WO2002031944A2

WO2002031944A2 - A system for monitoring and controlling a plurality of electrical loads

Info

Publication number: WO2002031944A2
Application number: PCT/IB2001/001897
Authority: WO
Inventors: Joseph Harry Sherman; Dennis Goldman
Original assignee: E-Tronics (Pty) Ltd.
Priority date: 2000-10-11
Filing date: 2001-10-11
Publication date: 2002-04-18
Also published as: WO2002031944A3; AU2001294094A1

Abstract

A system for monitoring and controlling a plurality of electrical loads in a building includes a measuring means for measuring a characteristic of a particular load and comparing it with a stored normal load characteristic. In the event of a discrepancy, the measured characteristic is transmitted via a DC bus to a master controller and an associate database. A variety of characteristics are stored in the database, which characteristics represent various fault conditions. The measured characteristic is compared with the stored characteristics of the various faults and a fault is identified. This is then displayed to a user of the system via a terminal. In this way, the status of the plurality of loads in an entire building can be monitored.

Description

A SYSTEM FOR MONITORING AND CONTROLLING A PLURALITY OF

ELECTRICAL LOADS

BACKGROUND OF THE INVENTION

THIS invention relates to a system and a method for monitoring and controlling a plurality of electrical loads.

In large buildings, the cumulative power consumed by lights, airconditioners and other electrical loads is significant, with the electricity bill making up a large portion of the running costs, in particular when such loads are left on unnecessarily.

Significant costs are also associated with the regular replacement of blown lights and the periodic maintenance of airconditioners and the like. Maintenance programs and schedules are labour intensive and are not particularly efficient, in that regular in situ inspections are required for the replacement and maintenance of lights and airconditioners. In order to save on manpower, maintenance and replacement routines are often not carried out as regularly as they should be, and stock levels of different types of lights often have to be kept unnecessarily high so as to cater for unexpected failures. SUMMARY OF THE INVENTION

A system for monitoring and controlling a plurality of electrical loads, the system comprising:

measuring means for measuring at least one characteristic of a particular load;

primary storage means for storing at least one parameter of that load, typically under normal operating conditions;

comparator means for comparing the measured characteristic of the load with the stored parameter;

a central controller responsive to the comparator means for diagnosing a fault condition on the basis of the at least one measured characteristic and the particular load type; and

display means for displaying the fault type to a user.

The system preferably further includes a plurality of remote single or multi-way monitoring units arranged to monitor a plurality of associated loads, each of the monitoring units including the measuring means, the primary storage means and the comparator means.

The central controller may be linked via a plurality of communication links to the monitoring units and a secondary storage means is associated with the central controller. ln one instance, the secondary storage means is in the form of a database associated with the central controller.

Each of the remote monitoring units and associated loads are preferably addressable and identifiable at the central controller via the communication links.

The typical parameters or characteristics of a plurality of different faults or other status conditions associated with particular loads may be stored in the database.

Each of the particular loads may include a plurality of luminaires, with the fault or status conditions corresponding to failures, absence or dimming of one or more of the luminaires.

Alternatively, the particular load is one of an air conditioner, smoke detector or any other load encountered in a building installation.

The communication links may be in the form of a mains-isolated DC bus.

The loads or remote monitoring units are preferably individually protected with resettable fuses, thereby reducing the number of circuit breakers required on a mains distribution board, and the resettable fuses may be self-resetting such as IGBT's.

The system may further include address means in the form of keypads, card or tag receivers or the like are linked to the communications link for addressing and controlling the operation of and access to predetermined addressable groups of loads. Preferably, the system further includes a relay or contactor to connect the particular load to an energy source, wherein the relay or contactor is controlled by a microprocessor which is programmed to switch the relay or contactor on and off at a particular point in the voltage or current cycle.

The present invention also extends to a load monitoring unit for monitoring and controlling the operation of at least one associated load, the monitoring unit comprising measuring means for measuring at least one characteristic of the load, primary storage means for storing at least one parameter of the load, typically under normal operating conditions, comparator means for comparing the measured characteristic of the load with the stored parameter, and data interface means for enabling the transfer of data associated with the measured load characteristic from the load monitoring unit in the event of the measured characteristic deviating from the stored parameter.

The data interface means may be arranged to receive incoming control data, and the load monitoring unit includes a controller which is remotely addressable by the incoming data for controlling the operation of the load.

The load monitoring unit is preferably a multi-way unit which is arranged simultaneously to control the operation of a plurality of associated loads.

The at least one characteristic of the load may be in the form of a plurality of load characteristics derived from a current and/or voltage waveform of the load which are sufficient to determine and diagnose the status of the load.

The load characteristics may be zero crossing characteristics, phase shift, peak and average current and/or voltage characteristics.

The load monitoring unit may further include diagnosing means in the form of a look-up table formed integrally with the load monitoring unit. The load monitoring unit may also further include load metering means for kWh metering of individual loads, monitoring units or groups of monitoring units.

The relay or contactor may connect the particular load to an energy source, wherein the relay or contactor is controlled by a microprocessor which is programmed to switch the relay or contactor on and off at a particular point in the voltage or current cycle.

The present invention also extends to a method of monitoring and controlling a plurality of electrical loads comprising the steps of :

measuring at least one characteristic of a particular load;

storing at least one parameter of that load, typically under normal operating conditions;

comparing the measured characteristic of the load with the stored parameter; and

in the event of the measured characteristic deviating from the stored parameter, diagnosing a fault type on the basis of the measured characteristic and the particular load type.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a highly schematic block diagram of a load monitoring and control system of the invention;

Figure 2 shows a circuit block diagram of a multi-way monitoring unit or module of the invention; Figure 3A shows a more detailed circuit diagram of a first embodiment of certain of the circuit blocks illustrated in Figure 2;

Figure 3B shows a detailed circuit diagram of a DC/mains isolated data interface circuit forming part of the load monitoring and control system of the invention;

Figures 4A & 4B show more detailed circuit diagrams of a respective DC data interface module and a keypad module forming part of the load monitoring and control system of Figure 1 ;

Figure 5 shows a waveform diagram illustrating current and voltage waveforms of a load corresponding to six low voltage lamps under normal operating conditions;

Figure 6 shows a waveform diagram illustrating voltage and current waveforms corresponding to a fault condition in which only two of the six low voltage lamps are burning;

Figure 7 shows a circuit diagram of part of a second embodiment of a multi-way monitoring unit incorporating an electronic fuse; and

Figure 8 shows a circuit diagram of a zero crossing relay for use with the present invention. DESCRIPTION OF EMBODIMENTS

Referring first to Figure 1, a monitoring and control system for controlling a plurality of electrical loads comprises a central or master controller 12 having a central database 14. The master controller and database are linked via a two wire bus 16 to a number of 8 channel section controllers 18.1 to 18.4. The section controllers are typically located in distribution boards on successive floors of a multi-storey building. A two wire DC/data interface circuit 20 links each of the section controllers 18.1 to 18.4. to a plurality of loads along a two wire bi-directional DC/comms bus 22. The loads include four-way light modules 24.1 , 24.2 and 24.3 which are supplied with AC power and linked to the bi-directional DC bus by means of DC/mains isolated data interface circuits 26. Airconditioner units 28 are similarly linked to the DC/comms bus 22 via the mains data interface units 26. Keypad units 30 are also connected to the DC/comms bus 22 for locally controlling access to operation of the various loads.

Referring now to Figure 2, a multi-way monitoring unit in the form of a four-way light module 24.1 is shown. A microprocessor 32 fed by a DC power supply 33 is at the heart of the module, and is arranged to control and monitor the operation of four loads in the form of light fittings 34.1 to 34.4. Each of the loads include a 300VA transformer which feeds six 12V low voltage lamps. The 300VA transformers are fed via four separate load driver and fuse protection circuits 36.1 to 36.4 respectively, one of which is shown at 36.1 in Figure 3A. The load is energized via control signals from the microprocessor 32 via LED 38 which turns thyristor 40 on and off. Thyristor protection is provided by a metal oxide varistor 42 and a live terminal 44 of the load receives load current which is converted to a voltage across a shunt 46. The load driver and fuse protection circuitry is in turn linked to fuse and thyristor monitoring circuitry 48 in the form of sets of serially linked resistors 50 and 52. The resistor set 50 is linked between monitoring terminal FIH and an input terminal MFIH of the microprocessor 32, and the resistor set 52 is linked between monitoring terminal FIL and an input terminal MFIL of the microprocessor 32. Each set of resistors is connected across a protective fuse 46 and three similar pairs of resistor sets 50 and 52 are connected between the monitoring terminals of the load monitoring circuitry 48 and the input terminals MF2H and MF2L to MF4H and MF4L.

In the event of a fuse blowing, there will be a different voltage output between the legs of the thyristor 40 when it is on. If the thyristor 40 is functioning then the input terminal MFIH will go high. In the event of the fuse 46 functioning, the input terminal MFIL will also go high. In the event of the fuse blowing on the negative half cycle of the mains, the terminal MFIL will go low. If the thyristor 40 is blown to an open circuit condition, then, although the microprocessor expects a high on the terminal MFIH, it will receive a low during the negative half cycle. If the thyristor 40 goes into a short circuit condition, the terminal MFIL, though expecting a low voltage negative half-cycle value when the thyristor should be off, will receive a high value. A resistor 54 to return the FIL terminal to neutral is included so as to detect an open circuit condition of the load arising from a disconnected or blown load. In the event of both the shunt 46 and the thyristor 40 being an open circuit condition, then only the thyristor fault will be detected.

Four measuring means in the form of four identical load current and power factor monitor circuits 58.1 to 58.4 circuits are provided for each of the respective four load driver and fuse protection circuits 36.1 to 36.4. The circuit 58.1 in Figure 3A includes an input capacitor C1 which shifts the voltage representing load current across shunt 60 to an inverting input of an op amp 62. This is amplified and presented to the microprocessor on analog input terminal ALL At a convenient time after the load has settled after switch-on, the processor then takes a suitable number of readings along the half wave representing the load current. Due to the nature of the different loads arising from different fault conditions, and in order to arrive at a correct diagnosis, measurement of the current alone will generally not yield a reliable result.

Figure 5 shows typical respective load voltage and current waveforms 64 and 66. The current waveform corresponds to a full normal load condition in respect of which six 12V low voltage lamps are burning. The measured characteristics of the current waveform include measurements of the average current slices along the positive half-cycle, as shown at 68, together with zero crossing voltage measurements 70 and 72 respectively. A phase angle measurement 74 as well as a peak current measurement 76 may be taken, together with an offset current reading 78 from zero to peak current. A zero voltage to zero current offset measurement 80 may also be taken. It will be appreciated that in certain instances only one or two of the above measurements will be required, providing such measurements are sufficient to distinguish between different fault and/or status conditions.

Referring now to Figure 6, a waveform diagram of voltage and current waveforms 64A and 66A are shown corresponding to a fault condition arising in which only two of the six low voltage lamps are burning, and the remaining four have blown and have gone open circuit. The same numerals suffixed by an "A" are used to indicate measurements similar to those of Figure 5. The shape of the waveform of Figure 6 differs significantly over that of Figure 5, and it is clear that this results in significant differences in the measured characteristics or parameters, which differences can readily be sensed at the microprocessor 32.

The above measured current and voltage waveform characteristics will allow, in the case of fluorescent fittings having magnetic ballasts, diagnosis of a damaged starter, dead tube(s), a dead capacitor, and dimming level confirmation. In the case of low voltage lighting, the measured characteristics will provide an indication of the number of lamps which are dead, together with dimming level confirmation. In the case of incandescent lamps, the number of dead lamps together with dimming level confirmation can also be diagnosed. In air conditioners, the state or mode of operation of the airconditioner can be sensed, such as fan only mode, heating mode and cooling mode. The state of the airconditioner filter can also be monitored, in that load current tends to decrease with progressive clogging of the filter. In the case of loss of gas, the load current will tend to increase.

Referring back to Figures 2 and 3A, in order to detect zero crossing points of the waveforms 64 and 66, a zero crossing circuit 82 is provided. To reduce inrush currents, RFI and EMI switching is done as close to the zero voltage level as possible. The switching off is handled automatically by the thyristor drive 40, which only turns off as the current falls close to zero. In the case of airconditioner circuits 28 which make use of a relay, it is ensured that the relay is turned off at a time offset from zero current by the response time of the relay. This is implemented in the load current and power factor monitoring circuit 58. Zero crossing timing is achieved by the interrupt generated as the mains voltage delivered by the three serially linked resistors 82.1 , 82.2 and 82.3 passes about the 2V transition of the input to the microprocessor.

A mains voltage measurement circuit 84 is connected to an input terminal ACV of the microprocessor by a voltage divider formed by resistors 84.1 and 84.2 and 84.3 and 84.4. Apart from measuring the voltage to obtain voltage drop information, the AC voltage is measured with a view to ensuring that a load change caused by a low input voltage is not incorrectly interpreted as arising from a dead lamp or faulty circuit. As is clear from Figure 3A, the microprocessor 32 includes a crystal oscillator circuit 86, with five analogue-to-digital converters, a serial port and a number of bi-directional ports. The unit is software programmable and is provided with a storage means in the form of an onboard non-volatile memory to store the unique address of the four-way light module 24.1 , together with voltage and current load parameters of the type described above with reference to Figure 5. These parameters are stored on instructions by the associated section controller 18.1 via the master controller 12 once the installation team has confirmed that all of the loads are fully functional and that the load characteristics correspond to normal operating conditions. A reset and brownout protection circuit 88 is linked to a reset input of the microprocessor 32. The transistor Q1 and the associated resistors R1 , R2 and R3 of the reset circuit cater for the slow rise time of the 5V power supply together with any brownouts that could cause the microprocessor not to function correctly.

In Figure 3B, a detailed circuit diagram of the DC/mains isolated data interface circuit 26 is shown for extracting incoming data off the two wire bi-directional DC bus 22 and feeding data into the bus from the microprocessor 32 whilst isolating the DC bus from the mains supply to the load. A diode bridge 90 provides the bipolar connection, and capacitor C12 and transistor Q4 extract incoming data off the bus. This data allows the constant current source constituted by LED L1 and transistor Q5 to be turned on and off and to pass the data to a receive input RX of the microprocessor 32 via an opto-coupler U3. A constant current source is used to compensate for the varying voltages arising from varying lengths of cables. Information to be returned back to the section controller 18.1 is passed from the TX output of the microprocessor via the opto-coupler U1 to the constant current source constituted by the LED L2 and the transistor Q2. The modulated current signal appears at the DC data interface circuit 20, from where it is received at the section controller 18.1 and ultimately at the master controller 12. The DC data interface circuit 20 is shown in more detail in Figure 4A. Data pulses from the section and master controllers are transmitted via a constant current source constituted by transistors SQ3 and SQ4 which allow the data pulses to be superimposed onto the DC bus 22. As each leg may have a varying number of loads and modules attached to it at different distances along the line, the constant current source allows the transmission amplitude to be kept constant. The received data is extracted from the link at output terminal LRX via capacitor C1, transistor Q1 and transistor Q2.

In Figure 4B, a typical keypad module 30 is shown. Power for the module is extracted from the DC bus 22 and a diode bridge 92 allows for bipolar connection of the bus. A keypad 80 is linked to a keypad IC 82 provided with LRX and LTX terminals for connection to the corresponding terminals in the data interface circuit 98, which is essentially identical to the interface circuit 20.

The operation of the load monitoring and control system of the invention will now be described in more detail.

The central database 14 at the master controller 12 includes a detailed layout of all the loads in the building requiring monitoring and controlling, together with details of the load types, such type of light fittings, type, number and wattage of lights accommodated in each light fitting, air conditioner specifications and the like. Once commissioning is complete, the current and voltage characteristics for normal load conditions of the particular loads are stored in the associated multi-way monitoring units or load modules. These parameters may be downloaded from the central database or alternatively may be measured in situ once the lamps associated with a particular light fitting are installed and operating normally.

Also stored in the database are load characteristics associated with various fault conditions in respect of a particular load. In the case of fluorescent fittings, these would include a damaged starter, one or more dead tubes and a damaged capacitor. Load characteristics associated with dimming levels may also be stored. At the microprocessor 32 associated with each of the load modules, the measured load characteristics are constantly compared with the stored normal load characteristics stored in the non-volatile memory of each microprocessor 32. In the event of a discrepancy arising, the measured characteristics are transmitted via the DC bus 22 to the master controller 12 and the database 14, where the characteristics are compared in a look-up table with characteristics associated with various fault conditions with respect to the identified type of load. A diagnostic procedure then takes place whereby the measured fault characteristics are compared with the stored fault characteristics. In the case of the waveforms of Figures 5 and 6, the various parameters of the Figure 6 waveform will thus be transmitted back to the database 14 and the particular fault condition arising, namely the existence of the four blown lamps in the six lamp configuration, will be identified in that the database will include a look-up table in which fault parameters essentially corresponding to those identified in Figure 6 will be stored, amongst others.

Once a match is arrived at, the fault is effectively diagnosed or analysed, and can immediately be identified on a display means in the form of a terminal at the master controller. The terminal at the master controller will thus indicate that four lamps have blown in the six lamp low voltage configuration. In this way, the load status of the entire building is kept current. Maintenance programs can therefore be tailored according to the nature and location of load faults. In addition, energy (kWh) consumption can be finely monitored, as a record is kept at the database of the load histories of the various loads, and exactly when they have been turned on and off. In a simple version, the power consumption (say 300W) of a particular load is known, and a kWh figure is arrived at at the central controller on the basis of the time periods that the load is on. In a more accurate version, kWh metering IC's could be provided to monitor the consumption of each load, to monitor the consumption of each group of loads controlled by a load monitoring unit, or to monitor the consumption in respect of each leg 22 of the DC bus to which the loads are connected.

It will be appreciated that although in the illustrated embodiment, diagnosis takes place at the master controller, it is possible to include diagnosing means in each of the monitoring units 24.

Due to the fact that, once triggered, the thyristors 40 remain conducting until the current falls below the hold current, some form of protection against load faults is required. This may take the form of normal circuit breakers or the previously described fuses 46.

In the present application a circuit breaker would generally not operate fast enough to protect the thyristors. Circuit breakers would also generally affect more than one area or system. For the same reasons, the fuse 46 would have to be an ultra-fast type. However, it would be highly inconvenient to have to go into the ceiling every time the fuse needs replacement.

Figure 7 shows an alternative embodiment in which a resettable fuse circuit 100 incorporating a resettable fuse in the form of an IGBT 102 is utilized. The IGBT fuse can disconnect fast enough to protect the thyristor 40, and can also be self-resetting, as a result of which the fuse system would reconnect a predetermined suitable time period after tripping. The circuit 100 is connected between live and neutral inputs, and includes a diode bridge 104 which is used to rectify the AC input and to produce a DC input for the IGBT 102 which is connected across the F+ and F- terminals within the bridge. An isolating and rectifying circuit 106 feeds an isolated and rectified 1mA 16V DC current to an over-current detection and hold-off circuit 108. The circuit 106 includes a charge pump sub-circuit in which the capacitor C1 is charged by a capacitor C4 via diodes D5 and D6 up to approximately 3 volts. A transistor Q1 and a ferrite transformer TX1 make up a self-isolating high frequency step-up transformer. A diode D7 charges capacitor C2 to 16 volts, which is limited by zener diode Z1 so as to create the 16V 1mA supply for the circuit 108. It will be appreciated that a conventional but generally more costly transformer could also be used.

A load current is fed through the shunt 60A and is measured by transistor Q2, with resistors R8 and R9 pre-biasing transistor Q2 so as to avoid a relatively high voltage (0.6V) from appearing across the shunt 60A. When the threshold of transistor Q2 is passed, Q2 turns on and, via CMOS inverter U1 F, turns off inverters U1A, U1B, U1D and U1E. This in turn shuts down the IGBT 102 rapidly. The greater the overload, the faster this occurs. At the same time, the inverter U1C and resistor R5 hold the system off via capacitor CT1 and resistor R3 for a period defined by the capacitor CT1 and the resistor R4. The reset time for resetting the capacitor CT1 on recovery is defined by diode D8 and resistor R6.

The IGBT may be replaced by a transistor, a FET or even a commutated SCR. Whilst the IGBT is on, then power is passed to the load terminal S2 via the diode bridge 104, with the power to the load being blocked in the event of the IGBT 102 turning off.

When used in conjunction with the intelligent multi-way modules 24.1 to 24.3, communication with the modules during the tripped period will be lost. On automatic reconnection, the modules will have details of the last operating modes stored in the on-board non-volatile memory. The module 24.1 will then attempt to reconnect, one-by-one, those loads 34.1 that were on. As each load is confirmed to be connected, a flag is set to indicate that the particular load is functional. When the load that caused the fault is reconnected, it will cause the unit to trip once again. In the case of an incandescent bulb causing the trip, which typically occurs when a bulb of this type blows, the module notes a change in the load current and the resettable fuse notes a trip on reconnection of this load. In the event of the re-trip occurring during the sequential reconnection procedure, the flag condition indicates the source of the fault and the corresponding port can then remain disconnected. A fault report is then generated which is transmitted back to the central controller. The particular module is remotely instructed to reconnect the disconnected fault-associated port once the fault condition has been repaired, by, for instance, replacement of the incandescent bulb.

Referring to Figure 8, a zero crossing relay can be used in conjunction with the multi-way monitoring units 26 in order to switch power to and from the loads 24.

In general, a triac could be used to switch AC loads. The advantage gained by using a triac is that the turn on can be timed occur as the AC passes through zero volts, thus limiting high inrush currents and therefore eliminating RFI and EMI suppression components. The other advantage is that the triac only turns off as the current passes through close to zero current (or below the holding current) this eliminates large switch off spikes when inductive components make up the load.

However, as the triac is a solid state device it always has some voltage constraints thus requiring protection. Invariably, with larger current there is a power loss which generates heat and which then requires a heat sink. More importantly, when a fault condition occurs, or even an incandescent bulb arcing over, the huge instantaneous current will tend to destroy the triac due to the inherent time lag that a protection fuse takes to become open circuit (and the ensuing arc within the fuse). One could overrate the triac, but the cost implications are high.

A much more robust solution is to use a relay or contactor to drive the load. The relay has a time lag which varies from relay to relay, even of the same type. Thus, even if one were to switch at zero voltage or current crossing the actual operation is delayed. When the relay switches on, there is also contact bounce. Both problems cause high voltage spikes which require large suppression devices and still cause RFI and EMI problems.

Protection fuses are able to prevent damage to the relay contacts. The contacts can withstand short term high voltage spikes.

An alternative solution is to control the relay such that the contacts open or close at the appropriate times.

The AC zero crossing voltage is monitored and after a period that takes the relay pull in delay time into account, the relay is operated. This period is such that the contacts close as near as possible to the AC voltage being zero.

By the same method the AC current zero crossing can be monitored and the drop out delay taken into account to cause the contacts to open at the desired moment.

During initial testing the relay pull in and drop out time periods can be calibrated for each individual relay and thereafter adjusted under operating conditions if the wear or aging of the relay produces undesirable drift of the operating points.

In the event that certain loads behave more advantageously at points other than zero crossing, this can be taken into account. Especially with regard to load power factor changes which would still be tracked.

The closing contact bounce causes minimal spikes as the voltage and thus energy is at a minimum. There is also the advantage that the power factor correction capacitor in fluorescent fittings are not subjected to the high inrush currents of turning on at the peak of the AC wave.

The turn off arc caused by the high residual dc component across the capacitor can also be eliminated by judicial choice of the turn off point.

It will be appreciated that the use of the relay will contactor to drive the load is appropriate in the context of the present invention because the voltage and current waveforms are in any event being monitored.

A circuit to implement the use of a reader or contactor to drive the load is illustrated in Figure 8. This replaces the part of the circuit marked 36.1 in Figure 3A. The fault monitoring and circuitry has been left off Figure 8 for ease of reference.

The zero crossing voltage of the AC supply is monitored by the processor 112 (this is the same processor as the processor 32 in Figure 3A) via R1 and compared to the GND REF.

The current is monitored at IZ. This current signal is derived via OP AMP U1 A which amplifies the voltage generated across current shunt SH1.

The input LV monitors the voltage after the relay contacts via R2.

Control of the relay is done by output RC.

Typically, as the AC voltage passes through zero crossing the processor will turn on the relay RL1 via R5 and Q1. The relay pull in time delay is then measured by monitoring either the load current or load voltage inputs. This time delay is then used to calculate an offset time from the voltage zero crossing point such that voltage will be applied to the load at a subsequent zero crossing.

Switching components on at or near the zero crossing obviously extends the life of the components.

The drop out time is similarly calculated but with reference to the current zero crossing point (IZ). Either the load voltage or current input can be monitored for the drop out time delay and thus a current offset time can be calculated such that the relay opens at a subsequent current zero crossing point.

Due to aging or heating of the relay the above times may change. Thus during operation the times may be monitored and when they move beyond chosen limits recalculated.

Claims

1. A system for monitoring and controlling a plurality of electrical loads, the system comprising:

measuring means for measuring at least one characteristic of a particular load;

display means for displaying the fault type to a user.

2. A system according to claim 1 wherein, the system further includes a plurality of remote single or multi-way monitoring units arranged to monitor a plurality of associated loads, each of the monitoring units including the measuring means, the primary storage means and the comparator means.

3. A system according to claim 2 wherein the central controller is linked via a plurality of communication links to the monitoring units and a secondary storage means is associated with the central controller.

4. A system according to claim 3 wherein the secondary storage means is in the form of a database associated with the central controller.

5. A system according to claim 4 wherein each of the remote monitoring units and associated loads are addressable and identifiable at the central controller via the communication links.

6. A system according to claim 5 wherein the typical parameters or characteristics of a plurality of different faults or other status conditions associated with particular loads are stored in the database.

7. A system according to claim 6 wherein each of the particular loads includes a plurality of luminaires, with the fault or status conditions corresponding to failures, absence or dimming of one or more of the luminaires.

8. A system according to claim 6 wherein the particular load is one of an air conditioner, smoke detector or any other load encountered in a building installation.

9. A system according to any of claims 3 to 8 wherein the communication links are in the form of a mains-isolated DC bus.

10. A system according to any of claims 2 to 9 wherein the loads or remote monitoring units are individually protected with resettable fuses, thereby reducing the number of circuit breakers required on a mains distribution board.

11. A system according to claim 10 wherein the resettable fuses are self- resetting

12. A system according to claim 11 wherein the resettable fuses are IGBT's.

13. A system according to any of claims 3 to 11 further including address means in the form of keypads, card or tag receivers or the like are linked to the communications link for addressing and controlling the operation of and access to predetermined addressable groups of loads.

14. A system according to any preceding claim further including a relay or contactor to connect the particular load to an energy source, wherein the relay or contactor is controlled by a microprocessor which is programmed to switch the relay or contactor on and off at a particular point in the voltage or current cycle.

15. A load monitoring unit for monitoring and controlling the operation of at least one associated load, the monitoring unit comprising measuring means for measuring at least one characteristic of the load, primary storage means for storing at least one parameter of the load, typically under normal operating conditions, comparator means for comparing the measured characteristic of the load with the stored parameter, and data interface means for enabling the transfer of data associated with the measured load characteristic from the load monitoring unit in the event of the measured characteristic deviating from the stored parameter.

16. A load monitoring unit according to claim 15 wherein the data interface means is arranged to receive incoming control data, and the load monitoring unit includes a controller which is remotely addressable by the incoming data for controlling the operation of the load.

17. A load monitoring unit according to claim 16 wherein the load monitoring unit is a multi-way unit which is arranged simultaneously to control the operation of a plurality of associated loads.

18. A load monitoring unit according to claim 17 wherein the at least one characteristic of the load is in the form of a plurality of load characteristics derived from a current and/or voltage waveform of the load which are sufficient to determine and diagnose the status of the load.

19. A load monitoring unit according to claim 18 wherein the load characteristics are zero crossing characteristics, phase shift, peak and average current and/or voltage characteristics.

20. A load monitoring unit according to claim 19 further including diagnosing means in the form of a look-up table formed integrally with the load monitoring unit.

21. A load monitoring unit according to claim 20 further including load metering means for kWh metering of individual loads, monitoring units or groups of monitoring units.

22. A load monitor unit according to any of claims 15 to 21 further including a relay or contactor to connect the particular load to an energy source, wherein the relay or contactor is controlled by a microprocessor which is programmed to switch the relay or contactor on and off at a particular point in the voltage or current cycle.

23. A method of monitoring and controlling a plurality of electrical loads comprising the steps of : measuring at least one characteristic of a particular load;

24. A system substantially as herein described with reference to the illustrated embodiments.

25. A load monitoring unit substantially as herein described with reference to the illustrated embodiments.

26. A method substantially as herein described with reference to the illustrated embodiments.