Note: Descriptions are shown in the official language in which they were submitted.
SELF-TESTING O,~BllSTION PRC)D_CT.5_Dr,r~'F,(~'rOR
Bac~ und of _he_Inventlon
The present invention relates to cornbustion prod-
ucts detectors and, in particular, to rneans ~or ,estiny
the sensitivity of such detecl:ors.
Devices for detecting combustion prod~cts, such as
smoke, are principally of two types, viz., ionization-
type detectors and photoelectric detectors. The princi-
ples of the present invention are applicable to any
type of combustion products detector, although the pre-
ferred enbodiment is described in connection with an
ionization-type detector.
In an ionization-type detector, the sensor is typ-
ically an active ionization chamber ~hich is relatively
open to ambient air. A reference impedance is typical-
ly provided by a reference ionization chamber which is
relatively closed to ambient air, a reference chamber
which is open to ambient air but insensitive to prod-
ucts of combustion, or a physical resistor. ~ach of
the chambers includes a pair of spaced electrodes, or
the chambers may share a common electrode therebetween,
and means are provided, such as a source of radioactive
energy, for ionizing air molecules between the elec-
trodes. With the chambers or chamber and resistor in
series to form a voltage divider, and with a voltage ap-
plied thereacross, an electric field is generated be-
tween the electrodes to establish a current flow
through the chambers or chamber and resistor by move-
ment of ions between the electrodes. The potential at
a sensing electrode at the junction between the active
S~
2~
chamber and reercnce imrJedance is then in accordance
wlth the rélative impedances o~ ~he t"o e]efnfnts.
A change in the ambient conditions, such as the
presence of combllstion products, affrcts the ion cur-
rent flow through the series elements and tllerefore the
impedances thereof. The voltage at the sensir,g elec-
trode is monitored by a detection circuit and when it
exceeds a preselected alarm level, the detection cir-
cuit energizes a suitable alarm circuit. In self-
contained~ i.e., battery-powered, combustion products
detectors of this type, it is known to provide a bat-
tery monitoring circuit which will cause a low battery
signal to be generated when the battery has been deplet-
ed to near a level at which successful operation of the
alarm circuit is no longer assured.
It is known to provide in cornbustion products de-
tectors means for testing the operation thereof. In
particular, means have been provided for testing the
sensitivity of the combustion products sensor by sim-
ulating the presence of combustion products. In loniza-
tion-type detectors, this test means may comprise a
manually-operated switch for connecting an impedance
across the ionization chambers, thereby to change the
voltage thereacross so that the sensing electrode volt-
age is equa] to that which would be produced if combus-
tion products were present in an amollnt beyond which
the generation of an alarm is necessary. Such arrange-
ments are disclosed, for example, in U.S. Patents No.
4,097,850 and 4,246,572. These test devices simply
check to see if the sensitivity of the sensor is above
a predetermined minimurn sensitivity. But it i5
important that the sensitivity not be too high, so as
to avoid frequent false alarrns. ~o prior test devices
are concerned with the rna~iml~rn sellsitivity of the
sensor.
All such manually operated test devices rely ~pon
the user to remember to test the cornbustion products de-
tector at regular intervals. But users frequently for-
get to make such tests. Furthermore, since combustion
products detectors are typically located on ceilings or
other relatively difficult to reach locations, rnanual
testing of the device may be sufficiently inconvenient
to deter the user from making such tests.
It is also kno~n to provide a circuit for self-
checking of the sensitivity of a combustion products de-
tector. Such an arrangement is disclosed in U.S.
Patents No. 4,306,230 and No. 4,302,753, which disclose
continuous monitoring o~ the clear-air voltage from the
sensor. But those devices necessitate an additional
voltage comparator for the clear-air voltage monitor-
ing, and they check only to be sure that the sensitiv-
ity is above a minimum sensitivity level. Furthermore,
the device of Patent No. 4,302,753 may not properly
check this minimum sensitivity level since the sensing
electrode voltage changes with various smoke levels and
is typically nonlinear due to chamber saturation, and
large errors in tested smoke levels may therefore
result
There have also been provided various types of
fault detection circuits which automatically periodical-
ly conduct a self-test of a systern in order to detect
the presence of certain faults. Such systems are dis-
closed, for exarnp]e, in ~.S. Patents No. 3,928,849 and
4,199,755. But none of these periodic self-testing cir-
; cuits are designed for testing sensitivity of a cornbus-
tion products detector. Typically, privr cornbustion
products detectors which test sensitivity by simulatiny
combustion products, operate on the principle that the
norrnal smoke alarm should operate under the test condi-
tions. I:f-the alarm fails to ooerate, due to improper
sensitivity of the sensor, a threat to life safety ~
occur. There is, therefore, a need for a combustion
products detector which will provide an automatic, pos-
itive indication when the sensitivity fails to meet the
test criteria for proper operation.
r Invention
It is a general object of the present invention to
provide an improved combustion products detector which
includes sensitivity testing means which avoids the dis-
advantages of prior combustion products detectors,
while affording additional structural and operating
advantages.
An important object of this invention is the provi-
sion of a combustion products detector which includes
means for testing to determine whether the sensitivity
of the sensor is below a predetermined maximum
sensitivity.
It is another object of this invention to provide
a combustion products detector of the type set forth,
~hich includes means for autol-natically perio~ic.ll]y
testing the sensitivity of the sensor.
Still another object of this invention is the pro-
vision of a cornbustion products detector of l~he type
- set forth, which includes rneans for testing ~hether the
sensitivity of the sensor is in a pred~terrnined range
between the minimum and rnaximum sensitivities.
It is another object of this invention to provide
a combustion products detector having a sensitivity
testing means which sirnulates cornbustion products and
provides a positive indication when the sensitivity
fails to rneet the test criteria.
These and other objects of the invention are at-
tained by providing a combustion products detector hav-
ing a sensor for producing an output signal in response
to the presence of an amount of cornbustion products in
excess of a threshold amount, wherein the threshold
amount varies inversely with the sensitivity of the sen-
sor, and wherein the desired sensitivity is in a prede-
terrnined range between minimum and maximumsensitivities, the improvement comprising: test means
for simulating the presence of combustion products in
an amount slightly less than the amount corresponding
to the maximum sensitivity, test rneans for simulating
the presence of combustion products in an amount slight-
ly greater than the amount corresponding to the minimum
sensitivity, control means for actuating the test
means, and alarm means coupled to the sensor and
responsive to an output signal therefrom for producing
an alarm indication, whereby an alarm indication is pro-
duced in response to actuation of the test ~ne-Jrls ,/hen
the sensitivity of the sensor exceeds the rna~.irnurn sensi-
tivity or when the sensitivity o~ the sensor is less
than the minimurn sensitivity.
The invention consists of certain novel features
and a combinat;on of parts hereinafter fully described,
illustrated in the accomparlying drawings, and partic-
ularly pointed out in the appended claims, it being un-
derstood that various changes in the details may be
made without departing from the spirit, or sacrificing
any of the advantages of the present invention.
Brief Description of the Drawinqs
For the purpose of facilitating an understanding
of the invention, there is illustrated in the accornpany-
ing drawings a preferred embodiment thereof, frorn an in-
spection of which, when considered in connection with
the following description, the invention, its construc-
tion and ~peration, and many of its advantayes should
be readily understood and appreciated.
FIG. 1 is a series of waveform diagrams illustrat-
ing the various clock signals produced by the test cir-
cuitry of the present invention; ~
FIG. 2 is a partially schematic and partially
block circuit diagram of the combustion products detec-
tor of the present invention.
Description of the Preferred Embodiment
Referring ~o FIG. 2 of the drawings, there is il-
lustrated a combustion products detector, generally des-
ignated by the numeral 10, constructed in accordance
w~th and embodying the features of the present inven-
æ~
tion. The detector 10 includes circuitry, "hich is con-
nected to a sensor 12 of the ionization t~pe. rhe
sensor 12 includes a reference ionization chamber 13
having an electrode ]~ connccted to a positive battery
supply voltage (B~) and an electrode 15, w}lich are main-
tained in a spaced relationship by a spacer (not sho~7n)
of insulating material, the electrodes 14 and 15 and
the spacer together forming a relatively irnperforate
closure. The sensor 12 also includes an active icniza-
tion chamber 16 which has an electrode 17 which may be
in the form of a relatively perforate conductive nous-
: ing cooperating with the electrode 15 to define the ac-
tive ionization chamber 16, the electrode 15 being
common to both chambers 13 and 16.
Means are provided, such as a radioactive source
(not shown) for ionizing air molecules within both of
the chambers, whereby with a voltage applied across the
electrodes 14 and 17 an electric field is yenerated
within each chamber to establish a current flow there-
through by movement of the ions between the electrodes
in a well known manner. The reference and active cham-
bers 13 and 16 thus form a voltage divider and they are
connected in series with a resistor 18 between the B+
supply and ground. Thus, the voltage at the electrode
15 is a function of the relative irnpedances of the cham-
bers 13 and 16. Resistor 18 is much lower in impedance
than the ionization chambers and will therefore normal-
ly not influence the sensing electrode voltage value.
Connected in parallel with the sensor 12 is the series
combination of a resistor 19 and a manually-operated,
~æ~
norrnally-open test s~itch 20 for rnanually testiny to
see that the sensitivity of the sensor 12 is above a
predeterrnined rninimum sensitivity in a well kno~ln
manner, as was described in great:er detail in the
aforementioned U.S. Patent l~o. 4,097,850.
The combustion products detector 10 also includes
a potentiometer 21 connected across the B+ supply and
having a wiper which is connected to the reference ter-
minal of a smoke comparator 22, t]le other terminal of
the comparator 22 being connected to the sensor elec-
trode 15. The output of the comparator 22 is connected
to one of three inputs of an OR yate 23, the output of
which is connected to the input of a horn driver 24,
the output of which is connected to an output terminal
25 to which may be connected a suitable horn (not
shown). The horn driver 24 may be a sinyle driver to
activate an associated electrornechanical horn or multi-
ple drivers to operate a piezoelectric horn. It will
be appreciatea that other types of annunciators could
also be provided.
The combustion products detector 10 also includes
a low battery comparator 26 having a reference input
terminal which is connected to an internal reference
voltage provided by a current source 27 connected to
the B+ supply, the reference voltage being regulated by
a Zener diode 28. The anode of the Zener diode 28 is
connected to the negative terrninal of a battery 29, the
positive terminal of which is the B+ supply and is
connected to the other input terminal of the comparator
26. The output of the low battery comparator 26 is con-
nected to one of two inputs of an ~D gate 31, the out-
put of which is connected to one of the inputs of the
OR gate 23. The other input of the ~ND gate 31 is con-
nected to the output line 1 of a c]ock 32, which output
is also connected to the reset terminals of two D-type
flip-flops 33 and 34, the set terminals of which are
connected to ground. The data inputs of the flip-flops
33 and 34 are connected to the output of the smoke com-
parator 22, while the clock inputs of the flip-flops 33
and 34 are:respectively connected to output lines 3 and
4 of the clock 32.
The clock 32 also has an output line 2 which is
connected to an inhibit terminal of the horn driver 24
and is also connected through an amplifier 35 to the
gate of a metal oxide semiconductor field-effect tran-
sistor t"~OSFET") switch 36, the drain of which is con-
nected to the electrode 17 of the sensor 12. Connected
in series between the source of the transistor 36 and
the B+ supply are two resistors 37 and 38. ~he resis-
tor 38 is connected across the source and drain of a'lOSFET 39, the gate of which is connected to the output
of an inverter amplifier 40, the input of which is con-
nected to output line 4 of the elock 32. It will be ap-
preciated that other types of eleetronie switch devices
could be used in place of the MOSFETS 36 and 39 and as-
soeiated amplifiers 35 and 40. The clock 32 also has
an output line 5 which is connected to one input of an
AND gate 41, the other input of which is connected to
the output of an OR gate 42 having two input terminals
which are respectively connected to the Q output of the
æ~
flip-flop 33 and the inverted Q output of t},e flip-flop
34. The output terrninal of the AND gate 41 is connect-
ed to the other input terrninal of the OR yate 23.
Referring now also to the wave~orm diagrams in
FIG. l, the operation of the combustion prod~cts d-stec-
tor 10 will be described. In norrnal operationr in the
presence of combustion products the irnpedance of the ac-
tive ionization chamber 16 will increase. ~hen the
voltage at the electrode 15 reaches the preset level at
the exter~al reference, as determined by the
potentio,neter 21, an output will be produced from the
smoke comparator 22, which is transrnitted through the
OR gate 23 to activate the horn driver 24. The associ-
ated horn (not shown) will remain activated as long as
the amount of combustion products is sufficient to main-
tain the voltage of the electrode 15 at or above the ex-
ternal reference.
If it is desired to manually test the operation of
the combustion products detector 10, the external test
switch 20 is closed, thereby connecting the voltage di-
vider consisting of resistors 19 and 18 in parallel
with the sensor 12. This operates to raise the voltage
at the electrode 15 in the same manner as it would be
raised by the presence of actual combustion products in
an amount sufficient to actuate the alarm.
Accordingly, the closure of the test switch 20 acts to
simulate the presence of combustion products, raising
the voltage of the electrode 15 above the external ref-
erence to produce an output from the smoke comparator
22.
There is also provic~cd a lo~ battery co;rlpar~tor 26
for monitoriny the B+ supply voltage, and producing a
fault siynal in the event that the b~ttery volt~ye
drops below a level necessary for proper oper~tion of
the combustion products detector 10. Thus, when the ~+
supply voltage drops below an internal refeLence level,
as determined by the reference source 27, a cont;nuous
output would be produced from the low battery compar-
ator 26. This output signal is applied to one terminal
of the AND gate 31, the other input of which is applied
from output line 1 of the clock 32. This clock signal
is illustrated in FIG. 1, the various waveforrns of
which are designated by the line numbers corresponding
to the output lines of the clock 32. It can be seen
that the waveform on line 1 comprises a short pulse 43,
typically approximately 10 ms in duration, which is pe-
riodically repeated at relatively infrequent intervals,
typically about one minute. In the presence of an out-
put signal from the low battery co-nparator 26, each
clock pulse 43 on line 1 produces an output from the
AND gate 31, which is applied through the OR gate 23 to
activate the horn driver 24. Thus, in the event of low
battery voltage, the combustion products detector 10
will produce a short 10 ms "beep" about once per min-
ute. This intermittent signal is easily distinguish-
able from the continuous alarm signal which is produced
in the presence of combustion products, for
unambiguously indicating the low battery condition.
All of the foregoing are well known operating fea-
tures of combustion products detectors. Referring now
to the waveforrns on lines 2-5 of FIG. l, the novel a5-
pects of the self-test circuit 30 of the pesent inven-
tion will be descr;bed in ~etail~ The clock siynal on
line l for enabling the low battery indication, is also
applied to the reset terrninals of each of the flip-
flops 33 and 34 for resetting them. Thus, about once
each minute each of these flip-flops 33 and 34 is re-
set, the occurrence of this reset signal being at a
time designated to in FIG. l.
It is a significant aspect of the present inven-
tion that a fault indication will be produced in re-
sponse to the self-test, only in the event that the
cornbustion products detector 10 is not operating proper-
ly, i.e., in the event that it fails the self-test.
Accordingly, at time tl, approximately 15 ms after
the termination of each pulse 43 on line l, the clock
32 produces an output pulse 44 on line 2, which is ap-
plied to the inhibit terminal of the horn driver 24.
This prevents actuation of the horn driver 24 for the
duration of the inhibit pulse 44 (about 2 seconds), so
that an alarm indication cannot be produced while the
self-test is in progress. This inhibit is removed at
the end of the pulse 44 so that an alarm signal can be
produced after the self-test is completed. The pulse
44 on line 2 is also applied through the amplifier 35
to the gate of the MOSFET 36, turning it on and thereby
connecting the voltage divider consisting of resistors
37, 38 and 18 in parallel with the sensor 12. This
causes a change in the voltage at the electrode 15 in
generally the same manner as was described above in con-
nection with the operation of the manual e~tcrnal testswitch 20.
Because of the fact that there are different types
of combustion and, ~ccordir,gly, different types of corn-
- bustion products which can trigger tlle sensor 12, it is
not possible to set the sensitivity of the sensor 12 at
a level which will respond to all types of combustion
products equally. Thus, for example, while a certain
concentration of one combination of cornbustion products
from a particular type of combustion might ~e suffi-
cient to raise the voltage at the electroae 15 above
the external reference level, another cornbination of
combustion products from a different type of combustion
might have to be present in a slightly higher concentra-
tion in order to raise the voltage of the electrode 15
above the reference level. Thus, it is typically the
practice to establish the sensitivity of the sensor 12
at a level such that it will be sensitive enough to be
capable of responding to all types of fires. In a pre-
ferred embodiment of the invention, this minimum sensi-
tivity is such that the sensor will respond to produce
a smoke alarm indication when the amount of cornbustion
products reaches 1.5% obscuration per foot (the higher
the sensitivity of the sensor 12, the lower the amount
of combustion products necessary in order to trigger it
into alarm).
But if the sensitivity is too high, the combustion
products detector 10 will frequently produce false or
nuisance alarms (such as in the event of someone smok-
ing a cigarette or cooking in the general vicinity of
the combustion products detector). Thus, in a p~e-
ferred embodiment, it is desired that the rna~imuln sensi-
tivity of the sensor 12 be such that it wi]l not be
trigyered into alarm by an amount of colnbustion prod-
ucts at .5~ obscuration per foot or less. Thus, it i5
desired that the sensitivity of the sensor 12 be in a
range corresponding to amounts of cornbustion products
in the range between .5% and 1.5~ obscuration per Eoot.
The values of the resistors 37 and 38 are chosen
so that they will cause a change in voltage at the elec-
trode 15 slightly less than the minimum needed to cause
an output from the smoke comparator 22 to occur. In
other words, the connection of the resistors 37 and 38
across the sensor 12 simulates an amount of smoke just
below the amount corresponding to the rnaximum sensitiv-
ity of the sensor 12, i.e., slightly less than .5%
obscura~tion per foot. Thus, if the sensitivity of the
sensor 12 is in the desired range, it ~ill not respond
to this combustion products simulation for producing an
output from the smoke comparator 22. If, on the other
hand, sensitivity of the sensor 12 is too high, i.e.,
the clear-air voltage of the electrode 15 is greater
than it should be, the closure of the transistor switch
36 will raise the voltage of the electrode 15 above the
external reference and produce an output signal from
the smoke comparator 22. This is again applied to the
horn driver 24 through the OR gate 23, but the horn
driver 24 is not activated since it is being inhibited
by the pulse 44 on clock line 2.
~%~
However, the output from the smoke comparator 22
is also applied to the data terminals of each of the
flip-flops 33 and 34 which ~ere j~st reset at tirne
to~ The flip-flop 33 now has its set and reset termi-
nals at ground or logic low level. In this condition,
the Q terminal will be low and can become high only in
the event that there is a logic hiyh at the data termi-
nals and a positive-going transition at the clock termi-
nal. At time tl the clock 3Z aiso produces on line 3
a negati~e-going pulse 45, of about 1 second duration.
I~hen the data input of the flip-flop 33 is high, as a
result of an output signal from the smoke cornparator
22, the positive-going transition 46 at the end of the
clock pulse 45 at time t2 will cause the Q output of
the flip-flop 33 to become high and rernain high until
reset at the next clock pulse 43 on line l, about one
minute later. This output signal is applied through
the OR gate 42 to one input of the AI~D gate 41.
However, the other input to the AND gate 41, which is
connected to clock line 5, is low at time t2 tsee
FIG. 1) so that no output is produced from the A~D gate
41 at this time. If, on the other hand, the rnaximum
sensitivity of the sensor is normal, no output from the
smoke comparator 22 will be obtained during pulse ~5
and the Q output of flip-flop 33 will remain low at
transition 4t;, and no signal will be applied to AND
gate 41.
Simultaneously with the positive going transition
~6 ~f the pulse 45 at time t2, the clock 32 produces
on line 4 a negative going pulse 47, having a duration
'~2~
of about 1 second, which is .,pplied to the in~ e~ am-
plifier 40 and to the clock input terrnir,al of tr,e flip-
flop 34. The inverter arnplifier 40 produces a high
output which is applied to the base of the transistor
switch 39, switching it on for shorting the resistor
38. Thus, now only resistor 37 ~orrns a voltaye divider
with resistor 18 which is connected across the sensor
12. The value of the resistor 37 is selected to cause
a change in the voltage at the electrode 15 which will
be just in excess of that which would be produced by an
amount of smoke corresponding to 1.5~ obscuration per
~ foot. In other words, the connection of the resistor
37 alone, together with resistor 18, across the sensor
12 simulates an amount of smoke just in excess of that
corresponding to the minimum permissible sensitivity
for the sensor 12. Accordingly, if the sensitivity of
the sensor 12 is in the desired range, the voltage at
the electrode 15 will be elevated above the external
reference and the smoke comparator 22 will produce an
output signal. This does not activate the horn driver
24 because it is still inhibited by the pulse 44. The
output of the smoke comparator 22 is also applied to
the data terminal of the flip-flop 34. Now the positive
going transition 48 of the pulse 47 will cause the in-
verted Q output terminal of flip-flop 34 to change
state to a logic low level at time t3 (the inverted Q
output is normally at a logic high level when the set
and reset terminals are at ground level, the inverse of
the Q output described previously), so as to not affect
the output of the OR gate 42. The inverted Q output
16
will remain at the loyic lo~ level until r~-s~t at the
next clock pulse 43, about 1 rninute later.
If, on the other hand, the sensitivity of the sen-
sor 12 is too low, no output will be produced froln the
snoke comparator 22, so that the data terrnina1 of the
flip-flop 34 rernains low. In this event, when the pos-
itive going transition 48 of the pulse 47 is applied to
the clock terminal of the flip-flop 34 at time t3,
the inverted Q output will rernain high, causing the out-
put of th~ OR gate 42 to go high and be applied to the
AND gate 41. sut, as explained above, since the other
input to the AND gate 41 is low, no output is produced
therefrom.
The pulses 44 and 47 both terminate at time t3
Thus, at this time, the transistor switches 36 and 39
are both opened, disconnecting the resistors 31 and 38
and, simultaneously the inhibit is removed from the
horn driver 24. About 15 ms thereafter, at time t4,
two short (preferably about 10 ms) pulses 49, with 10
ms in between are produced on line 5 of the clock 32
and applied to the AND gate 41. Thus, at this time if
the other input of the AND gate 41 is also high as a re-
sult of an output from the OR gate 42, the AND gate 41
will produce two brief high outputs which are applied
through the OR gate 23 to activate the horn driver 24
and produce a unique fault indication. Thus, at the
time of the clock pulses 49, if there is a high output
from either the Q terminal of flip-flop 33 (indicating
that the sensitivity of the sensor 12 is too high~, or
from the inverted Q output of the flip-flop 34
(indicating that the sensitivity of the se;l-;or is too
low), two 10 ms "beeps" close together "ill be pro-
duced to indicate this condition. ~t will be appreciat-
ed that the sequence of pulses indicated in FIG. I on
lines 1-5 are repeated about once each rninute. Thus in
the event that the sensor 12 fails either one of the
maximum or minimum sensitivity tests, two short, close--
ly spaced "beeps" close together about once each minute
will be produced to indicate this fault condition. If
both tests are successfully passed, then there will be
no output indication as the Q output of flip-flop 33
and the inverted Q output of flip-flop 34 will both be
at a logic low level, resulting in a logic low level at
one input of AND gate 41 during pulses 49 at the other
input of the A~D gate.
The specific timing indicated in FIG. 1 is merely
exemplary, and is not critical. It will be appreciated
that other timing sequences could be utilized to
achieve substantially the same result. If desired, the
circuitry enclosed in the dashed-line 50 could be an in-
tegrated circuit. In that case, the test resistors 37
and 38 could alternatively be connected external to the
integrated circuit for more precise control, if needed.
It will also be appreciated that the self-test circuit
30 could also be utilized for testing the sensitivity
of other types of combustion products detectors. In
photoelectric aetectors, as an example, the light
emitter output or light sensor input sensitivity or
internal reflective surfaces could be similarly
electronically controlled to simulate smoke and accom-
18
~2~
plish similar results. ~hile the preferrcd e:lriodi~n nt
of the invention has been disclosed with a battery pow-
er source, it will be appreciated that the invention
could be used ~ith cornbustion products detectors employ-
ing other power sources such as AC, remote power sup-
plies, etc., and may also be used with any type of
combustion products detector, such as residential, as
described herein, cornmercial, wherein the alarm and
fault outputs are electronic signals to a rnonitoring
system rather than audib]e annunciations, etc.
Frorn the foregoing, it can be seen that there has
been provided an improved apparatus for automatically
self-testing sensitivity of a combustion products detec-
tor at both ends of the desired sensitivity range, the
test method accurately simulating srnoke and producing a
unique fault output only in the event of failure of the
sensitivity test.
19
