Abstract:
An occupancy sensor with the following components is disclosed: a sensing probe to detect occupancy of a space monitored by the sensor and to produce a corresponding sensing signal; a comparator, including a voltage divider defining a comparison value, against which the sensing signal is compared to detect occupancy; and a voltage sensing means to sense a feed voltage applied to the sensor, where changes in the feed voltage to the sensor induce a change in the comparison value.

Description:
FIELD OF THE INVENTION 
       [0001]    The disclosure relates to occupancy-based control techniques. 
         [0002]    In various embodiments, the disclosure may relate to controlling lighting sources based on occupancy. 
       BACKGROUND 
       [0003]    Systems for controlling lighting sources, e.g. luminaries L, installed in a space to be lighted e.g. a room in a school, kindergarten or the like (as schematically shown in  FIG. 1 ) may include sensors S to detect occupancy of the space and cause the lighting source L to be activated e.g. without any manual intervention on switches or the like. 
         [0004]    In such systems configured as wireless networks with multiple occupancy sensors S bound to the same actuated device (e.g. a luminaire or a group of luminaires or any other device to be activated as a function of occupancy), every single sensor S periodically reports its detected occupancy state (occupied/not occupied) to the actuated device. This means that state reports are sent even if there is no presence in the detection area which is a common condition in most practical cases. 
         [0005]    On the one hand, this type of operation leads to high energy consumption on the sensor side, because transmitting and receiving usually is responsible for the largest part of the energy consumption in the energy budget of the sensor device. Especially for battery-powered devices this reduces significantly the battery lifetime. On the other hand, it becomes quite complicated for the actuated device to handle two different states reported from different sensor devices. 
         [0006]    For doing that, the actuated device has to be informed about the total number of sensors bound to it and which sensor device sent which state. 
         [0007]    For example, a luminaire which has received a “not occupied” status report has to know if there are other sensor devices which might send “occupied” state reports. 
         [0008]    The inventors have noted that these problems may be addressed by:
       using just a single actuator per network to transmit only status changes;   using multiple sensors, which will then result in non-synchronized switching and confusion of the user;   using more batteries or a permanent power supply;   causing the sensor devices always to listen to the wireless traffic and modify (e.g. synchronize) their own state reports according to the state reports of the other devices (e.g. no “not occupied” reports are sent as long as the other devices are sending “occupied” ones); this may means that the radios of the sensor devices have to be switched on all the time and this again, may have a strong impact on power consumption.       
 
         [0013]    Also, for handling different state reports from several devices the actuated device has to be informed about the total number of sensors bound to it and which sensor device sent which state; addressing this problem may require logic combinations (e.g. the actuated device such as e.g. a luminaire switches off only if all known sensor devices report a “not occupied” state): this requires a certain amount of memory in the actuated device, which is usually quite rare and also expensive. 
         [0014]    Also, the inventors have noted that in wireless networks with battery-powered occupancy sensors, reducing the energy consumption of the sensor modules is essential for ensuring a long lifetime (e.g. several years for standard batteries may be desirable). 
         [0015]    The inventors have similarly noted that the output voltage may decrease more than 30 percent over the lifetime of standard alkaline batteries, which has a strong impact on the power supply of the sensor and the circuit for signal conditioning which may be associated therewith. 
         [0016]    In the case of battery-powered occupancy sensors using a PIR (Passive Infra Red) sensor or probe, a decreasing battery voltage may lead to an undesired increased sensitivity with the ensuing increased risk of wrong detections. This is due to the fact that in various embodiments the signal conditioning circuit(s) may derive the signal levels from the battery voltage. 
         [0017]    The inventors have noted that this undesired effect might be avoided by using special batteries (e.g. lithium batteries, which may maintain their output voltage over most of their lifetime and exhibit a voltage drop only at the very end of their lifetime) or by using solar panels in possible conjunction with batteries to provide energy to the sensors. 
         [0018]    Such arrangements are inevitably expensive and unpractical. 
       OBJECT AND SUMMARY 
       [0019]    The invention has the object of overcoming the drawbacks of the solutions outlined previously. 
         [0020]    According to the present invention, the above object is achieved thanks to the characteristics set forth in the claims that follow. 
         [0021]    The claims form an integral part of the technical disclosure of the invention provided herein. 
         [0022]    In certain embodiments, to reduce the radio on time, and therefore the power consumption, only the status “occupied” may be periodically transmitted over the air (i.e. as a radio signal, as may be the case in a wireless system) as long as the sensor device is detecting presence while in the “unoccupied” state nothing is transmitted. 
         [0023]    In certain embodiments, in order to reduce energy consumption, a message is transmitted to the system only if presence (i.e. occupancy) is detected; otherwise there is no communication to the network. 
         [0024]    In certain embodiments, the actuated device (directly or via some other permanently powered sensor data aggregation devices) listens to the sensors—and other control devices (e.g. switches and remote controls) bound to them—and have an own internal logic (e.g. retriggerable timer) to decide about turning on or off the load (e.g. lamps) depending on the received trigger signals (“occupied” state reports) and the status reports of the other control devices influencing the behavior. 
         [0025]    In certain embodiments, the time between the “occupied” state reports of the sensor devices may be used to optimize energy consumption. 
         [0026]    In certain embodiments, the actuated device may be additionally informed about the reporting interval (e.g. by a fixed configuration or, to be more flexible, as additional information together with the “occupied” state report) and may automatically react (e.g. by switching the light off) if the reporting interval is exceeded with no further status report received within the reporting interval from any device. In this case it does not matter if the status report was sent by a single sensor device or multiple sensor devices, because each received status report may just reset the timer which controls the reporting interval in the actuated device. 
         [0027]    In certain embodiments, the actuated device will not have to be necessarily aware of the number and the individual status of each sensor device, because it will just automatically act as long as “occupied” state reports are received within the known reporting interval time and will react according to its application (e.g. switching off) if no state reports are received any more. 
         [0028]    In certain embodiments, the actuated device may also listen to commands of manual control devices and override the sensor state reports according to them if necessary. 
         [0029]    In certain embodiments, it will not be necessary for the sensor device to have the radio switched on all the time, as it will be enough to switch it on only when the reporting interval is exceeded and a presence has to be reported. For the rest of the time the device can be in low power mode with the radio switched off. 
         [0030]    In certain embodiments, it will be enough for the sensor device to switch its radio on only when the reporting interval is exceeded and a presence has to be reported; for the rest of the time, the device can be in sleep mode. 
         [0031]    In certain embodiments, in order to achieve a long battery lifetime the sensor (and primarily the microcontroller that may be included therein) may be in a sleep mode as long as no person is within the detection area. 
         [0032]    In certain embodiments, a circuit which comprises the signal conditioning functions of the sensor is may consume only a few microamperes and wake up the microcontroller as soon as presence is detected. 
         [0033]    Certain embodiments may compensate the change in sensitivity of signal monitoring of the occupancy sensors due to decreasing battery voltage. 
     
    
     
       BRIEF DESCRIPTION OF THE ANNEXED FIGURES 
         [0034]    The invention will now be now described, purely by way of non-limiting example, with reference to the annexed figures, wherein: 
           [0035]      FIG. 1  has been already described in the foregoing; 
           [0036]      FIG. 2  is a time diagram showing signals generated in certain embodiments; and 
           [0037]      FIGS. 3 and 4  are block diagrams of occupancy sensors. 
       
    
    
     DETAILED DESCRIPTION 
       [0038]    In the following description numerous specific details are given to provide a thorough understanding of embodiments. The embodiments can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail in order to avoid obscuring aspects of the embodiments. 
         [0039]    Reference throughout this specification to “one embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrase “in certain embodiments”, in various places throughout this specification are not necessarily all referring to the same embodiments. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments. 
         [0040]    The headings provided herein are for convenience only and do not interpret the scope or meaning of the embodiments. 
         [0041]    As already indicated,  FIG. 1  is schematically representative of an occupancy-based control system, in the exemplary form of a system for controlling a lighting source, e.g. one or more luminaries L, installed in a space to be lighted e.g. a room in a school, kindergarten or the like. The system includes a plurality of sensors S to detect occupancy of the space and cause the lighting source L to be actuated. 
         [0042]    The exemplary system illustrated in  FIG. 1  is configured as wireless network with multiple occupancy sensors S bound to the same actuated device (e.g. a lighting source L such as a luminaire or a group of luminaires or any other device to be activated as a function of occupancy). Activation of the controlled device may be either directly or via some other permanently powered sensor data aggregation device, i.e. a device adapted to collect the signals from the (e.g. battery operated) sensors S and to activate/deactivate the controlled device accordingly. 
         [0043]    Save for what will be described in the following, the general layout and operation of the system including the actuated device (e.g. a lighting source L) and the occupancy sensors S is conventional in the art, thus making it unnecessary to provide a more detailed description herein. 
         [0044]      FIG. 2 , including three portions designated a), b), and c), respectively, is a time diagram showing, over a common time scale t:
       an exemplary output signal emitted by any of the sensors S (portion a);   the presence P of a person (i.e. the occupancy) detected by the sensor in question (portion b); and   the activation(ON)/de-activation(OFF) of the device (e.g. a lighting source such as e.g. one or more luminaries) actuated i.e. controlled by the system.         
         [0048]    The output signal emitted by the sensor(s) varies between a low power level LP and a high power level HP. 
         [0049]    The representation of  FIG. 2  assumes that the output signal is at the low power level LP when a “presence” P (i.e. an occupancy) is detected at a time TP. 
         [0050]    As a result of this, the sensor switches for a time frame t TI  to high power mode (radio turned on) in which the sensor connects to the network to get in contact with the actuated device L (or its bound actuators) to send its “occupied” state reports and then returns to the low power level LP. 
         [0051]    In  FIG. 2 , t DI  denotes the time between two high power node time frames t TI  in which the sensor device is in low power mode LP (radio turned off). In this mode the device may be running its application for detecting presence or being asleep. 
         [0052]    Finally, in  FIG. 2 , t RI  denotes the time frame between two “occupied” state reports. An internal timer associated with the actuated device (e.g. the lighting source) is set to this value after having received an “occupied” state report. If another “occupied” status report is received within this time the timer is reset to t RI . If no “occupied” status report is received within that time span the actuator will switch off its load. 
         [0053]    It will be appreciated that neither the power consumption nor the time line is scaled. In reality the time t TI  for transmitting and receiving will be generally much shorter in comparison with t DI . 
         [0054]    Also the difference between “low power mode” LP and “high power mode” HP will be relatively much larger than the difference between the base line and “low power modes”. 
         [0055]    In the exemplary embodiments considered herein:
       the state reports are not sent periodically in general, but only the “occupied” state is transmitted if some presence P is detected and this report is sent periodically only as long as the state does not change to unoccupied;   additionally, the acting device may be informed about the reporting interval (e.g. by a fixed configuration) and automatically react (e.g. by switching the light off) if the reporting interval is exceeded and no further status report has been received within the reporting interval from any device: in this case, it does not matter if the status report was sent by a single sensor device or multiple sensor devices, because every received status report just resets the timer which controls the reporting interval in the acting device.       
 
         [0058]    As a result, in the exemplary embodiments considered herein, it is not necessary for the activated device L to be aware of all sensor devices S, because it will just automatically act as long as “occupied” state reports are received within the known reporting interval time and react according to its application (e.g. switching off) if no state reports are received anymore. Consequently, it will not be necessary for the sensor device to have the radio switched on all the time. 
         [0059]    The block diagram of  FIG. 3  is representative of an occupancy sensor S using a sensitive element  101 —of any known type, e.g. a PIR (Passive Infra Red) sensor or probe. 
         [0060]    The signal produced thereby (which may be indicative of occupancy, e.g. the presence of one or more persons in the detection area covered by the sensor S) may be amplified and filtered by two or more cascaded amplifier stages  102 ,  103 . The resulting signal thus possibly conditioned is fed to a window comparator  104  including two comparator elements such as e.g. operational amplifiers  104   a,    104   b  defining upper and lower thresholds or limits, respectively. When the signal fed to the comparator  104  reaches a certain upper or lower threshold level, the output of the window comparator  104  changes from low to high and may “wake up” the circuitry (e.g. a microcontroller)  105  of the sensor which was previously in “sleep” mode, with reduced consumption. 
         [0061]    Certain embodiments may adopt such a window comparator (that is two thresholds) as the probe  101  may provide, when no movement is detected, a constant output voltage lying between the upper and lower levels thresholds of the window comparator and react only to a change of the infrared radiation. 
         [0062]    For instance, the probe  101  may include a lens with several facets which project the infrared radiation on the sensing surface: when a person moves from the area covered by one facet to the area covered by another facet, the infrared radiation onto the sensor surface changes and the sensor signal increases or decreases (depending on the direction of the movement); consequently, the signal (which is between the upper and lower level of the window comparator when no movement is detected) may go up (and exceed the upper level) or down (und go below the lower level). In certain embodiments, the signal-conditioning circuitry (e.g.  102 ,  103 ) may amplify only this change of the sensor output voltage. 
         [0063]    A basic concept underlying the exemplary embodiment of  FIG. 3  (and similarly of FIG.  4 ) is having a voltage divider which defines at least one comparison value against which the signal produced by the sensor or probe  101  (as possibly conditioned by the stages  102  and  103 ) is compared to detect presence/occupancy in the detection area of the sensor S. 
         [0064]    In the exemplary embodiment of  FIG. 3 , the voltage divider interposed between the power voltage (V Battery ) and ground includes first, second and third resistors RA, RB, RC in series. 
         [0065]    The intermediate point A between the first and second resistors RA and RB is connected to the inverting input of the op-amp  104   a  and thus defines the upper threshold or limit of the detection window of the comparator  104 . 
         [0066]    The intermediate point B between the second and third resistors RB and RC is connected to the non-inverting input of the op-amp  104   b  and thus defines the lower threshold or limit of the detection window of the comparator  104 . 
         [0067]    This means that the voltage divider RA, RB, RC defines at least one comparison value against which the signal produced by the sensor or probe  101  (as possibly conditioned by the stages  102  and  103 ) is compared to detect presence/occupancy in the detection area of the sensor S and correspondingly wake-up the transmitting part of the sensor (i.e. the microcontroller  105 ). 
         [0068]    In such a sensor S, when battery powered (i.e. with the various elements  101 ,  102 ,  103  and—primarily  104 —fed with a voltage V Battery —derived from one or more batteries) a decreasing battery voltage V battery  may lead to an undesired increased sensitivity with the ensuing increased risk of wrong detections. 
         [0069]    This effect is largely independent of a number of factors, such as e.g.:
       the type of the sensor element  101 ,   the specific circuit layout of the stages  102 ,  103 , and   the specific arrangement of the elements defining the comparison value or values of the comparator  104 .       
 
         [0073]    The following disclosure provided in connection with  FIG. 4  will thus also apply e.g. to sensor elements  101  other than a PIR probe, as well as to conditioning stages  102 ,  103  (if present) and a comparator  104  having a layout different from the one exemplified in.  FIGS. 3 and 4 . 
         [0074]    In that respect, parts and components which are identical or equivalent are indicated with the same references in both  FIGS. 3 and 4 ; for the sake of brevity, the relative description already provided in connection with  FIG. 3  will not be repeated in connection with  FIG. 4 . 
         [0075]    In the exemplary embodiment of  FIG. 4 , before being fed to the comparator  104 , the signal from the sensor  101  (e.g. PIR) is passed through the stages  102  and  103  for conditioning before being fed to the comparator  104 . The comparator  104  monitors the signal and wakes up the microcontroller  105  as soon as movement is detected. 
         [0076]    The microcontroller  105  sends a RF message to the wireless network (e.g. to switch on the light source L with a message to the network to switch on the light source for a certain time T on ) and returns to the sleep mode immediately thereafter. 
         [0077]    In certain embodiments, the possibility for the microcontroller  105  to wake-up may be inhibited, that is de-activated, for a certain off-time (e.g. 2 seconds). 
         [0078]    When in the sleep mode (and not possibly temporarily inhibited) the microcontroller  105  can be woken-up again by the sensor. 
         [0079]    In certain embodiments, the microcontroller  105  may be configured so that, whenever woken-up by the sensor, the microcontroller  105  checks if the end of the time period T on  is reached, and in that case the message “light on for T on ” may be renewed. 
         [0080]    The exemplary embodiment considered herein may be adapted to operate with standard alkaline batteries having an output voltage which decreases (e.g. linearly) during the battery lifetime. This may result i.a. into a corresponding change (e.g. decrease) in the width of the detection window of the comparator  104 , with the ensuing drawbacks already discussed in the foregoing (increased sensitivity, increased risk of wrong detections). 
         [0081]    In certain embodiments, this undesired effect may be compensated by causing the resistance RB between the points A and B (see  FIG. 3 ) to be replaced or supplemented (as depicted in  FIG. 4 ) by a set of resistors R 1 , R 3 , R 3 , . . . , Rn having associated electronic switches Q 1 , Q 2 , Q 3  . . . , Qn (such as e.g. MOSFETs) controlled e.g. by the micro controller  105 . In the exemplary embodiment illustrated in  FIG. 4 , n=3. 
         [0082]    When “on” (i.e. conductive), each switch Q 1 , Q 2 , Q 3 , . . . will short-circuit the respective resistor R 1 , R 3 , R 3 , . . . thus yielding a zero resistance. 
         [0083]    When “off” (i.e. non-conductive), each switch Q 1 , Q 2 , Q 3 , . . . will permit the respective resistor R 1 , R 3 , R 3 , . . . to add a non-zero resistance value to the resistance between the points A and B. 
         [0084]    In the exemplary embodiment considered, “digitally” (i.e. on/off) activating an increasing number of the resistors R 1 , R 3 , R 3 , . . . will cause the voltage at A to increase and the voltage at B to decrease, with a consequent effect on the width the detection window of the comparator  104  in order to compensate for the change (e.g. decrease) in the detection window width due to the change (e.g. decrease) in the battery voltage V battery . 
         [0085]    The exemplary embodiment considered will minimize current (i.e. power) absorption since electronic switches Q 1 , Q 2 , Q 3 , . . . such a MOSFETs will exhibit a current absorption in the range of microamperes. 
         [0086]    Also, in certain embodiments, selecting resistance values as R 1 =R, R 2 =2R, R 3 =4R, . . . , Rn=R 2 ̂(n−1)—that is with resistance values arranged in an increasing series of powers of two—will permit to control the detection window with 2̂n equidistant levels. 
         [0087]    In certain embodiments, switching (i.e. selectively turning on and off) the switches Q 1 , Q 2 , Q 3 , . . . may be controlled by the microcontroller  105 . 
         [0088]    In order to do so, the microcontroller  105  may sense the voltage V battery  either directly (as depicted in  FIG. 4 ) or indirectly (e.g. by sensing a voltage at a point of the divider at the input of the comparator  104 ) and act on the switches Q 1 , Q 2 , Q 3 , . . . to maintain the voltage drop between A and B (substantially) constant. 
         [0089]    In certain embodiments, a simple procedure to do this may involve activating the resistors R 1 , R 2 , R 3  in such a way that the sum of the resistance values of the resistors activates gradually increases as the voltage V battery  decreases. 
         [0090]    A concept underlying the exemplary embodiment of  FIG. 4  can thus be summarized as involving two basic steps:
       detecting any changes (e.g. a decrease) in the voltage (e.g. V battery ) which powers the sensor S, and   acting on a voltage divider which defines at least one comparison value of a comparator against which the signal produced by the occupancy sensor or probe is compared in order to keep the at least one comparison value substantially constant, thus countering any changes induced thereon by a change (e.g. a decrease) in the voltage which powers the sensor S.       
 
         [0093]    In certain embodiments (such as exemplified in  FIG. 4 ) the signal produced by the occupancy probe  101  is compared against a comparison value given by the width of a window (i.e. between an upper and a lower threshold). Any changes (e.g. a decrease) in the voltage which powers the sensor S being detected may lead to acting on the voltage divider (RA, RB, R 1 , R 2 , R 3 , RC) in order to keep the width of said window substantially constant. 
         [0094]    Of course, without prejudice to the underlying principles of the invention, the details of construction and the embodiments may vary, even significantly, with respect to what is described and illustrated herein, without thereby departing from the scope of the invention, as defined by the annexed claims.