CONTROL DEVICE RESPONSIVE TO INFRARED RADIATION

Abstract: An improved device for controlling a current line to such items as interior lighting and room air conditioners includes a pyroelectric infrared detector (25) having its own preamplifier to produce an output signal in response to a person moving within the field of view of the detector. The output signal is successively amplified in two stages (30), (40) and sent to a control unit (100) to close a current line. A timing circuit (80) is included to end the signal to the control unit when no motion of a person is sensed within a predetermined time period. The device provides adequate signal to noise ratio with minimum sophisticated or expensive components.

Description: CONTROL DEVICE RESPONSIVE TO INFRARED RADIATION §._l i__._ ll_i≤.-_._I-l£-i The present invention relates to an improved de¬ vice able to control such items as interior lighting in response to the presence or absence of a person within the service area of the item. • Control devices responsive to heat radiating from a human body are known and recently a device has been pro¬ posed which is particularly useful for controlling a cur¬ rent line to such items as interior lighting or room air conditioners in order to deactivate these items when no one is within their service area. This control device is described in united States patent application serial No. 053,249 filed June 19, 1979, and includes an infrared de- tector comprised of a thermopile formed by thin-film techniques for producing signals which must be amplified significantly by a series of amplifier stages. The ampli¬ fied signals are then digitalized for receipt by a reset port of a digital timing circuit which develops a control signal directing opening of a current line when no signal is received at its reset port for a time period longer than that normally expected between movement of a human body within the field of view of the detector. The thermopile used in the infrared detector de¬ velops a signal of a relatively low level which must be amplified repeatedly to provide a signal of a level which can be digitalized for receipt by the timing circuit. Consequently, it is quite difficult to maintain a ade¬ quate signal-to-noise ratio without, sophisticated and relatively expensive components. Further, several circuit components are necessary to properly digitalize the ampli¬ fied signal, and the timing circuit itself includes a dis- crete digital counter receiving a train of clock pulses, generated by a digital clock circuit. The device des¬ cribed in the application noted above thus includes both analog and digital components of a relatively large number and thus is relatively ' expensive. Additionally, it is often desired to reduce the circuitry of such a device to one or perhaps two integrated circuits and thus enable the control device to be included directly within such items as the fixture for a fluorescent light. Accordingly, it is an object of the present in- vention to provide a control device able to control an auxiliary item in response to the presence or absence of a person within the item's service area which is both rela¬ tively inexpensive and of a minimal number of components, and yet is highly reliable. This and other objects of the present invention are attained by a control device having means including a pyroelectric infrared detector sensing infrared radiation in the frequency spectrum emitted form the human body for producing a detection signal in response to a change in the level of radiation within that spectrum. The detection signal is received by circuitry producing a control signal 5 usable for controlling * n auxiliary current line, and this circuitry includes a timing circuit which ends the control signal upon failing to receive another detection signal in a time period longer ' than that expected between movements of a person within the field of view of the detector. In 10 preferred form, the device also includes control means which close the auxiliary current line upon receipt of a control signal of a predetermined voltage level and thereafter open the current line upon the ending of the control signal. The timing circuit preferably includes a capaci- 5 tor initially charged by the control signal and connected to . ** threshold detector continuing the control signal as long as the capacitor maintains a prescribed charge level. A resistor is connected to the capacitor to enable the capaci¬ tor to maintain its prescribed charge level for the neces- Q sary time period. The pyroelectric detector may include an optical filter coated to pass only a narrow band containing the frequency spectrum and may be fitted within a housing having a window, spaced from the side of the detector receiving 5 radiation. Such window is preferably made from polyethy¬ lene and serves to prevent convective heat transfer to the detector. The control device of the present invention pre¬ ferably includes several circuit elements to provide re¬ liable sensitivity and these include a filter circuit for attenuating signals produced below a certain frequency to retain those higher frequency signals corresponding to movement of a human body. Also, a comparator circuit may be included which receives the amplified detection signal and produces the control signal only when the detection signal exceeds a predetermined value. These and other objects, features and advantages of the present invention will become further apparent from the following description of a preferred embodiment thereof made with reference to the accompanying drawings, in which: Fig. 1 is block diagram illustrating electronic components of a preferred embodiment of the present in¬ vention; Fig. 2 is a sectional view of one form of housing for the electronic components of the present invention; Fig. 3 is a top plan ipw- of portions of the housing, of Fig. 2 taken along line 3-3 of Fig. 2; Fig. 4 is a side plan view of the locator of Fig. 2; and Fig. 5 is a diagram illustrating the circuitry of a preferred embodiment of the present invention. The electronic components of the control device of the illustrated embodiment are shown generally in the block diagram of Fig. 1, and inlcude an infrared detector 25 able to produce detection signals in response to infrared radiation in the frequency spectrum emitted from the human body. The detector 25 includes a preamplifier to provide an output signal of relatively high value, and a pyroelec- trie detector such as the model 5L21 pyroelectric detector of Plessey Optoelectronics and Microwave, Ltd. of Northamptonshire, England is preferred. The signal produced by the detector 25 is sent to a first amplifier stage 30, and then to a second ampli- fier stage 40 which has a low pass filter for those signals changing at a frequency below a predetermined value. The infrared detector will respond with relatively low fre¬ quency signals to changes in temperature of a stationary object within its field of view, and will respond with higher frequency signals to movements within the field of view of an object having a relatively constant temperature level. Consequentl ,. the low pass filter will serve as an electronic filter eliminating signals produced by mere temperature change of a stationary object, such as those produced by incident radiation from a carpet being warmed or cooled from sunlight or an incandescent light bulb, and retain the higher frequency signals corresponding to moverren of a body emanating radiation in the desired spectrum. The signals emerging from the amplifier stage 40 are sent to a comparator 60 which produces a control signal when the signal from amplifier stage 4Q exceeds a predetermined level. The control signal from the comparator 60 is passed by a timer 80 to a control unit which pre¬ ferably closes a current line in response to the presence of the control signal. The timer 80 serves to end the sig¬ nal from the comparator 60, and thus open the current line, when the detector fails to produce another detection signal for a time period longer than that expected between move¬ ments of a person within the field of view of the detector. The control device of the illustrated embodiment of the present invention may be housed in any of several ways and, as illustrated, is fitted within housing 1 formed of a synthetic material such as ABS copoloiπer plated with a metallic finish by know vacuum techniques. The housing includes a generally rectangular base portion 2 having a central recess area 3 surrounded by a peripheral seat por- tion 4. The peripheral seal portion carries a plurality of spacers 5 lying oppositely to spacers 6 carried by the back plate 7 of the housing. A printed circuit board 8 is held between aligned spacers 5 and 6 and carries the majority of the electronic components of the device. Depending from the central recess area 3 is a depending neck portion 9 adapted to receive a retaining element 10 on its lower portion. The infrared detector 25 includes a hermetically sealed container 26 fitted within the lower portion of the neck portion 9 n ^ having a small opening covered by a filter of infrared-transparent germanium coated to pass only a narrow band of infrared radiation containing the 79 rfrequency spectrum emitted by the human body. This band preferably includes radiation having only wavelengths be¬ tween 8 microns and 14 microns so the filter thus serves as an optical filter narrowing the spectral sensitivity of the 5 detector. The control device may be installed easily even in existing building structures and the like by placing the base portion 2 behind an opening 14a in a ceiling or wall unit 14 or the like with suitable resilient spacing ele- Q ments 15 placed between the base portion and ceiling unit. The neck portion 9 may then be inserted through, the opening 14a until its lower portion protrudes into the service area of an item to be controlled by the control de¬ vice. The retaining element 10 will then be tightened down on the protruding: * lower portion to secure the control de¬ vice in place. The retaining element 10 preferably is threaded onto the lower portion of the neck portion, but may be secured in other ways, such as by being press-fitted or snapped into place through resilient locking tabs. The neck portion 9 is generally circular in cross- section and receives a locator 16 fitting axially therein and having a rear surface 17 ' secured to the printed circuit board 8 by defor able posts 17a_ fixed within mating apera- tures in the board. In its end portion, the locator 16 has a recess 18 surrounded by a rim portion 19. The back w Λall:, 18a of the recess receives and holds the container 26 for the infrared detector. The upper portion of the locator 16 has a plurality of longitudinally extending ribs 19 spaced circumferentially therearound. These ribs are complementary with longitudinal recesses 20 formed in the inner wall of the neck portion 9. In this way, the locator will.be easily placed and held within the neck portion to position: the de¬ tector accurately within the control device. The end portion of the neck portion 9 includes a bottom wall 21 having a central opening 21a_ therethrough. An outer window 22 lies over this central opening-and is held in spaced relation from the detector 25 by an O-ring 23 compressed between the rim portion 19 of the iocator and the outer window 22. The outer window prevents air currents from reaching the surface of the detector container 26 to thereby reduce false triggering of the detector by convec- tive heat transfer. The outer window 22 must, of course, be transparent to infrared radiation and preferably is an inexpensive sheet of polyethylene. The filed of view of the detector 25 is defined by the geometry of the opening 21a in the bottom wall of the neck portion and the opening 24 formed in the retaining ele¬ ment 10. The openings 21a_ and 24 are each preferably in the form of a conical frustum flaring outwardly to provide a conical field of view having an angle of between 90° and 120* " at its apex. "ΪS ^ An an optional feature, the control device may be provided with a cover member fitting over the entire housing and adapted to be mounted to a wall or ceiling unit. In this way, the device may be mounted directly to the outer sur¬ face of the wall or ceiling unit without the need for pro¬ viding a hole therethrough. Such a cover could be snapingly engaged with the housing and would, of course, have a small opening aligned with the detector. The circuit diagra of Fig. 5 illustrates the cir¬ cuitry of the illustrated embodiment in more detail. ' A regulated power source 11 of 12V is formed by the one amp bridge rectifier 11a connected throught the resistor lib across the capacitor ll£ and three terminal 12V voltage regulator lid. The infrared detector 25 is connected as shown to the power source and includes a pyroelectric ele¬ ment 27 which changes its electrical field characteristics according to changes in the radiant energy impinging on its surface. Whenever a person moves within the field of view of the pyroelectric element 27 there is a net change in the level of radiation reaching the pyroelectric element, and this net change of radiation produces a corresponding sig¬ nal to the gate of the J-FET preamplifier 28 having its source and drain connected across the regulated voltage supply. The J-FET preamplifier and pyroelectric element are formed as a single circuit component and thus produce a relatively high quality output signal. The change in voltage level thus produced across the J-FET preamplifier produces a changing signal whose AC components are coupled to the amplifier stage 20 by the capacitor 29. Amplifier stage 20 includes an operational 10 amplifier 32 which may be one of four operatonal amplifiers provided on a single integrated circuit, such as the LM324N sold by National Semiconductor. The pin connections for such an integrated cir- σuit containing four operational amplifiers are shown in Fig. 5 where it can be seen; the input pin 9 of operational amplifier 32 receives a fixed bias supplied by the voltage divider formed by resistors 34 and 35. The AC signal from the detector 25 is coupled to the input pin 10 to produce an output at pin 8 corresponding to the net change in the AC signal, which may be an increasing signal produced by motion toward the detector 25, or decreasing signal pro¬ duced by motion away from the detector. Resistors 36 and 33 are selected to set an overall gain of about 100 for the amplifier stage 30, and capacitor 38 is selected to reduce the adverse effects of higher frequency noise, such as those which, may be produced from 60Hz transmission lines or the like. Further amplification takes place in the second amplifier stage 40 comprised of operational amplifier 42 • preferably formed by another of the operational amplifiers of the single integrated circuit. Resistors 44 and 45 are selected to provide an AC gain of about 60. Further, am¬ plifier stage 40 includes a low pass filter formed by re- sistor 44 and capacitor 46 which serve to attenuate gradual changes in the signal input to pin 12. In this way, the DC gain of the second amplifier stage can be set * at 1 to produce a low output signal for inputs changing gradually, 11 - _ . such as those expected from signal generated by the station¬ ary object. Capacitor 48, similar to capacitor 38 of the first amplifier stage, serves to eleminate environmental noise. A third operational amplifer 62 fro s part of a comparator circuit 60 receiving the output of the second amplifier stage by way of the coupling capacitor 50 and resistor 52. Input pin 2 of operational amplifier 62 re¬ ceives a bias voltage fixed by the voltage divider formed by resistors 64 and 66. Operational amplifier 62 serves to produce an ouput at pin 1 for any signal at input pin 3 having a voltage more positive than the fixed bias to pin 2. Consequently, a changing output signal coupled by capacitor 50 and developed by resistor 52 that exceeds a predetermined voltage level of, for example 4.9V, will cause the output of operational amplifier 62 to rise from zero volts to a higher level approaching the regulated voltage supply. In this way, the comparator 60 will serve to produce an output signal for only those amplified signals reaching a pre- selected value corresponding to motion of a person within the field of view of the detector. The output from the comparator 60. is passed throug the diode 70 and the timing circuit 80 to the base of an NPN switching transistor 102 by way of resistor 103. The switching transistor, which may be the 2N3471, is rendered conductive by a signal at is base to activate relay 104 adapted to close an auxiliary current line, preferably through, a step up transformer. The high voltage output from the comparator 60 also serves to charge the capacitor 82 relatively instantaneously to a voltage near the regulated line vol¬ tage. This voltage also appears at input pin 6 of the fourt operational amplifier 84 which servies to pass a voltage to the base of transistor 102 sufficient to bias the tran¬ sistor conductive as long as the voltage at input pin 6 is more positive than the voltage produced at pin 5 by the voltage divider formed by resistors 86 and 88. Resistor 90 is connected to capacitor 82 and serves as-a discharge path for the charge * placed on the capacitor 82. Consequently, when the signal from the comparator 60 returns to its low voltage state, i.e. , when no change in radiation corresponding to movement of a per- son is noticed by detector 25, capacitor 82 will discharge slowly through resistor 90 at a rate set by .the values of capacitor 82 and resistor 90. The operational amplifier 84 serves as a threshold detector in that when the voltage on capacitor 82 falls below the threshold needed to maintain the output from operational amplifier 84, the output signal at pin 7 of the operational amplifier 84 is ended to render the transistor 102 non-conductive and de-activate realy 104 so as to open the auxiliary current line. The values of capacitor 82 and resistor 90, as well as those of the resistors 86 and 88 fixing the threshold operating voltage of the operational amplifier 84, are selected to assure that the output from operational amplifier 84 will be maintained for a time 13 , period longer than that expected between movements of a person within the field of view of the detector 25. ' A time period of, for example, about eight minutes has been found satisfactory. In this way, the transistor 102 will become conductive to close a current line to interior lighting or the like whena person first enters the field of view of the detector, and will become non-conductive to open.the current line eight minutes after the detector fails to sense any human activity. From the above, it is apparent that the present invention includes important features in both, its circuitry and structural aspects of its illustrating housing. The control device may be installed readily and includes both optical and electronic filters to provide a high discrimina- tion. Further, the devicecan be adapted for many uses and, as set forth above, can be made to close a current line to interior lighting or the like whenever someone enters the field of view of the detector, and will keep the current line closed as long as even slight motion. such as simple hand motions or even writing at a desk, are made within the detector's field of view. Thereafter, the control de¬ vice will open the current line soon after no motion is sensed within the detector's filed of view , i.e., after all persons have left the field of view, * and will reclose the current line should someone again re-enter the field. Further, the above functions, have been attained with relatively few circuit components and thus the control OM?I 14 device can not only be produced inexpensively, but may also be reduced quite simply to one or two integrated circuits easily fitted directly within the item to be controlled. For example, the control device could be fitted within flourescent light fixtures to control activating current to the ballast with only minimal modification to conventional fixtures. These and other important features may be em¬ ployed in forms other than those described for the preferred embodiment and still incorporate the substance of the in¬ vention which is intended to be defined by the appended claims.

Claims: 15 What is. claimed is: . ι 1. A device responstive to heat emanating from a human body for controlling an auxiliary current line comprising means including a pyroelectric detector sensing infrared ' radiation in the frequency spectrum emitted from 5 the human body for producing a detection signal in response to a change in radiation in said spectrum, circuit means adapted to receive said detection signal for producing a control signal usable for controlling said current line, said circuit means including timing means for ending said Q control signal upon failing to receive another detection signal in a time period longer than that expected between movements of a human body within the field of view of said detector. 2. A device according to claim 1, further including control means for closing said current line upon receipt of a control signal of predetermined voltage level and thereafter opening said current line upon the ending of 5 said control signal. 3. A device according to either claim 1 or 2, said timing means including a capacitor initially charged by said control signal and connected to a threshold detec¬ tor continuing said control signal as long as said capaci- $ tor maintains at least. a predetermined level of charge, and a resistor connected to said capacitor to enable said capacitor to maintain said at leat predetermined level of charge for said time period. 4. A device according to claim 1, said detector having an optical filter coated to pass only a narrow band containing said frequency spectrum. 5. A device according to either claim 1 or 4, said detector being fitted within a housing having a window spaced from the side of said detector receiving radiation to prevent convective heat transfer to said detector.

Inventors: DUNBAR ROBERT A
Applicants: DUNBAR ROBERT A, KITSON BLISSET, ROTHENHAUS ROBERT, BLISSET KITSON
Application year: 1981
Main classification: G08B13
IPC codes: G01V8, G08B13, H03K17