Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present inventlon relates to rake oE temperature
change detectors partlcularly though not excluslvely for
use as "rate of rise" ire detectors, and ko fire alarm and
fire extinguishing systems employing such detectors.
Detectors in accordance with the invention include so-
called shape memory efEect (SME) elements. An SM~ element
is made from a material, usually an alloy, which undergoes
a transformation in its crystallographic structure when
heated or cooled through a particular temperature range,
this transformation being accompanied by a significant
change in elastic modulus. By appropriate thermal and
mechanical treatment of an element made from such material,
the element can be arranged to exhibit a first stable shape
at temperatures below the appropriate transofrmation range
and a different stable shape at temperatures above that
range, the element being capable of changing reversibly
between its low and high temperature shape conditions when
heated and cooled~ through the transformation range. In
other words the element behaves in a manner indicative of
retaining a "memory" for either shape.
Such elements are know, examples o alloys which exhibit
the shape memory effect including certain nickel-titanium
and copper-zinc-aluminium alloys.
An im~ortant application for a rate of temperature change
detec-tor accordin~ to the invention is as a so-called "rate
of rise" fire detector. Such devices must be capable of
responding primarily to specified rates of increase in
ambient tempexature in the region monikored, as opposed to
the absolute (i.e instantaneous) value of temperature,
although i.- is desirable that they shall also respond to a
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predetermincd max:imum ambierlt temperature irrespect.ive of
the rate of change of temperature at that time. For
example, the relevant European Standard ~54:Part 5 (-- BS
5~5: Part 5:1977~ lays down various response times for
such devices at different rates o rise of air temperature
commencing from a standard temperature of 25C, ranging
from a response time of between 29 minutes and 45 minutes
40 seconds at a rate of rise of 1C/minute (for the
intermediate response grade 2) to a response time of
between 15 seconds and 1 minute 34 seconds at a rate of
rise of 30C/minute. Additionally, with rates of rise
less than 1C/minute the detector must not operate at an
air temperature below 54C but must operate between
54C and 70C. The specifi~ed upper limits of response
time to the given rates of rise of ternperature are of
course intended to ensure that detectors respond
sufficient].y quiclcly to a fire, while a lower limit of
response time is also specified in order to minimise the
incidence of false alarms due to changes in the ambient
temperature where no fire has occurred. The upper and
lower limits to the a~solute temperature to which detectors
must respond under "static" conditions (ie with a rate of
rise less than 1C/minute) are specified for similar
reasons.
With the foregoing in mind, the invention provides in one
aspect a rate of temperature change detector comprising two
shape memory efect elements each one of which is adapted
to ~espond to specified changes of temperature within a
region wherein the detector is, in use; disposed; the
response exhibited by a first said element tending to
provide an Outpllt from the detector; the second said
element being coupled -to the first element whereby the
response e~libited by the second element opposes the
response of the fi~st element; and the arrangement being
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such that -the two said elements respond at different
effective rates to the same change of -temperature in the
region.
With a detector in accordance with the invention, the
response of the first SME element tending to provide an
output while the response of the second SME element opposes
the first element, the time taken for an output to be
provided when the monitored region exhibits a given rate of
change of temperature is therefore determined by the
relative effective rates of response of the two elements ,
which can be chosen to confer upon the device
characteristics approprate to a "rate of rise" fire
detector or to such other use as may be required.
Preferably, at least when used in fire detection, means are
also provided ~or limiting the response which can be
exhibited by the second element in opposition to the first
element, so that any further change of temperature which
occurs after that response of the second element will
result in an effective response by the first element only,
leading inevitably to the provision of an output when a
certain absolute ternperature is reached and thereby
ensuring the requisite "static" operation of the detector.
The different effective rates of response of the two SME
elements could be achieved by employing elements with
different inherent thermomechanical properties, such as
with different alloy compositions. It is generally more
covenient, however, to employ two similar elements and to
provide or the different rates of response by arranging
that temperature changes occurring in the monitored region
are transmitted to the first element more rapidly than to
the second element, such as by surrounding the second
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elemerlt with structure o a lower thermal transmissivity
than that (if any) surrounding the first element and/or by
coating the second element with heat insulative material.
~he form of the SME elements comprised in a detector
according to the invention is open to considerable
variation. One preferred form comprises a cylindrical coil
of shape memory effect material which element tends to
expand axially when heated through the transformatlon
temperature range of the material. A second preferred form
comprises a flat spiral of the material which tends to
expand in part-conical form when heated through the
transformation temperature range, and a third preferred
~orm is in effect the opposite, namely a part-conical
spiral of the material which tends to contract towards a
flat spiral form when heated through the transformation
range.
Generally, each such SME element will be fixed in position
at one location upon the respéctive element while another
location upon that element is capable of displacing
relative to the one location upon change of temperature of
the element through the transformation range. However,
substantial spatial movement of part of an element need not
always be an essential to operation of a detector according
to the invention where, for example, the element is
constrained against movement and the variation in force
applied to the constraining means by the element as it
undergoes its crystallographic transformation in the
appropriate temperature range is detected. In practice a
two-stage type of response may be exhibited, where for
example the aforesaid first element must first overcome a
biasing load as ~t transforms under change of temperature
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and thereaEter deflects b~ a small distance to provide an
output from the detector.
The output from a detector as defined above may be used to
exert a control and/or to give an indication as appropnate
to the use to which the detector is put. As previously
indicated such a device is particularly useful in fire
detection and in a second aspect the invention resides in a
fire alarm system comprising at least one detector
according to the first aspect of the invention sensitive to
the rate of increase of temperature within a respective
region and me~ns responsive to the output of the or any
such detector to indicate the existance of an alarm
condition.
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In a third aspect the invention resides in a fire-
extinguishing system comprising at least one detector
according to the first aspect of the invention sensitive to
the rate of increase of temperature within a respective
region, and means responsive to the output of the or any
such detector to initiate the delivery of a fire
extinguishing agent into the respective region.
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Three illustrative embodiments of fire detectors made in
accordance with the invention will now be more particularly
described with reference to the accompanying schematic
drawings in which:
Figure 1 is a sectional view of the first detector;
Figure 2 ;s a sectional view of tAe second d-tector;
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Fi~ure 3 is a plan view of the form of SI~E element employed
in the detector of Figure 2, in its low temperature
condi-tion;
Figure 4 is an elevation of the SME element of Fi~ure 3,
in its unconstrained high-temperature condition; and
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Figure 5 is a sectional view of the third detector.
With refernece to Figure 1, the illustrated detector is
assumed to be mounted to the ceiling or a room and to be
one of a plurality of fire detectors distributed throughout
a building, all connected electrically to a central control
station tnot shown). It comprises a plastics casing 1
within which is mounted a cup-shape plastics sleeve member
~ which in turn serves for the mounting of a cylindrical
coil 3 of SME alloy and other parts of the mechanism to be
described below. The two or so turns at the centre of the
coil 3 are held rigidly by the member 2 and play no part in
the actual operation of the device. However, the portions
4 and 5 of the coil 3 to either side of this central
portion are not ri~idly restrained and are appropriately
treated such that below a particular temperature they
exhibit a compressed form but when heated through the
transformation temperature range of the alloy (preferably a
brass) of which the coil is made they increase in stiffness
and thereby extend axially. Since the coil portions 4 and
5 are parts of the same continuous element 3 and since they
receive identical treatement during the manufacture of that
element, their therrnomechanical properties are
substantially the same, which means that (in the absence of
external constrai.nts) when they are heated to the same
temperature portion 4 will tend to e~tend upwardly from the
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central: coil porti.on by the same distance as portion 5
extends d~nwardly.
The free end of the upper S~IE coil portion ~ engages a
flange 6 towards the upper end of a sleeve 7 disposed
within the coi.l 3. A further sleeve 8 is disposed in
telescoping relationship with the sleeve 7 and these two
components are coupled together resiliently through an
ordinary (ie non-SME) coil spring 9 compressed between webs
lO and ll at the respective lower ends of the sleeves 7 and
8. rrhe free end of the lower SME coil portion 5 engages
the head 12 of a rod 13 which extends upwardly through the
two sleeves 7 and 8 and carries at its upper end a smaller
head, defined by a snap ring 14 fast with the rod, which is
dispose~ in telescoping relationship within the upper
sleeve 8. rrhis rod 13 is coupled resiliently to the sleeve
8 throu~h an ordinary coil spring 15 equivalent to the
spring 9 and compressed betwen the web ll and ring 14.
It wil~ be appreciated from the above that the sleeve ~3 is
effectively suspended, by means of the two springs 9 and
15, acting on opposite sides of its web ll, between the web
lO of sleeve 7 and the ring 14 fastened to rod 13, and t'nat
the position of the sleeve 8 with respect to the fixed
structure of the detector is thereby determined at all
times by the r~lative positions of the rod 13 and sleeve 7.
rrhe sleeve 7 carries an electrical contact 16 which is
normally spaced from a fixed contact 17 mounted to
the me~nber 2, but i~ the sleeve 8 is moved downwardly
through an appropriate distance the two contacts are
brought together to complete an electrical circuit and this
event .is detected at the control station, vla suitable
leads (not shown), as an indication o fire. The alignment
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between the two contacts during this movement is malntained
by a pair of cheeks 22 (of which one is seen in the Figure)
provided on the member 2 and extending to either side of
the contact 16.
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It will be further appreciated that the tendency of
e~tension of the lower SME coil portion 5 is to move the
rod 13 downwards, thereby tending also to move the sleeve 8
and contact 16 downwards by further compression of the
springs 9 and 15. On the other hand, the tendency of
extension of the upper SME coil portion 4 is to oppose the
extension of portion 5, through the resilient coupling
provided by springs 9 and 15. It has been indicated that
the response of the two SME coil portions 4 and 5 to
equivalent temperatures is to extend by equal amounts;
their response to thermal conditions outside the detector
structure is not, however, the same, and this can be
explained by considering the relative dispositions of the
two coil portions with respect to the external ambience.
Thus, the upper coil portion 4 is surrounded by structure
1,2 of low thermal transmissivity. The lower coil portion
5, on the other hand, is surrounded by a thin, thermally
transmissive sheath 18, of copper or aluminium for example.
The casing 1 may be extended, as shown, as a series of
"claws" 19 in the vicinity of the sheath 18 to provide
impact protection for that area of the device, but these
claws are spaced apart and well ventilated such that they
do not si~nificantly impair heat transmission from the
surrounding environment to the sheath. It follows that any
fluctuations in the air temperaure of the region in which
the detector is sited will be transmitted to the lower SME
coil portion 5 more rapidly than they are transmitted to
the upper coil portion 4.
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In use of the device, at temperatures below the
transformation range of the SM~ coil 3 (the lower limit of
which is, say, 23C) both coil por-tions 4 and 5 remain in
their compressed condition, as illustrated, and the contact
16 remains spaced from the contact 17. In the event that
the ambient temperature rises above that lower limit both
coil portions 4 and 5 will begin to extend, but as the
lower coil portion 5 has a quicker response to rising
temperature in the monitored region, as explained above,
its extension will lead the extension of portion 4. Due to
this differential extension of the two ~ME coil portions
there is a net movement of the sleeve ~ and contact 16 in
the downward direction. This movement will continue so
lon~ as the ambient temperature continues to rise at a
si~nificant rate until the point is reached where the
extension of coil portion 5 exceeds the extension of coil
portion 4 sufficiently to bring the contact 16 into
abutment with the contact 17. The signal producecl thereby
is detected at the control station as an indicaton of fire
and functions automatically to raise the alarm and, i
fitted, to initiate the discharge of fire extinguishing
agent into the monitored region eg through an associated
C02, sprinkler or the like system.
It will be appreciated that the greater the rate of rise of
temperature in the monitored region, the sooner will the
differential extension between the SM~ coil portions 4 and
5 reach the value required to close the contacts 16/17, and
the device can t]lUS exhibit the charac-teristi.cs specified
for a "rate of rise" type of fire detector as previously
indicated. ~t rates of rise of ambient temperature less
than about lC/minUte, however, the effects of the la~
in response of the coil portion 4 behind that of the coil
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portion 5 become less si~nifi.cant so that whlle hoth coil
portions continue to extend (assuming, of courRe, that the
temperature continues to rise) they remain more or less in
balance, and there is thus little or no net movement of the
contact 16. Thls is of importance in ensuring -that false
alarms are not given due to slow moving environmental
temperature changes even when these give rise to relatively
high ambient temperatures (eg where the detector is used in
foundries or the like locations where heat-producing
industrial processes are carried out). It is also
important, however, that the device should react if the
ambient temperature rises to a certain maximum temperature,
at whatever rate it is reached, and this can be ensured in
the "static" temperature condition by the provision of an
additional component 20. This is a ring which is screwed
into the member 2 and has a flange 21 which lies in the
path of movement of the flange ~ of sleeve 7 when the uppex
SME coil portion ~ extends. After the coil portion 4 has
extended by an amount to brin~ the flange 6 into abutment
with the flange 21 further extension of that portion is
physically prevent; there is, however, no additiono~
restraint on the further extension of coil portion 5 so
that a further increase in temperature will result in
extension of that portion only, with a resultant movememnt
of the contact 16 towards the contact 17. It can thus be
ensured that the extension of coil portion 5 will cause
closure of the contacts 16/17 when a specified absolute
temperature pertains in the monitored region, even if that
temperature is reached at a slow rate which does not in
i~self cause ac-tivation of the device.
In the illustrated embodiment two means of adjustment are
provided which enable devices of this type to be accurately
calibrated notwithstandin~ certain variati~ns in the
thermal txansmissivities of the deteckor structures and in
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the performance of SME coils 3 (particularly Ln the precise
temperature at which transformation commences). Thus the
con~act 16 is in threaded engagernen-t with the sleeve 8 so
that relative rotation of these two parts adjusts their
relative axial positions. In effect -this provides a means
of setting the initial spacing of the contact 16 from the
contact 17 to ensure appropriate "rate of rise" response
times from the device. Secondly, the ring 20 can be
screwed in or out of the member 2 to adjust the distance
through which the upper SME coil portion 4 extends before
its movement is terminated, thereby to ensure appropriate
"static" response from the device.
Turning to Figure 2, this shows a rate of rise fire
detector comprising two separate SME elements 23 and 24 of
different form to the "elements" 4 and 5 in the Figure 1
embodiment. In this case each element is formed and heat
treated to have a flat spiral shape at temperatures below
the transformation range, as more clearly seen in Figure 3,
and to expand progressively in part-conical helical form
with rise of temperature through that range, the
unconstrained high-temperature form of these elements being
indicated in Figure 4. In the low temperature condition of
the device shown in Figure 2 the element 23 is held flat
against the base of a thermally conductive sheath 25 of eg
copper or aluminium, by a plastics spacer 26 engaging its
outermost turn (the spacer comprising two rings 26A
interconnected by a series o webs 26B), and by a plastics
moulding 27 held in the centre of the element. The sheath
25 is held in plastics casing 2~ which may, as in the case
of Fiyurè 1, be extended downwardly around the sheath in a
series oE protective but ventilated "claws" 29. A platform
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30 is held in the caslng 28 by an upper housing member 31
screwed into the casing, and in -the illustrated low
temperature condition of the device the second SME element
24 is held flat against this platform, above and spaced
from the element 23, by the spacer 26 enyaging its
outermost turn and by a plstics moulding 32 held in the
centre of the element. ~le two mouldings 27 and 32 are
biased apart by an ordinary coil spring 33.
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The moulding 32 has an integral stem part 34 which is
slidably borne in a central bore 35 of the platform 30. A
rod 36 is in turn slidably borne by the moulding/stem 32/34
and seats at its lower end in a recess 37 in the moulding
27. At its upper end the rod 36 carries a metal cap 38
which functions as a moving electrical contact, normally
spaced from a stationary lbut adjustable) contact 39
screwed into the housing member 31. A further ordinary
coil spring 40 ls compressed between the cap 38 and the
housing member 31.
The two elements 23 and 24 are identical in manufacture
and, as has been indicated, their -tendency when heated
through the relevant transformation temperture range is to
expand in a part-conical form. Element 23 is mounted with
its outer turn fixed in position by spacer 26 and is
arranged to expand upwards so that its central part carries
the moulding 27 upwards when such expansion occurs.
Element 24 is mounted in opposition to element 23 with its
outer turn fixed in position by spacer 26 and is arranged
to expand downwards so that its central part carries the
moulding 32 downwards when such expansion occurs. As will
be appreciated, the axial position of the rod 36 and cap
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38 is determine~ by the po.sition of ihe central part of the
element 23, the cap 38 being moved to close the electrical
con-tact gap between itself and contact 39 when -the element
23 has expanded through a predetermined distance.
Element 23 is in heat conductive relationship with the
sheath 25 so that temperature fluctuations occurring in the
region where the detector is sited are very quickly
transmitted -to that element. The element 24 is, however,
relatively isolated from temperature changes outside the
detector and its own temperature will not rise so rapidly
as that of element 23 when a detectable rate of increase in
ambient temperature occurs. It will be noted, though, that
element 24 is biased towards its flat condition by the load
in spring 33, whereas element 23 is biased towards its flat
condition by both the load in spring 33 and the load in
spring 40. The net effect of these measures in that when
the detector is subject to a rate of temperature increase
to which it is intended to react, although the element 23
heats up more rapidly than element 24, element 24 begins to
expand before element 23, because the element 23 must
overcome a greater biasing load before the force generated
by its crystallographic transformation results in any
change of shape. Of course, the expansion of element 24
itself adds further to the biasing load on element 23 by
compression of the spring 33 and the extent to which the
expansion of element 24 delays expansion of element 23
through the distance required to close the contacts 38/39
is a function of the temperature difference between the two
elements. By this means the device can be arranged to
exhibit the characteristics specified for a "rate of rise"
type of fire detector as previously indicated.
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In addition, to ensure that the device reacts appropriatelyto a specified maximum ambient temperature under "static"
conditions a nut 41 is threaded on to the end of the stem
34, wllich nut comes into abutment with the platform 30 to
prevent further expansion of element 24 after it has moved
through a predetermined distance and thereby limits the
bias applied to element 23 by element 24. Calibration of
the device as appropriate for its "rate o rise" and
"static" response can be achi~ved by adjusting the position
of the contact 39 in the housing member 31 and adjusting
the position of the nut 41 along the stem 34,
respectively.
The detector of Figure 5 has much in common with the
embodiment of Figure 2 and once again makes use o two
separate SME elements which are capable of undergoing a
transformation between a flat spiral form and an e,~panded
part-coni.cal form. In this case, however, the low and
high-temperature forms of the elements are reversed so
that, as shown in the Figure, at temperatures below the
transformation range the two elements 42 and 43 are in the
part-conical form. In the illustrated condition of the
device the lower element 42 is held in contact with a
thermally conductive sheath 44 of complementary shape, by a
plastics spacer ring 45 engaging its outermost turn and by
a plastics moulding 46 held in the centre of the element.
The upper element 43 is held against a platform 47 and
complementary backing member 48 by the spacer ring ~5
engaging its outermost turn and by a plastics moulding 49
held in the centre of the element. The mouldings 46 and 49
are each provided with a circumferential series of inclined
fingers 46A and 49A which support the respective elements
42/43 internally.
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The moulding 49 has an inteyral .stem part 50 which is
slidably borne in the platform 47. Also provided are a
spring 51, rod 52, cap, 53, contact 54, further spring 55
and nut 56, functionally equivalent to the components
33,36,38,39,40 and 41 respectively of the Figure 2
detector. The operation of this detector is therefore
completely analgous to that of the Figure 2 embodiment, in
ths case the SME elements 42 and 43 tending to con-tract
towards the flat form to displace the respective mouldings
46 and 49 when heated through the transformation range.
In any of the above-described embodiments the thermally-
conductive sheath 18, 25 or a4 may be fluted (eg as
indicated at 44A in Figure 5) or otherwise augmented (eg
with one or more fins as indicated at 44B in Figure 5) to
increase the surface area of the sheath available for heat-
collection from the environment. As a further modification,
the various biasing springs in any embodiment may have
negative rates such that the electrical contact gap is
closed by a snap action rather than the more progressive
action which ccurs with positive rate springs.
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