U.S. patent number 3,860,919 [Application Number 05/428,094] was granted by the patent office on 1975-01-14 for smoke and gas detection and alarm apparatus.
This patent grant is currently assigned to Donald E. Funck. Invention is credited to John L. Aker.
United States Patent |
3,860,919 |
Aker |
January 14, 1975 |
SMOKE AND GAS DETECTION AND ALARM APPARATUS
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.
Inventors: |
Aker; John L. (Chanute,
KS) |
Assignee: |
Funck; Donald E. (Overland
Park, KS)
|
Family
ID: |
23697527 |
Appl.
No.: |
05/428,094 |
Filed: |
December 26, 1973 |
Current U.S.
Class: |
340/527; 331/65;
340/634; 340/628; 340/384.72; 340/309.8; 340/309.16 |
Current CPC
Class: |
G08B
17/117 (20130101) |
Current International
Class: |
G08B
17/10 (20060101); G08B 17/117 (20060101); G08b
021/00 (); G08b 003/00 () |
Field of
Search: |
;340/237,384E,309.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Caldwell; John W.
Assistant Examiner: Myer; Daniel
Attorney, Agent or Firm: Schmidt, Johnson, Hovey &
Williams
Claims
I claim:
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 parameter 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
for delaying 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 said sensing terminal means and a
reference potential derived from said power source, and output
terminal means coupled with said control terminal means of said
switching means.
9. The invention as set forth in claim 1, wherein said sensing
means is a Taguchi Gas Sensor.
10. The invention as set forth in claim 1, wherein said switching
means is a TRIAC.
11. The invention as set forth in claim 1, wherein said 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.
Description
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, A.C.
or D.C., 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 D.C. 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 14 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 company's 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 A.C. or D.C., 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 self-purging 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 90 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 1 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 40 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 D.C. 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 72-75 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 1-1.5 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 D.C. 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 between the 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 A.C.
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 operability of the apparatus by electrically simulating
conditions that would otherwise prevail only during the detection
of a hazard condition, etc.
The TRIAC switching device 24 is controlled or "gated" 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 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 D.C. reference
voltage, preferably equal to about one-third of the supply voltage,
is applied to terminal 5 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
non-conductive 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 reproducing 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 140 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 170 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 14 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 TRIAC 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, sufficient
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 device 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 5 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 1 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 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 OR VALUE
______________________________________ Power source 10 Ordinary 12
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
110 25K ohms Resistance 116 100K ohms Resistance 120 820 ohms IC
packages 140 and 194 Type 1458 dual op amp (Motorola) Resistance
144 10K ohms Resistance 148 4.7 ohms Resistance 156 3.3 megohms
Diodes 158, 180 and 200 Type IN4148 Resistance 162 820 ohms
Resistance 168 390 ohms Capacitances 170 and 172 .68 mfd
Capacitance 174 .22 mfd Resistance 184 3.3 megohms Capacitance 190
100 mfd Resistance 198 3.3 megohms Resistance 206 22K ohms
Resistance 212 1 megohm Resistance 218 3.3 megohms Capacitance 224
.1 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.
* * * * *