GB2373110A

GB2373110A - Proximity switch controller

Info

Publication number: GB2373110A
Application number: GB0129543A
Authority: GB
Inventors: Thomas William Bach
Original assignee: SENSATECH Ltd
Current assignee: SENSATECH Ltd
Priority date: 2000-12-08
Filing date: 2001-12-10
Publication date: 2002-09-11
Also published as: GB0030002D0; GB0129543D0

Abstract

A controller for controlling the supply of electrical power to a load 2 comprises an AC power supply inlet 8, and a sensing means 12. The sensing means is partially coupled to the AC power supply such that in use the potential of the sensing means 12 follows that of the AC power supply 8. The sensing means is further arranged such that in use the degree of following the AC power supply increases or decreases when a part of a body, such as a hand, is brought into the proximity of the sensing means 12. This change may be used to control an electrical device 2 - e.g. to switch it on or off.

Description

Control of Electrical Devices

This application relates to the control of electrical devices, especially mains powered devices.

In particular it relates to proximity switches and controllers for such devices, which do not require moving parts.

It is these days well known to provide switches for electrical equipment which operate without moving parts by sensing the presence of part of a user's bodytypically the finger. In the earliest forms of such switches the presence of a finger was sensed effectively by treating the user's body as a high-value impedance which would be placed electrically in series with a high-value resistor by the user placing his or her finger on a conductive sensor plate to which the high-value resistor was connected. This would cause a small current to flow through the resistor as it leaked to earth via the user. This current could be measured by a high-gain amplifier such as an operational amplifier. This arrangement is shown in Fig 1.

More recently the capacitance of the user's body has been used to sense presence of part thereof. In one arrangement a local oscillator and transmitter plate are provided in the vicinity of a receiver plate. When the user brings his or her hand near to the two plates, the capacitive coupling between them changes which causes a measurable change in the oscillation amplitude at the receiver plate. The actual change in amplitude will depend upon the relative capacitance between the user's body and earth compared to that between it and the plates. For example the receiver plate will measure higher voltages in the presence of a hand as long as the capacitance of body to earth is less than that of transmitter plate to body. This arrangement is shown in

Fig 2.

In another arrangement an RC oscillator is used to sense the presence of the user's hand. The capacitance of the hand in the proximity of a sensor plate connected to the circuit causes a change in characteristic frequency of the oscillator which can be measured. This arrangement is shown in Fig 3.

Whilst the arrangements described above can be made to work, there exists the need for a simpler and thus more cost-effective sensing arrangement.

When viewed from a first aspect the present invention provides a controller for controlling the supply of electrical power to a load, comprising an AC power supply inlet, and a sensing means at least partially capacitively coupled to the AC power supply such that in use the potential of the sensing means follows that of the AC power supply, the sensing means further being arranged such that in use the degree of coupling and thus the amplitude of its potential increases or decreases when a part of a body is brought into the proximity of the sensing means.

When viewed from a second aspect the invention provides a controller for controlling the supply of electrical power to a load, comprising an AC power supply inlet, and a sensing means partially coupled to the AC power supply such that in use the potential of the sensing means follows that of the AC power supply, the sensing means further being arranged such that in use the degree of following the AC power supply increases or decreases when a part of a body is brought into the proximity of the sensing means.

Thus it will be seen by those skilled in the art that in accordance with the invention the presence of a user's body may be sensed by a change in the potential referenced to the AC power supply seen by the sensing means. This change in potential results from a change in the effective coupling between the sensing means and

earth. In other words, in accordance with the invention, the controller operates in a similar fashion to known arrangements in which an external oscillator is provided, but obviates the need to provide the oscillator by effectively using the AC supply as the driving oscillator instead.

Conveniently the AC power supply is the ordinary mains power supply or derived from it. In preferred embodiments only two external connections to the controller are necessary-to one side of the AC power supply and to the load respectively. This allows the controller to be directly replaced for a conventional on/off switch in an existing installation.

Power to the load may be controlled in any convenient way for example the controller may be arranged to effect isolated switching of the load-e. g. by means of a relay or opto-isolator. Preferably though, the load is controlled as part of the controller circuit-e. g. using a transistor or more preferably a triac. This is beneficial in minimising the number of external connections to the controller which are required.

The AC power supply to the controller may be separate to the power supply for the load if isolated switching, e. g. a relay or opto-isolator, is used. It is preferred however that the controller power supply and load power supply are derived from the same sourcee. g. the ordinary domestic mains supply.

The controller and load may simply be connected to the power supply in parallel, although this would require at least three external connections to the controller (two for the power supply and one for the load. Alternatively and preferably the controller derives power during an interval which is not used to power the load. Thus in accordance with this feature the AC power supply may be used to power both the load and the controller itself on a time division basis,

albeit that the power requirement of the controller will typically be several orders of magnitude lower than that of the load.

Most preferably the controller is powered during a fraction of successive AC power supply cycles or halfcycles. In the preferred embodiment a triac is used to control power to the load in a substantially zero-crossing configuration. This minimises electromagnetic interference generated when the triac is fired. Thus the triac is preferably delayed for a short period of time after the zero-crossing point of each cycle or half-cycle. During this short delay the power supply is used to power the controller itself.

This arrangement is believed to be novel and inventive in its own right and thus when viewed from a second aspect the invention provides a controller for controlling the supply of power from an AC power supply to a load wherein the controller is arranged to be powered from the AC supply during an interval in which the load is not powered.

Preferably the interval is a fraction of successive cycles or half cycles of the supply. As mentioned above, the portion of the AC cycle used to power the controller preferably follows a zero-crossing point. As with the previous aspect of the invention, it is preferred that the power control is effected by a triac or the like.

Preferably means for storing power, e. g. a capacitor, is provided for smoothing the power supplied to the controller.

The interval over which the controller is powered, e. g. the proportion of each AC cycle utilised, will depend upon its power requirements. Where the power it requires is relatively fixed the length of the interval may be set accordingly. However, where its power requirements fluctuate there may be instances when the controller is insufficiently powered in a particular

cycle or over a longer period. This can give rise to undesirable effects such as flickering of the power to the load.

In preferred embodiments a voltage monitoring means is provided to monitor the voltage of the power supply to the controller. This will indicate whether the circuit is being powered sufficiently. For example the voltage across the smoothing capacitor may be measured if one is provided.

This result of the voltage monitoring could, for example, be used to vary the length of the interval over which the controller is powered, e. g. the proportion of the AC power supply cycle which it receives. In a preferred embodiment though, the voltage monitoring means comprises a comparator which is arranged so as to reduce or interrupt the supply of power to the load in the event that the comparator detects an insufficient voltage on the supply to the controller. In other words the controller is arranged briefly to deny power to the load if it is insufficiently powered itself.

A separate voltage monitor could be provided or alternatively a monitor of the voltage at the load could be used additionally to provide this monitor function.

Thus the firing of the triac can be disabled either by using a separate voltage monitor of the power supply or by monitoring the voltage on the load. Both methods improve the functioning of the device. The method chosen will typically be based on cost and performance issues.

Normally it is expected that such circumstances will not persist for long and the temporary lack of power to the load may not even be perceptible. This is particularly so where, as is preferred, the controller is powered during an interval in which the load is not powered, since if the load is not powered at all the controller my be powered exclusively. This will rapidly satisfy a temporary excessive power requirement on the

part of the controller.

Preferably the controller is arranged to prevent firing of a triac in any given cycle or half cycle in which an insufficient power supply voltage is detected.

The controller which has been heretofore described may be used on its own to control a load-e. g. as a direct replacement for a light switch or other electrical switch. Equally, a plurality of such controllers may be used in conjunction to control a load. Controllers used in this way could be completely independent of one another. For example if the controllers are able to act as changeover switches rather than simply on-off switches, they may be used in a classic'staircase light'configuration in which each of a pair of switches at the top and bottom of a staircase respectively is able to switch on the light if it is off or switch it off if it is on.

However, the Applicants have realised that it would be beneficial for a plurality of controllers which control the same load to be able to signal to one another. This allows much more flexible shared control and can also simplify the external wiring between the controllers. In a preferred embodiment for example, each controller is able to signal to the others that it has control over the load if that controller is operated by a user.

The controllers may use any convenient means to communicate with each other. Such means could be wired or wireless, possible examples being infra-red, ultrasonic or microwave transmission. The Bluetooth communications protocol could be used. Preferably though, the controllers communicate by means of a cable carrying power to the load-e. g. a mains cable in the example of a domestic electrical installation. The communication may take the form of a modulation of the AC power supply-e. g. a high frequency (compared to the frequency of the AC supply) amplitude modulation.

The Applicants have now realised however that by varying the point during the AC supply cycle at which a triac is made to fire (and thereby convey power to the load), a controller may signal to other controllers on the same power circuit since each of these can detect the change in voltage on the supply line when power is supplied to a load. In other words the controllers can determine when power is being supplied to the load by another controller.

This is novel and inventive in its own right, not just in the context of proximity sensor controllers.

When viewed from a further aspect therefore, the present invention provides a control network comprising first and second electrical devices connected or adapted to be connected to a common AC power supply, at least said first device being adapted selectively to power a load from said power supply by applying and/or removing power to the load at a predetermined point during successive cycles of the AC power supply, wherein said second device is arranged to measure the point in the cycle at which the first device applies or removes power to the load.

Thus it will be seen that the first device can signal to the second by means the timing of its application of power to the load. For example the first device could vary, from a predetermined nominal point, the point on the AC cycle at which it applies power or removes power to the load.

The signal thus transmitted could convey information for many different potential purposes. As will be appreciated, the amount of information that can be conveyed will depend upon the precision with which the second device can measure the timing of the application of power to the load. For example the signal could be a simple binary one with the first device either employing the normal timing or a different, say slightly later, timing. Alternatively

the signal could have many possible values.

If the signal takes the form of a deviation from a normal timing scheme it does not mean that the normal timing scheme need be constant. To illustrate, in some embodiments the average amount of power supplied by the controller is variable. For example a light may be dimmed or a motor slowed by applying less than maximum power.

In such embodiments the average power level could be applied by means of the mark-space ratio of whole cycles or half-cycles, but it is preferably determined by the gross point on the AC cycle or half cycle at which power is applied to the load. For example a light bulb could be operated at half brightness by applying power half-way through each half cycle. In such circumstances, it is intended that the precise point of the cycle at which power is applied will be a slight perturbation relative to this basic point, normally one sufficiently small that it has no significant effect on the average power applied. The second device may therefore be arranged to wait for a few cycles or half cycles to see whether a change in firing point corresponds to a change in average power or is temporary - indicating that the first device is signalling to the second. Alternatively the amount by which the firing point changes may make the distinction clear-for example if deliberate changes in brightness are only made in discrete steps which correspond to a change in the firing point larger than that used to signal.

When it is desired to apply full power to the load, the signalling in accordance with the invention will effectively take the form of a small gap in the applied power. Either the duration or this gap, or its gross point in the cycle, or both may be used to signal information.

As preferred embodiments of the previous aspects of the invention, the first device preferably comprises a

triac for controlling the load, the second device detecting the point (s) on the AC cycle or half-cycle at which the triac fires.

The first and second device could be configured simply as transmitter and receiver respectively of the signal but preferably at least one and preferably each is arranged both to transmit and to receive. This arrangement could, for example, simply allow an acknowledgement signal to be transmitted by the second device upon receipt of a signal from the first device; or it could range up to full two-way communication.

Most preferably the first and second devices have equal signalling functionality and, in the preferred embodiment, are the same.

It is envisaged that the second device could be integral, either physically or electrically, with the load itself. In other words, as well as powering the load, the first device may pass it further information.

This could, for example, instruct the load to operate in a particular mode.

In the presently preferred embodiments however, both devices are configured to be able to power the load individually. It is desirable in such circumstances that only one device has control at any given time.

Preferably therefore, the devices use the signalling mechanism described hereinabove to establish a'master' device which has control. The other device (s) may therefore be termed slave (s).

Preferably the devices are arranged such that a slave may signal that it wishes to take control and thus swap roles with the master. Preferably a or the slave device is arranged to apply power to the load before the master device, or remove power to the load after the master device (in other words to pre-empt the master) in order to signal that it wishes to take control. The master device can detect when power is being applied to the load other than when it is applying power itself and

deduce that another device is signalling.

Preferably the master device sends an acknowledgement signal by varying the point in the AC cycle or half cycle at which it applies power-e. g. even earlier than the original slave.

The amount of time by which the slave pre-empts the master in applying power to the load may be fixed.

Alternatively this time difference may be used to signal which of a plurality of devices is sending the signal, i. e. with each device being designated by a characteristic time delay (in this case the master could use the characteristic time delay to send its acknowledgement).

An example application of the principles set out above is a number of switch units which may all be used to turn a common light on or off. This could, for example, be a light for a stairwell with the switch units being at the top and bottom respectively. A user will expect to be able to turn the light on or off using either of the switches. So the light may be turned on using the switch at the bottom of the stairs. If the user then operates the switch at the top of the stairs, he will expect the light to be switched off. For this to happen the switch unit at the top (which will be a slave in the terminology above) will send a signal to the master by powering the light in a part of the AC cycle when the master is not. The master may then acknowledge and stop powering the light. If the switch unit at the top of the stairs is operated next, that unit may simply apply power to switch the light on, but if the switch unit at the bottom is operated next it will need to signal and receive an acknowledgement before continuing to power the light. Instead an alternative configuration could have control passing automatically to whichever unit is operated first from the'load off'condition.

Although there are known configurations of two

changeover switches connected to each other by two wires that will allow a light to be controlled by two separate switches, the embodiment of the invention described allows a simpler arrangement in that the control devices need only be connected by an ordinary cable.

Furthermore the arrangement of the invention is easily expandable to include further control units whereas the known arrangement is not.

Another advantage of arrangements in accordance with the invention is that the control devices may be arranged to apply variable power to the load-e. g. to dim a light.

The control devices in accordance with the foregoing aspect of the invention may be of any suitable form. Preferably though at least one and preferably both or all are proximity sensors; most preferably in accordance with the first aspect of the invention.

Certain preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figs. 1 to 3 are schematic block diagrams of known proximity sensors, shown for reference only; Fig. 4 is a schematic block diagram of a proximity sensor in accordance with the invention; Fig. 5 is a more detailed block diagram of the embodiment of Fig. 4; and Fig. 6 is a schematic block diagram of a further possible embodiment of the invention.

Turning to Fig. 1 there may be seen a known sensor arrangement in which the change in resistance between a sensor plate F and ground resulting from the user touching the plate is measured. This arrangement is a touch sensor rather than a proximity sensor.

Fig 2 shows a capacitive sensor. An oscillator A transmits electromagnetic waves via a transmitter plate B to a receiver plate. A voltage measurer D measure the voltage induced on the receiver plate C. When the

receiver plate C is approached, or touched through an insulating plate, the reception of the signal from the oscillator A is amplified or attenuated depending upon the relative capacitive coupling of the user's body to ground and of the user's body to the transmitter and receiver plates B, C.

Fig. 3 shows a similar arrangement but with no external oscillator. In this arrangement the presence of a finger or hand is measured by a change in the frequency of an RC oscillator caused by the resulting change in capacitance.

Fig. 4 shows a schematic block diagram of an embodiment of the present invention. This embodiment is a proximity sensor switch unit for switching a load 2 on or off. This load could, for example, be an electric light or motor.

The switch unit is in circuit between the live side 4 of the mains AC supply (e. g. 50 Hz, 240 V RMS in the UK) and the load 2. The other side of the load 2 is connected to the neutral side 6 of the mains supply.

The live side 4 of the mains supply is connected to a power supply unit 8. This is a standard configuration based on a Zener diode and smoothing capacitor but is novel in that it operates on a part of each mains half cycle before the load is powered. As well as powering the rest of the switch unit's circuit, the power supply unit 8 is connected to a voltage sensor 10 which is able to determine whether the smoothing capacitor is sufficiently charged to operate the circuit. The power supply explained in greater detail later with reference to Fig 5.

A conducting sensor plate 12 is provided, typically on the inside of the outer body of the switch unit such that a user may bring his or her hand close to it, whilst remaining electrically isolated from it. The sensor plate 12 is sufficiently reactively coupled to the live side 4 of the mains compared to its coupling to

earth that it follows the cyclically varying mains potential at a potential of approximately I 310 V (the full mains potential being approximately I 340 V for a 240 V RMS supply). However when a user's fingertip 13 is brought into close proximity of the sensing plate 12, the capacitive coupling to earth Hearth will increase relative to that to the mains live 4 and so the amplitude of the cyclic variation in potential on the sensing plate 12 will be reduced to approximately I 290 V.

The potential of the plate is measured by a high impedance voltage measurer 14 connected to it.

Alternatively a charge pump could be used. The measured voltage is fed into the circuit intelligence 16, which may be based based around a microprocessor. The circuit intelligence 16 is thus able to detect the change in the potential on the plate resulting from a user's hand being brought near it.

The microprocessor 16 determines when to fire the triac 18 and therefore when to apply the mains live 4, by means of the triac 18, to the load 2 in order to power it. The microprocessor 16 also takes inputs from the PSU voltage sensor 10 and a load voltage sensor 20.

The microprocessor 16 is arranged so that if the PSU voltage sensor 10 returns an output below a predetermined threshold voltage indicating that the smoothing capacitor of the PSU 8 is insufficiently charged, it will suppress firing the triac 18 in that particular mains cycle or half-cycle. This allows the capacitor to be charged during that cycle or half-cycle and prevents unstable operation of the switch unit, such as flickering, as may occur when an insufficient voltage is applied.

The load voltage sensor 20 measures the voltage on the load 2 with respect to earth and is therefore able to determine whether power is being applied to the load, and at what point in the mains cycle or half-cycle.

This enables the microprocessor 20 to determine if another similar switch unit (not shown) controlling the same load is sending a signal by applying power to the load at an earlier point in the cycle or half cycle than the switch unit shown in Fig. 4.

A more detailed schematic circuit diagram is shown in Fig. 5. The same reference numerals are used for elements common to Fig. 4. For reasons of clarity, only certain discrete components are depicted. A person of ordinary skill in the art will be able to determine appropriate values and positions for the other components which are not shown.

The first point to note regarding Fig. 5 is that only two wires are required to connect the switch unitto the live side of the mains 4 and the load 2 respectively.

Within the switch unit, the triac 18 is connected between the load line 2a and the live line 4. The trigger terminal 18t of the triac is connected to the microprocessor 16 by means of a resistor Rl and a capacitor Cl. Power to the circuit is provided by a power supply unit comprising a zener diode 22, a diode Dl, an electrolytic smoothing capacitor 24 and a serial resistor and capacitor arrangement R2, C2. The circuit shown uses the mains live side 4 as its reference voltage-i. e. the mains live 4 is taken to be the local 0 V. The arrangement is such that when the triac 18 is off, a residual current passes through the load 2, the resistor R2 and capacitor C2 and the diode Dl to charge the smoothing capacitor 24. The diode Dl provides halfwave rectification, although when the load is being powered, only the first few milliseconds of each cycle is used to charge the capacitor. The zener diode 22 limits the voltage across the capacitor to approximately 10 volts.

The charging current is of the order of a few microamps and is therefore insignificant in comparison

the load's normal operating current. When the triac 18 is fired however, the load supply line 2a is pulled down to the live line 4, i. e. the local 0 V reference. The capacitor 24 therefore stops charging.

As well as deriving power from the capacitor 24, the microprocessor 16 monitors the voltage across the it. This allows it to suppress firing of the triac 18 if the smoothing capacitor 24 has not sufficiently charged to operate the circuit stably.

The microprocessor 16 also has an input 26 connected to a voltage divider R3, R4 connected between the load line 2a and the live (local OV) line 4. This allows the microprocessor 16 effectively to measure the potential difference across the load 2. The microprocessor 16 can thus determine whether power is being applied to the load at any given instant-e. g. by a similar switch unit.

The metallic sensor plate 12 is shown in Fig. 5 connected to the base of a voltage measurer configuration 28. Alternatively a charge pump could be used. Although there are no specific discrete components, by virtue of its physical disposition within the apparatus-specifically its proximity to the mains live line 4-the sensing plate 12 is reactively coupled to the live line 4.

The voltage measurer 28 is coupled to the microprocessor by a capacitor C3. The microprocessor 16 is thus able to monitor the AC voltage on the plate 12 via the voltage measurer 28.

The circuit shown in Fig. 5 operates as follows.

For this exemplary explanation, the load 2 comprises a light bulb. In the quiescent state (with the bulb off) the voltage on the sensing plate 12 (with respect to earth) follows the variation of the mains voltage on the live side 4 at a potential of t 310 V. Taking the live line 4 as reference potential, the potential on the plate 12 will therefore vary sinusoidally with the same

period between 0 V and 30 V. This is measured by the microprocessor 16 via the voltage measurer arrangement 28 and coupling capacitor C3.

During the first, positive-going, part of each mains cycle the smoothing capacitor 24 is charged up to approximately 10 V limited by the zener diode 22.

When the user brings his or her hand into close proximity with the sensor plate 12, the capacitive coupling of the user's body with earth pulls down the potential on the sensing plate 12 with respect to earth to approximately I 290 V. This increases the potential difference between the plate 12 and the live line 4 which is measured by the configuration 28.

The microprocessor 16 recognises the increased amplitude of this signal beyond a threshold and issues a pulse to the triac trigger 18t to fire the triac 18.

This pulse is issued 1 millisecond into the 10 ms half-cycle of the 50 Hz mains supply, measured from the zero-crossing point. The first millisecond of the half-cycle is used to recharge the smoothing capacitor 24. The microprocessor 16 measures the voltage across the capacitor 24 at the end of this 1 ms period and compares it with a predetermined threshold for corresponding to the minimum amount of charge required to operate the circuit for a cycle. The microprocessor 16 will only trigger the triac 18 to fire if this threshold is exceeded.

Once the triac 18 is fired, the microprocessor will trigger it to fire 100 ms into every mains half-cycle so that the light bulb 2 will remain lit. It will continue to do this until the user again brings his or her hand into the proximity of the sensing plate 12, thereby increasing the amplitude of the AC signal derived from it, as explained above. In other words the circuit toggles between the on and off states whenever a user's hand is sensed. However other configurations are possible for example there may be separate sensing

plates for switching on and off respectively, or the microprocessor could be arranged to switch the load on for a predetermined time.

Although the power supplied to the light bulb 2 is less than the theoretical maximum since it is only applied for 9/10 of each half-cycle, in practice the reduction in power is onyl approximately 0. 4% which is too small to be noticeable.

The microprocessor 16 also monitors the voltage across the light bulb 2 by means of the voltage-divider R3, R4 via its input 26. This input part 26 also detects whether the mains is in a positive or negative half-cycle (the appropriate bias network not being shown, but being easy to construct by those skilled in the art) and is thus able to determine the zero-crossing point.

If the voltage across the load should be pulled down to the live potential (local 0 V) 100 microseconds before the triac 18 is fired, it is interpreted that another switch unit has signalled to the switch unit that it wishes to take control of the light. The microprocessor responds to this with an acknowledgement by firing the triac 100 ns earlier still-i. e. only 0.8 ms into the half-cycle. The increase in power resulting from this is negligible, particularly as it only applies typically for two half-cycles. If the light 2 is on when such a request is received, the microprocessor 16 will turn it off once the acknowledgement has been sent.

In another embodiment (not depicted) the control units are able to dim the bulb rather than just turning it on or off. The microprocessor in this embodiment has two sensing plates for increase and decrease of brightness respectively (the lowest level of brightness being off). In this embodiment the nominal firing point of the triac is not fixed (e. g. at 1 ms) but is variable to give differing brightness levels. Thus before a

control unit can send a signal to another, it must ascertain where on the cycle the light is presently being powered. This is easily done using the load voltage monitor, like the voltage divider R3, R4 of Fig. 5. Once this has been ascertained, the control unit can send a signal by firing its triac 100 As before the currently determined firing point.

It will be seen that in this embodiment the signalling between units allows one to take control from another smoothly by sending a signal to the current master, receiving an acknowledgement and then in the next half-cycle the previous master can cease firing its triac whilst the new master begins to fire its triac at the point in the half-cycle corresponding to the appropriate brightness level (one up or one down from the previous, depending upon which sensor plate sensed the user's hand.

Finally Fig. 6 shows schematically a further embodiment which makes use of a known arrangement comprising an external oscillator 30 and transmitter plate 32 for sensing proximity of the user's hand, but which utilises the novel and inventive signalling arrangement between switches. This operates in exactly the same way as the embodiment described with reference to Figs. 4 and 5 except for the reactive coupling between the sensor plate 12 and live line 4.

It will be appreciated by those skilled in the art that many variations on the described embodiments are possible within the scope of the invention. For example the load being controlled need not be a light but may be any other suitable load, for example one containing a motor.

Also the signalling method proposed is widely applicable. It will be appreciated that such signalling could instead comprise one control maintaining power after the controlling one has removed it, rather than applying power before the controlling one.

Claims

Claims : 1. A controller for controlling the supply of electrical power to a load, comprising an AC power supply inlet, and a sensing means at least partially capacitively coupled to the AC power supply such that in use the potential of the sensing means follows that of the AC power supply, the sensing means further being arranged such that in use the degree of coupling and thus the amplitude of its potential increases or decreases when a part of a body is brought into the proximity of the sensing means.
2. A controller as claimed in claim 1 comprising only two external connections
3. A controller as claimed in claim 1 or 2 arranged so that the load is controlled as part of the controller circuit.
4. A controller as claimed in claim 1,2, or 3 wherein said load and said controller are arranged to derive power from the same source.
S. A controller as claimed in any preceding claim arranged to derive power during an interval which is not used to power the load.
6. A controller as claimed in claim 5 wherein the controller is powered during a fraction of successive AC power supply cycles or half-cycles.
7. A controller as claimed in any preceding claim comprising a triac for applying power to said load.
8. A controller as claimed in claim 7 wherein the triac is used to control power to the load in a

substantially zero-crossing configuration.
9. A controller as claimed in any preceding claim wherein power is applied to the load a short period of time after the zero-crossing point of each cycle or half-cycle of the AC power supply.
10. A controller for controlling the supply of power from an AC power supply to a load wherein the controller is arranged to be powered from the AC supply during an interval in which the load is not powered.
11. A controller as claimed in claim 10 wherein the interval is a fraction of successive cycles or half cycles of the supply.
12. A controller as claimed in claim 11 wherein the portion of the AC cycle used to power the controller follows a zero-crossing point.
13. A controller as claimed in claim 10,11 or 12 comprising a triac or the like for supplying power to the load.
14. A controller as claimed in any of claims 9 to 13 comprising means for storing power for smoothing the power supplied to the controller.
15. A controller as claimed in any preceding claim comprising a voltage monitoring means for monitoring the voltage of the power supply to the controller.
16. A controller as claimed in claim 15 comprising a comparator arranged to reduce or interrupt the supply of power to the load in the event that the comparator detects an insufficient voltage on the supply to the controller.
17. A controller as claimed in claim 15 or 16 arranged in use to prevent firing of a triac in any given cycle or half cycle of the AC power supply in which an insufficient power supply voltage is detected.
18. A network of controllers as claimed in any preceding claim arranged to control a common load and further being adapted to signal to one another in use.
19. A network as claimed in claim 18 wherein said controllers are arranged to communicate by means of a cable carrying power to the load.
20. A network as claimed in claim 19 wherein at least a first controller is adapted to signal to a second controller by varying the point during the AC supply cycle at which the first controller supplies power to the load.
21. A control network comprising first and second electrical devices connected or adapted to be connected to a common AC power supply, at least said first device being adapted selectively to power a load from said power supply by applying and/or removing power to the load at a predetermined point during successive cycles of the AC power supply, wherein said second device is arranged to measure the point in the cycle at which the first device applies or removes power to the load.
22. A network as claimed in claim 20 or 21 wherein the average power level applied to the load is determined by the gross point on the AC cycle or half cycle at which power is applied to the load.
23. A network as claimed in claim 20 wherein said first device comprises a triac or the like for controlling the

load, the second device being arranged to detect the point (s) on the AC cycle or half-cycle at which the triac fires.
24. A network as claimed in any of claims 19 to 23 wherein at least one and preferably each of said first and second devices is arranged both to transmit and to receive said signal.
25. A network as claimed in any of claims 19 to 24 wherein the devices are arranged to signal one another to establish a master device which has control over the load at a given time.
26. A network as claimed in claim 25 wherein another of said devices is arranged to apply power to the load before the master device, or remove power to the load after the master device, in order to signal that it wishes to take control.
27. A network as claimed in claim 25 or 26 wherein the master device is arranged to send an acknowledgement signal by varying the point in the AC cycle or half cycle at which it applies power.
28. A network as claimed in any of claims 20 to 27 wherein at least one of said first and second devices comprise proximity sensors.
29. A network as claimed in any of claims 20 to 28 wherein at least one of said first and second devices comprises a controller as claimed in any of claims 1 to 17.
30. A controller for controlling the supply of electrical power to a load, comprising an AC power supply inlet, and a sensing means partially coupled to

the AC power supply such that in use the potential of the sensing means follows that of the AC power supply, the sensing means further being arranged such that in use the degree of following the AC power supply increases or decreases when a part of a body is brought into the proximity of the sensing means.
31. A controller or network substantially as hereinbefore described with reference to Figs 4 to 6 of the accompanying drawings.