GB2261945A

GB2261945A - A photosensitive electrical controller for street lighting

Info

Publication number: GB2261945A
Application number: GB9125728A
Authority: GB
Inventors: Graham Philip Penlington
Original assignee: ROYCE THOMPSON ELECTRIC LIMITE
Current assignee: ROYCE THOMPSON ELECTRIC LIMITE
Priority date: 1991-11-30
Filing date: 1991-11-30
Publication date: 1993-06-02
Also published as: GB9125728D0

Abstract

An electrical controller for supplying power to a load eg. street lighting, according to the intensity of ambient light as sensed by a photosensor D3. At predetermined thresholds of ambient light a latchable relay RLY is opened/closed by application of a pulse. One embodiment uses a capacitor C1 to supply the triggering pulse. Another embodiment (figure 2) has a latchable relay with two windings that can be alternatively energised to control the load. <IMAGE>

Description

Title: "Electrical controller and method of controlling energisation of an electrical load".

Description of Invention The present invention relates to the control of the supply of electrical power to an electrical load and has been devised primarily for use in street lighting.

It is common for street lighting to be controlled in accordance with the ambient light level so that the lighting is switched on when the ambient light level falls below a predetermined threshold and is switched off when the ambient light level rises above a further, possibly different, threshold. It is also desirable to minimise the consumption of electrical energy by the controller used to control energisation of the lighting. There have been various proposals for street lighting controllers. However, the prior proposals do not achieve all of satisfactory reliability of operation at the required ambient light levels, minimal consumption of electrical power and low capital cost.

According to a first aspect of the present invention, there is provided an electrical controller for controlling the supply of electrical power to an electrical load according to the intensity of ambient light, the controller comprising a relay for switching the electrical power supply to the load, control means for the relay, a transducer which provides a signal dependent on the intensity of ambient light and a processor for processing said signal to provide an output to the control means, wherein the relay is settable by application to the relay of electrical power in either one of an open condition and a closed condition, each of which conditions can be sustained without consumption by the relay of electrical power, and wherein the control means is arranged to apply to the relay, when said output goes high, a pulse of electrical energy which sets the relay in one of said conditions and to apply to the relay, when said output goes low, a pulse of electrical energy which sets the relay in the other of said conditions.

According to a second aspect of the invention, there is provided a method of controlling the supply of electrical power to an electrical load wherein there is provided a relay which is settable in an open condition and in a closed condition, each of which conditions can be sustained without consumption by the relay of electrical power, contacts of said relay are connected in series with an electrical power source and said load, a pulse of electrical energy is applied to the relay to change the condition of the relay, a capacitor is charged by said pulse and wherein, to change subsequently the condition of the relay again, the capacitor is discharged through the relay.

According to a third aspect of the invention, there is provided an electrical controller for controlling the supply of electrical power to an electrical load according to the intensity of ambient light, the controller comprising a relay for switching the electrical power supply to the load, control means for the relay, a transducer which provides a signal dependent upon the intensity of ambient light and a processor for processing said signal to provide a pair of outputs to the control means, wherein the relay comprises a pair of windings and is settable by application of electrical power to a selected one of the windings in either one of an open condition and a closed condition, each of which conditions can be sustained without consumption by the relay of electrical power.

Examples of controllers embodying the first and third aspects of the invention and one of which is used in a method according to the second aspect of the invention will now be described, with reference to the accompanying drawings wherein: FIGURE 1 shows a diagram of an electrical circuit of a street lighting controller.

FIGURE 2 shows an alternative controller.

The controller of Figure 1 comprises a relay, the energising winding of which is shown in the diagram at RLY. The relay is a known type of relay having contacts which are connected in series between a source of electrical power and a street light or other load. The relay has permanent magnets capable of maintaining the relay in either one of two stable conditions, in one of which the contacts are closed and in the other of which the contacts are open. The fields of the permanent magnets can be temporarily overcome by energisation of the winding RLY so that the condition of the relay can be changed. Flow of current in one direction through the winding RLY opens the contacts, unless they are already open, and flow of current in the opposite direction through the winding closes the contacts, unless they are already closed.The drawing shows a circuit for controlling energisation of the relay.

The illustrated circuit includes a photo-diode D3 which provides a signal dependent on the intensity of ambient light. That signal is amplified by the transistor TR and is applied through a resistor R2 to an integrated circuit IC which processes the signal. The integrated circuit also applies a suitable voltage across the transistor TR.

The integrated circuit compares the signal from D3, representing the actual intensity of ambient light, with a threshold value representing the intensity of ambient light at which the load is to be connected to the source of electrical power and to a threshold representing the intensity of ambient light at which the load is to be disconnected from the power source. These threshold values may be defined within the integrated circuit or may be defined by resistors or other components external to the integrated circuit.

The integrated circuit provides at a terminal OCO an output for use in controlling the relay. When the output at terminal OCO is low and capacitor C1 is not charged, connection of the circuit with a source of electrical power will charge capacitor C1 through relay winding RLY. The winding will be energised with a first polarity by a pulse of energy. Capacitor C1 will then remain in a charged condition but there will be no significant consumption of electrical energy by the control circuit, once the capacitor has been charged. If the output at terminal OCO then rises, transistor Q1 will become conducting and capacitor C1 will discharge through this transistor and the relay winding RLY, thereby energising the winding with opposite polarity.When the capacitor Cl had been discharged, the relay will remain in the condition to which it has been set by discharge of the capacitor C1 through the winding RLY.

When the output at terminal OCO again goes low, transistor QL1 will be turned off and capacitor C1 will again be charged through relay winding RLY, again changing the condition of the relay contacts. It will be noted that the electrical energy which is thus stored in capacitor C1 is subsequently used to change the condition of the relay when capacitor C1 is discharged. The condition of the relay is changed by a brief pulse of electrical energy.

There may be substituted for the photo diode D3 another transducer capable of providing a signal which is dependent upon the intensity of ambient light. The transducer may be mounted in a position remote from all of the components or from some of the components of the circuit shown in the accompanying drawing. For example, the transducer may be mounted at the top of a street light and the relay may be mounted near the bottom of the street light, where it is readily accessible for servicing.

The relay of the controller illustrated in Figure 1 may be replaced by an alternative relay having a pair of windings. For use in conjunction with the circuit of Figure 1, these windings are connected together in series between the capacitor C1 and the diode D2. The circuit modified in this way functions essentially in the same way as does the circuit of Figure 1.

A further alternative controller is illustrated in Figure 2. The controller of Figure 2 also includes a relay having a pair of windings, identified in the drawing by the numerals 1 and 2. A relay also comprises contacts connected in series between a source of electrical power and a load, in the same manner as contacts of the relay of Figure 1 are so connected.

The controller of Figure 2 comprises an integrated circuit IC2 corresponding to the integrated circuit IC of Figure 1 but the integrated circuit of Figure 2 differs in that it includes a pair of output terminals A and B. An output is provided at one of these when the load is to be connected with the power source and an output is provided at the other of the terminals A and B when the load is to be disconnected from the power source. Although not shown in Figure 2, a transducer corresponding to diode D3 of Figure 1 is connected with integrated IC2 in the same manner as diode D3 is connected with circuit IC of Figure 1. This transducer provides to the integrated 1C2 a signal dependent on the intensity of ambient light.The integrated circuit processes this signal, processing including comparison of the signal from the transducer with respective threshold values representing the intensity of ambient light at which the load is to be connected to the source of electrical power and representing the intensity of ambient light at which the load is to be disconnected from the power source.

The terminal A of integrated circuit IC2 is connected with the base of a transistor TR1 connected in series with the relay winding 1. When the output at terminal A goes high, the transistor conducts and winding 1 is energised to change the condition of the relay contacts, unless the contacts are already in the condition to which they would be set by energisation of winding 1. Terminal B of the integrated circuit IC2 is connected with the base of a transistor TR2 connected in series with the winding 2 of the relay. When the output at terminal B goes high, TR2 conducts and winding 2 is energised to change the condition of the relay contacts from that to which they have been set by energisation of winding 1. When terminals A and B are both low, the transistors do not conduct and there is no consumption of electrical energy by the relay.

It will be understood that processing of the signals from the transducers may be carried out by means of discrete components, rather than by the integrated circuits mentioned herein.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

CLAIMS:

1. An electrical controller for controlling the supply of electrical power to an electrical load according to the intensity of ambient light, the controller comprising a relay for switching the electrical power supply to the load, control means for the relay, a transducer which provides a signal dependent on the intensity of ambient light and a processor for processing said signal to provide an output to the control means, wherein the relay is settable by application to the relay of electrical power in either one of an open condition and a closed condition, each of which conditions can be sustained without consumption of electrical power by the relay and wherein the control means is arranged to apply to the relay, when said output is high, a pulse of electrical energy which sets the relay in one of said conditions and is arranged to apply to the relay, when said output goes low, a pulse of electrical energy which sets the relay in the other of said conditions.

2. A controller according to Claim 1 wherein the relay has a single energising winding.

3. An electrical controller for controlling the supply of electrical power to an electrical load according to the intensity of ambient light, the controller comprising a relay for switching the electrical power supply to the load, control means for the relay, a transducer which provides a signal dependent on the intensity of ambient light and a processor for processing said signal to provide an output to the relay control means wherein the relay comprises a pair of windings which can be energised alternately by the control means to change the condition of the relay contacts repeatedly and wherein the control means is arranged to apply pulses of electrical energy alternately to the windings of the relay.

4. A method of controlling the supply of electrical power to an electrical load wherein there is provided a relay which is settable by application to the relay of electrical power in either one of an open condition and a closed condition, each of which conditions can be sustained without consumption by the relay of electrical power, contacts of said relay are connected in series with an electrical power source and said load, a pulse of electrical energy is applied to the relay to change the condition of the relay, a capacitor is charged by said pulse and wherein to restore the relay to its initial condition, the capacitor is discharged through the relay.

5. A lighting control circuit substantially as herein described with reference to and as represented in the accompanying drawing.

6. Any novel feature or novel combination of features disclosed herein or in the accompanying drawing.