BATTERY OPERATED SURVEILLANCE DEVICE
United States Patent 3846773
A battery powered condition responsive device characterized by exceedingly low power drain and a battery condition indicator. In a preferred embodiment the device is responsive to smoke and/or heat and employs light emitting diodes in the battery indicator and smoke detection circuits.
US Patent References:
Control circuit for indicating the voltage drop of a battery below a predetermined value
Paist - June 1962 - 3038110
Emergency signal radio receiver responsive to cessation of all but the emergency frequency
Taylor, Jr. et al. - September 1965 - 3205482
Battery condition indicator
Parke - February 1966 - 3234538
SELF CHECKING INTERUDER AND FIRE DETECTOR UNITS AND SYSTEM
Engh - November 1970 - 3543260
Control circuit for indicating the voltage drop of a battery below a predetermined value
Paist - June 1962 - 3038110
Emergency signal radio receiver responsive to cessation of all but the emergency frequency
Taylor, Jr. et al. - September 1965 - 3205482
Battery condition indicator
Parke - February 1966 - 3234538
SELF CHECKING INTERUDER AND FIRE DETECTOR UNITS AND SYSTEM
Engh - November 1970 - 3543260
Inventors:
Lintelmann, Willy (Old Saybrook, CT)
Frey, Peter J. (West Hartford, CT)
Frey, Peter J. (West Hartford, CT)
Application Number:
05/281947
Publication Date:
11/05/1974
Filing Date:
08/18/1972
View Patent Images:
Export Citation:
Primary Class:
Other Classes:
340/594, 340/636.100, 340/630, 340/636.150
International Classes:
G08B17/103; G08B19/00; G08B17/10
Field of Search:
340/237S,228R,249 250/218
Primary Examiner:
Caldwell, John W.
Assistant Examiner:
Myer, Daniel
Claims:
What is claimed is
1. A condition responsive alarm device for generating a warning signal upon the occurrence of a preselected degree of smoke density including:
2. A condition responsive device as in claim 1 including:
3. A condition responsive device as in claim 2 wherein said warning signal generating means includes:
1. A condition responsive alarm device for generating a warning signal upon the occurrence of a preselected degree of smoke density including:
2. A condition responsive device as in claim 1 including:
3. A condition responsive device as in claim 2 wherein said warning signal generating means includes:
Description:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to providing a warning of the existence of an unsafe condition in an area under surveillance. More specifically, this invention is directed to a condition responsive device for providing an audible alarm in response to smoke density and/or temperature in excess of predetermined levels. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
2. Description of the Prior Art
While not limited thereto in its utility, the present invention is particularly well suited for use in or as a fire alarm system. Accordingly, the invention will be described below in the context of such a system and particularly with respect to an alarm which is responsive to smoke density. As is well known, most fatalities suffered in fires result from smoke inhalation. As is also well known, in most fatal home fires the smoke density reaches a level sufficiently high to incapacitate the victims before there is sufficient temperature rise to trigger the conventional temperature sensitive alarm system.
While there have previously been smoke responsive alarm systems proposed, and in some cases commercialized, these prior art smoke detectors have been characterized by complexity and high expense. Additionally, a successful battery operated alarm device has not previously been available; the prior art sensor circuits being characterized by comparatively high current drain and thus unacceptably short battery life. The inability to operate from a battery has severely limited the utility of prior art alarm devices since house current powered alarm systems suffer obvious disadvantages including inoperability should there be an electrical power failure caused, for example, by a basement fire in the vicinity of the switch panel.
SUMMARY OF THE INVENTION
The present invention overcomes the above briefly discussed and other disadvantages of the prior art by providing a novel and improved condition responsive alarm device. The device of the present invention is characterized by extremely low power requirements and thus may be operated with inexpensive dry cell batteries. The present invention is also characterized by responsiveness to smoke density and/or temperature and by a battery condition indicator which provides a warning that the battery or batteries should be replaced.
The present invention employs a timing circuit which provides periodic current pulses to a photon generator which, in the disclosed embodiment, is a light emitting diode. Flashes provided by the light emitting diode are detected by a phototransistor which is included in the gate circuit of a silicon controlled rectifier. The SCR is connected in series with a suitable alarm device across the power supply, and the gate circuit prevents firing of the SCR as long as the phototransistor receives the periodic light pulses from the light emitting diode. Should smoke obscure the light emitting diode from the phototransistor, the gate circuit will cause firing of the SCR and energization of the alarm device.
A temperature responsive switch may be connected in parallel with the phototransistor so as to also cause the SCR to fire in response to an increase in temperature above a predetermined level.
A built-in battery indicator circuit, comprising a pair of series connected Darlington amplifiers, senses the condition of the power supply during each output pulse of the timing circuit. Should the voltage level sensed by the indicator circuit fall below a predetermined value, the indicator circuit will cause a second light emitting diode to flash simultaneously with the light emitting diode of the smoke detector circuit. This second flashing light is visible externally of the unit and provides a readily apparent indication of the need for battery replacement.
BRIEF DESCRIPTION OF THE DRAWING
The present invention may be better understood and its numerous objects and advantages will become apparent to those skilled in the art by reference to the accompanying drawing which is an electrical schematic diagram of a preferred embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
With reference now to the drawing, the battery power supply is indicated at 10. In one successful reduction to practice of the invention, power supply 10 comprised three standard 1.5 volt batteries connected in series. A normally closed reset switch S1 is connected in series with power supply 10 whereby current is delivered from the battery or batteries to the indicator and alarm circuitry. Insertion of the batteries in the power supply will, accordingly, render the device operative and, as will become apparent from the description below, should an alarm be sounded the circuit may be reset by the momentary opening of switch S1 to extinguish a switching device in the form of silicon controlled rectifier SCR-1.
A timing circuit 12 comprising transistors Q1 and Q2, resistor R1 and capacitor C1 is connected across power supply 10. Circuit 12 is a negative resistance relaxation oscillator which provides periodic pulses for the purposes to be described below. The "off" time of circuit 12 is determined by the RC time constant of resistor R1 and capacitor C1. The timing circuit "on" time is determined by the discharge of capacitor C1 through transistors Q1 and Q2 and the load on timing circuit 12; the load comprising the remaining circuitry as will be described below. Typically, timing circuit 12 will provide substantially square wave output pulses of 20 milliseconds duration with the period between pulses being 17 seconds.
The pulses provided by timing circuit 12 are applied to a common bus 14. Restated, during each firing period of transistor Q2 the battery voltage, less the IR drop of transistor Q2, is applied to bus 14. These positive pulses are applied to a light emitting diode, LED-2, via series connected resistor R11. The light emitting diode will accordingly periodically flash and the light pulses provided thereby are detected by a phototransistor 15. Phototransistor 15 is connected in series with bias resistor R12, and the resistor and phototransistor are in parallel with source 10. Each time the phototransistor 15 receives a light pulse it will conduct thereby applying a positive pulse to the base of a normally conductive transistor Q7. The timing pulses from circuit 12 are applied, via resistor R14, to the collector of transistor Q7. Application of the positive pulses from phototransistor 15 to the base of transistor Q7 will, accordingly, keep transistor Q7 in the conductive state. As long as transistor Q7 conducts its collector will essentially be maintained at ground potential.
The collector of transistor Q7 is connected to the gate electrode of a silicon controlled rectifier, SCR-1, which is in series with a suitable alarm device 16 across power supply 10. SCR-1 will be normally non-conductive whereby current will not flow through the alarm device 16 and the alarm will be deenergized. Alarm device 16 may, for example, be a solenoid driven mechanical oscillator which provides a loud audible warning signal. A capacitor C4 is connected in parallel with alarm device 16 to reduce the voltage ripple thereacross thereby allowing SCR-1 to latch in the "on" condition when rendered conductive. As noted, the gate electrode of SCR-1 is normally at ground potential due to the conductive state of transistor Q7. However, should a timing pulse be received at the collector of Q7 without there being a pulse simultaneously being applied to the base of Q7 via phototransistor 15, transistor Q7 will be turned off and the timing pulse will cause the silicon controlled rectifier SCR-1 to conduct. The RC circuit comprising resistor R15 and capacitor C3 will hold SCR-1 off during the transient time when the timing circuit 12 initially turns on. Resistor R16 is a gate clamp for SCR-1 and prevents false triggering and provides temperature stability. R16 may, of course, be adjustable if desired or necessary.
In operation, if smoke enters the detector circuit between phototransistor 15 and light emitting diode LED-2, the conduction of the phototransistor will be reduced thus reducing the "negative" bias applied to the base of transistor Q7 and permitting the transistor to be turned off by a positive timing pulse applied to the collector of Q7 via resistor R14. With transistor Q7 in the non-conductive state, the positive timing pulses will be applied to the now ungrounded gate of SCR-1 via the voltage divider defined by resistors R14 and R15 and the silicon controlled rectifier will be turned on thereby permitting current flow through the alarm device 16. A pair of output terminals 17 are provided whereby the voltage drop across the alarm device 16 may be utilized to trigger a transmitter which will deliver a warning signal to a remotely located master panel; the master panel for example being located at a guards station in a multiple detector installation. In such an instance the transmitter will also be battery powered.
A particularly novel feature of the present invention is a built-in battery testing circuit which comprises, in part, series connected Darlington amplifiers 18 and 20. The first Darlington amplifier, comprising transistors Q3 and Q4, provides an output signal during each timing pulse which is applied to the base of transistor Q5 of the second Darlington amplifier 20. The second Darlington amplifier, comprising transistors Q5 and Q6, is normally in the off condition whereby current may not flow through a second light emitting diode, LED-1, which is connected in series with transistor Q6 across power supply 10. As previously noted, the timing pulses supplied by timing circuit 12 are applied to bus 14 when transistor Q2 of circuit 12 fires. Transistor Q3 of Darlington amplifier 18 is biased on only when transistor Q2 conducts. When transistor Q3 is biased on, the base of transistor Q5 will be grounded via transistor Q4. Accordingly, application of the timing pulse to bus 14 will not render transistor Q5 conductive and, accordingly, transistor Q6 cannot conduct to complete a circuit through LED-1. A capacitor C2 connected between the emitter of transistor Q4 and ground provides compensation for the time delay of Darlington amplifier 18. Restated, when transistor Q2 of timing circuit 12 conducts, there will be a time delay between application of the positive pulse to bus 14 and the conduction of the Darlington amplifier. Capacitor C2 allows transistor Q4 to conduct hard thereby "firing" Darlington amplifier 18 before Darlington amplifier 20 can be rendered conductive by the timing pulse. A diode D2 connected in parallel with capacitor C2 provides a voltage reference for the "firing" of Darlington amplifier 18 thereby adding stability to the operation of the circuit. The "firing" point of Darlington amplifier 18 is determined by a voltage divider comprising resistors R2 and R3 and diode D1. Diode D1 has been added to the circuit to impart a "snap" action to transistor Q3. When the battery voltage is above a predetermined level, typically 3.9 volts, the Darlington amplifier 20 will be maintained in a nonconductive state during the pulsing of timing circuit 12. However, should the power supply voltage drop below the predetermined level, the first Darlington amplifier 18 will not conduct in response to the application of a timing pulse to bus 14. Accordingly, the positive timing pulse will be applied to the base of transistor Q5 of Darlington amplifier 20 via resistors R5 and R8 and the second Darlington amplifier will be "fired" thereby completing a current path through LED-1. Accordingly, when the battery voltage falls below the predetermined level, LED-1 will flash in synchronism with the pulsing of timing circuit 12 thus providing a warning that the batteries should be replaced.
It is to be noted that a temperature sensitive device, such as bimetallic switch S-2, may be connected between the positive side of power supply 10 and the gate electrode of SCR-1. The use of such an optional temperature sensitive device permits the invention to be sensitive to both the presence of smoke and increases in temperature; both conditions being indicative of a fire.
While a preferred embodiment has been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the present invention. Accordingly, it is to be understood that the invention has been described by way of illustration and not limitation.
1. Field of the Invention
The present invention is directed to providing a warning of the existence of an unsafe condition in an area under surveillance. More specifically, this invention is directed to a condition responsive device for providing an audible alarm in response to smoke density and/or temperature in excess of predetermined levels. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
2. Description of the Prior Art
While not limited thereto in its utility, the present invention is particularly well suited for use in or as a fire alarm system. Accordingly, the invention will be described below in the context of such a system and particularly with respect to an alarm which is responsive to smoke density. As is well known, most fatalities suffered in fires result from smoke inhalation. As is also well known, in most fatal home fires the smoke density reaches a level sufficiently high to incapacitate the victims before there is sufficient temperature rise to trigger the conventional temperature sensitive alarm system.
While there have previously been smoke responsive alarm systems proposed, and in some cases commercialized, these prior art smoke detectors have been characterized by complexity and high expense. Additionally, a successful battery operated alarm device has not previously been available; the prior art sensor circuits being characterized by comparatively high current drain and thus unacceptably short battery life. The inability to operate from a battery has severely limited the utility of prior art alarm devices since house current powered alarm systems suffer obvious disadvantages including inoperability should there be an electrical power failure caused, for example, by a basement fire in the vicinity of the switch panel.
SUMMARY OF THE INVENTION
The present invention overcomes the above briefly discussed and other disadvantages of the prior art by providing a novel and improved condition responsive alarm device. The device of the present invention is characterized by extremely low power requirements and thus may be operated with inexpensive dry cell batteries. The present invention is also characterized by responsiveness to smoke density and/or temperature and by a battery condition indicator which provides a warning that the battery or batteries should be replaced.
The present invention employs a timing circuit which provides periodic current pulses to a photon generator which, in the disclosed embodiment, is a light emitting diode. Flashes provided by the light emitting diode are detected by a phototransistor which is included in the gate circuit of a silicon controlled rectifier. The SCR is connected in series with a suitable alarm device across the power supply, and the gate circuit prevents firing of the SCR as long as the phototransistor receives the periodic light pulses from the light emitting diode. Should smoke obscure the light emitting diode from the phototransistor, the gate circuit will cause firing of the SCR and energization of the alarm device.
A temperature responsive switch may be connected in parallel with the phototransistor so as to also cause the SCR to fire in response to an increase in temperature above a predetermined level.
A built-in battery indicator circuit, comprising a pair of series connected Darlington amplifiers, senses the condition of the power supply during each output pulse of the timing circuit. Should the voltage level sensed by the indicator circuit fall below a predetermined value, the indicator circuit will cause a second light emitting diode to flash simultaneously with the light emitting diode of the smoke detector circuit. This second flashing light is visible externally of the unit and provides a readily apparent indication of the need for battery replacement.
BRIEF DESCRIPTION OF THE DRAWING
The present invention may be better understood and its numerous objects and advantages will become apparent to those skilled in the art by reference to the accompanying drawing which is an electrical schematic diagram of a preferred embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
With reference now to the drawing, the battery power supply is indicated at 10. In one successful reduction to practice of the invention, power supply 10 comprised three standard 1.5 volt batteries connected in series. A normally closed reset switch S1 is connected in series with power supply 10 whereby current is delivered from the battery or batteries to the indicator and alarm circuitry. Insertion of the batteries in the power supply will, accordingly, render the device operative and, as will become apparent from the description below, should an alarm be sounded the circuit may be reset by the momentary opening of switch S1 to extinguish a switching device in the form of silicon controlled rectifier SCR-1.
A timing circuit 12 comprising transistors Q1 and Q2, resistor R1 and capacitor C1 is connected across power supply 10. Circuit 12 is a negative resistance relaxation oscillator which provides periodic pulses for the purposes to be described below. The "off" time of circuit 12 is determined by the RC time constant of resistor R1 and capacitor C1. The timing circuit "on" time is determined by the discharge of capacitor C1 through transistors Q1 and Q2 and the load on timing circuit 12; the load comprising the remaining circuitry as will be described below. Typically, timing circuit 12 will provide substantially square wave output pulses of 20 milliseconds duration with the period between pulses being 17 seconds.
The pulses provided by timing circuit 12 are applied to a common bus 14. Restated, during each firing period of transistor Q2 the battery voltage, less the IR drop of transistor Q2, is applied to bus 14. These positive pulses are applied to a light emitting diode, LED-2, via series connected resistor R11. The light emitting diode will accordingly periodically flash and the light pulses provided thereby are detected by a phototransistor 15. Phototransistor 15 is connected in series with bias resistor R12, and the resistor and phototransistor are in parallel with source 10. Each time the phototransistor 15 receives a light pulse it will conduct thereby applying a positive pulse to the base of a normally conductive transistor Q7. The timing pulses from circuit 12 are applied, via resistor R14, to the collector of transistor Q7. Application of the positive pulses from phototransistor 15 to the base of transistor Q7 will, accordingly, keep transistor Q7 in the conductive state. As long as transistor Q7 conducts its collector will essentially be maintained at ground potential.
The collector of transistor Q7 is connected to the gate electrode of a silicon controlled rectifier, SCR-1, which is in series with a suitable alarm device 16 across power supply 10. SCR-1 will be normally non-conductive whereby current will not flow through the alarm device 16 and the alarm will be deenergized. Alarm device 16 may, for example, be a solenoid driven mechanical oscillator which provides a loud audible warning signal. A capacitor C4 is connected in parallel with alarm device 16 to reduce the voltage ripple thereacross thereby allowing SCR-1 to latch in the "on" condition when rendered conductive. As noted, the gate electrode of SCR-1 is normally at ground potential due to the conductive state of transistor Q7. However, should a timing pulse be received at the collector of Q7 without there being a pulse simultaneously being applied to the base of Q7 via phototransistor 15, transistor Q7 will be turned off and the timing pulse will cause the silicon controlled rectifier SCR-1 to conduct. The RC circuit comprising resistor R15 and capacitor C3 will hold SCR-1 off during the transient time when the timing circuit 12 initially turns on. Resistor R16 is a gate clamp for SCR-1 and prevents false triggering and provides temperature stability. R16 may, of course, be adjustable if desired or necessary.
In operation, if smoke enters the detector circuit between phototransistor 15 and light emitting diode LED-2, the conduction of the phototransistor will be reduced thus reducing the "negative" bias applied to the base of transistor Q7 and permitting the transistor to be turned off by a positive timing pulse applied to the collector of Q7 via resistor R14. With transistor Q7 in the non-conductive state, the positive timing pulses will be applied to the now ungrounded gate of SCR-1 via the voltage divider defined by resistors R14 and R15 and the silicon controlled rectifier will be turned on thereby permitting current flow through the alarm device 16. A pair of output terminals 17 are provided whereby the voltage drop across the alarm device 16 may be utilized to trigger a transmitter which will deliver a warning signal to a remotely located master panel; the master panel for example being located at a guards station in a multiple detector installation. In such an instance the transmitter will also be battery powered.
A particularly novel feature of the present invention is a built-in battery testing circuit which comprises, in part, series connected Darlington amplifiers 18 and 20. The first Darlington amplifier, comprising transistors Q3 and Q4, provides an output signal during each timing pulse which is applied to the base of transistor Q5 of the second Darlington amplifier 20. The second Darlington amplifier, comprising transistors Q5 and Q6, is normally in the off condition whereby current may not flow through a second light emitting diode, LED-1, which is connected in series with transistor Q6 across power supply 10. As previously noted, the timing pulses supplied by timing circuit 12 are applied to bus 14 when transistor Q2 of circuit 12 fires. Transistor Q3 of Darlington amplifier 18 is biased on only when transistor Q2 conducts. When transistor Q3 is biased on, the base of transistor Q5 will be grounded via transistor Q4. Accordingly, application of the timing pulse to bus 14 will not render transistor Q5 conductive and, accordingly, transistor Q6 cannot conduct to complete a circuit through LED-1. A capacitor C2 connected between the emitter of transistor Q4 and ground provides compensation for the time delay of Darlington amplifier 18. Restated, when transistor Q2 of timing circuit 12 conducts, there will be a time delay between application of the positive pulse to bus 14 and the conduction of the Darlington amplifier. Capacitor C2 allows transistor Q4 to conduct hard thereby "firing" Darlington amplifier 18 before Darlington amplifier 20 can be rendered conductive by the timing pulse. A diode D2 connected in parallel with capacitor C2 provides a voltage reference for the "firing" of Darlington amplifier 18 thereby adding stability to the operation of the circuit. The "firing" point of Darlington amplifier 18 is determined by a voltage divider comprising resistors R2 and R3 and diode D1. Diode D1 has been added to the circuit to impart a "snap" action to transistor Q3. When the battery voltage is above a predetermined level, typically 3.9 volts, the Darlington amplifier 20 will be maintained in a nonconductive state during the pulsing of timing circuit 12. However, should the power supply voltage drop below the predetermined level, the first Darlington amplifier 18 will not conduct in response to the application of a timing pulse to bus 14. Accordingly, the positive timing pulse will be applied to the base of transistor Q5 of Darlington amplifier 20 via resistors R5 and R8 and the second Darlington amplifier will be "fired" thereby completing a current path through LED-1. Accordingly, when the battery voltage falls below the predetermined level, LED-1 will flash in synchronism with the pulsing of timing circuit 12 thus providing a warning that the batteries should be replaced.
It is to be noted that a temperature sensitive device, such as bimetallic switch S-2, may be connected between the positive side of power supply 10 and the gate electrode of SCR-1. The use of such an optional temperature sensitive device permits the invention to be sensitive to both the presence of smoke and increases in temperature; both conditions being indicative of a fire.
While a preferred embodiment has been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the present invention. Accordingly, it is to be understood that the invention has been described by way of illustration and not limitation.