Note: Descriptions are shown in the official language in which they were submitted.
B~CKGROUND OF T~E INVENTION
1 Ionization detectors are desigrled to provide an output signal to actuate
o ~ all~rm when smok{! concelltr~tion at t~l~ detector reache~ a prede-lPrmined value,
3 by detec-ti-l~ th~ reduction of ion current in the chamber caused by the pre~ence
4 oi smoke particles. In a single chamber detector, in which the chamber electrodeY
are connected in series with a resistor across a power source, the change in
6 ion current flow change~ the volta~e at the junction between the detector and
7 the resistor. In a two chamber detector, having a detection chamber and a
8 cloaed re~erence chamher connected in series across a power ~ource, the reduction
9 of ion current cauqed by smoke entering the detector chamber changes the voltage
at the junction of the chambers. In a dual chamber detector, in which the
11 reference chamber ( or reference volume) ia disposed within the detector
12 chamber with a common ion source, a collector electrode i~ provided in the
13 chamber between the inner und outer electrodes (~ome-times forming the aeparation
14 between the two chambeIs), and the red~ction in ion current ilow chnng~s the
voltage on the collector electrode. This change in voltage iB utili~ed to
16 actuate an ala~m.
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Any of the above systems must be calibrated so
that the alarm output signal is provided at a definite
predetermined smoke concentration~ This smoke concen-
tration provides a particular voltage at the detector,
It has been common practice to test such
detectors by connecting the reference electrode to
ground, or to provide a slowly increasing voltage
across the srnoke detecting chamber, and determining the
voltage at which the alarm signal is produced. It has
also been suggested that a test electrode may be pro-
vided in the smoke chamber, to be connected to ground
or to a voltage varying device, to cause the alarm test
signal.
SUMMARY OF THE INVENTION
In accordance with a particular ernbodiment of
the invention, an ionization smoke detector comprises
first and second electrodes spaced to define therebe-
tween a smoke detecting chamber. The second elec-trode
is a collector electrode. An ion source is positioned
for emitting radiation into the smoke detecting chamber
for causing ionization of a gas therein, and a power
supply is connected to the first and second electrodes
to establish ion current flow through the srnoke detect-
ing chamber. Comparator circuitry is connected to the
collector electrode, the collector electrode being
adapted to apply a predetermined voltage to the compara-
tor circuitry during clean air conditions. ~ first
voltage divider network is connected to the power supply
and to the comparator circuitry, the first voltage divid-
er network generating a reference voltage for application
to the comparator circuitry. The reference voltage has
a predetermined offset value from the clean air voltage
applied to the comparator circuitry by the collector
electrode, the comparator circuitry being adapted to
generate an alarm signal when the voltage applied to the
comparator circuitry by the collector electrode is equal
to or less than the reference voltage. A te~t electrode
is disposed in the smoke detecting chamber between the
first and second electrodes. A second voltage divider
network is connected to the power supply circuitry and to
the test electrode. Switch means are connected to
the second voltage divider network, the switch means
having open and closed conditions and being connected
to the second voltage divider network such that, when
the switch means is in open condition, the voltage
applied to the test electrode is the same as the voltage
applied to the first electrode by the power supply.
When the switch means is in closed condition, a test
voltage is applied to the test electrode, the test
voltage on the test electrode being effective to re-
duce the voltage on the collector electrode to a value
equal to or less than the reference voltage to cause
the comparator circuitry to generate an alarm signal~
In accordance with this invention, an ioniza-
tion smoke detector may be provided with a test electrode
in the detector chamber, and means provided for apply-
ing to the test electrode a single predeterrnined voltage,having a value such that it will, in effect, simulate
the presence of smoke in the chamber of an amount to
which the detector should respond. For example, if it
is intended that the detector should produce an alarm
signal when the smoke concentration reaches 1% obscura-
tion (1% of the light passing through a column of smoke
l foot long is absorbed) the presence o-f this concen-
tration of smoke causes a certain change in the voltage
at -the collector or at the junction, depending on the
-type of detector. Therefore the test circuit is designed
to apply to the test electrode a voltage of ~ value such
that it causes this voltage change to occur at the collec-
tor or junction.
- 2b -
The test circuit is also designed to apply the
test voltage in such a manner that voltage surges that
might provide a false indication of satisfactory opera-
tion do not occur.
In one embodiment of the invention means is
provided for applying the test vol-tage from a remote
location.
BRIEF DESCRIPrrION OF ~ ~ FIGUBES OF TlE DRAWING
1 Figure 1 is a schematic view of an ioni~ation detector embodying the
2 features o:~ ~he invention, in which the detector is provided with a tes-t
~ electrolie alltl meari~ ~or al~)lyi~ e~ ie~~ ell voltagl to -the test electro~e
4 to simulat- a predl-t(~ led amoun~ of smoke in ~he ch~mber.
Fi~lre _ i.s a Ara~h illllstrating thc relation~hip between -Lhe volta~e on
6 the test elec-trode and the percent smokc which said voltage simulates.
7 Figures 3 and 4 illus-trate modified ~orms of -test circuits which allow the
8 detector to be tes-ted from a remo-te location.
Dl~`SCI~rl'TI~N 1)l` TF~` Il.l,USTRATED EMBOD ~i~TS
Refer~ g to Figllre I of the drawin~ there is i.Llustrated a schema~ic
diagrarn of an ioni~ation s~oke detector 10 which comprises a housing 12 ha~ing
11 an inner clectrode 16, an outer electrode 149 and a collector electrode 18.
12 The physical struc-ture of such detectors provides an i~ler or re~erence chamber
1~ 20 between the inner electrode 16 ~nd the collector electrode? and an outer or
l/~ smolie detectillg chambel 22 betwcen t~e re~ercllce ellcl.rode arld ~ oul.cr
electrode 14. r~c physical struc-tuIe o~ SUCil det,ectors i~ wcll knowrl in th(
1~ art, and are illustrated ill9 for example, U.S. patent 3J935l466 and United
17 Kingdom published application 2~013,39~A. An ioni~atio~ source 24 is provided
18 in the hou~ing to provide ion current flow when the detector i~ connected to a
19 power source p. The outer electrode 14 and the inner electrode 16 are connected
across the power source 80 that ion culrent flow of a definite magnitude
21 flows between the inner and outcr electrodes when clean air is in the detector.
22 This ion current flow establishe6 a ~oltage on the collector electrode
23 of predetermined value, which voltage is applied to terminal Tl of a comparator
24 C, to be compared ~i-th a reference voltage established at ter~inal T~ ilom the
junction 31 of a voltage divider consisting of resistors R1 and R2 connected
26 in serie~ across the powcr source P~
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1 When smoke enters the chamber, the smoke particles reduce the ion curren-t
2 flow, which reduces the voltage on the collector electrode. ~or example9 in
3 a particular detector, with a 9uppl~' voltage of ~ volts3 the voltage on the
4 collector electrode during clean air conditions, may be 5.5 volts. The
reYistor~ R1 and R2 have values ~uch that the voltage on terminal T2 of the
6 comparator i~ 4.5 volt~. There~ore when the smoke den~ity in the chamber
7 becomcs ~reat enough to reduce the collector voltage to 4.5 volt~g the com-
parator produces an output to the alarm actuating device A.
9 In the detector of this invention9 a test electrode 26 is provided
in the housing between the collector and the outer electrode, in the smoke
11 detecting cha~ber. To apply a predete~mined voltage to the test electrode,
12 a voltage divider is provided9 which consists oi resistors R3 and R4 in
13 serie~ throu~h a junction J2 and in ~cries with a ~witch S~ acro~s the power
14 gource P, with the test electrode being connected to the junckion J2.
The test electrode i~ normally maintained at the ~ame potential as the
16 outer electrode, ~ince it i~ connected -to the outer electrode and the power
17 ~ource throu~h re~istor R3, and 6ince no au~3tantial c~rent flows through ~aid
18 resi~tor when the ~witeh S1 i8 open.
1~ ~owever when ~w;tch S1 i~ closed, current through ~3 and R4 establish a
predetermined voltage on the te~t electrode tha-t is les~ than the voltage on
21 the ou-ter electrode 9 which causes a change in the electric iield distribution
22 in the chamber between the collector and the outer electrode. Thi~ ch~nge in
23 iield di~tribution causes a decrea3e in the volta~e on the collectorS and i~
24 the voltage applied to the te~t electrode i~ of the proper value, the collector
voltage is reduced to a value just equal to that of the comparator reierence
26 voltage. Applying the proper ~oltage to the test electrode therefore will
27 ~imulate the amount oi ~moke in the housing at which the alarm i~ to be actuated.
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1 Figure ~ is a grraph illustrating the relation between the voltage on
2 the test electrode and the percent smoke that each voltage simulates for a
3 particular detector.
4 If the detector is intended to provide an alarm signal when the concen-
tration of smoke in the ch~mber reaches 1~ (which i9 establi~hed by the ratio
of values of resistors R1 ~d R2, then it is secn rrom Figrure 2 that a test
7 voltage of about 5.8 vol-ts will be required to produce a test alarm nnder clean
8 air conditions. ~owever in the manufacture of such detectors in large quantities
9 manufacturing tolerances make it impractical to test the detectors to the
exact alarm point. Therefore if a regulation issued by a government or
11 industry regrul~tory body requires that the detector respond to 6~ smoke for
12 C~~pl e, the detector can be m~muIacturcd -to a ~oal of responding to 1% smoke,
1~ with the test circuit being designed to simulate a smoke percentage intermediate
14 the required alarm point of 6% ~o~e and the designed alarm point o~ 1~ smoke.
Therefore the resistorq R3 and R3 will have values that will produce a test
16 ~oltage when switch S1 is closed that will ~imulate, ~or e~ample 3% smoke.
17 In the eml)odiment of Figure -l, switch S1 may be a magrnetically operated
t~ switch so positione~ that the test may l)e con~ucte(l by applyin~ a magrnet to
1~ the exterior of the detector housing. The fact that the switch is in serie~
with the resistors ~3 ~d R4 prevents a surge of current when the swi-tch is
21 closed which migrht erroneously actua-te the alarm circuitry.
22 To enable the te3t to be conducted from a remote location, a ~odified
23 form of test circuit may be provided as illustrated in Figure 3. As shown
24 therein, the re~istors R3 and R4 are connected in series with the collector-
emitter path of tran~istor T. ~he base of transistor T is connected to the
26 Junction J3 of resi~3tors R5 and R69 which resistors are connected to the power
27 ~30urce P through a switch S2, whi~h may be at a remote location such as at a
28 central control panel.
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1 Closing of ~witch S2 cause~ a predetermined voltage to be applied to the base
2 of transi~tor T, sufficient to cause conduction in $he emitter-collector pa-th
3 ~o -that the tegt voltage applied at junction J2. If the line from switch S2
4 ~to the de-tector i9 lon~ enough to voltsgc -tr~l~icnts, a ~oi~e suppression
ca~acitor F may be pr~ idcd bctwe~n thc base f tran~i~-tor T and groimd.
6 Another embodiment of the invention that allows a remote test switch
7 iB shown in Figure 4, in which resi~tors R3 and R4 are connected in series
8 with a photo-re~ponsive device, such as photo-transistor PT, o~ an optically
9 coupled isclator. The light ~ource I, of the isolator may be co~nected -to the
power ~ource P through a resistor R7 o-f suitable value, and switch S3. As in
11 the embodiment of FiguIe 3, the switch S~ may be located at a remote location.
1~ When thc switch S3 i8 closed, the resulting illumination of light L allows
13 conduction through the photo-responsive device to cau~e the test voltage to
14 appear at junction J2.
Although in the illustrated embodiments of the inven-tion, the te~t
16 electrode end circui-t are ~hown ~ being incorporated into a dual chQmber
17 detector, the invention can al~o be incorporated into a 0ingle ch~ber de-tector
18 or into the detector cha~ber of a two chamber detector.
19 Since certain other changes apparent to one skilled in the art may be
made in the herein illustrated embodiments vf the device without depnrting
21 from the ~cope thereof, it i9 intended that all matter contained herein be
22 interpreted in an illustrative and not a limiting sense.
23
24
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