GB2507197A - Emergency lighting system that monitors mains supply by capacitive coupling - Google Patents

Abstract

An emergency lighting module for domestic premises comprises an effector module 4 in the form of a battery powered emergency light coupled to a mains sensor module 2 by a low voltage cable 6. The mains sensor module 2 is configured to detect a loss of mains electrical power and transmit an actuation signal to activate the emergency light 4. Mains power is monitored by non-contact capacitive coupling whereby a clip (100, fig. 7) comprising two copper strips (102 & 104, fig. 7) attaches to the outer casing of a mains supply wire (106, fig. 7). Since no direct electrical contact to the mains is required, the system may be easily installed by someone without electrical qualifications. Single or multiple emergency lights may be actuated by a single sensor module via either wired or wireless means. The effector module 4 may take alternative forms than that of a light, such as an audible alarm, sprinkler, fire extinguisher, etc.

Description

Title: Improvements in or Relating to Power loss-Actuated Systems

Field of the Invention

The present invention relates to a power loss-actuated system, specificafly an electrical power loss-actuated system, and in particular an emergency lighting system. The invention also relates to a method of operating such a system, and a method of installing such a system.

Background of the Invention

It is known to provide emergency systems which are normally quiescent or dormant but which are actuated by loss of electrical power within a facility or building, especially loss of a mains electrical power supply (e.g. due to a power outage, fire, flood or the like). In particular, buildings, especially commercial or industrial buildings, arc required to posscss emergency lighting systems which can come into operation in the event of failure (e.g. due to fire or power failure) of the normal lighting system. In the UK, emergency lighting systems are specified in BS5266.

Emergency lighting systems generally comprise either self-contained emergency lights or a central system. The self-contained emergency lights are individual light fittings, fed from the mains, with internal batteries that arc kept charged and are available, upon mains failure, to operate a lamp or lamps for a limited period -typically about 3 hours in the UK. Central systems comprise a central power supply and protected cables that are used to operate emergency light fittings from the central supply.

Self-contained fittings arc gencrally cheaper to buy and install, whereas central systems generally have a lower whole-of-life cost due to longer-life batteries and lower maintenance costs.

Emergency lighting is an essential emergency facility in many buildings, and as such must be installed and maintained by competent engineers. There is no legal requirement for domestic household properties to be protected by emergency lights: it is left to a home owner to decide if they require it and because of the cost and disruption of installing emergency lighting, most

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people opt to rely on torches, candles and the like. Unless the torches arc used regularly it is possible that they will be non-operational when needed in an emergency.

Due to the number of accidents and injuries linked to poorly installed or maintained electrical systems in homes, legislation has been introduced in the UK to discourage home owners from installing electrical products themselves, and requiring that electrical installers must be suitably qualified to perform the work in residential properties.

The essential feature of emergency lighting is that it is kept ready for operation in the event of an emergency and that it operates automatically in the event of failure of the mains supply.

Some systems have features that allow the emergency lighting to be turned off to save power for when it is needed, and in such cases it may be possible to bring the emergency lighting back on manually, but emergency lighting must always operate in the event of the mains failing and as such it is essential for the emergency lighting system to monitor the mains to determine when there is a failure.

Emergency lighting systems, including those of the central battery-type, are known to include sub-circuit monitoring or phase failure monitoring. Sub-circuit monitoring normally utilises relays to monitor the power supply to a local lighting sub-circuit. Phase failure monitoring monitors all three phases of a (three phase) AC supply, and failure of any one of the phases will normally trigger the emergency lighting. These monitoring systems are in electrical contact with the mains supply being monitored.

Emergency lights are usually installed such that they are connected to the mains supply and incorporate a rechargeable battery (either internally for self-contained, or remotely for central systems) that is kept filly charged by a battery charger operated from the mains supply.

Rechargeable batteries are normally employed so that they can be tested, to verify that they operate for the required duration and then be recharged again ready for operation when needed. The operation of keeping the batteries charged means that energy is constantly being used, albeit at a low level, and this energy is essentially being wasted and is part of the cost of keeping the system ready. Some battery technologies require more energy than others to keep the battery in the fully charged stage.

A particular object of the prcscnt invention, in prcfcrrcd embodiments, is to provide an emergency lighting system that complies with the main essential feature of emergency lighting, i.e. that it operates automatically; but that does not require a connection to the mains supply, so it can be installed by a non-skilled person; it uses a primary battery that does not consume energy to keep it charged and so is attractive for the home owner. The battery status is preferably monitored and a warning is given if it needs to be replaced and desirably the operation of the emergency light can be tested and switched off when not required.

Summary of the Invention

In a first aspect, the invention provides an electrical power loss-actuated system, the system comprising at least one effector module and at least one electrical power sensing module, the power sensing module being adapted and configured to detect, by non-contacting means, a loss of electrical power and, in thc event that a loss of electrical power is dctcctcd, to transmit an actuation signal to the at least one effector module.

The effector module preferably comprises a light, such as an emergency light or luminaire, but could in theory be some other sort of effector, such as an audible alarm, a sprinkler or gaseous (e.g. halon-based) fire extinguisher, a sign, door lock, generator start-up system, a gas valve shut-off system and the like.

"Non-contacting means" in the present specification, is intended to indicate that there is no electrically-conducting contact between a mains conductor being monitored and the sensing module. The sensing module operates by establishing a capacitive coupling with the mains conductor being monitored. It will be apparent to those skilled in the art that, unlike conventional power monitoring systems, the sensing module of the system of the invention is not in electrically-conducting contact with the electrical power supply (typically a mains electrical supply) being monitored.

The actuation signal may be transmitted to the effector module from the sensing module by means of a wireless communication or, more preferably, by means of a wired connection.

Thus, in preferred embodiments, there is an operable electrical contact between the sensing module and the effector module, such as a simple electrical lead or flex. It is also envisaged that both the sensing module and the effector module could be combined in a single unit (e.g. with a common housing), and indeed this arrangement may be preferred in some circumstances (e.g. a simple unit intended for use in householder and domestic contexts).

As explained above, the sensing module operates by means of "capacitive coupling" (or electrostatic induction) -this is a voltage-induced effect -rather than detecting the flow of current in the mains electrical supply. This is because, inter a/ia, monitoring systems which use electromagnetic induction require the passage of a current through the conductor being monitored. This implies that there is a load which is consuming power. This might lead to inappropriate actuation of the system if, for example, the circuit being monitored is a lighting circuit and all the lights are switched off -which an electromagnetic monitoring system would incorrectly interpret as a mains failure.

Typically the sensing module may comprise a capacitance to earth, to facilitate sensing of the mains voltage. Thus, for example, the sensing module may comprise a large capacitance relatively remote from the electrical power source being monitored, and a relatively small capacitance close to the power source (e.g. a mains cable) being monitored.

Preferably the present invention makes use of a balanced sensor that overcomes the potentially variable characteristics of the large and small capacitances noted above. In particular the sensor utilised in the present invention does not necessarily require any relationship to earth, and so can be positioned anywhere in a building either close to, or remote from, metal objects, whilst still providing a consistent differential signal. Preferred embodiments of balanced sensors comprising two parallel conducting tracks or elements are discussed in greater detail below.

Desirably the sensing module will not simply detect a voltage but will also monitor a change in the voltage. In this way, a static electrical charge near the sensor will not cause the sensing module to generate an erroneous output. Accordingly, the sensing module will desirably monitor variation of the detected voltage to check that the detected voltage varies with time in an expected manner. Thus, in the UK, mains voltage a.c. frequency is 50Hz, and the sensor would preferably monitor the voltage over at least 10 cycles (advantageously 20 cycles or more). In the USA, mains ac frequency is 60Hz. Other countries normally use either 50 or 60Hz ac mains supplies. Accordingly the sensing module is preferably capable, and indeed preferably configured and adapted, to be used to detect/monitor both a 50 or 60Hz ac supply.

The sensing module may monitor the power supply continuously or intermittently (thereby reducing power consumption). The frequency of monitoring may be for example once a minute, desirably at least once every 10 seconds and preferably at least once a second, in order to ensure prompt actuation of the emergency system in the event of a power-loss.

Advantageously the sensing module comprises or is operably associated with a microprocessor. In a preferred embodiment the sensing module comprises or is operably associated with an amplifier. Conveniently the amplifier amplifies the ac differential signal detected from a mains cable being sensed, and blocks the ac common mode signal. The dc input impedance of the amplifier, and the capacitance of the coupling, both block dc signals.

Desirably the microprocessor analyses the lengths of the pulses in the amplifer output (e.g. by detecting the "zero crossing" points in the cycle and counting the number of such points in a given period).

In preferred embodiment the sensing module searches over an approximate half-cycle of mains (8-lOmSec), and a counter is used to count good' pulses. Typically a plurality of consecutive good pulses (e.g. about 10) are required for the sensing module to consider that the mains supply is present, and a plurality (e.g. about 5) of consecutive "bad" or absent pulses are required to trigger the system to indicate a failure in the mains supply. It will be appreciated that each pulse can correspond to a respective half cycle in the ac mains voltage.

In the UK, mains power supply cables comprise at least two wires -a live and a neutral wire.

The sensing module in the system of the invention conveniently operates by sensing the difference in voltage between the live wire and the neutral wire. In a preferred embodiment, the sensing module will comprise two conducting elements or tracks, which conveniently will be arranged substantially parallel to one another, and the sensing module will advantageously be positioned (as close as possible to the mains cable being monitored) with the conducting elements or tracks placed substantially parallel to the live and neutral wires in the mains cable.

The actual shape of the two conducting tracks or elcmcnts is not critical, although thc applicant has found flat copper strips, 2-3mm wide and 35tm thick, to be effective.

Conveniently the two conducting elements or tracks are spaced apart with a spacing in the range 2-10mm, preferably 5-10mm. Preferably the two conducting tracks or elements are each about 10-50mm in length, more preferably about 20-40mm.

Desirably the two conducting elements or tracks are substantially parallel to the live and neutral conductors of a mains cable being sensed by the sensing module. Preferably the two electrically conducting tracks or elements of the sensing module are positioned between 0 and 25mm from the outer surface of an insulated mains cable being sensed by the sensing module.

In a preferred embodiment, the sensing module comprises a fixing (especially a snap fit fixing or clip fixing), which fixes to an insulated mains cable to be sensed, and which fixing retains the two electrically conducting tracks or elements of the sensing module in a desired orientation (i.e. substantially parallel) to, and a desired distance from, the conductors in the mains cable.

The two tracks or elements can act as a dual antenna which operates as a type of balanced sensor. Either element can detect a signal on the live or neutral conductor of the mains supply, the system providing a balanced close field capacitive sensor means that does not require a ground return path.

There are at least two approaches for sensing of the mains power supply: a) make the sensor very sensitive so that it will pick up any signal and assume that when the mains power fails all of the signal falls away; or b) sense the mains signal and establish a sensing threshold automatically so that the sensing module looks for that same signal level once the device is in operation. If the detected mains voltage signal falls below the threshold, an actuation signal is sent to the effector module.

It will be apparent to those skilled in the art that it may not be necessary for the mains power supply to fall to undetectable levels in order for the sensing module to actuate the effector module. For example, the monitored mains voltage may be detectable but below a desired threshold value, which is sufficient for the emergency system to be actuated. Thus the term "loss of electrical power" is not intended to be absolute, but is intended to encompass situations in which the level of electrical power supply falls below a desired minimum (e.g. about 50-60% of normal operating power levels).

A suitable microprocessor range for use in the sensing module is called the PlC 10 series (available from Microchip Technology Inc., Chandler AZ85224, USA) and have sufficient number of pins (6 or 8). There are versions which have an A to D converter, and/or which have an integral non-volatile memory, such as an EEPROM. When the sensing module is installed, the sensor may calculate the threshold signal, which is then stored in a non-volatile memory. A tab or the 111cc may be removed to connect the battery, which starts up the microprocessor which goes through a start-up/calibration routine and flashes a status indicator LED to indicate all is well and then settles down to monitor the presence of mains, or flashes the status indicator LED in a different pattern to indicate that there is no mains detected or that self-calibration could not be performed.

The sensing module (or the combined sensing/effector module where the two modules are accommodated in a single housing) is typically in the form of a small unit designed to locate over or clip onto the exterior of the (insulated) mains cable that is to be monitored. In a preferred embodiment, it is adapted and configured to operate on a single cable containing live, neutral and earth conductors, but will not operate on a screened cable such as SWA. A high impedance sensor is designed to sense the presence of mains voltage, specifically to detect for the presence of 50 or 60Hz ac and will not respond to DC voltages. The mechanism of detection is capacitive coupling, (or electrostatic induction). The preferred capacitive coupling mechanism is to sense the presence of mains voltage, rather than to detect the flow of current, which would be achieved by a current transformer or Hall-Effect sensor based on electromagnetic induction.

Conveniently a low voltage signal is passed from the sensing module to the effector module, where it is monitored. Actuation of the effector module may be caused by creation of a signal, when no signal is normally generated if mains power is present, or conversely by inhibition or blocking of a signal which is routinely generated if mains power is detected.

The effector module preferably comprises an emergency light, and conveniently takes the form of a substantially self-contained luminaire. Accordingly, in a preferred embodiment, the effeetor module will comprise a high efficiency light source (e.g. one or more LEDs), a battery, and a control unit.

The control unit is designed to operate at very low power so as to maxirnise the life of the battery. It monitors the output from the sensing module and if the voltage signal drops it will him on the LED(s) for a predefined time, e.g. one hour. This allows the effector module to operate for more than a single mains failure. The control unit may also monitor the battery condition and generate a warning signal (visible and/or audible) when the battery needs to be replaced.

In one embodiment, the sensing module detects the presence of mains electricity and monitors the level thereof to calibrate itself on the average signal (the reference level'). It will then operate the emergency light if the monitored mains voltage drops below a predetermined percentage (say, 60%) of the normal reference level. If the mains voltage rises to or above a predetermined percentage (say 85% or more) of the reference level then the emergency light is turned off again. If the sensed mains voltage changes by a small amount, but stays constant at the new level, then the unit will update its reference level to the new figure.

The control unit may also monitor the state of the battery (e.g. remaining charge or battery life). The precise measurement will depend on the battery technology used, but could simply be based on the off load battery voltage, alternatively it may be based on the battery internal resistance. The latter is measured by turning on the LED for a very short duration and measuring the increase of battery voltage when the LED is turned off In preferred embodiments, the cffector module will also comprise a visual indicator, such as one or more low power consumption indicator LEDs (different to the LED or LEDs used as the emergency light source), which may be coloured (e.g. green, red or one green and one red LED). Additionally, or alternatively, the effector module may comprise an audible alarm, such as a blccper.

When the battery is determined to be reaching the end of its life the indicator LED andlor bleeper may be operated intermittently to draw the attention of an individual (e.g. maintenance engineer, or householder in a domestic setting) to the fact that the battery needs to be changed.

In other embodiments, the visual indicator could be the same as the emergency light source, but operated for a series of short flashes, rather than continuously.

As the system of the present invention is primarily (but not exclusively) intended for residential use, readily available battery types are preferably selected to make battery changing easier. Suitable examples include alkaline or lithium-based batteries in AA, AAA, C, or PP3 sizes.

The above description describes an embodiment in which the mains sensor and the light fitting are connected together (e.g. by a low voltage cable). An alternative approach could be to connect them functionally, but not physically, via a radio signal. In such embodiments a battery or power source would be needed in both the sensing module and the effector module.

In the event of a failure of the mains a radio signal is sent by the sensing module and the emergency light turns on. A single sensing module could be used with multiple emergency light modules in this case.

If test controls and inhibit controls are required then they can be fitted to the units as described. The test control will simulate the absence of mains and the inhibit control will send a signal to the controller to switch off the emergency light and to not switch it on again until mains is sensed to return and then fail again.

In one embodiment, the system comprises: an emergency light fitting, having an enclosure, a light source and a battery; a remotely mounted mains sensor; and a control unit, which may be mounted in the sensing module, or in the effector module, or there may be provided a control unit in each of the sensing and effector modules; such that the emergency light can be mounted where it is required and the mains sensor module can be conveniently located where the mains is. An interconnecting cable may be used to monitor the mains and is not required for the operation of the light once the mains has failed, so it does not need to be fire rated. It may also operate at extra low voltage, so could be low cost bell wire.

Several different embodiments of the system are envisaged. In one, a general purpose light fitting is intended to be used in a variety of applications -above stairs, adjacent to fuse boards, in rooms, at emergency doors. Another embodiment comprises an emergency lighting system comprising an illuminated sign, which can be used to highlight where the exit door is, or can be used to point in the direction of where it is located. Yet another embodiment comprises a projector fitting, which can be used to illuminate a specific part of a building, but is located remotely from the feature it is illuminating. Yet a further embodiment comprises a special purpose product, which might be designed to be incorporated in a fuse box or alternatively a torch, located on a bracket, which can be removed and used where required in the event of a mains failure.

It will be appreciated that these embodiments are not mutually exclusive, and an emergency system according to the invention may comprise elements of any of the aforementioned embodiments.

In a second aspect, the invention provides a method of operating a power loss-actuated system, the method comprising the use of a system in accordance with the first aspect defined above.

In particular, the invention provides a method of operating an emergency lighting system, the emergency lighting system comprising a system in accordance with the first aspect of the invention, comprising at least one mains electrical power supply sensing module and at least one emergency lighting luminaire actuated by the sensing module in the event that the sensing module detects a failure in mains electrical power supply.

The prefened features of the system of the first aspect of the invention will, unless the context dictates otherwise, generally be incorporated into the method of the second aspect of the invention.

In a third aspect, the invention provides a method of installing a power loss-actuated system in a building, the method comprising the steps of installing at least one sensing module in a position such that it can detect andlor monitor mains electrical power supply by electrostatic inductive means, installing at least one effector module, and establishing signal connectivity bctwccn the sensing moduic and the cffcctor module, such that a signal generated by the sensing module in the event of a mains electrical power supply failure can be transmitted to, and cause actuation of, the at least one effector module.

The signal may be tranmitted by an electrical contact (e.g. low voltage cable) between the sensing module and the effector module. Altematively the signal may be transmitted wirelessly, in which case the sensing module will have a power source, typically a battery, contained within the module.

If desired, a single sensing module may transmit an actuation signal to a plurality of effector modules. This is achieved most conveniently by means of a wireless signal, but could also be accomplished by transmitting a signal along two or more wires.

The invention will now be further described by way of illustrative example and with reference to the accompanying drawings, in which: Figure 1 is a schematic representation of one embodiment of a system according to the invention; Figures 2 and 4 are circuit diagrams showing some of the components and the arrangement thereof in two different embodiments of a sensing module for usc in a system according to the invention; Figures 3, 3 & 6 arc circuit diagrams showing somc of thc components and the arrangement thereof in three different embodiments of an effector module for use in a system according to the invention.

Figure 7 is a sketch drawing showing one embodiment of a sensing module for use in apparatus in accordance with the invention, positioned relative to a mains cable which the sensing module is to monitor; and Figures 8-11 illustrate schematically one embodiment of an algorithm used by a microprocessor programmed to run in apparatus in accordance with the invention.

Examples

Example 1

A system according to the present invention is an emergency lighting system. The system comprises a sensing module 2 and an effeetor module 4, which are electrically connected via a low voltage cable 6.

The sensing module senses the voltage in a mains supply cable (not shown), which supplies electrical power to the normal lighting in a building. The sensor is not electrically connected to the mains supply and works by electrostatic inductance, in the event that the mains voltage falls below a threshold value, the sensing module sends an actuation signal, via cable 6, to the effeetor module 4. Similarly, if the electrical cable connection 6 between the sensing module 2 and the effector module 4 is severed, the effector module is actuated.

The effector module has a housing and comprises one or more high efficiency LEDs which act as an emergency light source, a battery to power the LEDs, an LED status indicator light and an audible alarm (bleeper).

Circuitry can be added to limit the length of time of discharge of the battery in the effector module, based on a timer, or based on an electrical property of the battery (e.g. residual charge). Alternatively, the emergency light source can be operated until the battery is depleted and insufficient power remains to power the emergency light source.

Example 2

The layout of the main components in an embodiment of a sensing module for use in the system of the invention (such as the embodiment illustrated schematically in Figure 1) is shown in schematic form in Figure 2.

Referring to Figure 2, a sensing module comprises a substrate, such as a PCB.

Two substantially parallel conductive tracks on the PCB are designed such that they are approximately spaced apart by the same distance as the live and neutral conductors in a mains wire to be monitored (e.g. typically about 3mm apart). The tracks are about 30mm long.

The two conductive tracks are connected to points SI (8) and S2 (10). UI (12) acts as an amplificr with input impcdancc in excess of IM ohm. When mains power is present the mains voltage is electrostatic inductively coupled to the two tracks and the amplifier Ui generates a square wave at its output with a frequency substantially matching that of the mains, i.e. 50 or 60Hz. A PIC1OF2O6 microprocessor, (14) is programmed to operate its output when it senses 50 to 60 Hz at its input.

When the output of microprocessor 14 turns on, it turns on QI (16) which takes an increased current from the power supply which is connected to via the cable (6) that interconnects the sensor module (2) to the emergency luminaire (4). The cable is connected via a diode bridge so that the polarity of the cable is unimportant.

Thus the operation of the unit is to take an increased current from the connection to the emergency luminaire when mains is prescnt in the cable that is bcing monitored.

Example 3

The layout of some of the components in one embodiment of an cffcctor module (an emergency luminaire in this instance) for use in the system of the invention is shown in schematic form in Figure 3. The effector module is intended for use with a sensing module as described in Example 2.

The module comprises a housing formed entirely or predominantly of a synthetic plastics material. The housing houses one or more high efficiency LEDs which act as an emergency light source, one or more batteries, a status indicator LED, an audible alarm, and associated circuitry, which latter is illustrated in Figure 3.

Referring to Figure 3, the function of the circuit is to turn the emergency light on or off, depending on the current drawn by the sensor circuit (shown in Figure 2) located in the sensing module. When mains voltage is sensed by the sensing module 4 the current drawn by the sensing module is sufficient to turn on Qi (20) in the effector module. Qi turns off Q2 (22) so that the emergency luminaire does not operate.

However, if the current in the cable (6) is reduced, either by the cable being broken or disconnected, or by mains power no longer being sensed by the sensing module 4, then Qi (2) turns off, which allows Q2 (22) to turn on via R3 (24) and this turns on the emergency light.

The battery of the emergency light is arranged to be connected to V+ and Ov and the emergency light source, e.g. an LED is connected between connections C and D. The details of the power supply, current limiting components and battery isolation switches (to ensure that the unit does not operate in storage) are all omitted for clarity.

Example 4

This example relates to a different embodiment of the mains sensing module. The arrangement of components is described with reference to Figure 4, and the general arrangement is similar to the embodiment illustrated in Figure 2, and like components are denoted by common reference numerals.

The amplifier 12 could be incorporated within the microprocessor 14 (since in some embodiments the microprocessor, such as the PlC 10F206 has an integral comparator), but is shown separately for clarity.

In the embodiment illustrated in Figure 2, the output of the microprocessor 14 operates when mains is present causing a change of current in the supply wires, thus allowing sensing the module to sense whether or not mains is present. This type of signalling is reliable, but not very energy efficient. The embodiment illustrated in Figure 2 is intended to operate from a primary battery, and a continuous load indicating mains present would rapidly discharge the battery.

Accordingly, in the improved arrangement illustrated in Figure 4, a power supply capacitor (30), Cl, is incorporated and diode D5 (32) allows a negative pulse to be applied to the supply wires. Therefore at a convenient frequency the PICIOF2O6 microprocessor (14) is able to pulse the supply terminals and the luminaire end is able to sense the pulse to confirm that mains is present. If no pulse is sensed for, say, 3 seconds, then the emergency luminaire would determine that mains has failed and then operate its circuit. Diode 32 allows the voltage on the supply wires to change without upsetting the supply to the microprocessor.

Example S

Yet another embodiment is illustrated in Figure 5, which is similar to the arrangement illustrated in Figure 4 except that the function of a timer circuit is programmed into a second microprocessor 34 (conveniently of the same type as microprocessor 14, but this is not essential). Current pulses from the mains sensor cause a change of voltage across resistor Ri (36) and this is sensed by the second microprocessor 34. An absence of pulses from the sensor will cause the microprocessor 34 to turn on the emergency output, which in this circuit is shown as Tl (38) turning on LEDI (40).

Moreover, using a microprocessor allows other functions to be incorporated into the unit. In this embodiment the battery voltage is monitored by the second microprocessor 34, so that if the battery voltage drops to a point where it is anticipated that the battcry will shortly fail, LED2 (an indicator LED, 42) can be turned on to warn building occupants that the battery needs to be changed.

As well as, or instead of, warning LED 42, the module could comprise a small buzzer, to attract attention to the unit. Other functions could be included such as a self-test momentary operation of the emergency circuit to ensure that it is functional; a timer could be incorporated so that the unit is only active for, say, 15 minutes, or the emergency LED could pulse to attract attention, rather than have additional LEDs.

Example 6

A simpler embodiment is illustrated in Figure 6 in which QI (44) is used to sense the current pulses. The timer circuit converts the pulses into an onloff signal which, via Q2 (46) is used to switch on or off the emergency circuit.

Example 7

Referring to Figure 7, an embodiment of a sensing module for use in apparatus in accordance with the invention is shown.

The sensing module comprises a moulded or extruded synthetic plastics substrate 100. On the underside of the substrate 100 are inserted two copper strips 102, 104. The strips are in substantially parallel relation and essentially identical. The strips 102, 104 are retained within suitable shallow channel-section grooves on the underside of the substrate. Each strip 102, 104 is about 2-3 mm wide and about 35 pm thick, and each strip is about 30 mm in length.

The separation between the strips 102, 104 is about 5 mm.

The substrate 100 will normally be opaque, but in the figure is shown as transparent, so as not to obscure the strips 102. 104. The substrate 100 is provided with resiliently deformable downward-projecting prongs (omitted for clarity) on each side, which form a snap-fit to the outside of the insulation of mains cable 106 which is to be monitored by the sensing module.

The mains cable comprises conventional live and neutral conductors, 108, 110 respectively, and an earth conductor 112.

Example 8

This example relates to an algorithm used by a microprocessor programmed to operate in apparatus in accordance with the invention.

The algorithm is illustrated schematically in Figures 8-11.

The figures employ a number of abbreviations, including: Abbreviation Meaning cnt/CNT good pdse count fran transition count long long pulse counter rnd "mains detected" flag gp "good pulse" flag pol "polarity" flag gpo! "good pulse/polarity" flag ip input Inc increment Dec decrement hiw hardware ret "return" Figure 8 shows the bu!k of the algorithm and a!so inc!udes (Fig. 8A) an example of a mains pulse pattern that would be considered by the apparatus so programmed to be "mains detected", and three examples of pulse patterns which would be considered as "mains fai!ure" or mains not detected.

Claims (23)

1. Claims 1. An electrical power loss-actuated system, the system comprising at least one effector module and at least one electrical power sensing module, the power sensing module being adapted and configured to detect, by non-contacting capacitive coupling means, a loss of electrical power and, in the event that a loss of electrical power is detected, to transmit an actuation signal to the at least one effector module.
2. 2. An emergency lighting system according to claim 1, wherein the at least one effector module comprises at least one emergency lighting luminaire.
3. 3. A system according to claim I or 2, wherein an electrically conducting link exists bctwccn thc sensing module and the at least one effector module.
4. 4. A system according to any one of the preceding claims, wherein the effector module is a self-powered luminaire and includes: a housing; an emergency light source; a power source and a control unit.
5. 5. A system according to claim 4, wherein the control unit detects or monitors a signal from the sensing module and/or detects or monitors the state of the battery.
6. 6. A system according to claim 4 or 5, wherein the effector module additionally comprises a visual status indicator and/or an audible alarm.
7. 7. A system according to any one of the preceding claims, wherein the sensing module comprises two mains power sensing circuits.
8. 8. A system according to any of the preceding claims, wherein the capacitive coupling means comprises a plurality of spaced apart electrically conductive elements each of which is capable of being capacitively coupled to a conductor for the electrical power.
9. 9. A system according to claim 8, in which each clement is connected to a respective input of a differential amplifier for amplifying the differential signal and blocking or attenuating the common mode signal from the conductive elements.
10. 10. A system according to claim 8 or 9, wherein the electrically conductive elements comprise two elongate electrically conductive tracks or elements which are substantially parallel to each other.
11. 11. A system according to claim 10, wherein the two electrically conducting tracks or elements are held in a spaced apart relationship with a spacing in the range 2-10mm, preferably 5-10mm.
12. 12. A systcm according to claim 10 or 11, wherein each of the two electrically conducting tracks or elements is between 10 and 40mm in length, preferably 20-40mm.
13. 13. A system according to any one of claims 10-12, further comprising a fixing which fixes to a mains cable to be sensed, and which retains the two electrically conducting tracks or elements in a desired orientation to, and a desired distance from, the conductors in the mains cable.
14. 14. A system according to any one of the preceding claims, wherein the system monitors electrical mains supply and determines a reference value, the sensing module automatically transmitting an actuation signal to the effector module if the electrical mains supply falls below a threshold value, which threshold value may optionally be calculated as a particular percentage of the reference value.
15. 15. A system according to any one of the preceding claims, wherein the effector module, if actuated, is deactivated if the sensing module detects that the electrical mains supply has been restored, or if a predetermined period of time has elapsed since the effector module was actuated.
16. 16. A system according to any one of the preceding claims, wherein the effector module is actuated if an electrical connection between the sensing module and the effector module is broken.
17. 17. A system according to any one of the preceding claims, wherein the sensing module and the effeetor module are provided as a single unit.
18. 18. A method of detecting an electrical power loss in an electrical power supply system, the method comprising monitoring the power supply system using an electrical power loss actuated system according to any one of the preceding claims.
19. 19. A method according to claim 18, wherein the electrical power loss actuated system is a system according to claim 10 or 11, and wherein the electrically conducting tracks or elements are substantially parallel to the live and neutral conductors of a mains cable being sensed by the sensing module.
20. 20. A method according to claim 19, wherein the two electrically conducting tracks or elements are positioned between 0 and 25mm from the outer surface of a mains cable being sensed by the sensing module.
21. 21. A method of installing a power loss-actuated system in a building, the method comprising the steps of installing at least one sensing module in a position such that it can detect and/or monitor mains electrical power supply by capacitive electrostatic induction means, installing at least one effector module, and establishing signal connectivity between the sensing module and the effector module, such that a signal generated by the sensing module in the event of a mains electrical power supply failure can be transmitted to, and cause actuation of, the at least one effector module.
22. 22. A building comprising a system according to any one of claims 1-17.
23. 23. An electrical power loss-actuated system as hereinbefore described and with reference to the accompanying drawings.