This invention concerns a illumination control system for the control of several different lighting circuits, which system comprises a control center unit incorporating a plurality of controlled outputs, each provided with a controller of the output voltage RMS value, and a microprocessor-based function control unit, which provides control information for the controlled outputs; in addition to the afore-mentioned, the system is provided with an arrangement for illumination level control in the lighting control circuits on the basis of room illumination level information obtained from illumination level sensors so that the illumination level in the room is maintained essentially constant or within defined limits, irrespective of variations in ambient illumination.

Known in prior art is a method for illumination level control in a room through a direct adjustment of input power to the room's luminaires with the help of a room-specific controller such as a trimmer potentiometer.

It is equally conventional to use an illumination sensor for maintaining room illumination essentially constant irrespective of variations in ambient illumination.

An object of the invention is to combine the afore-mentioned functions into an integrated system design, in which only a single processor serves for the control of several separate lighting circuits so that an independent control of each lighting circuit is obtained by room-specific controllers.

A further object of the invention is to provide an illumina¬ tion control system, in which the calibration of basic illumination levels in the lighting circuits is individually possible at a lighting circuit level by means of conventional controls such as pushbuttons.

These and other objects of the invention are achieved by way of what is stated in the characterizing parts of the appended claims.

In the following, the invention is described in greater detail with references to the attached drawings, in which

Figure 1 shows a block diagram of a system in accordance with the invention, and

Figure 2 shows a circuit diagram of an illumination sensor and control switch unit of the system.

The lighting control system comprises a control center 1, which can be placed in conjunction with, e.g., an electrical switchboard. For the power feed of lighting fixtures L, the control center 1 incorporates a power distribution circuit 2 with several controlled outputs 12 in parallel configuration, one for each lighting circuit. Each controlled output 12 has an output voltage RMS value controller, which can be, e.g., a phase-angle-controlled triac. The triac devices of the controlled outputs receive their trigger pulses from touch- control dimmer circuits 13, which can be, e.g., touch-conτ_rol dimmer circuits of type S576C or SLB0586 by Siemens. These circuits form the triac trigger pulse by way of the trigger pulse phase-angle control principle. The phase angle of the trigger pulse for the triac's conductive state is altered by taking the control voltage applied at a dedicated pin of the dimmer circuit 13 to a low level. If the control voltage is continuously held at a low level, the trigger pulse phase angle varies at a monotonous rate between 35 and 150 degrees of angle. The duration of a complete control cycle is about 7 s. When said voltage at the control pin is taken high, the phase angle remains at the value valid at the rise of the voltage. If said voltage at the control pin of the circuit 13 is held down less than 400 ms, the operation is interpreted as

a command for turning the triac on or off, depending on the previous off/on state of the triac, respectively.

Control voltages for the dimmer circuits 13 are obtained from a processor 3, which determines the required levels and durations for the control voltages on the basis of received control information. Control information to be applied to the processor 3 will be later described in detail.

Designated by the reference number 14 is a zero-crossing detector. In practice one zero-crossing detector 14 is provided for each phase leg of the service line. The zero- crossing detectors 14 generate synchronization pulses for the dimmer circuits 13. The synchronization pulse is common for all dimmer circuits connected to the same phase leg. In addition, the zero-crossing pulse is used for phase-angle measurement.

The supply voltages of +5 V and +15 V are generated by a power supply 9 connected to one leg of the service line. The input power to power supply from the line is, e.g., 3 W.

Each room or a control point of a single lighting fixture or circuit is provided with a control unit, which incorporates an illumination-level measuring light sensor unit 7 and a manual¬ ly operated control switch unit 8, which in the illustrated embodiment contains a conventional light pushbutton switch 8a and additionally, a group selector pushbutton, which can used for selecting the control of several lighting circuits, which are connected to the same group.

Each sensor and control switch unit 7, 8 is connected individually via an interface 4 to the processor 3.

The illumination level sensor unit 7 is functionally a light- controlled current source. The sensor unit 7 and the lighting

control pushbutton 8 are connected to a common power.supply as. illustrated in Fig. 2. Current is fed from the control center 1 via a diode 20 to the sensor 7. The output current signal of the sensor unit 7 is converted in a resistor R8 into a voltage signal U _out , which is converted in an interface unit 4 into a proper format to be applied to the processor 3.

An operational amplifier Nl acts as a current amplifier. Virtual ground of the sensor is formed by the combination of a resistor Rl and diodes 21. A photosensitive diode 19 provides an output current linearly proportional to the illumination level. The operational amplifier Nl tends to maintain voltage over a resistor R3 as well as over a transistor T2 at a constant value, whereby a preset current flows through the resistor R3. At a zero level of illumination, an output current level I _out of the sensor is determined by the current flowing through the resistor Rl, the quiescent current of the amplifier Nl, and the current drawn through a resistor R4.

Sensor sensitivity to illumination is determined by the value of a resistor R2. With the help of a capacitor Cl, the ampli¬ fier Nl acts as a low-pass filter with a fixed upper cut-off frequency.

When the light pushbutton 8a or group selector pushbutton 8b is not being operated, the transistor T2 is conductive. When either or both of the switches 8a, 8b is operated, the tran¬ sistor T2 stops conduction and consequently, isolates the effect of prevailing illumination level on the output current I _out . At the operation of the light pushbutton 8a, the current I _out is determined by the value of the resistor Ro, and at the operation of the group pushbutton 8b, by the value of the re¬ sistor divider R6 and R7. On the basis of voltage levels U _out , the processor decides whether the control is based on the measurement signal from the sensor 7 or issued as a manual

control signal from the pushbutton 8a or 8b of the control switch unit.

Each of the above-described light sensors 7, together with the associated pushbuttons 8a, 8b, is assigned to a single light circuit, whereby the control center 1 controls the illumina¬ tion level detected by a sensor 7 to a constant level by controlling the lighting circuit L associated with said sensor. The sensor/control switch unit 7, 8 is connected to the control center 1 over a two-wire line.

Selection between manual or automatic control is possible by means of a switch 17. In the manual control position of the switch 17, all program-controlled functions are inhibited, and the control center operates as determined by the design speci¬ fications of the dimmer circuits 13. Correspondingly, if a temporary need arises for switching off the automatic illumination control of lights according to ambient illumina¬ tion under the control of the sensors 7, the manual position of the switch 17 is available for setting the brightness of the lamps L to a desired level.

A main switch 18 is provided for switching all lights off.

The processor 3 is further complemented with a controller interface 6, through which the illumination control system can be interfaced with an external controller. The external controller can incorporate, e.g., different timer functions, whereby desired lighting circuits can be turned on and off, or the brightness of lights can be automatically adjusted at timed moments. In addition, an external controller can be used for permanently altering the set basic values. Via the interface 6, the processor 3 can provide the external controller with information on the current set basic values of illumination level in the different lighting circuits.

Furthermore, the processor 3 is provided with a digital input. and output port 5, through which program update and altera-. tions can be done with the help of a dedicated programming device. The control program is stored in an EPROM circuit attached to the external bus of the processor 3. The processor 3 can be e.g., a single-chip CMOS microcontroller of the type MC68HC11A1P by Motorola. This processor incorporates, i.a., an 8-bit central processing unit, 250-byte RAM working memory, and a 512-byte EEPROM acting as the parameter value memory.

The operating principle of the program executed by the processor 3 is as follows. The program runs in an infinite loop, called a background loop, whose background program performs tasks assigned with lower priority in execution timing or time. The execution of this background program is repetitively interrupted by three types of different interrupts: timer interrupts, phase zero-crossing interrupts, and interrupts by phase measurement timing control.

The timer interrupts handle the majority of operations related to the control of lighting circuits. Thence, operations related to illumination control are processed under timer interrupts generated by the internal timer of the processor 3. These interrupts are served in a loop, which processes tasks required for handling the control operation that include, e.g., reading the current preset values, reading sensor and control information entered via the sensor/control switch unit interface 4, and controlling the dimmer circuits 13. The program serves each lighting circuit in succession.

Further, an important part of the control center 1 is a selector switch 15, 16, which has a calibration position for the adjustment of basic illumination levels in the individual lighting circuits and a minimum level calibration position for the adjustment of minimum illumination levels in the individual lighting circuits. The neutral position of the

selector switch 15, 16 retains the basic illumination levels and minimum illumination levels unchanged in the processor EEPROM memory.

Turning the selector switch 16 to the calibration position of the basic illumination levels (calibration position) sets the processor in a state which does not perform automatic control of illumination. In dark or night-time with the curtains closed, the lights in those lighting circuits which require setting of basic illumination levels, are turned on. The rest of lighting circuits must have lights turned off. Illumination is set by light pushbutton 8a to a desired level, after which the calibration switch 15, 16 is set to the center position, that is, the neutral position, whereby the set values of basic illumination levels are stored in the EEPROM memory. Storage is thus performed only for the illuminating lights. Set values for turned-off lights are retained unchanged. With the help of the light pushbutton 8a, illumination in the rooms can be adjusted, as necessitated by temporary needs, different from the basic level used in normal conditions by operating the pushbutton 8a. If the automatic constant illumination level control based on the illumination sensor is not desired, the switch 15, 16 may be left in the calibration position.

When the switch 15, 16 is set in the calibration position of minimum illumination level (pushbutton 15 depressed), the minimum brightness of the lighting circuits can be set. For fluorescent lamps, the minimum brightness is set just to the limit where no flicker is detectable, after which the switch 15, 16 is set to the center position. Then, the phase angles of trigger pulses are read from the feed-back loops into the EEPROM memory for those lighting circuits which are lit.

Consequently, the basic value settings of illumination levels are associated with the output signals of the illumination sensors 7, while the minimum value settings are directly

associated with brightness levels of the lamps L themselves. Thus, the minimum values can be calibrated independently from. the prevailing ambient illumination level.

As is evident from the preceding description, the lights are always turned on and off by operating either the light pushbutton 8a or the group selector pushbutton 8b. Lights- in a ■single lighting circuit (e.g., in a room) are turned on by momentarily pushing the light pushbutton 8a. Lights in a single group (e.g., including the entrance, hall, and living room) can be turned on by a single depression of a group pushbutton 8b of any lighting circuit associated with the group. Subsequent momentary depressions of a light pushbutton 8a or 8b turn the lights on and off in succession. Longer depressions of the light pushbutton alternately increase or decrease lighting brightness. On the basis of information obtained from the illumination sensor 7, the system adjusts illumination to a preset (calibrated) basic value and maintains this level unchanged irrespective of variations in ambient illumination. There is, however, no danger of seif- controlled turning on and off of the lights, even if there would be, e.g., after the lights are turned on, a sufficient illumination made available by bright sunshine. This precaution avoids the possibility of leaving the lights on so that they could start turning on and off self-controlled, while the premises are unmanned.

As described in the preceding, the dimmer circuits incorporate "intelligence", whereby the dimmer circuit identifies on the basis of its built-in design specifications a depression of 50...400 ms duration as a turn-on or turn-off impulse, as appropriate. According to the inherent characteristics of the dimmer circuit 13, turn-on of lights could take place directly from total darkness to full brightness. In the system, however, the turn-on operation is handled by artificially extending the duration of the turn-on impulse with the help of

the processor 3, whereby the turn-on of lights is smoothed by controlling lamp brightness through a ramped increase up to the calibrated basic value.

If the program of the processor 3 is ill-behaved or halted, the internal watchdog circuit of the processor restarts program execution within two seconds. During this two-second interval, the triacs are controlled by the dimmer circuits 13, thus preventing any changes in illumination during this time. The processor is based on CMOS technology, which by nature is extremely unsusceptible to disturbance from the mains. In addition, the processor continually performs different self- test programs in the background loop such as testing of the RAM, EPROM and EEPROM memories. If the processor or its closely associated components would develop a sustained fault, the processor control can be disabled by the manual/automatic selector switch 17. Then, the lights are controllable through the touch-control dimmer circuits 13 alone using the conven¬ tional operating control switches 8.

A novelty of the above described invention is thus its ability to use only a single processor for controlling several lighting circuits, while the calibration of the basic and minimum levels of illumination can be done individually for each lighting circuit with the help of normal operating control switches distributed about the building. In addition, the illumination control circuit of the sensor 7 is closely integrated with the control switch unit 8.

Instead of the operating control switches 8, it is possible to use portable light controls, which communicate wirelessly to a receiver placed in the illumination level sensor unit 7. This kind of portable light control units may be provided with pushbuttons, whose function corresponds to that of the pushbuttons 8a and 8b.

The external controller attached to the "serial port 6 may have a higher priority than that of control switches 15...17 of the control center 1 or the control switch unit-8 or the sensors 7.