GB2264379A - Light installation - Google Patents

Abstract

The installation has a sensor unit 1 including an infra-red movement detector 11 and an ambient light sensor 18 which is connected to a remote control unit 2 by only two wires 100 and 101. The light sensor 18 and movement detector 11 are supplied with power from the control unit 2 via parallel diodes 19 and 39 connected to one of the wires 100. The light sensor 18 has a resistance that varies with light level and thereby varies the voltage across the two wires. The movement detector controls a switching transistor 15 connected across the two wires so that, when movement is detected, the wires 100 and 101 are short circuited momentarily via the transistor and voltage drops below the range established by the light sensor. The control unit 2 detects this voltage drop and, when it is followed by a low voltage indicative of a low ambient light level, switches on a lamp 3. <IMAGE>

Description

ELECTRICAL APPARATUS This invention relates to electrical apparatus and to installations including electrical apparatus.

The invention is more particularly concerned with passive infra-red movement detector apparatus which controls operation of a lamp or the like.

Passive infra-red detector apparatus are used in security applications, to detect the presence of intruders, and in courtesy light applications, where a light is turned on to illuminate a path or doorway as a person approaches. The apparatus can be incorporated entirely within the casing of a lamp or alarm mounted on an external wall. Alternatively, the infra-red detector can be mounted separately from the lamp or alarm. The detector is usually contained within a sensor unit that also includes a light level sensor so that the lamp is only turned on when there is a low ambient light level. Mounting the sensor unit separately has advantages in that the apparatus can make use of an existing lamp and the sensor can be located remote from the lamp so that the lamp is turned on earlier.In such apparatus, the conventional internal wall-mounted switch, by which the lamp is controlled, is replaced by a control unit including a low voltage power supply and circuitry for receiving the outputs of the light level sensor and the infra-red detector, to produce a switching signal for the lamp.

The control unit may also include a timing control and a control for setting the light level threshold. The interconnection of the sensor unit with the control unit has presented some difficulty because ofthe need for four wires to supply the power to the sensor unit and to supply the infra-red detector output and the light level sensor output from the sensor unit to the control unit. This complicates installation and often results in incorrect wiring. The need for four wires also means that a relatively large opening must be made in the wall or door frame through which the wire is led and that the wiring is relatively conspicuous. The cost of the wiring can also be high if the sensor is located at a distance from the control unit.

It is an object of the present invention to provide electrical apparatus which only requires two wires to interconnect the sensor unit and the control unit.

According to one aspect ofthe present invention there is provided electrical apparatus comprising a sensor unit and a control unit which controls operation of associated electrical equipment in response to the output ofthe sensor unit, the control unit being arranged to provide a current output to the sensor unit on a first wire and a current return from the sensor unit on a second wire, the sensor unit including a light level sensor arranged to vary the voltage between the first and second wires within a first predetermined range according to ambient light level, and infra-red detector means arranged to vary the voltage between the first and second wires within a second predetermined range outside the first range, and the control unit including a control circuit responsive to the voltage between the first and second wires to control the associated equipment accordingly.

The movement detector means preferably includes infra-red movement detector means.

The movement detector means is preferably arranged to reduce momentarily the voltage between the two wires to a value below that within the first range when movement is detected. The sensor unit preferably includes switching means, such as including a transistor, connected across the two wires, the switching means being controlled by the movement detector means such that the two wires are short circuited when movement is detected. The sensor unit may include two unidirectional current devices connected in parallel, one of said devices being connected in series with a light level sensor of variable resistance and the other device being connected in series with the movement detector means. The sensor unit is preferably mounted remotely ofthe control unit.The apparatus may include a diode bridge circuit connected between the two wires at the input ofthe sensor unit.

According to another aspect ofthe present invention there is provided an installation including apparatus according to the first aspect ofthe invention and a lamp connected to and controlled by the control unit.

A courtesy light installation including electrical apparatus according to the present invention, will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows the installation schematically; Figure 2 illustrates a modification to a part of the apparatus; and Figure 3 is a diagram illustrating operation of the apparatus.

The installation comprises a sensor unit 1, a control unit 2 and a lamp 3 which is controlled by the control unit 2. The sensor unit 1 is mounted on an outside wall to view the outer edge of a zone to be protected, such as the end of a path remote from a house. Two wires 100 and 101 connect the sensor unit 1 with the control unit 2 which is remotely mounted on an inside wall ofthe house. The control unit 2 replaces a conventional wallmounted switch that controls operation of the lamp 3 which may, for example, be an external porch lamp or the like which is located to illuminate the path.

The control unit 2 includes a power supply unit 20 connected to receive the mains power supply and arranged to produce a lower voltage output on line 21 to a current generator 22. The current generator 22 provides an output to a terminal 23 to which a first of the two wires 100 is connected. The control unit 2 also includes a control circuit 24 which controls operation of a relay 25 or other switching means such as a triac. The relay 25 is connected in series in the live line L from the mains supply to the lamp 3. The control circuit 24 receives two inputs derived from the sensor unit 1. The first of these, on line 26, is taken directly from the terminal 23 via a diode 27 and is indicative of light level. A capacitor 30 is connected between the cathode of the diode 27 and a second terminal 31 to which the second wire 101 is connected.The second input to the circuit 24, on line 28 is a trigger signal from a comparator 29. One input of the comparator 29 is connected directly to the terminal 23 whereas the other input is connected to a source 32 of a reference voltage V/n. Three useroperable controls 33, 34 and 35 are also connected to the control circuit 24. The first ofthese controls 33 is a three-way rocker switch which is used to override the control unit 2 and turn the lamp 3 on or off regardless of the status of the sensor unit 1. The second control 34 is a rotatable screw by which the light level threshold is set. The remaining control 35 is another rotatable screw by which timing of the control circuit 24 can be adjusted. The operation of the control unit 2 will be described later.

The sensor unit 1 includes a weatherproof housing 10 with an infra-red (IR) movement detector 11. The IR detector 11 may be of a conventional kind, such as described in GB 2251938A. Briefly, the IR detector 11 includes a pair of pyro-electric devices responsive to infra-red radiation emitted by the human body or other infra-red source. An array of lenses in front ofthe IR detector forms several infra-red images of the infra-red source which sweep across the pyro-electric devices causing them to change in output as the source moves in azimuth relative to the detector. It is this change in output that is indicative of the presence of a person and which causes an alarm output on line 12.The output on line 12 is supplied, via a capacitor 13 and resistor 14, to a switching transistor 15 connected between two terminals 16 and 17 ofthe sensor unit 1 to produce a momentary switching of the output voltage.

Also mounted in the housing 10 is a light level sensor 18 which may include a photocell.

The sensor 18 is mounted to receive ambient light falling on the unit 1 and provides an output accordingly. In particular, the light sensor 18 is arranged to have a resistance that varies with ambient light level and is connected between the two terminals 16 and 17 in series with a diode 19 or similar unidirectional current device. A second diode 39 is connected in parallel with the diode 19, in the same sense, with its anode connected to the input terminal 16 and its cathode connected to the detector 11. The second diode 39 provides a power supply path to the IR detector 11.

As shown in Figure 2, a diode bridge circuit 40 could be connected between the two wires 100 and 101 across the terminals 16 and 17 at the input ofthe sensor unit 1 so that operation of the sensor unit is independent of the polarity of the wires 100 and 101.

Operation of the apparatus will now be described with reference also to Figure 3. When no intruder or other person is detected, the transistor 15 in the sensor unit 1 will be open circuit so the voltage across the terminals 16 and 17 will be determined by the resistance of the sensor 18. The voltage might typically vary from V (eg. 12 volts) in full sunshine to V/2 (eg. 6 volts) in total darkness. The voltage across the terminals 16 and 17, in these circumstances, is illustrated by the voltage at time T 1 in Figure 3.

When someone moves across the field-of-view ofthe infra-red detector 11, the transistor 15 is momentarily switched to short circuit and then reverts to its open circuit state until movement is detected again. This results in a momentary drop in voltage to close to zero, as shown at time T2 in Figure 3. When this happens, the input ofthe comparator 29 connected to terminal 23 in the control unit 2 falls below that of the reference voltage V/n at the other input so that a trigger output signal is produced on line 28. The reference voltage V/n is set at some value below V/2 and above zero. The trigger signal causes the control circuit 24 to compare the voltage level on line 26, immediately aRer the drop in voltage, with a threshold level VT, as set by the control 34.Because the voltage on line 26 is greater than VT at this time, that is, the ambient light is too bright, the control circuit 24 keeps the relay 25 open and hence the lamp 3 off.

At a later time T3, the light level falls so that the voltage falls below VT. When movement is subsequently detected, at T4, this causes another drop in voltage below V/n.

The control circuit 24 then closes the relay 25 so that the lamp 3 is illuminated. The time for which the lamp 3 remains on is determined by the setting ofthe user control 35. Once this time has elapsed, the lamp 3 is turned off until the next movement is detected by the sensor unit 1.

Instead of a lamp, the control unit 2 could control operation of an alarm or, for example, a door opening device or the like.

Because the sensor unit 1 is connected to the control unit 2 by only two wires, which can be a conventional two-strand bell wire, installation is greatly facilitated. There is less risk of incorrect wiring, especially where the sensor unit or control unit includes a bridge circuit of the kind shown in Figure 2. The wiring between the two units can be relatively inconspicuous which is especially an advantage for that part of the length of wire inside the house.

Claims (12)

1. Electrical apparatus comprising a sensor unit and a control unit arranged to control operation of associated electrical equipment in response to the output of the sensor unit, wherein the control unit is arranged to provide a current output to the sensor unit on a first wire and a current return from the sensor unit on a second wire, wherein the sensor unit includes a light level sensor arranged to vary the voltage between the first and second wires within a first predetermined range according to ambient light level, and movement detector means arranged to vary the voltage between the first and second wires within a second predetermined range outside the first range, and wherein the control unit includes a control circuit responsive to the voltage between the first and second wires to control the associated equipment accordingly.

2. Apparatus according to Claim 1, wherein the movement detector means includes infra red movement detector means.

3. Apparatus according to Claim 1 or 2, wherein the movement detector means is arranged to reduce momentarily the voltage between the two wires to a value below that within the first range when movement is detected.

4. Apparatus according to any one ofthe preceding claims,wherein the sensor unit includes switching means connected across the two wires, and wherein the switching means is controlled by the movement detector means such that the two wires are short circuited when movement is detected.

5. Apparatus according to Claim 4, wherein the switching means includes a transistor.

6. Apparatus according to any one of the preceding claims, wherein the sensor unit includes two unidirectional current devices connected in parallel, and wherein one ofthe devices is connected in series with a light level sensor of variable resistance and the other of the devices is connected in series with the movement detector means.

7. Apparatus according to any one of the preceding claims, wherein the sensor unit is mounted remotely ofthe control unit.

8. Apparatus according to any one of the preceding claims including a diode bridge circuit connected between the two wires at the input of the sensor unit.

9. Apparatus substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

10. Apparatus substantially as hereinbefore described with reference to Figures 1 and 2 as modified by Figure 3 ofthe accompanying drawings.

11. An installation including apparatus according to any one ofthe preceding claims and a lamp connected to and controlled by the control unit.

12. Any novel feature or combination of features as hereinbefore described.