Note: Descriptions are shown in the official language in which they were submitted.
CA 02098602 2000-O1-24
Specification
A fire detecting device
The invention relates to a device for detecting fire in ven-
tilated appliances or machines, such as electronic data pro-
cessing equipment and similar electronic means, comprising a
measuring chamber through which flows the main current of
cooling air or a representative fraction thereof and further
comprising at least one detector arranged in the measuring
chamber in the air flow for sensing a fire characteristic
magnitude and connected to an alarm means, an extinguishing
and/or a switch off device, for example by way of an electro-
nic circuit.
The invention also relates to a device of the kind mentioned
above which additionally comprises an exhaust air channel sup-
plying the main current of cooling air or the representative
fraction thereof to the measuring chamber.
Such devices are known also, for instance, by the technical
term "equipment protection devices". Typical fields of appli-
cation for equipment protection devices are electronic data
processing installations, especially individual components
thereof, and similar electronic equipment, such as measuring,
regulating and control units, switching and exchange apparatus,
Computerized Numerical Control (CNC) production machines and
industrial robots, Computer Aided Design/Computer Aided Manu-
facturing (CAD/CAM) systems, as well as printers. It is like-
wise known that the electronic modules of such instruments or
machines must be cooled, for instance by ventilation, because
of the heat they develop, a distinction being made, in accor-
dance with the generation of the ventilation, between forced
ventilation_type apparatus, on the one hand, with which the
cooling air stream is generated by a fan inside the apparatus
and naturally ventilated apparatus, on the other hand, with
which convection of the room air, either natural or produced by
air conditioning apparatus, is utilized by virtue of the parti-
cular arrangement of the equipment at the place of
installation.
~0~~6~2
The term '°fire characteristic magnitude" is used to designate
physical magnitudes underlying measurable alterations in the
surroundings of a nascent fire, such as the ambient tempera-
ture, the contents of solids, liquid, or gas in the ambient
air (formation of smoke - particles or aerosols - or vapor) or
ambient radiation.
The significance of fire detecting devices or in short: equip-
ment protection devices is on a constant rise in parallel with
the greatly increasing dependence on electronic data pro-
cessing or electronically controlled manufacturing processes
in companies of all kinds. Whereas fire protection measures,
until some years ago, still were tailored to preserving the
buildings, nowadays fires must be detected as early and as re-
liably as possible at the appliances or machines themselves in
order to recognize a fire in its originating phase already.
The shortest possible time span between the moment of origina-
tion of a fire and the moment of detection of the fire, as
well as the corresponding measures, is of the greatest im-
portance, for example, with the electronic equipment mentioned
intially, especially because with such equipment it is not the
primary damage to the particular appliance which is decisive
but instead the secondary damage caused by strong development
of smoke in the affected room. After all, the material subject
to burning above all is plastics, like PVC and polyethylene,
such as used in cable insulations which release hydrochloric
acid gases upon combustion, reacting with water withdrawn from
the humidity of the air to form hydrochloric acid. The latter
then deposits as very fine fog on the appliances or machines
in the room and also enters into them via the room air. As a
consequence corrosion processes take place whose repair often
leads to shut-down of an entire plant.
The difficulty with early detection of fires in ventilated ap-
pliances or machines or, generally, in the rooms in which such
appliances are installed lies in the circulation of the air
generated by ventilation of the appliances or of the room,
which circulation is intended with the aim of obtaining the
best possible cooling. In air conditioned rooms, for example
in computer centers, the currents of air which predominantly
are directed from the bottom to the top often do not reach the
ceiling of the room so that smoke contained in the air stream
can be detected only very late by the known spot alarms fre-
quently installed at the ceiling. Another aspect is that the
main current of cooling air in a modular type of apparatus,
for instance, may change due to the fact that first the ap-
paratus is being used with less slide-in units and, subse-
quently, the addition of further slide-in units will con-
siderably alter the distribution of cooling air. As a result,
the placing of the conventional spot alarms later on often is
no longer correct.
It was in recognition of this fact that the fire detecting de-
vices mentioned initially were developed whose measuring cham-
ber is put directly on the apparatus to be monitored. These
known fire detecting devices, for example, suck a fraction of
the main cooling air stream through a fan and deliver this
cooling air strain to the detectors located in the measuring
chamber. To be able to detect the main current of cooling air,
these known fire detecting devices aspire the partial air by
means of funnels or suction tubes placed on the air outlet
openings of the ventilated appliance or machine. In this con-
text it must be observed that regulations stipulate that the
cooling air stream of the corresponding appliances not be
impaired.
The problem with these known fire detecting devices is that
due to the constant change in apparatus technology the masses
of air flow and also the flow velocities steadily increase so
that it becomes ever more difficult to tap a fraction off the
main current of cooling air of the ventilated appliance and
permit reliable detection of a fire characteristic magnitude
under good measuring conditions, especially the fire
characteristic magnitude "proportion of solids or liquid in
the air". Frequently the situation is such that a strong vor-
tex forms in the cooling air under the funnels or in the
,., 4 2o~ss~~
measuring chamber so that it would take too long to detect,
for instance, solid particles in the cooling air (smoke). The
detection times, when using the known fire detecting devices
of the kind mentioned initially, are approximately 60 seconds
which still is too long.
This problem is the point of departure of the instant inven-
tion which is considered to have for its object the shortening
of the detection period as well as increasing the reliability
of the known fire detecting devices.
This object is met, in accordance with the invention, with a
device for detecting fire in ventilated appliances or ma-
chines, such as electronic data processing equipment and
similar electronic means, comprising a measuring chamber
through which flows the main current of cooling air or a re- w
presentative fraction thereof and further comprising at least
one detector arranged in the measuring chamber in the air flow
7
for sensing a fire characteristic magnitude and connected to
an alarm means, an extinguishing and/or a switch off device,
for example by way of an electronic circuit, in that the
measuring chamber is designed as a chimney having a lower
cross sectional opening which is placed on a part cro$s sec-
tion of the air outlet of the ventilated appliance or ven-
tilated machine.
The "detection chimney" according to the invention, acting by
the effect of draft as known from the design of furnaces,
makes sure that the whirled up cooling air leaving the air
outlet of the ventilated appliance or ventilated machine is
steadied and converted into a laminar flow of cooling air.
This laminar flow of cooling air sweeps by the detector dis- .
posed in the detection chimney, thus permitting an extremely
quick and reliable detection of solid or liquid proportions in
the cooling air. Detection periods of a few seconds can be
achieved by the fire detecting device according to the inven-
tion.
x
The advantages of the device according to the invention fur-
thermore reside especially in the fact that the fraction of
air tapped from the principal cooling air stream need not be
fed to the measuring chamber through another fan which would
cause additional whirling up of the cooling air, instead the
cooling air is passed through the measuring chamber by utiliz-
ing the per se known chimney effect. In addition, the fire de-
tecting device according to the invention can do with a smal-
ler dimensioned power supply unit since no additional energy
is needed for a fan, apart from the energy to be furnished for
the detector or detectors.
Advantageous further developments of this solution according
to the invention are indicated in subclaims 2 to 8.
For instance, adaptation of the detection chimney to varying
quantities of air flow and also to varying flow velocities ad-
vantageously is obtained by the fact that the length of the
chimney is variable in longitudinal direction of the cooling
air flow passing through. With a great mass of cooling air
flow or high flow velocities, therefore, the length of the de-
tection chimney is increased until laminar flow conditions are
established at the detector located in the detection chimney.
The invention provides two advantageous alternatives for this
adaptation in length. According to the first solution the
change in length is effected by plug-in inserts which either
are added or removed. According to an alternative solution the
detection chimney is made to a length which corresponds to the
particular place of application.
It was explained initially that it is necessary to detect the
main current of cooling air by a fire detecting device. To
guarantee this even more effectively, preferably an exhaust
air dome is arranged between the chimney or the lowest inert
and the air outlet from the ventilated appliance or ventilated
machine, the cross section of the dome widening in the direc-
tion of the air outlet. This widening of the cross section
6 209~6~~~
most preferably may terminate in circular shape by which it
becomes possible to guide the cooling air flow especially free
of vortices.
Of course, the fire detecting device according to the inven-
tion can be used also with ventilated appliances or machines
which have the air outlet located laterally. In this case
either the exhaust air dome or one of the plug-in inserts or
the detection chimney itself may be formed with a 90° bend,
for example, so as to guide the cooling air flow in the detec-
tion range in vertical direction, if at all possible, whereby
the formation of vortices is further reduced. With such an an-
gular detection chimney, it is preferably provided that the
detector be located in a section of the chimney which takes a
linear course so as to safeguard a laminar flow in the detec-
tion range.
The laminar flow of the cooling air is enhanced still further
by an advantageous modification of the invention according to
which the cross section of the chimney converges in the direc-
tion of flow. As is well known, this tapering of the cross
section increases the flow velocity and that counteracts the
formation of vortices or dissolves existing vortices..
For the frequent case of a plurality of ventilated appliances
or machines being positioned closely adjacent one another, it
is provided in particularly preferred manner that the chimney
is placed on an exhaust air channel which withdraws a partial
amount of the main current of cooling air of each ventilated
appliance or each ventilated machine and feeds it to the lower
cross sectional opening of the chimney - or that of the ex-
haust air dome.
The object underlying the invention, moreover, is met with the
known device specified above which, in addition, comprises an
exhaust air channel supplying the main current of cooling air
or the representative fraction thereof to the measuring cham-
ber, in that the measuring chamber is designed as a flat box,
2O~~6U~
open at two sides, having one open face end connected to the
outlet of the exhaust air channel, that the exhaust air chap-
nel likewise is of box-shaped design and includes a cover with
sidewalls attached to it, and that the exhaust air channel box
is placed with its open bottom on the air outlet of the ven-
tilated appliance.
The advantages of this solution according to the invention,
above all, reside in the space-saving flat design of the ex-
haust air channel and measuring chamber. Therefore, this embo-
diment of the fire detecting device is suitable wherever there
is not so much space available above or at the side of the
ventilated appliance to be protected - depending on the place
of installation of the device - or where the overall impres-
sion of the equipment is not be disturbed by a measuring cham-
ber projecting upwardly. With this flat embodiment of the fire
detecting device the desired laminar cooling air flow is gen-
erated inside the exhaust air channel already into which the
cooling air flows into the exhaust air channel box to be moved
in the direction of the measuring chamber. Moreover, this em-
bodiment of the fire detecting device is useful wherever the
air outlet of the ventilated appliance includes guide vanes ...
which already divert the cooling air flow which exits_from the
air outlet at a certain angle with respect to the plane of the
air outlet, for example 45°. The fraction tapped from the main
current of cooling air thus also flows at the same angle into
the exhaust air channel box, whereby accumulation or reflux of
the cooling air by reflection at the underside of the cover of
the exhaust air channel box is avoided. If, for instance, the
partial amount withdrawn from the cooling air flow enters at
an angle of 45° into the exhaust air channel box, the cooling
air at the underside of the cover is deflected once more by
45° and, therefore, flows in steadied fashion in the direction
of flow towards the measuring chamber.
Preferred modifications of this solution according to the in-
vention are indicated in subclaims 10 to 13.
2~~~6~2
For all those ventilated appliances whose air outlet consists
of a simple grid so that the issuing cooling air flows out of
the appliance vertically with respect to the grid, it is pre-
ferably provided that the exhaust air channel box ig of two-
part design in that the cover and the sidewalls form an upper
part and that a lower part is provided which comprises fin-
like air inlet slots in its bottom, the fins thereof being of
inclined design in the direction of flow, the lower part being
adapted to be inserted from below into the upper part.
The fins, for example, may extend at an angle of 45° with
respect to the bottom of the exhaust air channel. The cooling
air which exits vertically out of the air outlet of the ven-
tilated appliance thus is deflected for the first time by the
fins of the exhaust air channel in the area of the fire
detecting device in the direction of the measuring chamber and
then once again at the underside of the cover of the exhaust
air channel, whereupon the tapped cooling air stream calms
down and converts into a laminar flow. Reflection of the cool-
ing air entering from below into the exhaust air channel is
avoided at the underside of the cover of the exhaust air chan-
nel by virtue of the fact that the cooling air stream with-
drawn is deflected already once in the direction of flow by
the fins of the air inlet slots of the exhaust air channel
box. This is particularly the problem with the devices known
from the state of the art for withdrawing a fraction from a
cooling air stream. If the cooling air stream issuing from the
ventilated appliance hits a diverting baffle or the like at
right angles, for example the underside of the cover of the
exhaust air channel, a major portion of the tapped cooling air
stream is reflected and whirlled up, cooling air accumulates,
and that impedes or even prevents the transportation of smoke
particles, for instance, to the measuring chamber.
The length of the exhaust air channel in the direction of
flow, too, is variable in advantageous manner by plug-in in-
serts, similar to the detection chimney mentioned above, to
adapt it to different quantities of air flow and also to flow
2~~8~p~
velocities of different magnitude. The entire fire detecting
device thus can be built in modular fashion by assembling one
or more exhaust air channel units - in response to the desired
length of the overall device - and connecting the measuring
chamber to the end of the exhaust air channel which lies in
the direction of flow.
The spacing of the fire detecting device from the air outlet
of the ventilated appliance can be varied, according to an ad-
vantageous further development of the invention, by brackets
to avoid reflux of cooling air, depending on the magnitude of
the flow velocity of the cooling air exiting from the
ventilated appliance.
The following modifications relate to both solutions according
to the invention.
Preferably it is provided that two detectors, able to respond
to different fire characteristic magnitudes, are arranged in
the measuring chamber to improve the freedom from inter-
ference, i.e. to lower the false alarm rate. In per se known
manner, the two detectors are connected in two lines to a fire
alarm center. The two detectors may be smoke, gas, or.heat in-
dicators, depending on the specification requirement, with
either both detectors, for example, being smoke alarms or one
being a smoke alarm and the other one an indicator either of
gas or heat. Additionally, a temperature sensor may be dis-
posed in the measuring chamber or in the exhaust air channel
as well. The provision of two smoke indicators suggests itself
since in most cases, when a fire originates, the fire charac-
teristic magnitude "solids or liquid proportions in the
cooling air" is to be expected. In this context both optical
smoke alarms (O-indicators) as well as ionisation smoke alarms
(I-indicators) are used. Alternatively, in line with the
respective case of need, at least one of the two detectors can
be designed as a gas indicator or also as a heat indicator.
While a gas indicator is directed at detecting the fire
characteristic magnitude "proportion of certain gases in the
w l~ ~~
appliance cooling air", the heat indicator reacts to heat ra-
diation. The latter is to be employed, for example, where the
cooling air inevitably comprises a certain proportion of solid
particles, for instance, in the form of dust. Here a smoke in-
dicator would lead to false alarms due to the dust. The heat
indicator can be designed as a maximum indicator which
responds when the temperature measured exceeds a certain
threshold value for a given period of time, or as a differ-
ential indicator which responds when the speed of variation of
the temperature measured exceeds a fixed value for a predeter-
mined period of time, or as both maximum and differential in-
dicator combining both capabilities. Specifically the dif-
ferential measurement permits a very early indication of ab-
normal temperature rises of the apparatus cooling air.
According to another advantageous modification of the inven-
tion the two detectors are located opposite each and offset
with respect to each other in the direction of flow of the
measuring chamber. The advantage of the mutually offset and
opposed arrangement of the detectors, on the one hand, is that
the measuring chamber thus can do with a smaller cross section
and, on the other hand, that the positioning of the detectors
at different height above the air outlet of the ventilated ap-
pliance is another essential contribution to avoiding de-
ceiving alarms.
An advantageous alternative of the mutually opposed arrange-
ment of the detectors is to arrange them mutually offset in
the direction of flow, but at the same side. In that event the
detectors can be installed on a common board which is of ad-
vantage under aspects of the manufacturing technique and, on
the other hand, affords considerable simplification of the
maintenance of the fire detecting device because access to the
detectors for maintenance purposes is required from one side
only.
A preferred embodiment of the invention will be described in
greater detail below, with reference to a drawing, in which:
w
11 209~00~
Fig. 1 is a side elevational view of a detection chimney
according to the invention, comprising an exhaust
air dome and an insert plugged in between the chim-
ney and the exhaust air dome;
Fig. 2 is a top plan view of the detection chimney shown in
fig. 1; ... '
Fig. 3 is a front elevational view of the detection chimney
shown in fig. 1;
Fig. 4 shows the arrangement of a detection chimney accord-
ing to figs. 1 to 3 on a ventilated apppliance ca-
binet;
Fig. 5 shows the arrangement of a detection chimney accord-
ing to figs. 1 to 3 at the side of a ventilated ap-
pliance cabinet with an angled exhaust air dome;
Fig. 6 shows the arrangement of a detection chimney accord-
ing to figs. 1 to 3 on an exhaust air channel for
protection of a plurality of ventilated appliances
or machines;
Fig. 7 is a perspective view of an exhaust air channel as
component part of an alternative embodiment of a
fire detecting device;
Fig. 8 is a side elevational view of an insert having fin-
like ventilation slots and adapted to be inserted
from below in the exhaust air channel shown in fig.
Fig. 9 is a top plan view of the insert shown in fig. 8;
Fig. 10 is a perspective view of the exhaust air channel
shown in fig. 7 with built-in insert according to
figs. 8 and 9;
Fig. 11 shows the arrangement of a fire detecting device
comprising two exhaust air channel units and a
measuring chamber connected to them in flow direc-
tion on the ventilation grid of a ventilated ap-
pliance cabinet;
Fig. 12 shows the arrangement of an exhaust air channel unit
on the ventilation grid of a ventilated appliance,
12
the exhaust air channel being connected by means of
a supply conduit to the measuring chamber;
Fig. 13 shows the arrangement of two exhaust air channel
units, connected directly to a measuring chamber, at
the side of a ventilated appliance cabinet; and
Fig. 14 is a presentation, similar to fig. 13, of a fire de-
tecting device at the side of a ventilated appliance
cabinet, with two exhaust air channel units in this
case being connected by a supply line to a measuring
chamber.
Fig. 1 shows a side view of a device for detecting fires in
ventilated appliances or machines, essentially comprising a
measuring chamber through which flows the main current of
cooling air or a representative fraction withdrawn from the
same, and further comprising two detectors 12, 13 in the form
of smoke indicators arranged in the measuring chamber 2 in the
air stream which flows through the same. The smoke detectors
12, 13 are connected by an electronic circuit (not shown) to
an alarm means an extinguishing and/or switch-off device
permitting an optical and/or acoustical indication of a fire
alarm as well as the direct reaction by an extinguishing pro-
cess or also by switching off the appliance concerned.
The measuring chamber 2 is designed as a chimney 4 (below
also: detection chimney) the length of which is variable in
longitudinal direction of the cooling air stream which flows
through it. Adaptation in length of the chimney 4 to the
respective conditions prevailing in situ is necessary because
the air flow quantity as well as the flow velocity differ from
apparatus to apparatus so that flow channels 16 of different
lengths are needed to generate a laminar flow zone 17.
Finally, the air flow conditions also may change in modular
appliances by the addition or removal of slide-in units so
that an adaptation of the length of the detection chimney be-
comes necessary in order to obtain laminar flow.
13 ~fl98~~32
In the embodiment illustrated in fig. 1 the length of the
chimney 4 ws increased by a plug-in insert 8 and, in addition,
by an exhaust air dome 10. The cross section of the exhaust
air dome 10 becomes greater towards the bottom and terminates
in a circular cross section 11. At this circular cross section
11, the exhaust air dome 10 and thus the entire detection
chimney 4 is placed on the air outlet 6 of the ventilated ap-
pliance 1 which is no longer shown here. The cooling air is-
suing from the air outlet 6 of the ventilated appliance enters
the flow channel 16 through the lower cross sectional opening
3 of the exhaust air dome 10 or chimney 4 and is guided past
the two detectors 12, 13. The two detectors 12, 13 are dis-
posed opposite each other at different levels, both detectors
overlapping each other in transverse extension, whereby the
reliability of the fire detecting device is improved.
Fig. 2 is a top plan view of the detection chimney 4. Based on
this view, it can be seen that the exhaust air dome 10 widens
downwardly into a circular cross section 11, whereby on the
one hand a greater proportion of the main current of cooling
air is grasped and, on the other hand, the stalibility of the
overall device is enhanced.
Fig. 3 shows a front view of the chimney-like measuring cham-
ber 2 according to figs. 1 and 2. The variation in length of
the detection chimney 4, of course, can be achieved also by a
telescopic design of the chimney 4.
Fig. 4 shows the detection chimney 4 with a plug-in insert 8
and an exhaust air dome 10 on the appliance cabinet 1 of a
ventilated appliance. The circular enlargement of the exhaust
air dome 10 is secured on the air outlet 6 of the ventilated
appliance by mechanical connections, such as screws 7. The
cooling air of the ventilated appliance enters the flow chan-
nel 16 of the measuring chamber 2 through the exhaust air dome
10, sweeping past the detectors 12, 13 as a laminar flow and
leaving the detection chimney 4 through the upper cross sec-
tional opening 5 thereof.
14
Fig. 5 shows an embodiment which is identical with the fire
detecting device described above, with the exception of the
design of the exhaust air dome 10. Here the detection chimney
4 is fastened to the lateral air outlet slits 6 of a ventilat-
ed appliance 1. The exhaust air dome 10 has a 90° bend so that
the flow passage 16 inside the detection chimney 4 extends in
vertical direction within the detection range 17. Here again
the exhaust air dome 10 is of circular cross sectional design
at its end and secured to the air outlet 6 by screws.
Fig. 6 shows the embodiment of the detection chimney according
to figs. 1 to 4 as a fire detecting device for a series of
ventilated appliances 1, 1', 1", 1 "' arranged side-by-side.
Here the detection chimney 4 is mounted by its exhaust air
dome 10, which again is circularly widened in cross section,
on an exhaust air channel 14 which gathers a fraction of the
main current of cooling air from the air outlets 6, 6', 6",
6 "' of the individual ventilated appliance cabinets through
inlet openings 15. The cooling air flows withdrawn from each
ventilated appliance are supplied to the detectors 12, 13
through the exhaust air dome 10 and the plug-in insert 8 as a
joint air stream. With this embodiment the fire detection is
effected simultaneously in each instance for the intercon-
nected appliances 1, 1', 1", 1"'.
Fig. 7 shows the perspective view of an exhaust air channel 14
- or an exhaust air channel unit - as part of an alternative
embodiment of a fire detecting device whose overall function
will be explained below with reference to figs. 11 to 14. An
exhaust air channel unit 14 is spoken of inasmuch as the ex-
haust air channel shown with an open front end in fig. 7 also
can be combined with a plurality of almost identically struc-
tured exhaust air channel units to form an exhaust air channel
of any desired length.
The exhaust air channel unit 14 illustrated in fig. 7 is of
box-shaped design, including a cover 25 and sidewalls 26, 27
15 20~8~~1~
attached to the same. This exhaust air channel box 14 is
placed with its open bottom on the air outlet 6 of the ven-
tilated appliance 1. When an exhaust air channel box is used
in the fire detecting device one of the two face ends of the
exhaust air channel box 14 is closed, while the face end
located in the direction of flow of the cooling air stream is
connected to the measuring chamber 2 (cf. figs. 11 to 14). The
exhaust air channel box 14 illustrated in fig. 7 can be used
wherever the air outlet 6 of the ventilated appliance includes
guide baffles 29 which cause the exiting cooling air stream to
issue, for instance, at an angle of 45° with respect to the
plane of the air outlet (figs. 13 and 14).
Fig. 8 shows a lateral view of a lower part 23 including fin-
like air inlet slots 18 and adapted to be inserted from below
into the upper part 22 of the exhaust air channel 14 shown in
fig. 7. Here the lower part 23, for example, has a front end
wall 28 for terminating the exhaust air channel 14 at the face
end. Yet this is not needed when the exhaust air channel box
14, i.e. including the upper part 22 and the lower part 23, is
installed as a central unit in a longer exhaust air channel.
In such an event, of course, both face ends are open to let
the cooling air pass through. At one edge each which extends
transversely of the direction of flow, the fin-like air inlet
slots 18 of the lower part 23 comprise fins 24 extending at an
angle of approximately 45° with respect to the bottom sheet of
the lower part 23, being chamfered iw the direction of flow.
It is the function of these fins to effect a first deflection
in the direction of flow of the cooling air which enters the
lower part 23 through the air inlet slots 18 substantially
vertically with respect to the bottom sheet in order thus to
prevent the cooling air flowing into the exhaust air channel
14 from hitting the underside of the cover 25 perpendicularly
(fig. 7) as this would cause reflux of the cooling air. Such
reflux not only affects the function of the fire detecting de-
vice because transportation to the measuring chamber 2 of the
smoke particles or liquid proportions in the cooling air no
longer takes place or does so only with great delays in time.
16
On the other hand, an accumulation or reflux of the cooling
air is undesired on the part of the producer of the apparatus
to be monitored as well as on the part of the operator thereof
because undesirable overheating of structural elements may be
the consequence.
Fig. 9 shows a top plan view of the lower part 23 according to
fig. 8 to once again clarify the position of the fins 24.
Fig. 10 shows an exhaust air channel box 14 composed of an up-
per part 22 and a lower part 23. This exhaust air channel box
14 resulted from the lower part 23 according to figs. 8 and 9
having been inserted from below into the upper part 22 accord-
ing to fig. 7. The exhaust air channel box 14 is closed at one
face end by a front end wall 28. This exhaust air channel box
14 consequently presents a unit of the type used within a lon-
ger exhaust air channel, composed of a plurality of exhaust
air channel units 14, as the left end closing unit or as the
only exhaust air channel unit 14. When the exhaust air channel
box 14 is used as a middle unit to form a longer exhaust air
x
channel, the front end wall 28 is dispensed with. This makes
it clear that the length of the entire exhaust air channel is
variable in modular fashion by combining a plurality of ex-
haust air channel units which also may be of different
lengths. This adaptation in length provides an advantageous
adaptation of the fire detecting device to the dimensions of
the apparatus to be monitored and, by optimizing the length of
the exhaust air channel, laminar flow of the cooling air in
the exhaust air channel tawards the measuring chamber can be
effected especially efficiently.
For further reduction of the risk of an accumulation of air,
the exhaust air channel box 14 includes bracket slats 23 at
its sidewalls 26, 27 which project downwardly beyond the bot-
tom sheet of the insert 23 so that the air inlet slots of the
exhaust channel box 14 are spaced from the air outlet 6 of the
ventilated appliance. The height of these bracket slats - or
also of the brackets 20 according to fig. il - can be adapted
17 ~~~
to the flow velocity of the cooling air flowing out of the
ventilated appliance.
Figs. 11 to 14 illustrate a few different possibilities of ap-
plication of the flat embodiment of the fire detecting device
according to the invention. Figs. 11 and 12 each are concerned
with the use in an appliance cabinet 1 of which the air outlet
6 in the form of a simple grid is mounted on the top side of
the appliance cabinet 1 from which the cooling air, therefore,
rises substantially vertically. Two exhaust air channel units
14, coupled in flow direction with a measuring chamber 2, are
arranged on the air outlet grid 6 of the appliance cabinet 1
as shown in fig. 11. The two exhaust air channel units 14 sub-
stantially correspond to the exhaust air channel unit 14 il-
lustrated in fig. 10, with the difference that in the exhaust
air channel units shown in fig. 11 the bracket slats 30, 31
are replaced by transversely extending brackets 20. In the
area below the exhaust air channel units 14, the cooling air
which vertically leaves the air outlet 6 of the appliance ca-
binet 1 flows through the air inlet slots 18 into the exhaust
air channel units 14 and in doing so is deflected for a first
time by the fins 24 at an angle of approximately 45° in the
direction of flow towards the measuring chamber 2. The second
deflection of the cooling air takes place at the underside of
the cover 25 of the exhaust air channel units 14 (cf. fig. 7).
On the whole, therefore, deflection by 90° takes place of the
tapped fraction of the main current of cooling air, it being
assured - in response to the outflowing velocity of the cool-
ing air from the ventilated appliance 1 - that a laminar flow
of cooling air is formed within the exhaust air channel units
14 by selection of a corresponding length of the overall ex-
haust air channel. Without any deflection by the fins 24 of
the cooling air entering the exhaust air channel units 14, the
cooling air would impinge vertically on the underside of the
cover 25 of the exhaust air channel units and that would re-
sult in reflux and accumulation. Yet the two-fold deflection
of the cooling air within the exhaust air channel and the cor-
responding adaptation in length of the exhaust air channel
18 20J~~~~
make sure that the tapped fraction of the main current of
cooling air will enter the measuring chamber 2 as a laminar
flow, the cooling air being able to sweep past the two detec-
tors 12, 13 and leave the measuring chamber 2 at the front end
19.
Fig. 12 illustrates the use of another embodiment of the fire
detecting device on the same ventilated appliance cabinet 1.
Once more the cooling air exits substantially vertically from
the air outlet 6 of the ventilated appliance 1. Other than
with the ventilated appliance cabinet 1 of fig. 11, however,
here the cooling air issues at such low flow velocity that a
measuring chamber 2 is used which actively aspires the tapped
fraction of the cooling air through a supply line 21 from the
exhaust air channel box 14 by means of a fan of its own. At
such low flow velocities, also the spaced arrangement of the
exhaust air channel from the air outlet grid by means of
brackets 20 (cf. fig. il) or by projecting bracket slats 30,
31 (cf. fig. 10) may be dispensed with. Active aspiration can
be dispensed with only, and a fire detecting device according
to fig. 11 be used, beginning at exhaust air velocities of
about > 2 m per second.
Figs. 13 and 14 each show a ventilated appliance cabinet 1
with which the cooling air already leaves the air outlet 6 of
the ventilated appliance 1 at a certain angle. Deflection of
the cooling air here is effected by air guide baffles 29 which
already are available at the appliance cabinet end and deflect
the cooling air in the two cases illustrated by about 45° in
downward direction. The fire detecting devices in both cases
of figs. 13 and 14 are composed of two exhaust air channel
units 14 which in this instance, however, consist only of the
upper parts 22 according to fig. 7 and of a measuring chamber
2 each. As the cooling air leaving the ventilated appliance 1
through the air outlet 6 enters the exhaust air channel 14 al-
ready deflected in flow direction by the guide baffles 29,
provision of the lower part 23 according to figs. 8 and 9 is
not necessary in the instant case. The cooling air which al-
_.
ready enters the exhaust air channel 14 in oblique downward
direction is deflected once more in flow direction at the un-
derside of the covers 25 of the exhaust air channel units 14
so that here again a laminar cooling air flow results in the
direction of the measuring chamber 2.
In correspondence with the differences between figs. il and
12, different measuring chambers 2 are used also with the ap-
pliance cabinets of figs. 13 and 14. The ventilated appliance
1 according to fig. 13 is an appliance with which the cooling
air exits from the air outlet 6 at a flow velocity which is
higher than approximately 2 m per second. Therefore, active
aspiration of the cooling air from the exhaust air channel can
be dispensed with since the flow velocity of the cooling air
proper is sufficient for conveying the tapped fraction of the
cooling air through the exhaust air channel to the measuring
chamber 2.
The appliance cabinet 1 illustrated in fig. 14 is a ventilated
appliance with which the cooling air flow velocity upon
leaving the air outlet 6 is not sufficient to warrant reliable ,
conveyance of the tapped cooling air quantity through the ex-
haust air channel 14 to the measuring chamber 2. For this
reason the measuring chamber 2 once more comprises a fan by
which the tapped cooling air is sucked through a supply line
21 from the exhaust air channel 14 and fed to the detectors in
the measuring chamber 2.
