U.S. patent number 3,739,365 [Application Number 05/094,113] was granted by the patent office on 1973-06-12 for apparatus for detection of a fire or of flames.
This patent grant is currently assigned to Cerberus AG.. Invention is credited to Peter Muller.
United States Patent |
3,739,365 |
Muller |
June 12, 1973 |
APPARATUS FOR DETECTION OF A FIRE OR OF FLAMES
Abstract
Fire detecting apparatus includes two photoelectric devices,
each having different spectral sensitivities. A difference signal
corresponding to the difference between the output signals of the
photoelectric devices is generated and an alarm signal is developed
when the difference signal deviates by a predetermined amount from
a predetermined value or range of values, depending upon
application. A preferred embodiment also includes a delay means for
delaying generation of the alarm signal for a predetermined
time.
Inventors: |
Muller; Peter (Oetwil,
CH) |
Assignee: |
Cerberus AG. (Mannedorf,
CH)
|
Family
ID: |
4430498 |
Appl.
No.: |
05/094,113 |
Filed: |
December 1, 1970 |
Foreign Application Priority Data
|
|
|
|
|
Dec 3, 1969 [CH] |
|
|
18107/69 |
|
Current U.S.
Class: |
340/578; 250/554;
356/222 |
Current CPC
Class: |
G08B
17/12 (20130101) |
Current International
Class: |
G08B
17/12 (20060101); G08b 021/00 () |
Field of
Search: |
;340/228R,228S,228.1,228.2,171 ;250/83.3UV,83.3R,83.3H,200,220
;356/45,222 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Yusko; Donald J.
Assistant Examiner: Wannisky; William M.
Claims
I claim:
1. Apparatus for detecting fire or flames in the presence of
disturbing radiation of a predetermined spectral composition
resulting from ambient light which should not give an alarm
comprising:
first and second photoelectric devices, each having different
spectral sensitivities with respect to different spectral ranges
with maximum response, each in the different spectral ranges and
producing respective output signals;
electrical circuit means including said photoelectric devices for
generating a difference signal corresponding to the difference
between the output signals of said first photoelectric devices and
the output signals of said second photoelectric devices, said
difference signal being essentially zero for the disturbing
radiation and having an a-c component in a low-frequency range of
about between 2-50 Hz differing from zero in the presence of, and
due to the flicker of flames;
means sensing the a-c component in said low-frequency range only,
of said difference signal;
and alarm generating means responsive to the sensed a-c component
of the difference signal in said low-frequency range only for
generating an alarm signal when the a-c component of said
difference signal in said low-frequency range exceeds a
predetermined value.
2. Apparatus according to claim 1, wherein the low frequency range
of the a-c component to which the alarm signal generating means is
responsive lies between 5 and 25 Hz.
3. Apparatus according to claim 1 wherein said alarm signal
generating means includes:
filter means for passing only signals corresponding to said
difference signal within a predetermined frequency range; and
a discriminator means coupled to the output of said filter means
for generating said alarm signal when said difference signal
deviates by a predetermined amount from said predetermined
value.
4. Apparatus according to claim 1 wherein said alarm signal
generating means generates said alarm signal when the magnitude of
said difference signal deviates by a predetermined amount from
zero.
5. Apparatus according to claim 1 wherein said alarm signal
generating means generates said alarm signal when said difference
signal deviates by a predetermined amount with a predetermined
polarity from zero.
6. Apparatus according to claim 1 wherein said alarm signal
generating means includes means for delaying for a predetermined
period of time generation of said alarm signal when said difference
signal exceeds the predetermined value by.
7. Apparatus according to claim 1 comprising means for changing at
least one of the spectral sensitivity and the amplification of at
least one of said photoelectric devices such that the difference of
the output signals of said photoelectric devices for the
disturbance light radiation with a pre-specified spectral
composition is much smaller than the output signals of each
individual photoelectric device.
8. Apparatus according to claim 7 wherein said difference signals
for said disturbance light radiation with said prespecified
spectral composition is smaller by at least a factor of 10 than
said output signals of each individual photoelectric device.
9. Apparatus according to claim 1 wherein said photoelectric
devices are coupled together in series opposing relation and said
difference signal generating means comprises means coupling the
free terminal of said devices to said alarm signal generating
means.
10. Apparatus according to claim 1 wherein said difference signal
generating means comprises means coupling said photoelectric
devices together in parallel opposing relation and means coupling
said parallel connected devices to said alarm signal generating
means.
11. Apparatus according to claim 1 wherein each of said
photoelectric devices comprise at least one active photoelectric
element and a ballast resistance coupled thereto, the output signal
of the device being the potential drop at said ballast resistance
or part thereof.
12. Apparatus according to claim 1, wherein each of said
photoelectric devices comprise at least one passive photoelement, a
ballast resistance coupled thereto, and a direct-current supply
coupled thereto, the output signal of the device being the
potential drop at said ballast resistance or part thereof.
13. Apparatus according to claim 12 wherein said photoelectric
devices are opposingly connected together and to a common
direct-current supply.
14. Apparatus according to claim 13 comprising a potentiometer
coupled as a common ballast resistor to said photo-electric devices
such that one portion of said potentiometer is a ballast resistor
of one of said photoelectric device and that another portion of
said potentiometer is a ballast resistor of the other photoelectric
device.
15. Apparatus according to claim 1 wherein said photoelectric
devices include respective photoelements having different-type
photosensitive layers with differing spectral sensitivities.
16. Apparatus according to claim 1 wherein said photoelectric
devices include respective photoelements having photosensitive
layers of the same type and respective filters having differing
spectral permeability or reflection characteristics mounted in the
path of the light impinging on said photoelements.
17. Apparatus according to claim 1 comprising means for varying the
light impinging on at least one of said photoelectric devices.
18. Apparatus according to claim 1 wherein said photoelectric
devices include respective photoelements on a common base-material,
and means for causing said photoelements to exhibit a differing
spectral sensitivity.
19. Apparatus according to claim 1 comprising a dichroic filter
connected in front of both photoelectric devices which are arranged
such that the portion of the radiation passed by said dichroic
filter strikes one photoelectric element, while the portion of the
radiation reflected by said dichroic filter strikes the other
photoelectric device.
20. Apparatus according to claim 1 comprising a plurality of pairs
of oppositely connected photoelectric devices, each of said pairs
being connected in series relative to one another and arranged such
that each pair receives light radiation from a different
direction.
21. Apparatus according to claim 1, comprising means for
maintaining said alarm signal in its on condition when an alarm
signal has been generated.
22. Apparatus according to claim 3 wherein said discriminator means
comprises means for automatically maintaining said alarm signal in
its on condition when an alarm signal has been generated.
23. Apparatus according to claim 1 wherein said alarm signal
includes an optical signal for visually indicating said alarm
signal.
Description
FIELD OF INVENTION
The present invention relates to apparatus for the detection of a
fire or of flames by means of emitted rays.
Apparatus of this type is preferentially utilized as a fire alarm
or as a control unit for combustion installations.
BACKGROUND OF THE INVENTION
It is already known that the presence of a flame may be detected by
means of a photoelectric device which is responsive to the light
rays coming from a flame. Such a unit functions with the
possibility of a false alarm only if there is no disturbing ambient
light radiation present, such as sunlight or a similar strong light
source.
In order to detect a flame with certainty uninfluenced by light
rays coming from other external sources, it is therefore necessary
to distinguish the typical and specific characteristics whereby
flames differ from such disturbance light sources.
A known device utilizes the typical flickering of flames, i.e. the
variation of intensity of the light radiation of the flame in a
very low-frequency oscillation zone, as the distinguishing feature
of a flame vis-a-vis disturbance light radiation. In this known
device the radiation strikes a photoelectric element whose output
signal is conducted to a frequency-selective amplifier whose
band-pass lies in the order of magnitude between 5 and 25 Hz. The
amplifier then feeds the amplified signal to a switching network.
Even if the frequency band-pass of the amplifier optimally
corresponds to the rate of flickering of flames, disturbances and
false alarms are relatively common occurrences. If accidental
variations of intensity in the ambient light radiation lie in the
same frequency zone, for example through shadings or false flashes
due to vibrating or slowly moving objects, false flashes of
sunlight on water surfaces, flickering or wavering light sources,
etc., then a false alarm could be generated.
It has been attempted to eliminate the disturbance effect of
external light radiation sources by utilization of an infra-red
sensitive photo cell or by connecting of an infra-red filter which
is especially translucent for flame radiation in front of a photo
cell. However, this works only if the infra-red radiation of the
disturbance light source is very small. With this construction a
strong disturbance light source could cause a false alarm.
Another known device utilizes the fact that a flame possesses a
relatively large proportion of long-wave radiation (infra-red, for
example) and only a small proportion of short-wave radiation (blue,
for example). This known device utilizes two different
photoelectric devices, for example photo resistances with different
spectral sensitivity wherein one photo resistance is preferentially
sensitive to red light, and the other to blue light. An alarm
signal is generated if the relation of the red light radiation to
the blue light radiation exceeds a specified value, i.e. if the
long-wave portion of the light radiation becomes preponderant. This
is achieved in this known device by connecting the two photo
resistances in series to a power source. The variation of voltage
at the junction point of the two photo resistances is conducted to
a control circuit to generate an alarm signal when the voltage at
the junction point has a certain value. In a device of this type a
false alarm can be generated by constant infra-red light radiation
sources, such as heaters or heating ovens. On the other hand, with
known device, an alarm signal can not be generated if a high
intensity disturbance radiation in the short-wave zone is present.
This apparatus is thus only conditionally utilizable, with the
result that a D.C. amplifier must be used whose operating point
must be kept stable. This leads to complicated circuitry and
additional expenditures.
A simple combination of the best features of the two known devices
described above, namely the detection of the typically wavering
intensity of light radiation of flames as well as of the relation
between long-wave and short-wave radiation, is unfortunately not
possible. For example, the utilization of an A.C. amplifier with
the known device using two photo resistances in series having
different spectral sensitivity would produce an inoperable system.
This is because in a flame, the red portion of the light radiation
exhibits almost the same intensity fluctuations in time as the blue
portion, and the resulting red-blue fluctuation relation remains
almost constant. Thus, at the junction point of the two photo
resistances an almost constant A.C. potential without marked A.C.
variation occurs.
It is therefore the main object of the present invention to provide
a reliable apparatus for flame detection that will be substantially
uninfluenced by external disturbance light radiation sources.
SUMMARY OF THE INVENTION
In accordance with the present invention, two photoelectric
devices, each having different spectral sensitivities are provided.
A difference signal corresponding to the difference between the
output signals of the photoelectric devices is generated, and an
alarm signal generator is responsive to the difference signal for
generating an alarm signal when the difference signal deviates by a
predetermined amount from a predetermined value.
A particularly effective embodiment of the present invention
comprises at least one pair of photo elements having different
spectral sensitivities connected in series or in parallel with
opposite polarities. The output of the photo element arrangement,
which is the difference between the output signals of the two photo
elements, is coupled to the input of an analyzer that is sensitive
over a limited low-frequency A.C. range. The analyzer includes a
discriminator circuit which emits an alarm signal when the output
signal of the analyzer deviates by a predetermined amount from a
predetermined value.
In a particularly suitable embodiment, the spectral sensitivities
of the two photo elements are varied in such a way that for
predetermined disturbance light radiation, the difference of the
output signals of the two photo elements is smaller (i.e., by at
least a factor of 10) than the individual signals, that is, the
difference signal is essentially zero.
DRAWINGS
FIG. 1 is a schematic representation of a device in accordance with
the present invention;
FIG. 2 illustrated a circuit for passive photo elements with two
oppositely connected switching networks;
FIG. 3 illustrates a circuit for passive photoelements with two
oppositely connected switching networks and a common direct-current
supply;
FIG. 4 illustrates a circuit for active photoelements;
FIG. 5 illustrates a circuit for active photoelements with a common
tuning potentiometer;
FIG. 6 illustrates a circuit for current-emitting
photoelements;
FIG. 7 illustrates a dual photoelement;
FIG. 8 illustrates two photoelements with sensitivities that are
variable by means of a common screen or light shield;
FIG. 9 illustrates a device comprising two photoelements with
reflection filters;
FIG. 10 illustrates a device comprising two photoelements with a
common dichroic filter;
FIG. 11 illustrates a circuit for the evaluation of the signals of
the photoelectric; and
FIG. 12 illustrates a device with more than two photoelements.
DESCRIPTION OF PREFERRED EMBODIMENTS
FIG. 1 represents schematically a fire detection device in
accordance with the present invention. The red light rays r and
blue light rays b emitted from flame 1 simultaneously strike
photoelectric cells 2 and 3, respectively. The term photoelectric
cells is understood to mean any device which under the action of
light radiation changes its electrical characteristics. Examples of
active photoelements are selenium cells, silicon cells, solar
cells, etc. Examples of passive photoelements are gas-filled or
vacuum photo cells, photo diodes, photo resistances, etc.
Photoelectric cells 2 and 3 have a different spectral sensitivity.
Cell 2 is responsive to red light and cell 3 to blue light. This
can for example be effected either in that the photosensitive
layers of the cells consist of different materials, in that filters
of different spectral permeability r or b are placed in the path of
the light rays, or in that reflection filters with different
spectral reflection are used for the two cells. The two
photoelectric devices emit coherent electric signals, for example,
voltages or currents of differing intensity depending upon
impinging light. The intensity of the two signals of cells 2 and 3
can be tuned (or varied) in different ways independent of each
other, such as by mounting a mechanical screen in front of the
photoelements, by using various ballast resistors connected to the
photoelements, or by using additional amplifiers and other circuit
devices.
The output signals of the photoelectric devices are conducted to a
device 4, which generates an output signal which is a function of
the difference between the two signals from cells 2 and 3.
This difference signal is conducted to a band pass filter 5, which
passes only the A.C. portion of the difference signal which lies in
a specified frequency range. The frequency range between 2 and 50
Hz has been found to be particularly suitable in practice. If still
better selectivity of the flame radiation as against disturbance
light radiation is desired, this frequency range (i.e. the band
pass of filter 5) may be even more narrowly restricted, for
example, to the range between 5 and 25 Hz.
The out put of band pass filter 5 is conducted to an amplifier 6,
the output of which is conducted to a discriminator 7.
Discriminator 7 generates an alarm signal which is fed to an alarm
or control device 8 if the incoming signal thereto exceeds or falls
short of certain predetermined values. Discriminator 7 is
preferably a circuit which emits an output alarm signal if the
input signal thereto deviates positively or negatively by a certain
amount from a fixed value, or in either direction by a certain
amount from zero. Alternatively, an alarm signal can be fed to
alarm device 8 if the effective value or another appropriate mean
value of the output signal from amplifier 6 exceeds a given
threshold value.
The sensitivities of the photoelectric devices (i.e., cells 2 and
3) can be tuned (or varied) as described above, in such a way that
for a disturbance light radiation that occurs particularly often,
i.e. for sunlight or for especially strong light sources in the
vicinity of the monitoring apparatus, the output signals of the
photoelectric devices for a radiation of this spectral composition
would be equal. Thus, the difference signal becomes zero, and the
discriminator circuit 7 will in this case under the action of such
a disturbance radiation emit no alarm or control signal. With all
other light radiations having different spectral compositions the
difference of the electrical output signals of photoelectric
devices 2 and 3 will not be zero, but will deviate from zero in one
direction or the other. The discriminator circuit will in this case
emit an alarm signal to be fed to claim device 8. In this manner
the "screening-out" of certain known disturbance light radiations
which would normally cause a false alarm is easily effected without
great expense.
The discriminator circuit 7 can also be designed such that an alarm
signal is emitted only when the difference signal from circuit 4
deviates from zero with a certain predetermined polarity. Thus, a
disturbance light radiation of quite specific spectral composition
which would normally cause a false alarm may be easily and
completely screened out, and that beyond this, an alarm can be set
off only if, in the light radiation striking the photocells, the
longwave portion is preponderant. In special cases, the system can
be such that an alarm will be generated when the shortwave portion
is preponderant, for example with fire alarms which react only to
the ultraviolet light radiation of a flame.
In addition, the discriminator circuit 7 can also contain an
integrator (or other appropriate delay means) so that an alarm will
not be set off immediately upon receiving short voltage impulses,
but only when the exceeding of the predetermined values exists for
a specified length of time. In this manner short duration
disturbances, through voltage impulses of short duration, will not
cause generation of a false alarm.
Further, the discriminator circuit 7 may include a locking or
latching circuit such that upon the setting off of an alarm, the
alarm automatically holds in its "on" condition, and can be re-set
from a central station. This can be easily effected by connecting a
latching relay, bistable multivibrator, or the like, to the output
of the discriminator as is well known in the art. The actuating of
the alarm device can also be indicated by an optical indicator
device 9 such as a light, which is installed either in the flame
detection unit itself or in the alarm central control station and
can serve for the localization (i.e., identification) of an
actuated alarm unit. Optical indicator 9 can be connected to alarm
device 8 (as shown) or to discriminator 7.
The sequence of the steps of generation of the difference signal,
frequency filtering and amplification -- can be changed at will.
Naturally the different circuits can be comprised single elements,
as shown, or by combined special devices. For example, the
generation of the difference signal can be accomplished by
corresponding coupling of the photoelectric devices. The band pass
filter amplifier and discriminator can be comprised in a single
analyzer unit, which may also include a circuit for generating the
difference signal (or its equivalent).
For the connection of the device of the present invention with a
central alarm station, known circuits for fire alarm systems may be
utilized. For example, a device for function-monitoring of the
system may also be provided whereby a signal is emitted from the
central station to produce alarm-simulating conditions in the
device so that the device is enabled to emit an alarm signal that
can be registered in the central station. Such function-monitoring
can be carried out in a known fashion through digital analysis,
through logical circuits or through additional A.C. signals.
Throughout the drawings, the same reference numerals are used to
designate the same or similar elements.
FIG. 2 illustrates an arrangement in which two photoelectric
devices 11 and 12 are connected together in a differential circuit,
which is connected to an analyzer 10. The photoelectric devices 11
and 12 each comprise a passive photoelement 13, for example a photo
resistance or a photo diode, a ballast resistor 14 and a battery
15. Any suitable D.C. source can be used in place of batteries 15.
In front of the photoelement 13 is a filter 16 having a certain
spectral permeability. The photoelectric device 12 differs from
device 11 only in that the filters 16 possess different spectral
permeabilities. Device 11 is made sensitive to red light and device
12 is made sensitive to blue light, as is indicated in FIG. 2. The
potential drop at ballast resistor 14 serves as an output signal of
the photoelectric mechanism. The two devices 11 and 12 are now
connected with each other at either end of the ballast resistors 14
in such a way that the respective potential drops at the two
ballast resistors have opposite polarities. The resistors 14 are
connected with the analyzer 10 via leads 17 and 18. The signal
.DELTA.U appearing across leads 17 and 18 is the difference
.DELTA.U of the voltage at the two ballast resistors 14, and thus
the difference of the output signals of the two photoelectric
devices 11 and 12. The analyzer 10 then combines the functions of
circuits 5, 6 and 7 of FIG. 1.
FIG. 3 illustrates a circuit in which two photoelectric devices 11
and 12 of the type described in FIG. 2 are connected together in
such a way that they commonly utilize a single battery 15. Instead
of a battery 15 any other suitable D.C. source can naturally be
used, for example a local D.C. supply or the D.C. supply of the
central control station. The voltages at ballast resistors 14 once
more have opposite polarity, so that again the signal .DELTA.U
representing the difference of the output signals of devices 11 and
12, is conducted to analyzer 10. With this arrangement, the greater
part of the output signals of both photoelectric devices can be
modulated independently of each other and optimal tuning of
response characteristics, to remove sensitivity to a specified
disturbance radiation may be obtained.
FIG. 4 illustrates two photoelectric devices 11 and 12, which
comprise active photoelements 13. To this end selenium, silicon, or
solar cells may be used, or any other type of photoelectric cell
which gives a voltage or a current in response to light. The
coupling network for active photoelements needs no voltage source
and the photoelectric devices 11 and 12 can, in its simplest form,
consist only of a photoelement 13 and a ballast resistor 14. The
photoelements are again connected with opposite polarity so that at
leads 17 and 18 from the ballast resistors, once more the
difference of the output signals exists and can be conducted to
analyzer 10.
Additionally, on one of the ballast resistors 14, a reference
potential may be tapped off and fed to analyzer 10 via lead 19. The
reference potential can be used in the analyzer 10 to detect the
sense (or polarity) of the difference of the output signals of the
photoelectric devices. In this manner, not only a specified
disturbance radiation can be prevented from generating false
alarms, but additionally the alarm is set off only when the
radiation becomes preponderant in a specified portion of the light
spectrum.
In FIG. 5 two networks with active photoelements 13 with differing
spectral sensitivity as in FIG. 4 are connected together. However,
the ballast resistors for the two photoelements are made up of a
single common potentiometer 20 with a variable tap. One portion of
the resistance of potentiometer 20 serves as the ballast for
circuit 11, the remaining portion serving as a ballast resistor for
circuit 12. By means of the variable tap, the relation of the two
resistance portions and also the sensitivity-relation of the two
devices 11 and 12, may be varied and tuned to eliminate sensitivity
to a particular disturbance radiation. Instead of voltage, current
can also serve as output signal of the photoelectric mechanism.
In FIG. 6 there are two active current-sending photoelements 11 and
12, for example selenium or silicon cells with differing spectral
sensitivty, connected in parallel with each other and in parallel
with analyzer 10. The current difference .DELTA.I of the two
photoelements 11 and 12 then flows into the conductors and analyzer
10. In this case, analyzer 10 must be modified to have a small
input resistance relative to the internal resistance of
photoelements 10 and 11, to sense the current .DELTA.I.
FIG. 7 illustrates an arrangement of two photoelectric elements in
the form of photo-resistances, on a common base material 21. This
constitutes a dual element whose two halves 22 and 23 have the same
characteristics. The two photoelectric elements 22 and 23 are
covered by optical filters 24 and 25, which, however, pass
different frequency ranges of the light radiation spectrum. Such an
arrangement has the advantage that in use, both photoelements are
impinged by very nearly an equal light radiation intensity.
Alternatively dual cells with layers 22 and 23 of different
spectral sensitivity can be used. The two layers 22 and 23 can be
arranged on top of each other, whereby the top layer is permeable
for the radiation for which the lower layer is sensitive.
FIG. 8 shows an example of a mechanism for adjustment of the
effective characteristics of two photoelements 27 and 28. A
mechanically movable screening device 26, such as a diaphragm,
damping filter or other material for either blocking, reducing or
otherwise changing light transmission characteristics, can be moved
in such a way that one or both of the photoelectric devices 27 and
28 may be partially screened.
FIG. 9 illustrates an arrangement in which the incoming light
radiation is impinged on two reflection filters 29 and 30 with
different spectral reflection characteristics, the light being then
conducted onto photoelements 27 and 28. This is equivalent to
various other arrangements described above. In FIG. 10 a dichroic
filter 31 is mounted in the path of incoming light radiation.
Filter 31 reflects only the portion of the radiation having a
specified spectral composition on to a photoelement 27. Filter 31
passes another portion of the radiation with differing spectral
composition therethrough onto photoelement 28. With this
arrangement, exactly equal radiation for both photoelements 27 and
28 is obtained. As a dichroic filter 31 may be used very tyin metal
layers, for example gold and copper or transparent optical layers
whose thickness lies in the order of magnitude of the light-wave
lengths, as well as combinations of such layers with different
refractive index (which have recently become known as cold-light
mirrors, warm-light mirrors or interference filters).
FIG. 11 illustrates the circuitry of an analyzer 10. Input leads 17
and 18 are the leads shown, for example, in FIGS. 2 to 6. The
difference signal of two photoelectric devices is conducted to
analyzer over leads 17 and 18. Thus, in this embodiment, a circuit
(such as circuit 4 of FIG. 1) for generating the differential
signal in this case is not necessary. The difference signal,
conducted over terminals 17 and 18 to the analyzer 10, is fed
through an input capacitor 32 to a first transistorized amplifier
stage 33. Capacitor 34 on the output of amplifier stage 33 serves
to limit the high frequencies. The output 35 of the first amplifier
stage 33 is coupled to further amplifier stages (not shown) and
then to the discriminator circuit. The discriminator includes the
two rectifiers 36 and 37 which serve for rectification and signal
doubling; and capacitor 38, its charging resistance 39 and its
bleeder resistor 40, which serve as an integration stage with a
specified time constant, i.e. for the time lag of the
discriminator. Once the charge on capacitor 38 reaches a specified
value, break-down (Zener) diode 41 which is coupled to the output
of the integration stage becomes conductive and turns on controlled
rectifier (i.e., SCR) 42. This causes a signal to be fed to
alarm-lead 43, thereby actuating an alarm device 44 which can give
off an acoustic or an optical signal, or which controls an
appropriate switching operation. In this embodiment, analyzer 10
includes also a control or alarm device 8 of FIG. 1. The controlled
rectifier 42 is connected such that once turned on, it remains
turned on even when the input signal falls below the actuating
threshold value as determined by break-down diode 41. Controlled
rectifier 42 can be turned off by means of circuit breaker 45 which
effectively opens lead 43. An optical indicator device 46 is
connected into the switching network of the controlled rectifier
42; this permits visual recognition of the actuating state of the
controlled rectifier 42 and of the alarm device.
Naturally for a flame- or fire-detection device of the type
described above any and all other circuits known in the art may be
utilized, as long as they serve the same function to carry out the
present inventive concepts. Instead of working with transistors and
semiconductors the circuit can also be fabricated with vacuum tubes
and instead of a controlled rectifier, an ionical relay, for
example a cold cathode valve, can be utilized, which can
simultaneously serve as a visual indicator for the state of the
circuit instead of using a separate indicator device.
Likewise, other known discriminator circuits can be used, for
example, those that generate the effective value of the signal or
those that generate an alarm signal when the instantaneous value of
the A.C. signal is exceeded in a predetermined direction. Also,
digital discriminators may be used which, for example, when a
predetermined limit is exceeded, generate an impulse and only give
out an alarm signal if a specified number of impulses have been
generated within a predetermined period of time.
The input amplifier stages of analyzer 10 must have input
impedances which are compatible with the impedances of the
photoelectric devices.
Furthermore, it is not necessary that only two photoelectric
devices be used in the present invention. To provide a greater
input signal to the analyzer, a greater number of photoelectric
devices can be coupled together such that the outputs of all
devices having one spectral sensitivity are additively combined,
and the outputs of all devices having the other spectral
sensitivity are additively combined. Also, devices of equal
spectral sensitivity can be grouped in a unit, or also, devices of
differing sensitivity can be connected alternatively in series.
Further, pairs of oppositely connected photoelectric devices of
differing sensitivity can be connected in series in such a manner
that each pair is sensitive for radiation coming from a specified
direction. In this manner, fire- or flame-alarm device with good
peripheral sensitivity may be constructed.
FIG. 12 represents such a peripherally sensitive device with four
pairs of photoelectric devices. Each pair contains two active
photoelements 47, in front of which a red filter 48 or a blue
filter 49 is mounted as shown in FIG. 12. The pairs can naturally
also be set up as dual-photoelements. For such pairs are connected
in series such that each pair is sensitive only to radiation from a
given direction. The ends of the series connection of pairs of
elements are conducted over leads 17 and 18 to an analyzer, which
is similar to analyzer 10 discussed hereinabove. The operation of
FIG. 12 should be apparent.
* * * * *