complete cycles at the correct frequency to provide an output, and thus does not respond to interruptions in the supply or to electrical noise which is often found on mains wiring due to light switches, refrigerator motors, central heating and similar apparatus.

Claims

CLAIMS 1. A detector and signalling system, comprising a detector connected to a mains power supply, a transmitter for generating an oscillating signal in response to an output from the detector and for injecting the signal into the mains power supply, and a receiver connected to the mains power supply at a location remote from the detector and arranged to detect the oscillating signal and to provide an output control signal in response thereto. 2. A detector and signalling system according to Claim 1, wherein the detector is a passive infra-red detector. 3. A detector and signalling system according to Claim 1 or 2, wherein the receiver is arranged to provide an output control signal in response to detection of a predetermined number of cycles of the oscillating signal, thereby providing isolation from mains fluctuation. 4. A detector and signalling system according to Claim 1, 2 or 3, wherein the output signal is used to control a relay switching alarms or lighting. 5. A detector and signalling system according to Claim 4, wherein the relay is associated with a time-delay so that the alarm and/or lights continue to operate for a period after the output from the detector ceases. 6. A detector and signalling system according to any preceding claim, wherein the transmitter derives its operating power from the existing power supply of the detector. 7. A detector and signalling system according to any preceding claim, wherein the signal is at a frequency in the range of 125 to 150 kHz. 8. A detector and signalling system according to any preceding claim, wherein the period of transmission of the signal is less than 1 second. 9. A detector and signalling system, substantially as described with reference to the drawings. AMENDMENTS TO THE CLAIMS HAVE BEEN FILED AS FOLLOWS CLAIMS

1. A detector and signalling system, comprising a detector connected to a mains power supply, a transmitter for generating an oscillating signal in response to an output from the detector and for injecting the signal into the mains power supply, and a receiver connected to the mains power supply at a location remote from the detector and arranged to detect the oscillating signal and to provide an output control signal in response thereto, wherein the receiver is arranged to provide said output control signal in response to detection of a predetermined number of cycles of the oscillating signal, thereby providing isolation from mains fluctuation.

2. A detector and signalling system according to Claim 1, wherein the detector is a passive infra-red detector.

3. A detector and signalling system according to Claim 1 or 2, wherein said predetermined number is at least 30.

4. A detector and signalling system according to Claim 1, 2 or 3, wherein the output signal is used to control a relay switching alarms or lighting.

5. A detector and signalling system according to Claim 4, wherein the relay is associated with a time-delay so that the alarm and/or lights continue to operate for a period after the output from the detector ceases.

6. A detector and signalling system according to any preceding claim, wherein the transmitter derives its operating power from the existing power supply of the detector.

7. A detector and signalling system according to any preceding claim, wherein the signal is at a frequency in the range of 125 to 150 kHz.

8. A detector and signalling system according to any preceding claim, wherein the period of transmission of the signal is less than 1 second.

9. A detector and signalling system according to any preceding claim, wherein the receiver comprises a capacitor, an electrical circuit arranged to detect the oscillating signal and to add to the charge stored in the capacitor at each cycle of the oscillating signal, and control means for providing said output control signal when the charge on the capacitor reaches a predetermined level.

10. A detector and signalling system according to Claim 9, wherein the control means is a comparator provided with a reference voltage.

11. A detector and signalling system, substantially as described with reference to the drawings.