US 3860919 A
An improved Taguchi Gas Sensor type detection and alarm system for smoke, gases or the like, which is particularly adapted for use in environments where the only available source of electrical operating power is an ordinary storage battery, is provided and employs an electrical oscillator coupled with the storage battery for providing both the low voltage high current electrical power required for activating the Taguchi Gas Sensor and an audio frequency output signal for operating an audible warning component of the system when the sensor has detected the presence of smoke, gases or the like. The electrical circuit coupling the audio warning component with the output of the oscillator includes an electrically controlled switching device responsive to detection of existence of a hazardous condition by the sensor; and such circuit also includes in the coupling between the sensor and the switching device, means for providing a suitable delay prior to operation of the switching device to prevent the generation of false warning signals during warm-up or "purging" of the sensor upon start-up of the system. The preferred embodiment of the invention further provides an auxiliary oscillator of substantially lower frequency than the first mentioned oscillator which is coupled with the latter to provide a distinctive dual tone warning signal alternating between different audio frequencies. The improved apparatus is adapted for implementation by means of integrated circuit modules for the primary active electronic components.
Description (OCR text may contain errors)
United States Patent [191 Aker 14 1 Jan. 14, 1975 SMOKE AND GAS DETECTION AND ALARM APPARATUS John L. Aker, Chanute, Kans.
Donald E. Funck, Overland Park, Kans.
Filed: Dec. 26, 1973 Appl. No.: 428,094
 US. Cl 340/237 R, 331/65, 340/237 S, 340/309.1, 340/384 E Int. Cl. G08b 21/00, G08b 3/00 Field of Search 340/237, 384 E, 309.1
References Cited UNITED STATES PATENTS Primary Examiner]ohn W. Caldwell Assistant Examiner-Daniel Myer Attorney, Agent, or Firm-Schmidt, Johnson, Hovey & Williams  ABSTRACT An improved Taguchi Gas Sensor type detection and alarm system for smoke, gases or the like, which is particularly adapted for use in environments where the only available source of electrical operating power is an ordinary storage battery, is provided and employs an electrical oscillator coupled with the storage battery for providing both the low voltage high current electrical power required for activating the Taguchi Gas Sensor and an audio frequency output signal for operating an audible warning component of the system when the sensor has detected the presence of smoke, gases or the like. The electrical circuit coupling the audio warning component with the output of the oscillator includes an electrically controlled switching device responsive to detection of existence of a hazardous condition by the sensor; and such circuit also includes in the coupling between the sensor and the switching device, means for providing a suitable delay prior to operation of the switching device to prevent the generation of false warning signals during warm-up or purging of the sensor upon start-up of the system. The preferred embodiment of the invention further provides an auxiliary oscillator of substantially lower frequency than the first mentioned oscillator which is coupled with the latter to provide a distinctive dual tone warning signal alternating between different audio frequencies. The improved apparatus is adapted for implementation by means of integrated circuit modules for the primary active electronic components.
12 Claims, 1 Drawing Figure meg SMOKE AND GAS DETECTION 'AND ALARM APPARATUS This invention relates to detection and alarm apparatus for use in detecting and providing a warning of the presence of smoke, gases or the like such as would indicate the commencement of a fire or other potentially hazardous condition. More particularly, the invention provides improvements for such apparatus, especially with respect to providing such apparatus that is adaptable for practical use in environments such as motor homes, wherein the only available source of continuous electrical power may be from a battery.
One of the most reliable of the available instrumentalities for detecting the presence of smoke or unburned hydrocarbon gases is commercially known as the Taguchi Gas Sensor. Such sensors are extremely sensitive in the detection of smoke, gases or the like and are employed in various previous fire detection and prevention systems for use in normal commercial and domestic environments in which an essentially unlimited supply of electrical energizing power therefor is available from the regular electrical supply lines. However, Taguchi Gas Sensors are characterized by their requirement of electrical activating power of relatively high current at low voltage, typically around 0.6 Ampere at 1 Volt, AC. or DC, which heretofore has been regarded as rendering their use impractical in environments where the only available power source may be a battery whose charge would be quickly dissipated by such a heavy current drain during continuous operation of the hazard monitoring system. Similarly, the means employed in conventional systems for providing a warning of the detection of a hazard condition normally imposes additional, and often substantial, electrical power requirements on the supply source. Additionally, conventional systems of this general type are commonly subject to various other limitations and disadvantages such as susceptibility to false warning signals, inadequacy in providing a positive and distinctive type of warning signal, a tendency toward either limited reliability or undue complexity and space requirements, etc.
It is, therefore, the primary object of this invention to overcome the foregoing and other limitations and disadvantages of conventional detection and alarm systems through the provision of improved apparatus for such purpose.
It is another important object of the invention to provide such improved apparatus which is particularly adapted for use in environments having as their only conveniently available source of electrical power a storage battery of considerably higher voltage rating than required for operation of a Taguchi Gas Sensor but of considerably lower current drainage characteristics for continuous operation than would be required by a Taguchi Gas Sensor operating at its rated voltage.
It is another important object of the invention to provide such apparatus employing an audio frequency oscillator, operating in a switching mode for highest power conversion efficiency, for converting the relatively high voltage low current DC. power normally available from a storage battery or the like into an audio frequency output of substantially lower voltage and substantially higher current characteristics for use both in supplying activating power to a Taguchi Gas Sensor or comparable sensing instrumentality and in supplying an audio warning signal to a suitable audio transducer component when the alarm portion of the apparatus is to be operated responsive to sensing of the existence of a hazardous condition by the sensor.
It is another important object of the invention to provide such apparatus in which the activating circuit for the audio warning component is controlled by an electrically responsive switching device coupled with the sensor and including means for delaying actuation of the switching device for a suitable period of time to prevent the generation of false warning signals upon initial start-up of the operation of the apparatus.
It is another important object of the invention to provide such apparatus in which a secondary lower frequency oscillator is employed for producing a control signal of subaudio frequency, which is coupled with the main oscillator for causing the output of the latter to alternate between a pair of different audio frequencies in order to provide an audible warning signal of distinctive dual tone characteristics.
Still other important objects of the invention, including certain significant details of construction, will be made clear or become apparent to those skilled in the art from the accompanying drawing and the detailed description of a preferred embodiment of the invention that follows.
In the drawing, the single FIG. 1 is a schematic diagram of a preferred embodiment of the invention showing the various components and electrical connections employed in the improved apparatus.
Referring to the drawing, the currently preferred embodiment shown in FIG. 1 broadly includes an electrical power source 10, a system activating main power switch 12, a positive polarity supply lead 14, a negative polarity supply lead 16, a hazard condition sensor 18, a main audio frequency oscillator 20, an audio warning signal transducer 22, an electrically controlled switching device 24, control and delay means broadly indicated at 26 for coupling the sensor 18 with the switching device 24, and an auxiliary low frequency oscillator broadly indicated at 28 coupled with the main oscillator 20 for alternating the output of the latter between a pair of different audio frequencies.
In the types of applications for which the invention is especially suited, the power source 10 will normally be an ordinary electrical storage battery 30, preferably of the kind having a nominal voltage output of 12 volts direct current, in order to provide a convenient supply source for the various active electronic components of the system hereinafter described when such components are to be provided through the employment of widely available integrated circuit packages and other solid state devices.
The positive and negative supply leads l4 and 16, including the main power switch 12 preferably included in the former, are conventional and, presuming employment of a 12 volt storage battery 30 for the source 10, will provide avenues of connection with such source of 12 volt electrical operating power for the system. If desired, one of the leads 16 may be grounded, as indicated in dotted lines at 32. Those skilled in the art will appreciate, however, that, by employing different specific solid state components than those illustrated and used in the preferred embodiment, various electrical polarities could be reversed; and, also, that there is no inherent requirement that the system must be operated with either of the leads 14 and 16 at absolute ground potential.
The sensor 18 is preferably a Taguchi Gas Sensor Model T.G.S. 308 manufactured by Figaro Engineering, Inc. of Osaka, Japan, and available in this and other countries through various distributors of such companys products. If and when equivalent devices of domestic manufacture become available, they could also be employed. The mentioned presently preferred component for use as the sensor 18, however, internally includes input and output electrode structures schematically represented in the drawing as coils 34 and 36 respectively coupled with each other by a zone of variable electrical conductivity represented schematically in the drawing by the space 38 between coils 34 and 36. During operation of the sensor 18 in effective monitoring condition for detecting the presence of smoke, unburned hydrocarbon gases or the like, the application of an electrical activating potential of approximately 1 volt, either AC. or DC, across the terminals of structure 34 is required, which serves both to heat the coupling zone or space 38 and to provide a potential from which the conductivity between the structures 34 and 36 may be sensed at the terminals of the structure 36. The sensor 18 draws approximately 0.6 Ampere of current when in such standby monitoring condition and even more when in the conductive state thereof caused by detection of a hazard condition. When the ambient atmosphere or medium, which is admitted to the zone or space 38, contains even quite minute quantities of smoke or unburned hydrocarbons, the conductivity between the structures 34 and 36 increases markedly and electrical current flows therebetween in sensible amount. Although means hereinafter described are provided for appropriately adjusting (i.e., limiting) the sensitivity of the apparatus, in order to prevent undesired response to a normal atmosphere containing usual amounts of cigarette smoke or the like, the sensor 18 itself is extremely sensitive and quick in its response to the presence of any appreciable quantity of hazard indicating media.
In view of the previously noted relatively high current drain characteristics of the sensor 18, it will be perceived that operation thereof on a continuous basis from dry cells or the like would be highly impractical, not only due to the short life of low voltage batteries under such conditions of heavy current drain, but also because, even while there might remain sufficient electrical power for operating the sensor 18 to accomplish a detection, there would not likely be sufficient power available or remaining for operation of conventional alarm or warning devices for any appreciable period of time. It has been found, however, that, with the apparatus of this invention, reliable and efficient operation of such systems from an ordinary storage battery can be achieved by deriving the power for'the sensor 18 (at the voltage and current levels it requires) through the provision of an oscillator powered by the battery 30, together with the employment of an audio type alarm or warning signal produced from the same oscillator output used to power the sensor 18 without need for any separate warning generator or any source of additional electrical power for operating the warning portion of the system.
It should be noted that the Taguchi Gas Sensor 18 requires an initial warming up period, upon activation thereof, during which moisture or gases accumulated in the space 38 during a period of idleness may be purged therefrom, and in order to permit the temperature of the zone or space 38 to'stabilize at the desired level to which it is heated during normal operation. The period required for this purpose will normally be of the order of about 1 minute. During such warm up and selfpurging period of the sensor 18, it may, however, exhibit a conductive condition between its electrodes 34 and 36, which gives rise to the need for the delay means incorporated into the control and delay portion 26 of the apparatus of this invention, in order to avoid the occurrence of false warning signals as hereinafter more fully explained or the equally undesirable alternative of having to provide some sort of manual silencing button that must be held during the warm up and purging period.
The main oscillator 20 is conveniently provided in the preferred embodiment through the use of a Type MFC 8010 integrated circuit package 40, which is made and commercially distributed in this and other countries by the semiconductor products division of the Motorola Corporation, together with means for providing the desired feedback paths and other connections hereinafter described. Such packaged active component 40 used in the oscillator 20 is usually employed in moderate power audio amplifiers, but, for purposes of this invention, is operated as a square wave power oscillator functioning in a two state (rather than a linear) mode, in order to attain higher efficiency (approaching percent) in the conversion of direct current electrical power from the source 10 into lower voltage high usable current power for the sensor 18 and other parts of the system yet to be fully described. As employed in the oscillator 20 of this invention, the component 40 effectively converts 12 volt power from the battery 30 into a square wave alternating current output of approximately 2 volts peak-to-peak at approximately 0.6 Ampere with a preferred frequency of around 1 to 1.5 kilocycles (which it is noted is not only adequate for powering the sensor 18, but also is within the audio portion of the spectrum and in that range of the latter that is normally most distinctively perceived by the human ear), and accomplishes such conversion with a current drain on the 12 volt battery 30 of the order of only about 60 milliamperes (due to the low power dissipation of individual active elements of the package 40 during half-cycles of the switching mode in which the oscillator 20 is operated).
Since the internal design of the integrated circuit package 40 per se does not of itself constitute an aspect claimed in connection with the present invention, and since technical data regarding the same is available from the manufacturer of such component, it is not deemed necessary to fully describe the internal construction of the package 40. Rather, the limits of the package 40 are indicated in the drawing by a dotted line box with the terminals of the package 40 numbered to correspond with the terminal reference numbers conventionally associated with the commercial component, and the general network of constituent elements within the package 40 is herein schematically indicated in the drawing without detailed description thereof merely for the possible convenience of those skilled in the art who may already be familiar with such component package 40, or who will readily grasp the nature thereof from the schematic representation included in the drawing. It may be helpful in passing, however, to
note that terminals 7 and l of the package 40 are respectively the positive and negative supply terminals thereof, which are appropriately coupled with the power leads 14 and 16 of the apparatus of this invention; that terminal 8 of the package 40 is its output terminal; that terminal 4 of the package 40 is its main input terminal, which is non-inverting (i.e., a terminal with respect to which an electrical input wave applied thereto is not inverted in the wave form of the resultant output at terminal 8); and that terminal 3 of the package 40 is an inverting input terminal thereof (so that terminals 3 and 4 provide for the application to the package 40 of differential inputs).
The oscillator 20 is provided with a negative feedback path and network and a positive feedback path and network; the negative feedback path is traceable from the output terminal 8 of the package through lead 42, resistance 44 and lead 46 to the inverting input terminal 3 of the package 40, with the divider network being completed by lead 48, capacitance 50 and lead 52 coupled with the main negative power lead 16; the positive feedback path is traceable from the output terminal 8 of the package 40 through lead 54, resistance 56, lead 58, capacitance 60, lead 62, resistance 64 and lead 66 to the non-inverting input terminal 4 of the package 40, with the divider network being completed by a connection through lead 68 to the midpoint of the voltage divider presented by lead 70 coupled to main positive power lead 14, resistance 72, lead 74, resistance 76 and lead 78 coupled to the main negative power lead 16. Terminals 2 and 5 of the package 40 are conventionally bypassed to the negative supply lead 16 through capacitances 80 and 82 respectively. Terminal 6 of the package 40 is coupled with the output terminal 8 through lead 84, a bootstrap pull-up resistance 86, lead 88 and the output coupling capacitance 90, it being noted that the resistance 86 thus serves to assure that the pull-up output transistor elements of the package 40 become saturated during positive half-cycles of the operation of the oscillator 20, as hereinafter explained, thereby assuring minimum internal power dissipation and maximum efficiency of the switched mode oscillator 20.
The oscillator 20 functions essentially as follows, it being noted that the duty factor thereof is determined by the value ratio of the resistances 72 and 76 of the voltage divider identified above as associated with the main or non-inverting input terminal 4 of the package 40, equal values for the resistances 72 and 76 being preferred in order to establish the DC. potential on input terminal 4 at a level equal to one-half of the supply voltage existing between leads 14 and 16. An output signal voltage at terminal 8 produces a current flow in resistances 56 and 64 of the positive feedback path traced above, thereby changing the voltage potential at the input terminal 4 (in either direction from the reference potential derived from the supply voltage divider 72-76, depending upon the polarity of the output at terminal 8). As the potential at terminal 4 thus is changing, capacitance 50 will charge (or discharge) toward the new potential at terminal 4 through resistance 44 of the negative feedback path traced above until the potential at input terminal 3 equals that at input terminal 4, which will cause the oscillator 20 to commence to switch states. The positive feedback from the output terminal 8 completes such switching and continues the other half-cycle of the operation regeneratively until the opposite extreme of potential differential between the input terminals 3 and 4 is attained (as determined by component and supply voltage values), whereupon discharging (or charging) of the capacitance 50 will attain momentary equilibrium, then be reversed and continued under influence of the feedback to sustain the oscillatory cycling of the oscillator 20.
During such cycling of the oscillator 20, the capacitance 50 alternately charges and discharges during successive half-cycles, with the wave form of the potential at terminal 3 essentially in the nature of a saw-tooth wave composed of upward and downward exponential ramps extending alternately above and below the reference potential provided by the divider 7275 by an amount determined by the maximum potential change or differential permitted by component values and the supply voltage. Meanwhile, the wave form of the output at terminal 8 is a square wave of amplitude varying from a potential of near zero to a positive potential determined by the component parameters and supply voltage, although such amplitude will preferably be at least somewhat greater than the voltage required for excitation of the sensor 18. The frequency of the output from terminal 8 of the package 40 of oscillator 20 is essentially determined by the RC time constant of resistance 44 and the capacitance 50 and, of course, by the amount of maximum swing of the voltage differential at the input terminals 3 and 4 in relation to the supply voltage (since an increased swing will require a longer period for the capacitance 50 to charge or discharge sufficiently to equalize the potentials at the terminals 3 and 4 with any given supply voltage, thereby decreasing the frequency of the output, or vice versa). As previously noted, an output frequency of l-1.5 kilocycles is preferred for the oscillator 20, and an output amplitude of about 2 volts peak-to-peak is quite suitable for a sensor 18 using a Model T.G.S. 308 Taguchi Gas Sensor. As hereinafter more fully explained, the preferred embodiment of the invention contemplates that the output frequency will alternately be switched between two different frequencies, which may conveniently be near opposite extremes of the above-noted range.
Although the type of oscillator 20 illustrated and described in connection with the preferred embodiment of the invention is believed to approach being optimum from the standpoints of functional characteristics in efficiently providing for conversion of DC. power from a storage battery source 30 into an A.C. output adapted both for exciting a Taguchi Gas Sensor and driving an audio warning transducer and of economics as to cost, space requirements and availability of components, nevertheless, those skilled in the art will appreciate that specifically different forms of oscillators could be employed without departing from the novel and advantageous aspects of the invention, as long as certain primary particular functional requirements are met (especially the ability to efficiently produce a suitable audio frequency alternating current output adapted to drive both the sensor 18 and the transducer 22 with a minimum of current drain upon power initially derived from a relatively higher voltage lower current drainage capacity D.C. source such as an ordinary storage battery).
The square wave audio frequency A.C. current output from the oscillator 20 is coupled from terminal 8 of IC package 40 through the coupling capacitance 90 and leads 88 and 92 with one end terminal of an autotransformer 94, the opposite end terminal of which is coupled by lead 96 with the positive supply lead 14. A tap 98 on the autotransformer 94 is coupled with one terminal of the electrode or primary structure 34 of the sensor 18, and the opposite terminal of the primary structure 34 is coupled by leads 100 and 96 with the positive supply lead 14. The tap 98 is appropriately adjusted to apply the excitation power derived from the output of the oscillator 20 to the sensor 18 at the appropriate voltage for the particular component employed as the sensor 18' (about 1 volt for the Model T.G.S. 308 Taguchi Gas Sensor). It will be noted that the excitation power from the oscillator 20 for the sensor 18 thus works against or is referred to the positive supply voltage, since one of the terminals of the structure 34 is connected directly to the positive supply lead 14; those skilled in the art will appreciate, however, that this has been done for convenience in the preferred embodiment, in the light of the particular components and relationships of the other portions of the overall circuitry, but that an equivalent reversed polarity version of the apparatus could just as well be employed with appropriate choice of components and connections.
When the sensor 18 is in a hazard detecting state (i.e., when it is sensing the presence of smoke, unburned hydrocarbon gases or the like), the electrical conductivity of the space or zone 38 will increase to permit a flow of current betweenthe electrode structures 34 and 36 through an overall path traceable from the positive supply lead 14 through leads 96 and 100 to the electrode 34, through the conductive path created in zone 38 to the electrode 36, through conductors 102 and 104 connected to the opposite end terminals of the electrode structure 36 and a lead 106 to a connection point 108, thence through a sensitivity adjusting potentiometer 110 having an adjustable shorting tap 112, thence through a lead 114, a resistance 116, a lead 118, a resistance 120 and a lead 122 to the negative supply lead 16. The flow of current through the circuit just traced when the sensor 18 is rendered conductive by the detection of a hazard condition creates a voltage potential at the connection point 108, the significance of which is hereinafter further explained, it being sufficient for present purposes merely to note that adjustment of the tap 112 of potentiometer 110 permits the voltage potential level at point 108 to be adjusted to different values for a given degree of conductivity of the sensor 18, and thereby provides a means of selectively setting the concentration of hazardous gases that will be required for the sensor 18 to permit sufficient current flow through the last traced circuit to provide a predetermined triggering potential level at the connection point 108.
The audio frequency output from the oscillator 20 is also coupled from the terminal 8 of the IC package 40 through the coupling capacitance 90 and a lead 124 with the audio frequency transducer 22. With an output from the oscillator 20 of the amplitude being considered in conjunction with the preferred embodiment, the transducer 22 may merely consist of any suitable form of loudspeaker; if desired, however, those skilled in the art will understand that the transducer 22 could be provided with conventional further audio amplifier means for strengthening the audio signal to permit driving a larger loudspeaker of a plurality of loudspeakers.
The terminal of the transducer 22 opposite from the lead 124 is coupled through a lead 126, a reset switch 128, a lead 130, the electronic switching device 24 and a lead 132 with the positive supply lead 14, assuming the conductivity of the switching device 24 under conditions next to be discussed. In passing, it is noted that the audio frequency output of the oscillator 20 also works against the positive supply potential with respect to the output utilization branch incorporating the transducer 22, but that those skilled in the art could easily provide a reversed polarity equivalent arrangement, if desired.
The electronic switching device 24 of the preferred embodiment is a silicon bilateral solid state switch of the type commonly referred to as a TRIAC, which is characterized by its ability to conduct anode current at terminal 134 of either polarity with respect to its cathode terminal 136 whenever control current has been caused to flow between its gate terminal 138 and its cathode terminal 136. Once so triggered, the TRIAC device 24 is further characterized by its property of maintaining the conductivity path established between its anode and cathode terminals 134 and 136 until the flow of such anode-cathode current has been externally interrupted, as by manual operation of the reset switch 128. Accordingly, once the alarm transducer 22 has been activated to audibly reproduce a signal from the oscillator 20 by virtue of the TRIAC device 24 having been triggered into its conductive state, such alarm signal will be continued until it has been recognized by the user of the apparatus and such user has'cutoff the warning signal and reset the apparatus by momentarily manually opening the reset switch 128. In the preferred embodiment, it has been found that the Type 40528 TRIAC, made and distributed in this and other countries by Radio Corporation of America, operates most satisfactorily, and particularly with respect to that further attribute of TRIAC switching devices by which they are adapted to maintain their conductive state, once triggered by an appropriate control signal, even though the switched signal applied thereto is of the AC. type, provided that the transition period of such signal from one polarity to the other is sufficiently rapid. In the preferred embodiment, since the output from the oscillator 20 has a square wave type wave form, such transition period is so short that no problem has been encountered, since the minimal transition period involved with such square wave signal is too short to allow the charge carriers of the TRIAC device 24 to clear.
Thus far, the basic operation and interrelationships of the oscillator 20, the excitation power circuit for the sensor 18, the audio warning transducer 22 and the TRIAC switching device 24' associated with the latter have been considered; it remains, with respect to the most basic portions of the improved apparatus, to explain the manner in which the TRIAC switching device 24 (and therefore the warning transducer 22) are controlled in response to the sensing of a hazard condition by the sensor 18. Then, it will be most appropriate to further consider certain additional features incorporated into the preferred embodiment for providing advantageous special functions in the apparatus such as an automatic delay of any operation of the warning transducer 22 until the sensor 18 has warmed up and become stabilized, the provision of a dual tone warning signal, the provision of simple means for testing the opgated from an operational amplifier (OP AMP) 140 operated in a voltage comparator mode. The component employed for the comparator 140 in the preferred embodiment is one-half of a type 1458 dual OP AMP such as made and distributed in this and other countries by Motorola Corporation, the other half of such component being employed in the auxiliary oscillator 28 hereinafter to be described. The terminals of the portion of the component used for the comparator 140 as indicated on the drawing are those conventionally associated with the various terminals of the commercial component itself. Due to the commonness of such integrated circuit packages for providing operational amplifiers, and since the internal details thereof are both well understood by those skilled in the art and do not a per se constitute an aspect of the present invention, the
circuitry of the preferred embodiment associated with the comparator 140 need herein be explained only with reference to the connections made to the various terminals of the OP AMP component being employed in order to operate the same in a voltage comparator mode. A DC. reference voltage, preferably equal to about one-third of the supply voltage, is applied to terminal of the comparator 140 by means of a voltage divider including lead 142, resistance 144, lead 146, and resistance 148 coupled between the supply leads 14 and 16, with a tap lead 150 connecting the intermediate lead 146 of the divider with the terminal 5 of comparator 140. It may be noted that the terminal 5 is a non-inverting input terminal and that the reference voltage applied thereto is compared by the comparator 140 with any voltage applied to the inverted input terminal 6 thereof through the lead 152 coupled therewith. The lead 152 is connected with the positive supply lead 14 through a connection point 154 and a resistance 156, and the connection point 154 is coupled with the connection point 108 by a diode 158. As long as the voltage potential at connection point 154 (and therefore at terminal 6 of comparator 140) is lower than the reference voltage applied to terminal 5 of the comparator 140, the output of the comparator 140 at output terminal 7 thereof will be maintained near the positive supply voltage. The output from terminal 7 of the comparator 140 is coupled through a lead 160, a resistance 162 and a lead 164 with the control element 138 of the TRIAC device 24. As long as the output from the comparator 140 applied to the control terminal 138 of the switching device 24 remains near the positive supply voltage level, the device 24 will not be triggered and will present a nonconductive path or essentially open circuit between the anode 134 and cathode 136 of the device 24, thereby preventing the warning transducer 22 from responding to and repro ducing the audio output signal from the oscillator 20. If the voltage potential at point 154 and terminal 6 of comparator 140 should become more positive than the reference voltage at terminal 5 of the comparator 140, however, the output of the comparator 140 at terminal 7 thereof will change to near the negative supply potential thereby causing gating current to flow through the resistance 162 to the control terminal 138 of the TRIAC device 24 thence through the latter to the cathode 136 thereof and back through lead 166 to the lead terminal 8 of the comparator 140. A resistance 168 coupled between the control terminal 138 of the TRIAC device 24 and the lead terminal 8 of the comparator provides for development of a sufficient potential difference between the control terminal 138 and the cathode 136 of the TRIAC device 24 to assure triggering of the device 24. Whenever the device 24 is thus triggered, the previously traced circuit for operation of the transducer 22 will be completed through the conductive path then established between the anode 134 and the cathode 136 of the switching device 24 and, as previously noted, such circuit will be maintained unless and until the reset switch 128 is operated, even though the output from the comparator 140 might thereafter change toward its standby condition (for example, upon interruption or cessation of a hazard condition being detected by the sensor 18). Capacitances and 172 respectively connected between terminals 5 and 6 of the comparator 140 and the negative supply lead 16 serve to by-pass electrically transients from external sources to minimize the chances of false triggering of the warning alarm transducer 22, it being noted that a by-pass capacitance 174 is preferably provided for similar reasons and connected between the supply leads l4 and 16 by leads 176 and 178.
As is believed apparent, when a hazard condition is detected by the sensor 18, the positive potential at connection point 108 tends to rise due to conduction between the electrodes 34 and 36 as previously explained; this rise in positive potential at the connection point 108 is passed through the diode 158 to connection point 154 and lead 152 to the terminal 6 of the comparator 140 to bring about triggering of the TRlAC switching device 24 whenever a hazard condition is detected by the sensor 18.
It will be noted, however, that the connection point 154 is also coupled through an oppositely facing diode 180 with a connection point 182 that is in turn coupled with the positive supply lead 14 through a resistance 184 and with the negative supply lead 16 through lead 186, capacitance 188 and lead 190. Such last mentioned additional circuitry provides a needed automatic delay against premature triggering of the TRIAC device 24 upon initial startup of the apparatus in the following manner. The voltage potential at connection point 154, which provides the input to terminal 6 of the comparator 140, can approach the voltage potential established at connection point 108 by the sensor 18 being rendered conductive by detection of a hazard condition only if the voltage potential stored by the capacitance 188 and appearing at connection point 182 is at least somewhat more positive than the voltage potential occurring at the connection point 108. Upon initial start up of the system, however, any voltage potential at the connection point 182 will be very low due to the fact that the capacitance 188 will have been discharged during any inactive period of the apparatus through a path around through the resistances 184, 144 and 148. Accordingly, after initial start up of the apparatus, sufiicient time must elapse for current flow through the resistance 184 to charge the capacitance 188 so that the potential at connection point 182 will be at least slightly more positive than the reference voltage applied to terminal 5 of the comparator 140; any voltage at connection point 108, no matter how positive, then can operate to trigger the switching de vice 24. The values of the resistance 184 and capacitance 188 may be chosen to provide any desired interval for such delay period, a delay of about one minute being employed in the preferred embodiment.
After the mentioned automatic delay for warm up and stabilization of the sensor 18 after initial start up of the apparatus, an extremely comprehensive and reliable test of the functional condition of the apparatus may be made by manually opening the test switch 192, which is coupled in parallel with the resistance 116. It will be observed that the switch 192, when not operated to its test position shunts across the resistance 116; however, when the additional resistance of component 116 is introduced into the circuit providing impedance from the connection point 108 to the negative supply lead 16 by virtue of opening of the test switch 192, this will cause the small residual current which normally flows through a properly functioning sensor 18 even in its standby or non-hazard sensing condition to generate a sufficient voltage across the resistance 116 to raise the voltage potential at connection point 108 to or above the potential of the reference voltage being applied to terminal of comparator 140. When this occurs, the increased potential at point 108 is passed to a point 154 and terminal 6 of comparator 140 to effect a simulated sensing of a hazard condition by the sensor 18 and resultant operation of the switching device 24 and the warning transducer 22, if the oscillator 20 and the various control circuits associated with the sensor 18 are properly operating as previously described. Note that such test even verifies that operability of the automatic delay feature of the control portion of the apparatus, since the test will not produce an affirmative result by way of an audible signal from the transducer 22 unless or until the delay period has elapsed and the sensor 18 achieved operating equilibrium after any start up of the apparatus. Thus, upon opening the test switch 192 during normal standby operation of the apparatus, if an audible warning signal is immediately heard to emanate from the transducer 22 and to continue even after reclosure of the test switch 192, the user may feel well assured that the apparatus is properly functioning. After any such test, as after any hazard triggered operation of the alarm portion of the apparatus, the audible warning from the transducer 22 will continue until the reset switch 128 is momentarily operated to cutoff anode current to the TRIAC device 24, thus restoring the apparatus to its normal standby or monitoring condition.
Also incorporated in the preferred embodiment of the invention is a secondary oscillator also operating in a two state or switch mode to provide a substantially square wave output therefrom, but such auxiliary oscillator 28 is arranged to operate at a substantially lower frequency than the primary oscillator 20, which should be below the audible range and preferably may be approximately one cycle per second. The secondary oscillator 28 employs a conventional OP AMP 194, which is conveniently provided by the other half of the dual OP AMP integrated circuit package that is used to provide the comparator 140. As indicated in the drawing, the terminals 1, 2, 3 and 4 of the commercial integrated circuit package are those used in connection with the OP AMP 194 employed in the secondary oscillator 28. Terminal 4 of the OP AMP 194 is connected to the negative supply lead 16, while terminal 3 thereof is coupled with the positive supply terminal through lead 196, resistance 198, leads 66, 68 and 74, resistance 72 and lead 70. The terminal 1 of the OP AMP 194 is the output terminal of the auxiliary oscillator 28 and varies in square wave fashion between potential levels respectively near that of the negative supply lead 16 and that of the positive potential applied to the terminal 3. Those skilled in the art will recognize the negative feedback path for maintaining oscillations in the auxiliary oscillator 28 as including leads 204, 202 and 210, resistance 212 and leads 214 and 196 leading from the output terminal 1 to the input terminal 3 of the auxiliary oscillator OP AMP 194. The positive feedback path for the auxiliary oscillator 28 is similarly traceable through leads 204, 216, resistance 218 and leads 220 and 222 to the other input terminal 2 of the OP AMP 194.
During the half cycle of the oscillatory output of the oscillator 28 during which the potential at output terminal l of the OP AMP 194 is relatively positive, the diode 200 that is coupled with the output terminal 1 through leads 202 and 204 will be reversely biased, so that the positive half cycles of the output from oscillator 28 will not affect the operation of the primary oscillator 20 in any way. However, during the more negative half cycles of the output from the auxiliary oscillator 28 the diode 200 will conduct so that current may flow through the resistance 206 to a point of connection 208 with the positive feedback path associated with the primary oscillator 20 during the more positive half cycles of the output of the oscillator 20; this results in an attenuation of the positive feedback signal from terminal 8 to terminal 4 of the IC package 40 of the primary oscillator 20, and thereby a decrease in the magnitude of 7 change of the potential at terminal 4 of package 40 relative to the reference potential normally applied thereto. Since the frequency of the primary oscillator 20 is dependent upon the magnitude of such potential change at terminal 4 of the package 40, as previously explained, this results in operation of the oscillator 20 at a higher audio frequency than its normal frequency of oscillation during any periods during which the diode 200 is caused to conduct by the output from the auxiliary oscillator 28. The capacitance 224 is provided to prevent changes in the D.C. potential occurring when diode 200 is conductive from being effectively transferred back to the input of the primary oscillator package 40, since a steady state change in such input voltage would tend to cause the duty factor of the primary oscillator 20 to depart from 50 percent (which would be undesirable by tending to reduce the magnitude of the effective output otherwise available from the primary oscillator 20).
As previously indicated the significant effect of the provision of the auxiliary oscillator 28 is its noted operational effect upon the frequency of oscillation of the primary oscillator 20 so that the output of the latter will alternate between two different audio frequencies. In the preferred embodiment in which the lower of such frequencies is approximately 1 kilocycle and the higher of the same approximately 1.5 kilocycles, such alternating variation in the frequency of the output from the oscillator 20 has virtually no effect upon the efficient energization of the sensor 18, but does have the desired result of providing an alternating dual tone warning signal from the alarm transducer 22 which is of such distinctive characteristics as to attract immediate attention even in otherwise relatively noisy environments.
It may be noted that the following component types and values have been found quite satisfactory in the preferred embodiment of the invention:
COMPONENT TYPE 0R VALUE Power source l0 Ordinary l2 volt storage battery Sensor 18 Model T.G.S. 308 Taguchi Gas Sensor (Figaro Engineering Co.) Transducer 22 Ordinary permanent magnet loudspeaker, 8 ohms Switching device 24 TRIAC Type 40528 (R.C.A.) IC package 40 Type MFC 8010 audio amplifier module (Motorola) Resistance 44 47K ohms Capacitance 50 .1 mfd Resistance 56 22K ohms Capacitance 60 .022 mfd Resistance 64 47K ohms Resistances 72 and 76 4.7K ohms Capacitances 80 and 82 .22 mfd Resistance 86 10K ohms Capacitance 90 100 mfd Autotransformer 94 5:1, 2 ohms Potentiometer l 10 K ohms Resistance ll6 100K ohms Resistance 120 820 ohms lC packages 140 and 194 Type 1458 dual op amp (Motorola) Resistance 144 10K ohms 25 Resistance 148 4.7 ohms Resistance 156 3.3 megohms Diodes 158, H and 200 Type lN4l48 Resistance 162 820 ohms Resistance 168 390 ohms Capacitances 170 and l72 .68 mfd Capacitance l74 .22 mfd 30 Resistance 184 3.3 megohms Capacitance 190 100 mfd Resistance 198 3.3 megohms Resistance 206 22K ohms Resistance 212 l megohm Resistance 218- 3.3 megohms Capacitance 224 .l mfd Those skilled in the art will readily appreciate that a number of minor modifications might be made from the preferred embodiment shown and described for purposes of illustrating the invention without departing from the true spirit or real essence of the improvements provided by the invention. For example, different specific commercially available components of equivalent nature could be employed with conventional related alteration of electrical polarities, voltage or current values and the like. Accordingly, it is contemplated that the scope of the invention should be fairly deemed to extend not only to the scope of the subject matter defined by the claims which follow, but also to structural and functional equivalents thereof.
1. In electrical detection and alarm apparatus for sensing the presence of smoke, gas or the like and providing an audible warning thereof, which is adapted for operation with a limited permissible amount of continuous current drain from a supply source of direct current electrical power of predetermined voltage such as an electrical storage battery:
means for sensing the presence of smoke, unburned hydrocarbon gases or the like,
said sensing means requiring for operation thereof the application thereto of electrical energizing power of voltage substantially lower than the voltage of said supply source and of current drain substantially higher than said permissible amount, said sensing means having sensing terminal means normally characterized by an electrical parameter of predetermined value therebetween, said param eter being changed to a different value when said sensing means detects the presence of smoke, unburned hydrocarbon gases or the like; electrical oscillatory means, coupled with said direct current supply source and deriving operating power from the latter, for providing an alternating current output of audio frequency and of voltage and current characteristics satisfying said energizing power requirements of said sensing means;
electrical circuit means for coupling said output of said oscillatory means with said sensing means for energizing the latter;
electrically responsive switching means having switched terminal means and control terminal means;
electrical circuit means for coupling said sensing terminal means of said sensing means with said control terminal means of said switching means for controlling switching operation of said switched terminal means of the latter responsive to the value of said parameter;
electrically responsive audio transducer means for providing an audio output when an input signal of audio frequency is applied thereto; and
electrical circuit means for coupling the output of said oscillatory means with said transducer means through said switches terminal means of said switching means.
2. The invention as set forth in claim 1, wherein is provided a secondary electrical oscillator for providing an alternating current output of substantially lower frequency than said output of said oscillatory means; and electrical circuit means for coupling said secondary oscillator with said oscillatory means for varying the frequency of said output of the latter between alternate audio frequencies at a rate alternating at said lower frequency of said output of said secondary oscillator.
3. The invention as set forth in claim 2, wherein said oscillatory means includes a feedback path from the output to an input thereof; and said output of said secondary electrical oscillator is coupled with said feedback path.
4. The invention as set forth in claim 2, wherein said output of said secondary electrical oscillator is a square wave of sub-audio frequency.
5. The invention as set forth in claim 1, wherein is provided means fordelaying switching operation of said switching means for a predetermined time following initial activation of said apparatus.
6. The invention as set forth in claim 5, wherein said delaying means includes a capacitor coupled through a diode with said circuit means for coupling said sensing terminal means of said sensing means with said control terminals of said switching means and oppositely coupled with one pole of said supply source.
7. The invention of claim 1, wherein said switching means includes electrical components operable to maintain a conductive path through said switched terminals of said switching means once said switching means has been operated and until electrical energization is removed therefrom.
8. The invention as set forth in claim 1, wherein said circuit means for coupling said sensing terminal means of said sensing means with said control terminal means of said switching means includes a voltage comparator having input terminal means respectively coupled with oscillatory means operates in a switching mode, and said output thereof is substantially a square wave.
12. The invention as set forth in claim 11, wherein is provided means for varying the frequency of said output of said oscillatory means between a pair of alternate different audio frequencies at a sub-audio frequency rate.