CA1056931A - Smoke detector - Google Patents
Smoke detectorInfo
- Publication number
- CA1056931A CA1056931A CA207,336A CA207336A CA1056931A CA 1056931 A CA1056931 A CA 1056931A CA 207336 A CA207336 A CA 207336A CA 1056931 A CA1056931 A CA 1056931A
- Authority
- CA
- Canada
- Prior art keywords
- pulse
- flip
- amplifier
- light
- output
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/47—Scattering, i.e. diffuse reflection
- G01N21/49—Scattering, i.e. diffuse reflection within a body or fluid
- G01N21/53—Scattering, i.e. diffuse reflection within a body or fluid within a flowing fluid, e.g. smoke
-
- G—PHYSICS
- G08—SIGNALLING
- G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
- G08B17/00—Fire alarms; Alarms responsive to explosion
- G08B17/10—Actuation by presence of smoke or gases, e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means
- G08B17/103—Actuation by presence of smoke or gases, e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means using a light emitting and receiving device
- G08B17/107—Actuation by presence of smoke or gases, e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means using a light emitting and receiving device for detecting light-scattering due to smoke
Abstract
ABSTRACT OF THE DISCLOSURE
A smoke detector of the type utilizing photo-electric detection of light reflected from smoke particles, which is almost completely immune to false alarms from changing ambient light and random electrical noise, with a sensitivity that is independent of ambient light, with a power consumption low enough to permit battery operation for a period of over 12 months. The light source is a light emitting diode which is pulsed at a low repeti-tion rate, such as one pulse every two seconds, by an extremely short pulse, such as 20 microseconds. Voltage pulses generated by the photo-generative cell when smoke is present in the housing are amplified and applied to a level detector, the output of which is applied to the "set" terminal of a flip-flop circuit. The amplifier is on continuously, however the level detector is pulsed to the on condition simultaneously with the on pulse to the light emitting diode, and for the same period of time. Simultaneously with the application of the pulse to the light emitting diode and the level detector, a shorter pulse is applied to the 're-set' terminal of the flip-flop circuit. The output of the flip-flop circuit may be applied through an integrator to an alarm energiz-ing switch. The integrator has a time constant that is longer than the pulse time, so that more than a single pulse from the flip-flop must be applied thereto to activate the alarm energizing switch. The photo-voltaic cell is capacitor coupled to the amplifier, so that constant or changing light, having a rate of change below that to which the amplifier responds, cannot affect the amplifier to cause a false alarm. Since the level detector is on only about 1/100,000 of the total time, a false alarm can be caused only by an extremely fast change in ambient light or a random noise pulse, that occurs at the exact instant the level detector is on, in two consecutive pulse times. In one embodi-ment of the invention, to prevent power supply voltage changes from affecting the operation of the amplifier, a capacitor is provided across the power leads to the amplifier, and means is provided between the capacitor and the power supply for electric-ally isolating the amplifier and capacitor from the transient voltages from the power supply, which are caused by the turning on of the light generating device, or from other causes. In one form of the invention said means comprises a choke coil in the line to the capacitor and a second choke coil in the line to the light generating device. In another embodiment of the invention the isolating means may be Zener diodes in place of choke coils.
In a third embodiment of the invention the means comprises a switch in the power line between the capacitor and the power supply, with means being provided to open the switch when the light generating device is energized. In each embodiment, the amplifier is isolated from transient voltage changes during the time the light generating device is energized, so that the pulse of energy required to power the amplifier is provided by the capacitor.
A smoke detector of the type utilizing photo-electric detection of light reflected from smoke particles, which is almost completely immune to false alarms from changing ambient light and random electrical noise, with a sensitivity that is independent of ambient light, with a power consumption low enough to permit battery operation for a period of over 12 months. The light source is a light emitting diode which is pulsed at a low repeti-tion rate, such as one pulse every two seconds, by an extremely short pulse, such as 20 microseconds. Voltage pulses generated by the photo-generative cell when smoke is present in the housing are amplified and applied to a level detector, the output of which is applied to the "set" terminal of a flip-flop circuit. The amplifier is on continuously, however the level detector is pulsed to the on condition simultaneously with the on pulse to the light emitting diode, and for the same period of time. Simultaneously with the application of the pulse to the light emitting diode and the level detector, a shorter pulse is applied to the 're-set' terminal of the flip-flop circuit. The output of the flip-flop circuit may be applied through an integrator to an alarm energiz-ing switch. The integrator has a time constant that is longer than the pulse time, so that more than a single pulse from the flip-flop must be applied thereto to activate the alarm energizing switch. The photo-voltaic cell is capacitor coupled to the amplifier, so that constant or changing light, having a rate of change below that to which the amplifier responds, cannot affect the amplifier to cause a false alarm. Since the level detector is on only about 1/100,000 of the total time, a false alarm can be caused only by an extremely fast change in ambient light or a random noise pulse, that occurs at the exact instant the level detector is on, in two consecutive pulse times. In one embodi-ment of the invention, to prevent power supply voltage changes from affecting the operation of the amplifier, a capacitor is provided across the power leads to the amplifier, and means is provided between the capacitor and the power supply for electric-ally isolating the amplifier and capacitor from the transient voltages from the power supply, which are caused by the turning on of the light generating device, or from other causes. In one form of the invention said means comprises a choke coil in the line to the capacitor and a second choke coil in the line to the light generating device. In another embodiment of the invention the isolating means may be Zener diodes in place of choke coils.
In a third embodiment of the invention the means comprises a switch in the power line between the capacitor and the power supply, with means being provided to open the switch when the light generating device is energized. In each embodiment, the amplifier is isolated from transient voltage changes during the time the light generating device is energized, so that the pulse of energy required to power the amplifier is provided by the capacitor.
Description
10~65~31 ~his invention relates to a smoke detector.
Many forms of smoke detectors are known that utilize the so-called Tyndall effect, in which light reflected from smoke particles is detected and the resulting signal amplified to actuate an alarm. Most commercial units utilize a continuously operating incandescent lamp as the light source. Such a detector that has achieved great commercial success is disclosed in U. S.
patent 3,382,762 issued January 25, 1966. Smoke detectors based on this principle have the disadvantage of high current consump-tion and susceptibility to false alarms due to changing levelsof ambient light and changes in line voltage. Hence such devices must be enclosed in a housing that allows diffusion of air into the housing without allowing ambient light to enter, the electric-~` al circuitry must provide means ror compensating ~or changes in line voltage, and the photo-electric detectors must have a high ; degree of uniformity and stability. Meeting these requirements adds considerably to the cost of the device.
To avoid some of the above disadvantages it has been proposed to utilize a flashing light source, such as a gas filled tube, to reduce the current consumption. It has also been pro-posed to modulate the pulsed light at a predetermined frequency and provide an amplifier that responds only to said frequency.
Such a system is illustrated in U. S. patent 3,316,410 issued April 25, 1967. It has also been proposed that the means ` amplifying the signal from the light sensitive element should be operative only while the light source is on, so that ambient light changes or electrical disturbances that occur during the period the amplifier is off cannot cause a false alarm. However, in such a system, ambient light changes and electrical disturbances that occur while the amplifier is on can nevertheless cause a `
-- false alarm. Examples of ambient light changes that can affect a detector of this type are flashlights, strong sunlight, turning ~ ....
lOS6931 on of room lights, camera flash bulbs, and lightning. Hence the use of a pulsed light source and a pulsed amplifier as shown in the prior art, although having the advantage of lower power ' consumption, does little to reduce the possibility of false ;, alarms, and hence to avoid false alarms from such causes the sensitivity of the device must be reduced.
It is often desired for certain installations that such devices be powered from a battery, however one difficulty with a battery power source results from the fact that when the light source is turned on, the internal impedence of the battery causes the voltage at the terminals to drop. If the amplifier is powered ~, from the same battery, the voltage to the amplifier also drops, which creates a transient signal in the amplifier which may pro-~` duce an output signal many times greater than the output signal produced by the photo-responsive device when smoke is present, - and it is difficult or impossible to separate the two signals. -The same problem may occur when a plurality of smoke detectors are connected to a loop from a common power source at a central control panel. Since detectors of this type draw very little current, one of their great advantages is the fact that small wire can be used for connecting them to the central control panel. However since the instantaneous current, on the energiz-ation of the light emitting device, may be as high as 7 amperes, a substantial voltage drop at the terminals of the smoke detector can occur, which would produce a false signal in the amplifier.
Various means have been used to prevent such transient changes in the power supply voltage. For example, it is possible to power the amplifier and the light emitting device from separate batteries. It has also been proposed that the amplifier should be normally off, and turned on only after the light emitting device is turned on, In a loop system powered from a central control panel, it is possible to run separate power supply wires . . .
for the light emitting devices and the amplifiers. All of these expedients involve additional expense that is not acceptable in the majority of smoke detector applications.
The smoke detector disclosed herein comprises a light emitting diode and a-photo-generative cell positioned to receive light reflected from smoke in the path of the beam from the light emitting diode. The photo-generative cell is capacitor coupled to an amplifier, the output of which is fed to a level detector -such as a differential comparator, The output of the level detector, which occurs only when the input signal is above a pre-determined value, is fed to the set terminal ofa flip-flop-circuit, the output of which is fed to an alarm energizing means.
A pulse generator is provided which pulses, simul-taneously, the light emitting diode on, the level detector on, and provides, through a discriminating circuit, a short pulse to 1 the re-set terminal of the flip-flop.
In a preferred embodiment of the device, the pulse has ` a duration of about 20 micro-seconds, and a repetition ràte of once every two seconds. The amplifier is designed to accept only ! 20 voltage pulses having a rise time corresponding to a frequency of between 1000 and 100,000 cycles, so that the amplified voltage pulse can reach its maximum value and achieve a constant value within the pulse time.
The amplifier is continuously energized, however the level detector is energized only for the duration of the pulse.
During the time between pulses, the level detector is turned off and the signal lead thereof is connected to ground, so that any ~ signal through the amplifier due to random noise during the period ¦ that the level detector is off, passes to ground.
In one embodiment of the invention, to further reduce the possibility of an alarm from a continuous source of random noise, the output of the flip-flop is fed to an integrating :
, : . - .
lOS6931 circuit having a time constant such that at least two consecutive pulses are required to allow a signal to pass from the integrator to the alarm activating device.
Hence during each cycle, the light emitting diode is ~ -turned on, the level detector is turned on, and the flip-flop is , pulsed to the off condition at the beginning of the pulse. If smoke is present, light reflected therefrom onto the photo-generative cell causes a pulse of voltage to appear at the amplifier input. If the amplified pulse at the level detector is 10 of sufficient magnitude to satisfy the requirements o~ the level detector, a signal passes therefrom to the set terminal of the flip-flop to actuate the alarm.
:
Ordinary changes in am~ient light cannot cause a false alarm, because the amplifier cannot respond to any voltage change -at the input with a rate of change corresponding to a frequency of less than about 1000 cyles, and such change would have to occur during the 20 micro-seconds that the pulse is being applied to the level detector. Similarly, random noise that might generate a signal at the amplifier input sufficient to produce an output high enough to pass through the level detector, would have to occur during the time the level detector is on, and would have to produce a signal at the amplifier input of the proper polarity.
In one embodiment of the invention means is provided for electrically isolating the amplifier from transient voltages from the power supply, by means of suitable filtering means, or by means of an electronic switch which is opened when the light generating device is energized. Capacitor means is provided for powering the amplifier during the period that it is disconnected from the power supply.
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1~)56931 In a specific embodiment, there is provided, in a detector of the type utilizing a pulsing light source and means for producing a voltage pulse in response to the pulsed light under predetermined conditions, the improvement comprising a level detector connected to the output of the voltage pulse producing means, said level detector producing an output signal only in response to an input voltage pulse above a predetermined value, a flip-flop circuit having set and re-set terminals, the level detector output being connected to the set terminal of the flip-flop circuit, whereby the flip-flop output is turned on when the level detector produces an output signal and means periodically applying a signal to the re-set terminal of the flip-flop, to turn off the flip-flop output, the output of the flip-flop being connected to an alarm actuating unit.
A further specific embodiment comprises, in accordance . with the invention, a smoke detector of the type utilizing light *
reflected from smoke particles to actuate an alarm, comprising a light emitting diode, a photo-voltaic device positioned to receive light from smoke particles illuminated by the light emitting diode, the output of the photo-voltaic device being connected to an amplifier, the amplifier output being connected to a differential comparator which is responsive only to an input signal of a pre-determined level to provide an output, the output of the differential compartor being connected to the set terminal of a flip-flop circuit, the output of the flip-flop circuit being connected to an alarm actuating device, said amplifier being continuously energized, said light emitting diode being normally de-energized, said differential comparator being normally incapable of providing an output signal, means providing pulses to energize the light emitting diode to provide pulses of light, means providing pulses to said level detector so timed in relation to the pulses to the light emitting diode that the level detector - 4a -~ ....
105.693~
is rendered capable of producing an output signal only when the light emitting diode is emitting light, and means for applying pulses to the reset terminal of the flip-flop circuit so timed in relation to the pulses to the light emitting diode that the flip-flop output is turned off after the termination of the light pulse. .~.
~ The invention will now be described with reference to - the accompanying drawings which show a preferred form thereof and wherein: : -:; ~
.:
.
, `
- 4b -,, 105~;93~
Figure 1 is a schematic diagram of an electrical cir-cuit for use in a smoke detector embodying the features of the invention.
Figure 2 is a diagram illustrating the time spacing of the pulses applied to the light emitting diode and the level detector.
Figure 3 is a diagram illustrating the voltage pulse appearing at the amplifier with 2% smoke in the view of the photo-generative cell at various ambient light levels.
Figure 4 is a schematic drawing of a smoke detector circuit embodying the features of the invention, in which the amplifier is isolated from the power supply, during the time that the light-emitting device is on, by means of a switch which opens when the light emitting device is turned on so that during the period when the amplifier is likely to receive a signal from the photo-responsive device, the amplifier, and associated equlpment, is being powered solely by the storage capacitor.
Figure 5 is a ~chematic drawing of the detector of Figure 1 in which choke coils are utilized to isolate the amplifier from voltage transients created when the light emitting device is turned on.
Figure 6 is a schematic drawing of the detector of Figure 1 in which Zener diodes are provided in the separate power leads to the amplifier and the light emitting device.
Referring to Figure 1, there is illustrated an electron-ic circuit for use in a smoke detector operating on the reflected light principle. The circuit includes a light emitting diode LED
and a photo-voltaic cell C positioned out of the direct line of the beam of light from the light emitting diode. In a preferred embodiment of the invention the cell C is positioned to view a portion of the beam in front of the LED at an angle of about 120 - 135 from the axis of the beam, to take advantage of the well-_ 5 _ las693l . known "forward scatter" effect.
The cell C is coupled through capacitor F to an ampli-fier A, the output of the amplifier being fed to the input of a level detector L, such as a differential comparator. The level detector output is fed to the "set" terminal of a flip-flop circuit FF, the output of which is fed to an alarm actuating device K.
In a preferred embodiment of the device, the different-ial comparator is normally off with the signal lead thereof clamped to ground by an electronic switch Sl.
Light emitting diodes presently commercially available are rated, for example, for a maximum current of 1/2 ampere on a continuous basis, or for 10 amperes in pulses not to exceed 1 micro-second at 200 pulses per second. However, I have found that such diodes can be pulsed at 10 am~eres for 20 micro-seconds, provided that the pulse repetition rate is much slower, for example 1 pulse every 1 or 2 seconds. As previously mentioned, this pulse duration allows the signal through the amplifier to j reach a constant value within the pulse time, 90 that minor variations in pulse width will not affect this alarm point.
For this purpose and for others to appear hereinafter, a pulse generator P is provided, which provides a 20 micro-second pulse to the LED every two seconds, and also simultaneously applies a pulse to energize the level detector and to open switch ~ Sl. Hence the differential comparator is energized and its ¦ signal lead ungrounded only during the 20 micro-seconds out of each two seconds that the LED is energized.
Simultaneously with the application of the pulse to the LED
¦ and the level detector, a pulse is applied to the re-set terminal t 30 of the flip-flop circuit through a differentiator D, which converts ~` said pulse to a spike of about 1 micro-second duration, occuring at the beginning of the pulse cycle.
. - . .;: .: ~ : .. :.. : .. . -:- - .
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1~56931 The operation of the circuit can best be understodd by reference to Figure 2 of the drawing, which is a graph of the response of the various components of the circuit during one pulse. The horizontal scale represents time, and the vertical scale represents response. The vertical scale is arbitrary de-pending on the type of response, and the magnitude of the various curves on the vertical scale have no relation to each other ex- -cept as described hereinafter.
Each cycle begins by the application of a pulse from the pulse generator to the LED, the level detector, and the flip-flop reset terminal. The pulse to the LED and the level detector are represented on the diagram by Pl, since they are of the same duration. They may, of course, be of different magnitudes and different polarities. me pulse appearing at the re-set terminal of the flip-flop after passing through the discriminator is re-presented by P2. The application of the pulse to the LED
produces a light output having a duration and relative intensity represented by curve Ll.
If there is no smoke in the portion of the beam viewed by the cell C, there will be no pulse of voltage generated by the cell and hence no output from the amplifier. If the detector is subjected to varying ambient light, the cell will generate a varying D. C. voltage (see Figure 3) which does not cause any amplifier response because of the capacitor coupling between the cell and the amplifier.
If there is smoke present in the pulsed light beam, a pulsed voltage signal will be produced by the cell, represented - by curve Vl of Figure 2, which will be amplified by the amplifier to produce a signal at the input of the differential comparator,-which signal will have a magnitude that is a function of the amount of smoke present. To avoid unnecessary alarms from accept-able amounts of smoke and dust in the atmosphere, the differential .. . .
105!;931 comparator is set to respond only to an amplifier output that corresponds to a predetermined smoke concentration. For example, in a preferred embodiment of the invention, the differential comparator is set to respond only if the smoke concentration i~
Many forms of smoke detectors are known that utilize the so-called Tyndall effect, in which light reflected from smoke particles is detected and the resulting signal amplified to actuate an alarm. Most commercial units utilize a continuously operating incandescent lamp as the light source. Such a detector that has achieved great commercial success is disclosed in U. S.
patent 3,382,762 issued January 25, 1966. Smoke detectors based on this principle have the disadvantage of high current consump-tion and susceptibility to false alarms due to changing levelsof ambient light and changes in line voltage. Hence such devices must be enclosed in a housing that allows diffusion of air into the housing without allowing ambient light to enter, the electric-~` al circuitry must provide means ror compensating ~or changes in line voltage, and the photo-electric detectors must have a high ; degree of uniformity and stability. Meeting these requirements adds considerably to the cost of the device.
To avoid some of the above disadvantages it has been proposed to utilize a flashing light source, such as a gas filled tube, to reduce the current consumption. It has also been pro-posed to modulate the pulsed light at a predetermined frequency and provide an amplifier that responds only to said frequency.
Such a system is illustrated in U. S. patent 3,316,410 issued April 25, 1967. It has also been proposed that the means ` amplifying the signal from the light sensitive element should be operative only while the light source is on, so that ambient light changes or electrical disturbances that occur during the period the amplifier is off cannot cause a false alarm. However, in such a system, ambient light changes and electrical disturbances that occur while the amplifier is on can nevertheless cause a `
-- false alarm. Examples of ambient light changes that can affect a detector of this type are flashlights, strong sunlight, turning ~ ....
lOS6931 on of room lights, camera flash bulbs, and lightning. Hence the use of a pulsed light source and a pulsed amplifier as shown in the prior art, although having the advantage of lower power ' consumption, does little to reduce the possibility of false ;, alarms, and hence to avoid false alarms from such causes the sensitivity of the device must be reduced.
It is often desired for certain installations that such devices be powered from a battery, however one difficulty with a battery power source results from the fact that when the light source is turned on, the internal impedence of the battery causes the voltage at the terminals to drop. If the amplifier is powered ~, from the same battery, the voltage to the amplifier also drops, which creates a transient signal in the amplifier which may pro-~` duce an output signal many times greater than the output signal produced by the photo-responsive device when smoke is present, - and it is difficult or impossible to separate the two signals. -The same problem may occur when a plurality of smoke detectors are connected to a loop from a common power source at a central control panel. Since detectors of this type draw very little current, one of their great advantages is the fact that small wire can be used for connecting them to the central control panel. However since the instantaneous current, on the energiz-ation of the light emitting device, may be as high as 7 amperes, a substantial voltage drop at the terminals of the smoke detector can occur, which would produce a false signal in the amplifier.
Various means have been used to prevent such transient changes in the power supply voltage. For example, it is possible to power the amplifier and the light emitting device from separate batteries. It has also been proposed that the amplifier should be normally off, and turned on only after the light emitting device is turned on, In a loop system powered from a central control panel, it is possible to run separate power supply wires . . .
for the light emitting devices and the amplifiers. All of these expedients involve additional expense that is not acceptable in the majority of smoke detector applications.
The smoke detector disclosed herein comprises a light emitting diode and a-photo-generative cell positioned to receive light reflected from smoke in the path of the beam from the light emitting diode. The photo-generative cell is capacitor coupled to an amplifier, the output of which is fed to a level detector -such as a differential comparator, The output of the level detector, which occurs only when the input signal is above a pre-determined value, is fed to the set terminal ofa flip-flop-circuit, the output of which is fed to an alarm energizing means.
A pulse generator is provided which pulses, simul-taneously, the light emitting diode on, the level detector on, and provides, through a discriminating circuit, a short pulse to 1 the re-set terminal of the flip-flop.
In a preferred embodiment of the device, the pulse has ` a duration of about 20 micro-seconds, and a repetition ràte of once every two seconds. The amplifier is designed to accept only ! 20 voltage pulses having a rise time corresponding to a frequency of between 1000 and 100,000 cycles, so that the amplified voltage pulse can reach its maximum value and achieve a constant value within the pulse time.
The amplifier is continuously energized, however the level detector is energized only for the duration of the pulse.
During the time between pulses, the level detector is turned off and the signal lead thereof is connected to ground, so that any ~ signal through the amplifier due to random noise during the period ¦ that the level detector is off, passes to ground.
In one embodiment of the invention, to further reduce the possibility of an alarm from a continuous source of random noise, the output of the flip-flop is fed to an integrating :
, : . - .
lOS6931 circuit having a time constant such that at least two consecutive pulses are required to allow a signal to pass from the integrator to the alarm activating device.
Hence during each cycle, the light emitting diode is ~ -turned on, the level detector is turned on, and the flip-flop is , pulsed to the off condition at the beginning of the pulse. If smoke is present, light reflected therefrom onto the photo-generative cell causes a pulse of voltage to appear at the amplifier input. If the amplified pulse at the level detector is 10 of sufficient magnitude to satisfy the requirements o~ the level detector, a signal passes therefrom to the set terminal of the flip-flop to actuate the alarm.
:
Ordinary changes in am~ient light cannot cause a false alarm, because the amplifier cannot respond to any voltage change -at the input with a rate of change corresponding to a frequency of less than about 1000 cyles, and such change would have to occur during the 20 micro-seconds that the pulse is being applied to the level detector. Similarly, random noise that might generate a signal at the amplifier input sufficient to produce an output high enough to pass through the level detector, would have to occur during the time the level detector is on, and would have to produce a signal at the amplifier input of the proper polarity.
In one embodiment of the invention means is provided for electrically isolating the amplifier from transient voltages from the power supply, by means of suitable filtering means, or by means of an electronic switch which is opened when the light generating device is energized. Capacitor means is provided for powering the amplifier during the period that it is disconnected from the power supply.
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1~)56931 In a specific embodiment, there is provided, in a detector of the type utilizing a pulsing light source and means for producing a voltage pulse in response to the pulsed light under predetermined conditions, the improvement comprising a level detector connected to the output of the voltage pulse producing means, said level detector producing an output signal only in response to an input voltage pulse above a predetermined value, a flip-flop circuit having set and re-set terminals, the level detector output being connected to the set terminal of the flip-flop circuit, whereby the flip-flop output is turned on when the level detector produces an output signal and means periodically applying a signal to the re-set terminal of the flip-flop, to turn off the flip-flop output, the output of the flip-flop being connected to an alarm actuating unit.
A further specific embodiment comprises, in accordance . with the invention, a smoke detector of the type utilizing light *
reflected from smoke particles to actuate an alarm, comprising a light emitting diode, a photo-voltaic device positioned to receive light from smoke particles illuminated by the light emitting diode, the output of the photo-voltaic device being connected to an amplifier, the amplifier output being connected to a differential comparator which is responsive only to an input signal of a pre-determined level to provide an output, the output of the differential compartor being connected to the set terminal of a flip-flop circuit, the output of the flip-flop circuit being connected to an alarm actuating device, said amplifier being continuously energized, said light emitting diode being normally de-energized, said differential comparator being normally incapable of providing an output signal, means providing pulses to energize the light emitting diode to provide pulses of light, means providing pulses to said level detector so timed in relation to the pulses to the light emitting diode that the level detector - 4a -~ ....
105.693~
is rendered capable of producing an output signal only when the light emitting diode is emitting light, and means for applying pulses to the reset terminal of the flip-flop circuit so timed in relation to the pulses to the light emitting diode that the flip-flop output is turned off after the termination of the light pulse. .~.
~ The invention will now be described with reference to - the accompanying drawings which show a preferred form thereof and wherein: : -:; ~
.:
.
, `
- 4b -,, 105~;93~
Figure 1 is a schematic diagram of an electrical cir-cuit for use in a smoke detector embodying the features of the invention.
Figure 2 is a diagram illustrating the time spacing of the pulses applied to the light emitting diode and the level detector.
Figure 3 is a diagram illustrating the voltage pulse appearing at the amplifier with 2% smoke in the view of the photo-generative cell at various ambient light levels.
Figure 4 is a schematic drawing of a smoke detector circuit embodying the features of the invention, in which the amplifier is isolated from the power supply, during the time that the light-emitting device is on, by means of a switch which opens when the light emitting device is turned on so that during the period when the amplifier is likely to receive a signal from the photo-responsive device, the amplifier, and associated equlpment, is being powered solely by the storage capacitor.
Figure 5 is a ~chematic drawing of the detector of Figure 1 in which choke coils are utilized to isolate the amplifier from voltage transients created when the light emitting device is turned on.
Figure 6 is a schematic drawing of the detector of Figure 1 in which Zener diodes are provided in the separate power leads to the amplifier and the light emitting device.
Referring to Figure 1, there is illustrated an electron-ic circuit for use in a smoke detector operating on the reflected light principle. The circuit includes a light emitting diode LED
and a photo-voltaic cell C positioned out of the direct line of the beam of light from the light emitting diode. In a preferred embodiment of the invention the cell C is positioned to view a portion of the beam in front of the LED at an angle of about 120 - 135 from the axis of the beam, to take advantage of the well-_ 5 _ las693l . known "forward scatter" effect.
The cell C is coupled through capacitor F to an ampli-fier A, the output of the amplifier being fed to the input of a level detector L, such as a differential comparator. The level detector output is fed to the "set" terminal of a flip-flop circuit FF, the output of which is fed to an alarm actuating device K.
In a preferred embodiment of the device, the different-ial comparator is normally off with the signal lead thereof clamped to ground by an electronic switch Sl.
Light emitting diodes presently commercially available are rated, for example, for a maximum current of 1/2 ampere on a continuous basis, or for 10 amperes in pulses not to exceed 1 micro-second at 200 pulses per second. However, I have found that such diodes can be pulsed at 10 am~eres for 20 micro-seconds, provided that the pulse repetition rate is much slower, for example 1 pulse every 1 or 2 seconds. As previously mentioned, this pulse duration allows the signal through the amplifier to j reach a constant value within the pulse time, 90 that minor variations in pulse width will not affect this alarm point.
For this purpose and for others to appear hereinafter, a pulse generator P is provided, which provides a 20 micro-second pulse to the LED every two seconds, and also simultaneously applies a pulse to energize the level detector and to open switch ~ Sl. Hence the differential comparator is energized and its ¦ signal lead ungrounded only during the 20 micro-seconds out of each two seconds that the LED is energized.
Simultaneously with the application of the pulse to the LED
¦ and the level detector, a pulse is applied to the re-set terminal t 30 of the flip-flop circuit through a differentiator D, which converts ~` said pulse to a spike of about 1 micro-second duration, occuring at the beginning of the pulse cycle.
. - . .;: .: ~ : .. :.. : .. . -:- - .
- . ' : . ... ~ ....... ....
1~56931 The operation of the circuit can best be understodd by reference to Figure 2 of the drawing, which is a graph of the response of the various components of the circuit during one pulse. The horizontal scale represents time, and the vertical scale represents response. The vertical scale is arbitrary de-pending on the type of response, and the magnitude of the various curves on the vertical scale have no relation to each other ex- -cept as described hereinafter.
Each cycle begins by the application of a pulse from the pulse generator to the LED, the level detector, and the flip-flop reset terminal. The pulse to the LED and the level detector are represented on the diagram by Pl, since they are of the same duration. They may, of course, be of different magnitudes and different polarities. me pulse appearing at the re-set terminal of the flip-flop after passing through the discriminator is re-presented by P2. The application of the pulse to the LED
produces a light output having a duration and relative intensity represented by curve Ll.
If there is no smoke in the portion of the beam viewed by the cell C, there will be no pulse of voltage generated by the cell and hence no output from the amplifier. If the detector is subjected to varying ambient light, the cell will generate a varying D. C. voltage (see Figure 3) which does not cause any amplifier response because of the capacitor coupling between the cell and the amplifier.
If there is smoke present in the pulsed light beam, a pulsed voltage signal will be produced by the cell, represented - by curve Vl of Figure 2, which will be amplified by the amplifier to produce a signal at the input of the differential comparator,-which signal will have a magnitude that is a function of the amount of smoke present. To avoid unnecessary alarms from accept-able amounts of smoke and dust in the atmosphere, the differential .. . .
105!;931 comparator is set to respond only to an amplifier output that corresponds to a predetermined smoke concentration. For example, in a preferred embodiment of the invention, the differential comparator is set to respond only if the smoke concentration i~
2%, defined as the amount of smoke that absorbs 2% of a light beam 1 foot long. As illustrated in Figure 2, the amplifier out-put level required to permit the output signal to pass through the differential comparator is represented by the horizontal dashed line S.
In a particular embodiment of the invention the differ-ential comparator may have a standby voltage difference between input terminals of about 100 millivolts, requiring a signal of over 100 millivolts from the amplifier to produce an output signal.
Means may also be provided at the level detector to adjust the standby voltage difference between terminals, to allow calibration of the system so that the alarm point will be at the desired 2%. In the present embodiment of the invention the calibration is accomplished by providing a voltage divider Rl across the power source, with the junction thereof connected to one of the inputs of the differential comparator, and providing a variable resistor R2 across the power supply with the center tap thereof connected to the other input.
If the amount of smoke in the view of the cell has t reached the specified concentration, the amplifier output will be ; as shown in curve Al reaching the line S at point Y, thereby , producing a differential comparator output rep~esented by line :
LDl, which applies a signal to the flip-flop set terminal, there-by turning on the flip-flop output (FFl on Figure 2) to energize i` the alarm.
At the end of the pulse to the LED and the differential comparator, both turn off so that the output from the differential comparator to the flip-flop is turned off. The flip-flop output, :
~OS6931 however, stays on until the beginning of the next pulse, at which time it is turned off by the pulse through the discriminator in the manner previously described.
As a greater concentration of smoke appears in the view of the cell, more reflected light is received by the cell, and the output voltage of the pulses applied to the amplifier in-creases, so that the amplifier output increases and reaches the required level S slightly sooner in the pulse cycle, as illustrated by curve A2, providing differential comparator out-put LD2 and flip-flop output FF2.
Although the amplifier may continue to provide an output for a short time after the end of the pulse to the LED and the differential comparator, no output can exist after the end of the pulse, because the differential comparator is de-energized and the signal lead thereof clamped to ground by switch Sl.
; A smoke detector utilizing the above described circuit has a number of advantages over detectors of the prior art that have utilized a pulsing light source and a pulsed amplifier. By the use of a pulse of very short duration with a slow repetition rate, an amplifier with a response only to very high rates of change of input voltage, and the use of a pulsed level detector after the amplifier, the occurrence of false alarms due to changing light levels or due to electrical transients is almost completely eliminated.
; A change of light level that could actuate the alarm must not only occur at an extremely h gh rate, but its occurrence must coincide with the time in which the level detector i9 on, ~ 7 which is only 1/100,000 of the total time.
- For example, the turning on of an incandescent light cannot cause a false alarm, since the rate of rise of the light output from an incandescent bulb is much too slow to create a voltage pulse that can pass through the capacitor. Although the ., . :
105693~
resulting increase in ambient light will increase the D.C. voltage at the cell terminals, subsequent pulses of light falling on the cell will cause the cell to generate an output voltage pulse on top of the D. C. voltage (assuming that the ambient light is not 80 strong as to saturate the cell) which will be detected by the amplifier.
This effect is illustrated in Figure 3 where curve Va represents the voltage at the cell due to ambient light level and Vp represents the cell voltage during the period that the LED is illuminated, with 2% smoke present. Since the response of the cell is substantially linear, the sensitivity of the device is not affected by changes in ambient light, since the pulse voltage at 2% smoke remains the same, regardless of the ambient light level, provided that the ambient light level is not so high as to cause saturation of the cell. In the curve of Figure 3, the relative height of the ambient light voltage curve and the height of the voltage pulses are necessarily not in proportion, since the D. C. voltage from ambient light may be on the order of ,1 volts whereas the additional voltage generated by the pulse of light reflected from smoke particles, at 2% smoke, is only about 600 microvolts.
Although certain light sources, such as lightning, some types of camera flash equipment, and welding apparatus may produce light with a rise time fast enough to b~ amplified and reach the level detector, such resulting signal not only must be great ` enough to satisfy the level detector requirements, but also must occur during the 20 micro-seconds that the level detector is on, ` The chance of a false alarm from such a source is therefore extremely remote.
In regard to possible false alarms from random electric-; al signals generated in the cell from radio transmitters, tran-s-ients on the power supply line, and the like, not only must such -signals occur at the proper instant and generate a signal of adequate magnitude, the signal appearing at the amplifier input must be of the proper polarity.
In the illustrated embodiment of the invention, the signal from the flip-flop is led to an integrator T, comprising a resistor-capacitor network, which integrates pulses received from the flip-flop to provide an output signal to the alarm energizing device R. In one embodiment, the integrator may have a time constant which is at least slightiy greater than the total time between pulses, so that two pulses from the flip-flop are required to reach an output level from the integrator to actuate the alarm energizing device.
Although the use of the integrator may not be required in all installations in which the smoke detector is used, it has been found effective in preventing false alarms in locations that are near sources of continuous noise, such as might be produced by arcing electrical apparatus.
Another major advantage of a smoke detector utilizing the circuit disclosed herein is its extremely low power consump-tion, Although the pulse to the LED may be of the order of 7amperes, the short duration of the pulse, and the fact that the level detector is on only during the pulse permits a power consumption of the order of 300 micro-amperes at 6 volts. This power consumption is low enough to allow the device to be operated for over one year on battery power units small enough to be contained within à detector housing, with enough reserve power to energize a self-contained alarm.
Referring to figures 4-6 of the drawing, there is lllustrated an electronic circuit for use in a smoke detector of the type operating on the reflected light principle. The circuit includes a light emitting diode LED and a photo-voltaic cell C
positioned out of the direct line of the beam of light from the -- 11 -- :
lOS~;93~
LED. Inapreferred embodiment of the invention the cell C is positioned to view a portion of the beam in front of the LED at an angle of about 120 to about 135 to the axis of the beam, to take advantage of the well known "forward scatter" effect.
The cell C is coupled through capacitor F to an amplifier A, the output of which is fed to a level detector L
such as a differential comparator. The level detector output is fed to the set terminal of a flip-flop circuit FF, the output of which is fed to an integrator, which energizes an alarm actuating device K.
In a preferred embodiment of the device, the different-ial comparator is normally off with the signal lead thereof being clamped to ground by an electronic switch Sl.
To energize the LED on an intermittent basis, a pulse generator P is provided which, in addition to providing an energizing pulse to the LED, also simultaneously applies a pulse to energize the level detector and applies a pulse to the re-set ; terminal of the flip-flop through differentiator D, which convertsthe pulse to a spike of voltage applied to the re-set terminal at the beginning of the pulse cycle.
The above described portion of the circuit is similar to that disclosed and described in more detail heretofore in connection with the embodiment of figures 1-3.
In the modification of the present invention illustrated in Figure 4, one lead Wl is provided from the power source Vl to the pulse generator, and a second lead W2 is provided from the power source to the amplifier, the level detector, and the flip-flop.
The line W2 contains a series connected electronic switch S2 between the power source and the components energized by said line, and a capacitor Fl is connected between ground and the line W2 at a point between the switch S2 and the flip-flop.
In the embodiment of Figure 4, the pulse generator, in addition to the functions previously described, also applies a pulse to the switch S2 to open said switch and thereby disconnect the amplifier and associated equipment on lead W2 from the power source during the time that the LED is energized, so that during this period, the amplifier and associated equipment operates solely from the charge stored in the capacitor.
The operation of the device may be summarized as follows:
The duration of the pulse which energizes the LED is very short, for example, 20 micro-seconds compared to the repet-ition rate, which is 1 or 2 seconds.
During the time that the pulse generator is off, capacitors Fl and F2 are charged from the power source V. When the pulse generator applies an energizing pulse to the LED, it simultaneously applies a pulse to the switch S2 to open said switch. The amplifier and other equipment on line W2 are there-fore, at the instant that the LED is turned on, disconnected from the power supply, and the energy necessary to operate the ampli-fier comes only from the capacitor Fl.
As described hereinbefore in connection with the embodiment of Figures 1-3, pulses of light are reflected there-from and fall on the photo-cell C, causing a series of voltage pulses at the input of the amplifier. If the amplifier pulses are of sufficient magnitude to satisfy the requirements of the .
.
level detector, a series of pulses are applied to the "set"
terminal of the flip-flop, which applies a series of pulses (since the flip-flop is re-set at the beginning of each pulse) to the ` integrator, to actuate the alarm.
At the end of each pulse to the LED, the switch S2 closes so that the capacitor can recover the small amount of .a~
. . .
charge used in powering the amplifier and associated equipment.
In the particular illustrated embodiment, the aurrent used to power the LED may be of the order of 7 to 10 amperes.
Although this ¢urrent is drawn for only 20 micro-seconds, it would nevertheless cause a sudden and substantial drop in the voltage at the amplifier (unless the impedence of the voltage source is so low that it would be impractical for a commercial installation). Without the presence of the switch S2 and capacitor Fl, a substantial drop in supply voltage to the amplifier would occur. Such drop in voltage would cause a sudden change in bias voltage in the amplifier, which would be interpreted by the amplifier as a signal, which could either cause or negate an alarm (depending on the phase relationship of the amplifier being used), since the change in supply voltage of such a magnitude could cause an output signal from the amplifier which is many times the output signal that would be created by a signal result-ing from light reflected from smoke particles.
If the system is being operated from a loop from a power supply at a central control panel, the isolation of the amplifier from the power supply by the opening of switch S2 during the time that the LED is emitting light also prevents transient voltages occurring on the loop from generating spurious responses in the amplifier.
Referring now to Figure 5, there is illustrated a modified form of smoke detector, with the portion of the circuit ., ~
shown therein enclosed in the dashed line being substituted for the portion of the circuit enclosed in the dashed line of Figure 4. The circuit of Figure 5 includes a choke coil CKl in place of .
switch S2, and a choke coil CK2 in series with the line to the pulse generator. The choke coils CKl and CK2 have electrical characteristics such that when the pulse generator turns on the LED, the choke coils isolate the amplifier from the high frequency ~..
, ' ' . .
negative pulse caused by the sudden drop in power supply voltage.
Since the power to the amplifier is itself a high frequency pulse which could not pass through the choke coil CKl, the power for the operation of the amplifier is supplied substantially entirely by capacitor Fl.
Referring now to Figure 6, there is illustrated a second modified form of smoke detector, with the portion of the circuit shown therein enclosed in the dashed line being substi-tuted for the portion of the circuit enclosed in the dashed line of Figure 4.
The circuit of Figure 6 includes Zener diodes Zl and Z2 connected between lines W2 and Wl respectively and ground, with i t ' "~;
resistors Rl and R2 being in series in lines W2 and Wl between ~-~ the connection to the Zener diode and the power source V2. In -~ the circuit of Figure 6, the power source V2 is higher than nec-; essary to operate the amplifier and the pulse generator, and the voltage is regulated to the correct amount by the Zener diodes.
~`1 When the pulse generator turns on the LED, power is , ~ drawn from the capacitor F2, and voltage drop at the capacitor - -input is prevented by the regulating effect of the Zener diode t Z2. Similarly, voltage to the amplifier is regulated by the Zener diode Zl so that no residual voltage change at the power source from the turning on of the LED or from other transients on the power line can affect the operation of the amplifier i'`` ' ~
It will be understood that various combinations of the illustrated modifications can be used, depending on the parti-cular installation, For example, when operated~ from battery power in which the same battery also powers the alarm device, the system of Figure 4 may include a choke coil in line W2 to the ~-::`
pulse generator to prevent transients on the line resulting from the energizing of the alarm unit from affecting the operation of the pulse generator.
~::
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The switch S2 may, if desired, be incorporated into the modifications of Figures 5 and 6.
'.4~
~ In any of the modifications of the invention or com-. i binations thereof, it is essential that during the period that ,.~, the amplifier is operative to amplify a pulse from the photo-generative device and pass it to the signalling device, the voltage on capacitors Fl and F2 be equal, except for the minute difference in voltage resulting from the fact that during the operative period, the light generating device may draw slightly more power from capacitor F2 than the amplifier and associated equipment drawsfrom capacitor Fl. However, the capacitors are sufficiently large in relation to the power needed for the operation of the components that the voltage drop thereof is very small in relation to the supply voltage, and hence the voltage difference between the capacitors at the end of a pulse is in-.. ~ .
.. ~t, appreciable.
Although specific embodiments have been illustratedin the above, this was for the purpose of describing, but not limiting, the invention. Various modifications which will come readily to the mind of one skilled in the art are within the scope of the invention as defined in the appended claims.
.
. . .
.
In a particular embodiment of the invention the differ-ential comparator may have a standby voltage difference between input terminals of about 100 millivolts, requiring a signal of over 100 millivolts from the amplifier to produce an output signal.
Means may also be provided at the level detector to adjust the standby voltage difference between terminals, to allow calibration of the system so that the alarm point will be at the desired 2%. In the present embodiment of the invention the calibration is accomplished by providing a voltage divider Rl across the power source, with the junction thereof connected to one of the inputs of the differential comparator, and providing a variable resistor R2 across the power supply with the center tap thereof connected to the other input.
If the amount of smoke in the view of the cell has t reached the specified concentration, the amplifier output will be ; as shown in curve Al reaching the line S at point Y, thereby , producing a differential comparator output rep~esented by line :
LDl, which applies a signal to the flip-flop set terminal, there-by turning on the flip-flop output (FFl on Figure 2) to energize i` the alarm.
At the end of the pulse to the LED and the differential comparator, both turn off so that the output from the differential comparator to the flip-flop is turned off. The flip-flop output, :
~OS6931 however, stays on until the beginning of the next pulse, at which time it is turned off by the pulse through the discriminator in the manner previously described.
As a greater concentration of smoke appears in the view of the cell, more reflected light is received by the cell, and the output voltage of the pulses applied to the amplifier in-creases, so that the amplifier output increases and reaches the required level S slightly sooner in the pulse cycle, as illustrated by curve A2, providing differential comparator out-put LD2 and flip-flop output FF2.
Although the amplifier may continue to provide an output for a short time after the end of the pulse to the LED and the differential comparator, no output can exist after the end of the pulse, because the differential comparator is de-energized and the signal lead thereof clamped to ground by switch Sl.
; A smoke detector utilizing the above described circuit has a number of advantages over detectors of the prior art that have utilized a pulsing light source and a pulsed amplifier. By the use of a pulse of very short duration with a slow repetition rate, an amplifier with a response only to very high rates of change of input voltage, and the use of a pulsed level detector after the amplifier, the occurrence of false alarms due to changing light levels or due to electrical transients is almost completely eliminated.
; A change of light level that could actuate the alarm must not only occur at an extremely h gh rate, but its occurrence must coincide with the time in which the level detector i9 on, ~ 7 which is only 1/100,000 of the total time.
- For example, the turning on of an incandescent light cannot cause a false alarm, since the rate of rise of the light output from an incandescent bulb is much too slow to create a voltage pulse that can pass through the capacitor. Although the ., . :
105693~
resulting increase in ambient light will increase the D.C. voltage at the cell terminals, subsequent pulses of light falling on the cell will cause the cell to generate an output voltage pulse on top of the D. C. voltage (assuming that the ambient light is not 80 strong as to saturate the cell) which will be detected by the amplifier.
This effect is illustrated in Figure 3 where curve Va represents the voltage at the cell due to ambient light level and Vp represents the cell voltage during the period that the LED is illuminated, with 2% smoke present. Since the response of the cell is substantially linear, the sensitivity of the device is not affected by changes in ambient light, since the pulse voltage at 2% smoke remains the same, regardless of the ambient light level, provided that the ambient light level is not so high as to cause saturation of the cell. In the curve of Figure 3, the relative height of the ambient light voltage curve and the height of the voltage pulses are necessarily not in proportion, since the D. C. voltage from ambient light may be on the order of ,1 volts whereas the additional voltage generated by the pulse of light reflected from smoke particles, at 2% smoke, is only about 600 microvolts.
Although certain light sources, such as lightning, some types of camera flash equipment, and welding apparatus may produce light with a rise time fast enough to b~ amplified and reach the level detector, such resulting signal not only must be great ` enough to satisfy the level detector requirements, but also must occur during the 20 micro-seconds that the level detector is on, ` The chance of a false alarm from such a source is therefore extremely remote.
In regard to possible false alarms from random electric-; al signals generated in the cell from radio transmitters, tran-s-ients on the power supply line, and the like, not only must such -signals occur at the proper instant and generate a signal of adequate magnitude, the signal appearing at the amplifier input must be of the proper polarity.
In the illustrated embodiment of the invention, the signal from the flip-flop is led to an integrator T, comprising a resistor-capacitor network, which integrates pulses received from the flip-flop to provide an output signal to the alarm energizing device R. In one embodiment, the integrator may have a time constant which is at least slightiy greater than the total time between pulses, so that two pulses from the flip-flop are required to reach an output level from the integrator to actuate the alarm energizing device.
Although the use of the integrator may not be required in all installations in which the smoke detector is used, it has been found effective in preventing false alarms in locations that are near sources of continuous noise, such as might be produced by arcing electrical apparatus.
Another major advantage of a smoke detector utilizing the circuit disclosed herein is its extremely low power consump-tion, Although the pulse to the LED may be of the order of 7amperes, the short duration of the pulse, and the fact that the level detector is on only during the pulse permits a power consumption of the order of 300 micro-amperes at 6 volts. This power consumption is low enough to allow the device to be operated for over one year on battery power units small enough to be contained within à detector housing, with enough reserve power to energize a self-contained alarm.
Referring to figures 4-6 of the drawing, there is lllustrated an electronic circuit for use in a smoke detector of the type operating on the reflected light principle. The circuit includes a light emitting diode LED and a photo-voltaic cell C
positioned out of the direct line of the beam of light from the -- 11 -- :
lOS~;93~
LED. Inapreferred embodiment of the invention the cell C is positioned to view a portion of the beam in front of the LED at an angle of about 120 to about 135 to the axis of the beam, to take advantage of the well known "forward scatter" effect.
The cell C is coupled through capacitor F to an amplifier A, the output of which is fed to a level detector L
such as a differential comparator. The level detector output is fed to the set terminal of a flip-flop circuit FF, the output of which is fed to an integrator, which energizes an alarm actuating device K.
In a preferred embodiment of the device, the different-ial comparator is normally off with the signal lead thereof being clamped to ground by an electronic switch Sl.
To energize the LED on an intermittent basis, a pulse generator P is provided which, in addition to providing an energizing pulse to the LED, also simultaneously applies a pulse to energize the level detector and applies a pulse to the re-set ; terminal of the flip-flop through differentiator D, which convertsthe pulse to a spike of voltage applied to the re-set terminal at the beginning of the pulse cycle.
The above described portion of the circuit is similar to that disclosed and described in more detail heretofore in connection with the embodiment of figures 1-3.
In the modification of the present invention illustrated in Figure 4, one lead Wl is provided from the power source Vl to the pulse generator, and a second lead W2 is provided from the power source to the amplifier, the level detector, and the flip-flop.
The line W2 contains a series connected electronic switch S2 between the power source and the components energized by said line, and a capacitor Fl is connected between ground and the line W2 at a point between the switch S2 and the flip-flop.
In the embodiment of Figure 4, the pulse generator, in addition to the functions previously described, also applies a pulse to the switch S2 to open said switch and thereby disconnect the amplifier and associated equipment on lead W2 from the power source during the time that the LED is energized, so that during this period, the amplifier and associated equipment operates solely from the charge stored in the capacitor.
The operation of the device may be summarized as follows:
The duration of the pulse which energizes the LED is very short, for example, 20 micro-seconds compared to the repet-ition rate, which is 1 or 2 seconds.
During the time that the pulse generator is off, capacitors Fl and F2 are charged from the power source V. When the pulse generator applies an energizing pulse to the LED, it simultaneously applies a pulse to the switch S2 to open said switch. The amplifier and other equipment on line W2 are there-fore, at the instant that the LED is turned on, disconnected from the power supply, and the energy necessary to operate the ampli-fier comes only from the capacitor Fl.
As described hereinbefore in connection with the embodiment of Figures 1-3, pulses of light are reflected there-from and fall on the photo-cell C, causing a series of voltage pulses at the input of the amplifier. If the amplifier pulses are of sufficient magnitude to satisfy the requirements of the .
.
level detector, a series of pulses are applied to the "set"
terminal of the flip-flop, which applies a series of pulses (since the flip-flop is re-set at the beginning of each pulse) to the ` integrator, to actuate the alarm.
At the end of each pulse to the LED, the switch S2 closes so that the capacitor can recover the small amount of .a~
. . .
charge used in powering the amplifier and associated equipment.
In the particular illustrated embodiment, the aurrent used to power the LED may be of the order of 7 to 10 amperes.
Although this ¢urrent is drawn for only 20 micro-seconds, it would nevertheless cause a sudden and substantial drop in the voltage at the amplifier (unless the impedence of the voltage source is so low that it would be impractical for a commercial installation). Without the presence of the switch S2 and capacitor Fl, a substantial drop in supply voltage to the amplifier would occur. Such drop in voltage would cause a sudden change in bias voltage in the amplifier, which would be interpreted by the amplifier as a signal, which could either cause or negate an alarm (depending on the phase relationship of the amplifier being used), since the change in supply voltage of such a magnitude could cause an output signal from the amplifier which is many times the output signal that would be created by a signal result-ing from light reflected from smoke particles.
If the system is being operated from a loop from a power supply at a central control panel, the isolation of the amplifier from the power supply by the opening of switch S2 during the time that the LED is emitting light also prevents transient voltages occurring on the loop from generating spurious responses in the amplifier.
Referring now to Figure 5, there is illustrated a modified form of smoke detector, with the portion of the circuit ., ~
shown therein enclosed in the dashed line being substituted for the portion of the circuit enclosed in the dashed line of Figure 4. The circuit of Figure 5 includes a choke coil CKl in place of .
switch S2, and a choke coil CK2 in series with the line to the pulse generator. The choke coils CKl and CK2 have electrical characteristics such that when the pulse generator turns on the LED, the choke coils isolate the amplifier from the high frequency ~..
, ' ' . .
negative pulse caused by the sudden drop in power supply voltage.
Since the power to the amplifier is itself a high frequency pulse which could not pass through the choke coil CKl, the power for the operation of the amplifier is supplied substantially entirely by capacitor Fl.
Referring now to Figure 6, there is illustrated a second modified form of smoke detector, with the portion of the circuit shown therein enclosed in the dashed line being substi-tuted for the portion of the circuit enclosed in the dashed line of Figure 4.
The circuit of Figure 6 includes Zener diodes Zl and Z2 connected between lines W2 and Wl respectively and ground, with i t ' "~;
resistors Rl and R2 being in series in lines W2 and Wl between ~-~ the connection to the Zener diode and the power source V2. In -~ the circuit of Figure 6, the power source V2 is higher than nec-; essary to operate the amplifier and the pulse generator, and the voltage is regulated to the correct amount by the Zener diodes.
~`1 When the pulse generator turns on the LED, power is , ~ drawn from the capacitor F2, and voltage drop at the capacitor - -input is prevented by the regulating effect of the Zener diode t Z2. Similarly, voltage to the amplifier is regulated by the Zener diode Zl so that no residual voltage change at the power source from the turning on of the LED or from other transients on the power line can affect the operation of the amplifier i'`` ' ~
It will be understood that various combinations of the illustrated modifications can be used, depending on the parti-cular installation, For example, when operated~ from battery power in which the same battery also powers the alarm device, the system of Figure 4 may include a choke coil in line W2 to the ~-::`
pulse generator to prevent transients on the line resulting from the energizing of the alarm unit from affecting the operation of the pulse generator.
~::
105693~
The switch S2 may, if desired, be incorporated into the modifications of Figures 5 and 6.
'.4~
~ In any of the modifications of the invention or com-. i binations thereof, it is essential that during the period that ,.~, the amplifier is operative to amplify a pulse from the photo-generative device and pass it to the signalling device, the voltage on capacitors Fl and F2 be equal, except for the minute difference in voltage resulting from the fact that during the operative period, the light generating device may draw slightly more power from capacitor F2 than the amplifier and associated equipment drawsfrom capacitor Fl. However, the capacitors are sufficiently large in relation to the power needed for the operation of the components that the voltage drop thereof is very small in relation to the supply voltage, and hence the voltage difference between the capacitors at the end of a pulse is in-.. ~ .
.. ~t, appreciable.
Although specific embodiments have been illustratedin the above, this was for the purpose of describing, but not limiting, the invention. Various modifications which will come readily to the mind of one skilled in the art are within the scope of the invention as defined in the appended claims.
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. . .
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Claims (10)
1. In a detector of the type utilizing a pulsing light source and means for producing a voltage pulse in response to the pulsed light under predetermined conditions, the improvement comprising a level detector connected to the output of the volt-age pulse producing means, said level detector producing an out-put signal only in response to an input voltage pulse above a predetermined value, a flip-flop circuit having set and re-set terminals, the level detector output being connected to the set terminal of the flip-flop circuit, whereby the flip-flop output is turned on when the level detector produces an output signal and means periodically applying a signal to the re-set terminal of the flip-flop, to turn off the flip-flop output, the output of the flip-flop being connected to an alarm actuating unit, chara-cterized in that said detector comprises means rendering said level detector capable of producing an output signal only when the light source is emitting light.
2. A detector as set out in claim 1 in which the signal lead of the level detector is normally connected to ground so as to be incapable of producing an output signal to the flip-flop, and the signal lead is disconnected from ground only during the time that the light source is emitting Light.
3. A detector as set out in claim 1 in which the level detector is a differential comparator, and means is provided at the input thereof for adjusting the voltage input required to produce an output therefrom.
4. A detector as set out in claim 1 in which means is provided for applying a pulse to the flip-flop re-set terminal after each pulse of the light source.
5. A detector as set out in claim 1 in which a pulse generator is provided for simultaneously applying a pulse to the light source to cause said source to emit light, to the level detector to render it capable of producing an output signal, and to the re-set terminal of the flip-flop to turn off the flip-flop output, said pulse to the flip-flop re-set terminal being of shorter dur-ation than the pulse to the light source.
6. A detector as set out in claim 1 in which means is pro-vided between the flip-flop and the alarm activating device for integrating the voltage received from the flip-flop and having electrical parameters such that the duration of the signal applied thereto required to produce an output to the alarm actuating de-vice is longer than the time between the initiation of the con-secutive pulses, whereby a signal resulting from a single pulse is insufficient to actuate the alarm.
7. A smoke detector of the type utilizing light reflected from smoke particles to actuate an alarm, comprising a light emitting diode, a photo-voltaic device positioned to receive light from smoke particles illuminated by the light emitting diode, the output of the photo-voltaic device being connected to an amplifier, the amplifier output being connected to a differential comparator which is responsive only to an input signal of a predetermined level to provide an output, the output of the differential comparator being connected to the set terminal of a flip-flop circuit, the output of the flip-flop circuit being connected to an alarm actuating device, said amplifier being continuously ener-gized, said light emitting diode being normally de-energized, ., said differential comparator being normally incapable of providing an output signal, means providing pulses to energize the light emitting diode to provide pulses of light, means providing pulses to said level detector so timed in relation to the pulses to the light emitting diode that the level detector is rendered capable of producing an output signal only when the light emitting diode is emitting light, and means for applying pulses to the reset terminal of the flip-flop circuit so timed in relation to the pulses to the light emitting diode that the flip-flop output is turned off after the termination of the light pulse.
8. A detector as set out in claim 7 in which said amplifier has a frequency response such that it is capable of achieving a steady output signal within less than the duration of the pulse to the light emitting diode.
9. A detector as set out in claim 7 in which a pulse generator is provided for simultaneously applying a pulse to the light emitting diode to cause it to emit light, to the different-ial comparator to render it capable of producing an output signal, and to the reset terminal of the flip-flop, said pulse to the flip-flop having a duration of less than the pulse to the light source.
10. A detector as set out in claim 7 in which the amplifier has a frequency response of between about 1000 and 100,000 cycles, and the pulse duration is not appreciably longer than required for the amplifier to achieve a constant output in response to an input pulse from the photo-voltaic device.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA295,627A CA1067175A (en) | 1973-11-26 | 1978-01-25 | Smoke detector |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US41920673A | 1973-11-26 | 1973-11-26 | |
| US449362A US3917956A (en) | 1974-03-08 | 1974-03-08 | Smoke detector |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1056931A true CA1056931A (en) | 1979-06-19 |
Family
ID=27024396
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA207,336A Expired CA1056931A (en) | 1973-11-26 | 1974-08-19 | Smoke detector |
Country Status (11)
| Country | Link |
|---|---|
| JP (1) | JPS50114275A (en) |
| BR (1) | BR7408707D0 (en) |
| CA (1) | CA1056931A (en) |
| CH (2) | CH580848A5 (en) |
| CS (1) | CS186786B2 (en) |
| DE (2) | DE2462876C2 (en) |
| FR (1) | FR2254024B3 (en) |
| GB (1) | GB1490866A (en) |
| IL (1) | IL45331A (en) |
| IN (1) | IN143206B (en) |
| NL (1) | NL7410079A (en) |
Families Citing this family (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5354000A (en) * | 1976-10-26 | 1978-05-16 | Matsushita Electric Works Ltd | Detection signal processing circuit of photoelectric type smoke detectors |
| US4125779A (en) * | 1977-07-13 | 1978-11-14 | Chloride, Incorporated | Smoke detector |
| CH638331A5 (en) * | 1979-02-22 | 1983-09-15 | Cerberus Ag | SMOKE DETECTOR. |
| DE3063643D1 (en) * | 1979-02-26 | 1983-07-14 | Cerberus Ag | Fire detector using pulsed radiation |
| BE881812A (en) * | 1979-12-17 | 1980-06-16 | Cerberus Ag | NOTIFICATION SYSTEM |
| JPS5716956U (en) * | 1980-06-30 | 1982-01-28 | ||
| JPS6014398B2 (en) * | 1981-03-18 | 1985-04-12 | ホーチキ株式会社 | photoelectric smoke detector |
| EP0145189B1 (en) * | 1983-10-21 | 1990-08-08 | COLE, Martin Terence | Improvements relating to smoke detection apparatus |
| JPS6151U (en) * | 1985-05-17 | 1986-01-06 | 京セラ株式会社 | Photoelectric smoke detection alarm device |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CH417405A (en) * | 1964-07-14 | 1966-07-15 | Cerberus Ag Werk Fuer Elektron | Device for the detection of aerosols in air |
| US3382762A (en) * | 1967-02-21 | 1968-05-14 | Alfred W. Vasel | Smoke detecting device |
| US3555532A (en) | 1968-10-29 | 1971-01-12 | Graham Stuart Corp | Vapor or particle detection device |
| GB1278205A (en) * | 1970-02-11 | 1972-06-21 | Shorrock Develpoments Ltd | Smoke detecting device |
| CH520990A (en) * | 1970-12-21 | 1972-03-31 | Cerberus Ag | Smoke detector |
-
1974
- 1974-07-22 IL IL45331A patent/IL45331A/en unknown
- 1974-07-26 NL NL7410079A patent/NL7410079A/en not_active Application Discontinuation
- 1974-08-01 IN IN1715/CAL/1974A patent/IN143206B/en unknown
- 1974-08-07 CH CH1079974A patent/CH580848A5/xx not_active IP Right Cessation
- 1974-08-07 CH CH560576A patent/CH599645A5/xx not_active IP Right Cessation
- 1974-08-16 JP JP49094109A patent/JPS50114275A/ja active Pending
- 1974-08-19 CA CA207,336A patent/CA1056931A/en not_active Expired
- 1974-08-22 CS CS7400005834A patent/CS186786B2/en unknown
- 1974-10-09 DE DE2462876A patent/DE2462876C2/en not_active Expired
- 1974-10-09 DE DE2448195A patent/DE2448195C2/en not_active Expired
- 1974-10-18 BR BR8707/74A patent/BR7408707D0/en unknown
- 1974-10-22 GB GB45706/74A patent/GB1490866A/en not_active Expired
-
1975
- 1975-01-31 FR FR7503156A patent/FR2254024B3/fr not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| GB1490866A (en) | 1977-11-02 |
| DE2462876C2 (en) | 1983-06-09 |
| DE2448195A1 (en) | 1975-05-28 |
| CS186786B2 (en) | 1978-12-29 |
| BR7408707D0 (en) | 1975-08-26 |
| AU7330074A (en) | 1976-03-18 |
| IN143206B (en) | 1977-10-15 |
| FR2254024A1 (en) | 1975-07-04 |
| IL45331A0 (en) | 1974-10-22 |
| CH599645A5 (en) | 1978-05-31 |
| FR2254024B3 (en) | 1979-02-02 |
| NL7410079A (en) | 1975-05-28 |
| JPS50114275A (en) | 1975-09-08 |
| IL45331A (en) | 1977-12-30 |
| DE2448195C2 (en) | 1984-08-23 |
| CH580848A5 (en) | 1976-10-15 |
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