Note: Descriptions are shown in the official language in which they were submitted.
~850~9
BACKGROUND ~F THE INVENTION
In smoke detectors of the reflscted light type,
in which a photo-responsive device is used to receive light
from smoke particles illuminated by a light source, one of
the major problems has been that of providing a light source
which is capable of operating over a long period of tim~
without failure. For this purpose, light emitting diodes
have recently been utilized.
However, commercially available light emitting
diodes have, at their rated current, insufficient light
output to function as an effective smoke detector. However,
it has been found that such a diode will produce light out-
put adequate for smoke detection purposes if it is operated
at a current considerably higher than the rated current
specified by the manufacturer, but its life is so short at
this higher current as to make its use in a commercial
smoke detector impractical.
However, I have found that if the light emitting
diode is energized at the higher current in short pulses,
its light output and service life will be adequate for a
continuously operating smoke detector,
r,,, ~:
~ 1 --
A detector utilizing light emitting diodes in
this manner is disclosed in U. S. patent 3,946,241 issued
to me on March 23, 1976. In the detector disclosed therein,
t:he pulse to the light emitting diode has a duration of
about 20 micro seconds, with the repetition rate being 1
pulse every 2 seconds. The detector described therein is
designed to produc~ an alarm only if smoke is detected on
two consecutive pulses.
However, it has been found desirable in some
cases to increase the degree of immunity from false alarms,
to require the detection of smoke by 4 or more pulses to
produce an alarm, and it has also been found desirable to
reduce the pulse repetition rate to, for example, 5 seconds,
to increase the life of the light-emitting diode. However,
the combination of these two modifications would result in
an alarm response time of 15 seconds, which i~ an unaccept-
able length of time.
It has been suggested that on the detection of
smoke by a pulse, the reptition rate could be increased,
so that the required number of output pulses to produce the
alarm would be produced in a shorter period of time. How-
ever, if there are no subsequent output pulses (such as when
the first pulse is a result of a spurious response), the
pulse rate would nevertheless continue at the high rate.
This not only reduces the life of the light emitting diode,
but also increases the possibility of another false alarm
being received during the period of increased pulse rate.
' ~ .'
'
1085019
MMARY OF THE INVENT~O~
To increase the life of the light emitting diode by
reducing the pulse repetition rate thereof without increasing
the response time of the detector, I provide a means for
shortening the time to the next light pulse after a light
pulse has illuminated smoke present at the detector to pro-
duce an output response from the detection amplifier.
In accordance with a specific embodiment of the
invention, a detector comprises: a radiant energy-producing
device pulsing at a predetermined interval, first means ~or
producing a signal pulse in response to the pulsed radiant
energy under predetermined conditions, and second means
responsive to a predetermined number greater than one of
produced signal pulses to provide an output signal, the
improvement comprising means responsive to a first signal
pulse to decrease the interval to at least the next light
pulse to less than that of the predetermined interval.
In one embodiment, if the second pulse also
produces an output, the following pulse is caused to occur
at the shortened interval, with the shortened interval between
pulses continuing as long as the preceding pulse has produced
an amplifier output. If any pulse does not produce an
amplifier output, the time interval to the following pulse
returns to the longer stand-by interval.
In one form of circuit operating in accordance
with this first embodiment of the invention, on each pulse
to the light emitting diode, a shorter pulse is applied to a
bi-stable switching device, to insure that the switching device
cannot pass an output signal to an integrating device The
bi-stable switching device may be a flip-flop with the shorter
pulse being applied to the re-set terminal thereof at the
~ _ 3 _
~V85019
beginning of the pulse to the light emitting diod~. If smoke
is present during a first pulse, the resulting output occur-
ring during the pulse to the light emitting diode but after
t]he short pulse to the re-set terminal of the flip-flop, is
fed to the set terminal of the flip-flop to cause an output
pulse to appear at the pulse integrator. The output pulse
from the flip-flop is also fed to an electronic switch,
associated with the pulse generator, to change its condition
so as to increase the pulse rate. The interval to the next
or second pulse is thereby shortened.
On the second pulse, the initial short pulse to
the re-set terminal of the flip-flop, in addition to turning
off the output to the integrator, also returns the electronic
switch to its former condition. Honce if no output signal
is created by the second pulse, the interval to the follow-
ing or third pulse returns to the original stand-by pulse
interval, however, if an output
: ,
- 3a -
108S0~9
ign~l is created by the ~eco=d pul=e~ tbe inter~al to the tbird pulse~ is
al BO ~hortened.
In a second embodiment of the invention, I provide a 8ystem wherein after
a light pulse has illuminated smoke pre8ent at the detector and an output
response from the detection amplifier has been produced, the pulse generator
thereafter produces, at a faster rate, the predetermined number of pulses
required to produce an alarm. If smoke i6 present during said predetermined
number of pulses, the alarm is activated.
If smoke i~ not detected on each of the pulses after the first (or on the
number of pulses required to activate the alarm, if less) then after the
predetermined number of pulses at the faster rate have been completed the
pulse rate returns to the slower 8tandby pulse rate.
In one form of this second embodiment of the invention, the increased
pulse rate may be created for a predetermined short time interval rather than
for a predetermined number of pulses; however, the operation of the 6ystem is
lotherwise identical~ in that if the required number of responses to smoke are
¦received in the predetermined time interval, the alarm is sounded. Otherwise
¦the pulse rate returns to the slower standby rate at the end of the predetermine
time interval.
I In another form of this second embodiment of the invention, each pulse
¦¦that detects smoke after the first re-sets the timer~ so that so long as
smoke is present~ the pulse generator continues to run st the faster rate. As
soon as $he smoke concentration has dropped below a predetermined level, the
pulse rate will return to the slower rate a predetermined number of pulses,
or a predetermined time, after the last pul8e that causes a response due to
smoke~ ~
In another form of this 8econd embodiment of the invention, the first
pul8e that detects smoke causes the pulse rate to increase to the faster rate
for a predetermined number of pulses or for a predetermined time~ with the
subsequent pulses at the higher rate that detect amoke having no effect on the
-4-
~()850~9
time or number of pulses during which the pulse generstor runs at the faster
rate. In this embodiment, if all of the predetermined number of pulse6
detect smoke, the alarm sounds and the pulse generator returns to the standby
rate while the alarm is sounding. At the beginning of the next pulse, the
alarm is de-energized. If said next pulse produces smoke, the pulse rate again
increases, and if the following predete~mined number of pulses detect smoke,
the alarm is again sounded. This system therefore produces an alsrm that
sounds intermittently.
In another form of thi6 second embodiment of the invention, such as might
be used in a detector system having many detectors, once the alarm has sounded,
the alarm may be locked in the alarm condition, and the pulse generator, and
! Ihence the light-emitting diode~ de-energized until the alarm is turned off.
A portion of the circuitry contained in the above forms of this second
embodiment may be similar to that shown in my U.S. patent 3,946,241 in which,
on each pulse to the light-emitting diode, a shorter pulse is applied to a
bi-stable switching device~ to insure that the switching device cannot pass
an output signal to an integrating device. The bi-stable switching device may
¦be a flip-flop with the shorter pulse being applied to the re-set terminal
thereof at the beginning of each pulse to the light-emitting diode. If smoke
is present during a first pulse, the resulting output occurring during the
pulse to the light-emitting diode but after the short pulse to the re-set
tcrminal of the flip-flop, iB fed to the set terminal of the flip-flop to cause
'an output pulse to appear at the pulse integrator. The output pulse from
¦the flip-flop iB also fed~ through a pulse counter or timer~ to an electronic
switch, associated with the pulse generator~ to change its condition BO as to
increase the pulse rate as described hereinbefore.
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~/46
~e 5
108S0~5~
BRIEF DESCRIPTION OF THæ DRAWING
._ ,
Fig~re 1 is u achematic diagram of an electrical circuit for use in a
8moke detector embodying the features of the first embodiment of the invention.
Figure 2 is a diagram illustrating the time spacing of the pulses applied
to the various components of Fig. 1.
Figure 3 is a schematic diagram of an electrical circuit for use in a
8moke detector embodying the features of the second embodiment of the invention,
Figure 4 i8 a time-response disgram illustrating the response of various
components of the circuit of Fig. 3 during the pulses.
Figure 5 is a diagram illustrating the time-spacing of the pulses occurrin
in the circuit of Fig. 3 when only a single pulse has detected smoke.
¦¦ Figure 6 iB a diagram similar to that of Fig. 5 illustrating the response
when smoke is continuously pre~ent.
Fig~re 7 is a schematic diagram of a modi~ied form of electrical circuit
jlfor use in a,smoke detector embodying the features of the second embodiment
liof the invention.
Figure 8 is a diagram illustrating the time-spacing of the pulses occurring
in the circuit of Fig. 7 and the response when smoke is continuously present.
: 'I
DESCRIPTION OF T~E ILLUSTRATED EMBODIMENT
il Referring to Figure 1 of the drawlng~ there is illustrated an electronic
"circuit for use in a smoke detector operating on the reflected light principle.
Certain portions of the illustrated circuit are disclosed and claimed in
U.S. Patent 3~946~241 issued to me on March ~3~ 1976.
!I The circuit includes a light-emitting diode LED and a photo-voltaic cell C
- ,Ipositioned out of the direct line of the beam of light from the LED. In a
preferred embodiment of the invention the cell C iB positioned to view a
portion of the beam in front of the LED at an angle of about 135 from the
!1-- . ~
108S0~9
a~is of tlle beam, to take advantsge of the well known "forward scatter" effect.
The output of cell C i8 utilized as the input to amplifier A, the output
of which is fed to the set terminal of a bi-stable ~witching device such as a .
flip-flop F.
The term "amplifier" is meant to include any required circuitry for
transforming a signal from the cell C into a signal usable by the flip-flop,
including any nece~sary stages of pre-amplification, and any means allowing
5/46
ge 7
0850~9
an output therefrom only when the output signal reaches a
predetermined level, such as a level detector. The flip-flop
0~1tpUt is ~ed to an integrator T and to an electronic switch
Sl, which closes in response to the flip-flop output, for a
purpose to appear hereinafter. The integrator T may have any
desired time constant so that a predetermined number of pulses
into the integrator are required to provide an output there-
from to the alarm K.
To provide a pulse of current to the LED and for
other purposes to be described, a pulse generator P is pro-
vided, which connects to a power supply through a resistor Rl.
me electronic switch Sl and a resistor R2 are connected in
parallel with the resistor Rl. With the switch Sl open, the
current to the pulse generator P has a value such that the
pulse rate is, for example, 1 pulse every 5 seconds. When
the switch Sl is closed, so that resistor R2 is in parallel
with resistor Rl, the increased current increases the pulse
rate to 1 pulse every 2 seconds.
In addition to providing a pulse to the LED, the
pulse generator also applies substantially simultaneously a
pulse of substantially the same duration to a normally closed
switch S2 to pulse it to the open condition for the duration
of the pulse and a pulse to the set terminal of the flip-flop
through discriminator D which converts the pulse to a spike
at the beginning of the pulse cycle,
The switch S2 is connected between the output of
the amplifier and ground, so that the amplifier output is
shorted to ground except during the time that the switch S2
is pulsed open by the pulse generator.
The operation of the device can best be described
by reference to Figure 2, which i5 a graph of the response
-- 8 --
10850~9
of the various components of the circuit during a pulse with
a predetermined level of smoke present in the light beam.
The horizontal scale represents time and the vertical scale
re]presents response. The vertical scale units are arbitrary
an~ the height on the vertical scale of the various curves
have no relation to each other except as described herein-
after.
Each cycle begins with the application of a pulse
from the pulse generator to the LED, the amplifier output
clamp switch S2, and the re-set terminal of the flip-flop.
The pulse torthe LED and the switch S2 are both represented
on the diagram by Pl, since they are of the same duration.
They may, of course, be of different magnitudes and different
polarities.
~ he pulse appearing at the re-set terminal of the
flip-flop after pa~sing through the discriminator is represented
by PDl, and insures that the flip-flop is turned off at the
beginning of each pulse cycle. The application of the pulse
to the LED produces a light output having a duration and
relative intensity represented by curve Vl.
If there is no smoke in the portion of the beam
viewed by the cell C, there will be no pulse of voltage
generated by the cell and hence no output from the amplifier,
and at the end of the pulse Pl the LED is de-energized and
the switch S2 again closes to clamp the amplifier output to
ground,
However, if there is smoke present in the light
beam, a pulse of voltage will be produced by the cell, re-
presented by curve Vl of Fig 2, which will be amplified by
the amplifier to produce a signal at the set terminal of the
flip-flop, provided that the amount of smoke is great enough
_ g _
1085(~19
to produce an output signal of the predetermined level. For
example, it is common to allow an output signal, and hence
an alarm, only when there is a predetermined concentration
of smoke, such as 1 or 2%
The percent smoke is us~lally defined as the amount
of smoke that absorbs that percent of a light beam 1 foot long.
As illustrated in Fig. 2, the amplifier signal level
necessary to allow an output to the flip-flop is represented
by dashed horizontal line L. Adjustment means ~not shown) may
be provided in the amplifier to adjust the calibration of the
system so that the alarm point will be at the desired smoke
percentage,
If the amount of smoke viewed by the cell has reached
the specified concentration, the amplifier output will be as
shown in curve A reaching line L at point Y, thereby applying
a signal to the flip-flop set terminal, thereby turning on the
flip-flop output (illustrated by curve FF) and closing switch
Sl to increase the current to the pulse generator (illus-
trated by curve Cp).
The output pulse from the flip-flop is stored in
the integrator T. The increased current through the pulse
generator P increases the pulse rate to a predetermined value,
such as one pulse every .2 seconds or 5 pulses per second.
As illustrated in Fig. 2, the pulse repetition rate during
stand-by operation (case A) is 5 seconds, if smoke has not
been detected. However, if smoke of the specified amount
has been detected, as illustrated in Fig. 2, the time to the
next pulse (P2) is reduced to .2 seconds (case B).
At ~he beginning of pulse P2, the LED is again
energized, the switch S2 opened, and a spike pulse applied
to the flip-flop re-set terminal. Hnece at the beginning of
,~ - 10-
~.08S0~9
the second pulse, the flip-flop output is turned off, so
that the switch Sl opens, returning the pulse generator to
its previous rate of one pulse per 5 seconds. Hence if the
second pulse does not detect sufficient smoke to produce an
o~tput from the amplifier to the flip-flop, the pulse rate
remains at the stand-by rate.
However, if the second pulse also detects smoke,
the various components will react in the same manner as illus-
trated in Fig. 2 resulting from pulse Pl, the pulse generator
will again return to the faster rate, by reason of the second
flip-flop output and a second pulse will be stored in the
integrator.
- lOa -
108501~
Altho~gh the ewitch Sl upens at the beginning oS each pul~e, if ~ e i~
detected during that pulse~ the switch Sl closes again after about 10 micro-
~econds (depending on the smoke concentration and the resulting rate of rise
of the amplifier output~ which determines the time at which curve A reaches
level L).
~ ence 80 long as each pulse detects smoke, the pulse generator will
continue to run at the faster rate~ since the open time of switch Sl is only
about 10 micro-seconds out of 200,000 micro-seconds (.2 minutes).
If the integrator T is designed to actuate the alarm R when the integrator
has received 5 consecutive pulses, the alarm will be sounded in le~s than one
second after the first pulse is received, even though the stand-by pulse rate
is one every 5 seconds.
Il In one form of this embodiment of the invention the pulses will continue
to run at the faster rate until the smoke has cleared from the detector, at
which time the alarm will shut off and the pulses will return to the stand-by
rate.
~ owever~ in 80me systems utilizing the detector it may be desirable to
lock the alarm into the energized condition when the required number of pulses
iare received by the integrator.
To prevent the pulser from continuing to run the TT.~ at the increased
rate until the alarm is manually de-energized~ means may be provided to de-
energize the pulser when the integrator produces an alarm actuation signal.
For example, a switch S3 may be provided in the pulser circuit which is opened
by the output signal from the integrator. Hence when the alarm sounds~ the
~,pulser is de-energized and remain8 de-energized until the signal from the
integrator to the alarm iB manually terminated by opening switch S4 in the
lintegrator power supply line.
Although in the illustrated embodiment the ~ormally closed ~witch S2
lamps the amplifier output signal to ground to prevent an output ~ig~al from
the amplifier during the time that the LED is not energized, it will be
/46 -11-
.
',
~085u19 ~
understoold that this switch may be positioned with equal effectivene~s at other
points in the system. The means for preventing the passage of a signal when
the LFn ifi not energized may be a normally open switch dispo~ed in series in
the amplifier output line which is pulsed closed when the LED iB energized.
Referring to Figure 3 of the drawing, there i6 illustrated an electronic
circuit for use in a smoke detector operating on the reflected light principle,
incorporating a second embodiment of the invention.
Certain portions of the illustrated circuit are disclosed and claimed in
U.S. Patent 3,946,241 issued on March 23, 1976.
The circuit of Fig. 3 includes a light-emitting diode LED and a photo-
voltaic cell C po8itioned out of the direct line of the beam of light from the
L~. In a preferred embodiment of the invention the cell C is positioned to
view a portion of the beam in front of the LED at an angle of about 135 from
l the axis of the beam~ to take advantage of the well known "forward scatter"
! effect.
The output of cell C is utilized as the input to amplifier A, the output
Ilf which is fed to a bi-stable switching device such as to the set terminal of
lla flip-flop F.
¦ The term "amplifier" i8 meant to include any required circuitry for
;¦transforming a signal from the cell C into a signal usable by the flip-flop,
',including any necessary stages of pre-amplification~ and any means allowing
an output therefrom only when the output signal reaches a predetermined level,
! 8uch as a level detector. The flip-flop output is fed to an integrator I and
through a pulse counter PC to an electronic switch Sl~ which closes in response
¦¦to the flip-flop output~ in a manner and for a purpose to appear hereinafter.
The integrator I may have any de6ired time constant RO that A predetermined
lnumber of pulses into the integrator are required to provide an output therefrom
to the alarm ~.
To provide a pulse of current to the LED and for other purposes to be
de8cribed9 a pulse generator P is provided, which connect8 to a power supply
5/46 -12-
e 12 i ¦
~ .
1 10850~9
through a resi~tor Rl. The electronic awitch Sl and a resistor R2 are
connected in parallel with the resistor Rl. With the switch Sl open, the
current to the pulse generator P has a value such that the pulse rate i6, for
example, l pulse every 5 seconds. When the switch Sl is closed, so that
resistor ]~2 is in parallel with resi6tor Rl, the incressed current increases
the pulse rate to l pulse eYery .2 seconds.
In addition to providing a pulse to the LED, the pulse generator also
applie6 substantially simultaneously a pulse of substantially the same duration
to a normally closed switch S2 to pulse it to the open condition for the
duration of the pulse and a pulse to the set terminal of the flip-flop through
discriminator D which converts the pulse to a spike at the beginning of the
¦pulse cycle.
The switch S2 is connected between the output of the amplifier and ground,
so that the amplifier output is shorted to ground except during the time that
the 6witch S2 is pulsed open by the pulse generator.
The function of the various components of the device during a single pulse
Ican best be de6cribed by reference to Fig. 4, which i8 a graph of the response
¦of the various components of the circuit during a pulse with a predetermined
llevel of smoke present in the light beam. The horizontal scale represents time¦and the vertical scale represents response. The vertical scale units are
¦arbi*rary and the height on the vertical scale of the various curves have no
; ¦relation to each other except as described hereinafter.
Each cycle begins with the application of a pulse from the pulse generator
to the T.Fn, the amplifier output clamp switch S2, and the re-set terminal of the
flip-flop. The pulse to the LED and the switch S2 are both represented on the
diagram by Pl~ since they are of the same duration. They may~ of course, be of
different magnitudes and different polarities.
The pulse 8pike appearing at the re-set terminal of the flip-flop after
passing through the diacriminntor is represented by PDl, and insures that the
flip-flop ia turned off at the beginning of each pulse cycle. The spplication
of the pul~e to the LED proauces a light output having a duration and relative
intensity represented by curve n.
If there is no smoke in the portion of the beam viewed by the cell C, there
'46 will be no pulse of voltage generated by the cell and hence no output from the
13 -13-
~-` 1085019
amplifier, aDd at the end of the pulse Pl tbe LED is de-energized and the
switch S2 again closes to ciamp the amplifier output to ground.
~ owever, if there is smoke present iD the light beam, a pulse of voltage
will be produced by the cell, represented by curve Vl of Fig. ~, which will
be amplified by the amplifier to produce a signal at the set terminal of the
flip-flop, provided tbat the amount of smoke is great enough to produce an
output signal of the predetermined level. For example, it is common to allow
an output signal, and bence an alarm, only when there is a predetermined
concentration of smoke, such as 1 or 2~.
Tbe percent smoke is ~sually defined as the amount of smoke that obscures
that percent of a light beam per foot of length.
As illustrated in Fig. 4, the amplifier signal level necessary to allow
an output to the flip-flop is represented by dashed hori~ontal line L.
Adjustmcnt mcans (not shown) may be provided in the amplifier to adjust the
calibration of the system so that the alarm point will be at the desired smoke
percentage.
The output from the flip-flop from the first pulse is stored in the
integrator I. If the 4 succeeding pulses also detect enough smoke to cause a
flip-flop output, a total of 5 pulses will have been received by the integrator
in the required time period, which will actuate the alarm.
~ owever, if smoke is not detected by each of the 4 pulses following the
first, the alarm will not be actuated.
/1-6 ~ -14-
,1
'~
- 1085V~9
Although in Figure 4, the vertical line repre~enting the flip-flop output
and the vertical line representing the increase in current through the pulse
generator are separated by a small horizontal distance, it will be underfitood
that this is for clarity, since these two events occur ~ubstantially
simultaneously.
In one form of this ~econd embodiment of the invention, a first pulse
such as Pl (see Figs. 4, 5, and 6) that produces a flip-flop output is fed to
a timer T, the output of which operates 6witch Sl. In this form the first
pulse Pl that detects the predetermined level of smoke causes timer T to
close switch Sl and thereby increase the pulse rate to 5/second for a minimum
time of 5 pulses. If each of the following pulses do not produce a flip-flop
output, the requirements of the integrator I are not satisfied, and at the
end of the 5th pulse, P5, the timer T opens switch Sl and the pulse generator
returns to the 6tandby rate of 1 pulse each 5 second6. This is illustrated
¦!in Fig. 5.
¦¦ However~ as illustrated in Fig. 6, if each of the subsequent 4 pulses
¦¦produces a flip-flop output due to the continuing presence of smoke, the alarm
is sounded on the fifth pulse, and each pulse from the flip-flop to the timer
jre-~tarts the timer, 80 that the pulsing continues at the fast rate so long
as smoke is pre6ent, plus ~ pulses. That is, if the smoke clears and pulse P~
~¦and subsequent pulses do not detect smoke~ at the end of pulse P~+3, the pulse
Igenerator will return to the standby rate.
~eferring to Figures 7 and 8~ there is illustrated another form of the
! !second embodiment of the invention, which i6 similar to the embodiment of Fig. 3
in that a pulse counter or timer Tl iB provided which iB responsive to a first
pul~e from the flip-flop to close switch Sl~ as in the previous embodiment to
increase the pulse rate. However, Tl i~ not responsive to subsequent pulses
from the flip-flop to e~tend the time during which switch Sl is closed, but
hold~ switch Sl clo~ed for a predetermined time whether or not any further flip-
flop output The predetermined may be establi~hed in any convenient manner, suc]
-15-
108SO~L9
as by an RC circuit, or by pulses from the pulse generstor P.
If smoke iB not detected on each of the subsequent pulses the requirements
of the integrator I are not satisfied, and the alarm is not sounded. ~owever,
as illustrated in Fig. 8, if smoke is detected on all of the subsequent pulses,
the alarm i8 sounded, and the pulse generator return8 to the 810w rate.
Since the flip-flop output to the integrator continues after the end of an
pulse by which smoke wa6 detected, the alarm will continue to be energized until
the beginning of the next pulse at which the spike pulse to the re-set terminal
of the flip-flop at the beginning of pulse P6 turn8 off the flip-flop output,
which turns off the alarm.
If smoke is still present, the pul8e P6 will cause a pulse to the ~et
terminal of the flip-flop~ which will again start timer Tl, closing switch Sl
to again increase the pulse rate. If smoke continues to be present on the
subsequent 4 pulses~ the alarm will again be energized on pulse P10.
Hence during the presence of 8moke, the alarm will be energized only
between pulses when the pul8e generator iB running at the 810w rate, and is off
during the period that the pulse generator i~ running at the fast rate. This
¦Inot only provides an intermittent alarm signal~ which is considered to be more
attention-getting than a 8teady 8ignal~ it al80 prevents line transients caused
¦by the energized alarm from affecting the amplifier output.
Although the circuit of Fig. 3 utilizes a timer and the circuit of Fig. 7
¦utilizes pulse6 from the pulse generator to establi6h the time during which the
¦¦switch Sl is closed, it will be understood that either method may be used in
either embodiment.
¦ In the illustrated embodiments a standby pulse rate of 1 pulse every 5
6cconds, and a detection pulse rate of .2 seconds and a requirement of 5
consecutive pulses to energize the alarm is u~ed by way of example only.
Either embodiment may utilize the system disclosed and claimed in my
patent ~917,956, wherein the detector is isolated from the power supply during
the time the light-emitting diode is energized, and during this period is
powered by a charge stored in a capacitor.
Since certain other changes apparent to one skilled in the art can be made
in the herein illu~trated embodimenta of the invention, it i6 intended that all
matter contained herein be interpreted in an illustrative and not a limiting
'~6 - nse.
l6 -16-
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