GB2278437A - Counting people entering and leaving a zone - Google Patents

Abstract

A counting device can be used to switch the lighting on when a person enters the room and switches the lighting off when the room is empty. The device has a passive infra-red sensor which emits a pulse whose polarity is dependent on the direction of movement of a person into or out of the room. The pulse is passed to a counter which is incremented or decremented accordingly. The value of the count is representative of the number of persons present in the room. When the count indicates the room is empty the lighting is extinguished. The sensor may comprise two pyroelectric detectors A and B wired in opposed parallel manner and having spaced fields of view through a slit X. Movement of a person in direction Z produces a positive pulse followed by a negative pulse, whiist movement in the opposite direction produces a negative then a positive pulse. Further circuitry detects the polarity of the first pulse of the pair. <IMAGE>

Description

COUNTING DEVICE The present invention relates to a counting device and more particularly to such a device which counts persons entering or exiting a zone in security and lighting control applications.

It is well known for lighting systems to be controlled by passive infra-red sensors. When movement of a warm body is detected in the range of the sensor, the change in state of the sensor output is used to activate a light or lighting system such that the room or zone in which the body was detected is illuminated. Such systems are commonly used domestically inside or outside the property to conserve energy by ensuring that lighting is energised only when a person is present in the room or zone as well as to act as a deterrent to potential intruders.

One of the problems with the systems described above is determining whether the person who activated the lighting is still present in the room or zone and hence whether the lighting can be turned off. In general systems which employ passive infra-red sensors can be defeated by an occupant who remains still by, for example, reading quietly in a chair and the lights are eventually automatically turned off, as such sensors detect only the movement of a warm body and not simply its presence.

Some systems employ a microphone to detect the sound of the occupant or a timer which switches the lighting off after a set period has expired. The former system can be defeated by the occupant being quiet for a period of time and the latter system makes no attempt to ascertain whether the occupant is still present.

One other system employs an intelligent camera which detects the presence of warm bodies. However, these cameras are too expensive for general use in the domestic market.

U.S. 4993049 describes an infrared sensitive system which maintains a count of the number of occupants within a room. The system activates electronic equipment (e.g. lights) when it senses a person entering an empty room and deactivates the equipment when the last person exits the room. The system employs two sensors facing in opposed directions in a common housing.

As a person approaches the entrance to the room a first sensor is triggered and a positive pulse is generated on a first sensor line. Once the person has entered the room a second sensor is triggered and a negative pulse is generated on a second sensor line. The reverse sequence of signals is generated by a person leaving the room (i.e. a negative pulse on the second line followed by a positive pulse on the first line). The count is incremented or decremented depending on whether the sequence of signals represents the entry or exit of a person respectively.

A change to the cotint is activated by the receipt of a positive pulse on the first line. the count being incremented when the status of the second line is high and decremented when the status is low. This arrangement requires two separate signal lines thereby increasing the circuitry required to amplify. monitor and manipulate the signals generated.

It is an object of the present invention to obviate or mitigate the aforesaid disadvantages.

According to the present invention there is provided a counting device for a zone comprising a movement direction sensor having an output signal in the form of a pulse whose polarity is dependent on the direction of movement of a warm body detected entering or leaving the zone. and a counter connected to the sensor, the counter maintaining a count which is incremented or decremented depending on the polarity of the pulse received from the sensor output to give a count representative of the number of wann bodies occupying the zone.

The sensor is preferably an infra-red sensor and may be pyroelectric with two fields of view. The polarity of the pulse generated is preferably dependent on in which field of view movement is detected.

Conveniently the sensor is located at or near the entrance to a room in place of a conventional light switch such that persons entering or leaving the room are detected easily. The conventional light switch socket can easily be converted to accommodate the new sensor device.

In one preferred embodiment there is provided a timer which indicates the time of entry or exit of a warm body into or out of the zone.

In security applications, when an intruder is detected the lighting may be flashed on and off as an alarm signal to supplement the conventional siren and xenon flashing light mounted in a bell-box on the exterior of the premises.

A specific embodiment of the present invention will now be described with reference to the accompanying drawings in which: Figure 1 is a schematic block diagram of a lighting control device; Figure 2 is a circuit diagram of the lighting control device; Figure 3 shows a sensor of the present invention; Figure 4 is a diagrammatic representation of the operation of the sensor of Figure 3; and Figure 5 is an example of an ideal pulse generated by the sensor of Figure 3.

Referring now to the drawings, Figure 1 shows in block form a lighting control system for a room. Movement direction sensor 1 is a standard passive infra red sensor incorporating a pyroelectric sensor which is placed near the entrance to a room. The sensor 1 outputs a pulse whose polarity depends on the direction of movement of a warm body into or out of the room. Although pyroelectric sensors have been used previously they have not been employed as movement direction sensors as the polarity of the output pulse has not been utilised. The output pulses are passed to a threshold comparator 2 which feeds an up/down counter 3.If the comparator 2 detects a positive pulse of predetermined magnitude representing, for example, entry of a person into the room the counter 3 is incremented and if a negative pulse is detected the counter 3 is decremented to indicate that a person has left the room. Thus the value present in the counter 3 is indicative of the number of people present in the room and is passed to a lighting control circuit 4.

While the count remains positive the lighting in the room is maintained in the illuminated state. As soon as the count falls to zero representing a empty room the lighting is automatically turned oft The detailed circuit diagram is shown ill Figure 2. The circuitry at the top of the diagram represents a standard arrangement for a D.C. power supply generated from the mains. The D.C. supply has an output relay RE1 which is actuable to switch the lighting (not shown) on or oft.

The lower portion of Figure 2 represents the passive infra-red sensor circuit.

A pyroelectric sensor S1 is mounted close to the entrance to a room e.g. in place of a conventional light switch adjacent the door. The construction and operation of the sensor is described in more detail below with reference to Figures 3 to 5. Figure 3 shows the pyroelectric sensor circuit arrangement. Two completely separate lithium tantalate or ceramic pyroelectric crystai sensor elements A and B are connected in parallel with opposed polarities. The sensor elements A, B are connected in turn to a FET source follower T. One suitable commercially available pyroelectric sensor is the LHi 958 supplied by Siemans-Heimann. The arrangement of the sensor elements A, B in a parallel opposed manner provides for low noise and high signal to noise ratio. The sensor elements A, B are arranged in a common housing H provided with a slit X (see Figure 4). The field of view of each sensor element A, B is shown in outline ill Figure 4 (field of view of element B is shown hatched) .

The sensing operation will now be described with reference to Figures 4 and 5. When sensor element A detects the movement of a warm body a positive pulse is generated, whereas a negative pulse is generated when sensor element B senses movement. A person moving past the sensor unit Sl ill the direction bf arrow Z from the bottom to the top of Figure 4 would first pass through A's field of view (positive pulse), then through a "blind" area between the two fields of view (no pulse generated) and finally through Bs field of view (negative pulse generated). The resulting pulse wave torm generated is shown in Figure 5 in an ideal form.In reality the form of the pulse will be distorted and dependent on a number of parameters such as the distance between sensor elements A and B, the size of slit X, how close to the warm body moves to the sensor and the size of the body. If the person walks in the opposite direction (top to bottom of Figure 5) a negative pulse will first be generated. The important part of the waveform signal generated is the first pulse and in particular its polarity which is detected by the associated circuitry.

Reference to a pulse in the following description will relate to this part of the waveform.

Referring again to Figure 2 the sensor Sl outputs a small positive pulse if, for example, movement of a warm body from right to left across the field of view is detected, and a small negative pulse if movement is detected in the opposite direction. The pulse is then passed through two band pass gain amplifiers IC1 (pins 5,6,7), and IC1 (pins 8,9,10). The amplified pulse is output at pin 8 of ICl and passed to a window comparator represented by two OP-amps of IC1 (pins 1,2,3 and 12,13,14). The output from the amplified stage is compared with the predetermined thresholds set by the voltage dividers represented by R22,R23 and R24. The outputs from pins 1,14 of the comparator IC1 are normally low.When a negative pulse is received on input pin 13 of ICI which exceeds the set threshold a positive pulse is emitted at the output of the comparator ICI at pin 14. When a positive pulse exceeding the set threshold is detected on pill 3 a positive pulse is emitted from output pin 1 of ICi.

The pulses from the window comparator (lC l pins 1,14) are fed into the clock inputs of D-type flip-flops IC4. The D input (pins 5,9) of each flip-flop is tied HIGH to the 5V rail. When a positive edge of a pulse is received at the clock input (pins 3,11) of either flip-flop of IC4 the HIGH signal on the D input (pins 5,9) is passed to the respective output (pins 1,13). The outputs (pins 1, 13) of the flip-flops of IC4 are fed to pins 1,2 of a NOR gate IC3. These pins are normally LOW, being connected to the OV rail via resistors R5 and R6. NOR gate IC3 pins 1,2,3 acts as a low impedance driver to an analogue timing circuit represented by diode D2, capacitor C23 and resistor R7.The output on pin 3 of IC3 is passed to the inputs 5,6 of a second NOR gate of IC3 which acts to invert the signal. The output on pin 4 of 1C3 is fed to the clock pulse input CP of an up/down counter IC2, and also via an inverting NOR gate (IC3 pins 8.9. 10) to the reset of each flip-flop (IC4 pins 4,10). The inputs 8,9 of NOR gate IC3 are tied HIGH via resistor R8.

A positive edge present on the clock input of the counter IC2 causes the count to increment or decrement depending on the status of the up/down control pin UP/DN. If the control pin UP/DN is HIGH then the count is incremented and if the control pin UP/DN is LOW the count is decremellted. The binary value of the count is passed to the input of an OR gate Ices. Capacitor C26 and resistor R10 together with a load circuit set at 000l (see 1C2) ensure that the count is incremented or decremented by one on receipt of each pulse at the clock input.

The lighting control relay Rl- has normally closed contacts maintaining the live supply to the lighting such that it is illuininated. The output of IC5 is fed to a transistor TR2 which activates relay KEI. When the count is 0000 the output of IC5 is LOW and the transistor TR2 base is LOW which causes the relay coil to be deenergised such that the contacts are open. When the relay RE1 contacts are open the live supply to the lighting is interrupted and the lights are extinguished.

In operation, if a person enters the room (say right to left movement) the sensor S1 detects the movement and outputs a positive pulse which is amplified and passed to the window comparator lC l (pillS 1,2,3,12,13, 14). If this pulse exceeds the pre-set threshold of the comparator a HIGH pulse appears at the pin 1 output of the comparator. This HIGH pulse is fed to the clock input (pin 3) of the upper flip-flop of IC4 resulting in a HIGH at the output (pin l). The output of the flip-flop is fed to a first NOR gate (pins 1,2,3) of lC3 which gives a LOW output in response to the HIGH input.The LOW signal is then inverted thorough the second NOR gate of IC3 (pins 4,5,6) and the resultant HIGH signal is passed to the clock input CP of the counter IC2. The control input UP/DN of the counter lC2 is HIGH by virtue of the HIGH output (pin 1) of the upper tlip-tlop of lC4 and accordingly the counter IC2 is incremented by one in response to the positive edge received at the clock input CP.The count value passed to OR gate ICS represents the number of people present in the room at any particular time and incrementing the count by one indicates that another person has entered the room Capacitor C23 discharges thorough R7 over a period of a second or two producing a delayed negative edge Oil pin 4 of lC3. The resultant positive pulse appearing at the output pin 10 of the third NOR gate acts to reset the flip-flops of IC4. The timer R7, C23 acts to delay the reset of the flip-flops as the sensor output is unpredictable after the initial triggering pulse. The unpredictability is attributable to the variation in size, speed and distance from the sensor of the moving body.

When the sensor S1 detects movement out of the room (left to right), a negative pulse is emitted and passed in its amplified form to the comparator of IC1.

If the pulse exceeds a pre-set lllresllold a HIGH pulse appears at pin 14 of It 1. The pulse clocks the lower flip-flop of 1C4 and the otitptit of 1C4 at pin 13 is forced HIGH. The HIGH signal propagates throngh the NOR gates of IC3 as before and provides the clock input CP of the coulter IC2 with a positive edge. In this case the control input UP/DN to the coulter will be LOW as the output of the upper flipflop has remained LOW and accordingly the count is decremented to indicate that a person has left the room. The flip-flop IC4 is then reset as described above.

The above described circuitry provides a method of ascertaining how many occupants there are in a room at any one time and controlling the room lighting such that only when the room is empty are tlie lights extinguished. Ideally the sensor is positioned at the entrance of the room to detect movement into and out of the room easily. A conventional light switch Unlit at or near the room entrance may be easily converted to accommodate the sensor Sl and associated circuitry. The device thus provides an effective lighting management and security lighting control device at relatively low cost.

A background light sensing circuit can be included to avoid the lights being switched on during dayligllt.

The device may be supplemented by a timer coupled to a real-time clock. The time of entry and exit of the persons could then be recorded for security purposes.

This may have particular application in premises which may be partially occupied, such as offices at the week-end. The normal alarm systems will be disabled to cater for partial occupation, and therefore a record of entry into a particular room in the premises could be of value.

It will be appreciated that the counting device described can be used in other applications such as market research (e.g. counting the number of people entering a supermarket or store over any specified period), or as a safety feature to a building (e.g. maintaining a count of people remaining in a building when it is being evacuated in the event of a fire).

The device can be fitted witll the usual alarm features which are activated when an intruder is detected, for example. there may be an external bell-box fitted to the outside of the building with a llashillg xenon light and a loud siren, and a user control panel may be fitted. The alarm could be supplemented by having the lights which are being controlled flashing on and off.

When the building is left empty the last person can switch from a lighting control operation to a standard security alarm operation and vice versa when an authorised person returns to the building.

Claims (12)

CLAIMS:

1. A counting device for a voile comprising a illoveilleilt direction sensor having an output signal in the forlll of a pulse close polarity is dependent on the direction of movement of a warm body detected centering or leaving the zone, and a counter connected to the sensor. é counter lllaiiltaiiliilg a count which is incremented or decremented depending on the polarity of the pulse received from the sensor output to give a count representative of the nuinber of warm bodies occupying the zone.

2. A counting device according to claim l, wherein the sensor is a passive infrared sensor.

3. A counting device according to claim 2, wherein the sensor is of the pyroelectric type.

4. A counting device according to claim 2 or 3, wherein the sensor has two fields of view.

5. A counting device according to claim 4. wherein the polarity of the pulse generated depends on in which field of view movement is detected.

6. A counting device according to any preceding claim, wherein the sensor is located at or near the entrance to a room in place of a conventional light switch.

7. A counting device according to any preeedillg claim. wherein there is provided a timer which indicates the time of entry or exit of a warm body into or out of the zone.

8. A counting device according to any preceding claim, wherein when an intruder is detected the lighting is flashed on and off.

9. A counting device according to any preceding claim, wherein there is provided an anti-intruder mode in which detection of an authorised intruder causes activation of an alarm.

10. A lighting control device incorporating a counting device of any one of claims 1 to 9, wherein lighting in the zone is extinguished only when the count is representative of an empty zone.

11. A counting device substantially as hereinbekfore described with reference to the acconlpanying drawings.

12. A lighting control device substantially as hereinbefore described with reference to the accompanying drawing.