An Improved Method of and Means for Working Electric Fire-alarms.
Year: 1895

page_text: Date of Application, 27th July, 1895-Accepted, 14th Sept., 1895
COMPLETE SPECIFICATION.
An Improved Method of and Means for Working Electric
Fire-alarms.
I, JOHANNES ANDREAS BAKKER, of 11, Kenaupark, Haarlem, in the Kingdom
of the Netherlands, Mechanician, do hereby declare the nature of this invention
and in what manner the same is to be performed to be particularly described and
ascertained in and by the following statement:-
This invention relates to electric fire-alarm apparatus in which an alarm bell is
sounded, or warning given, upon two metal strips or two tubes of unequal trans-
verse section being exposed to a sudden increase of temperature, the differential
expansion resulting affecting the equilibrium of a steelyard which in turn controls
an electric circuit.
In the accompanying drawings, I have illustrated apparatus adapted for carrying
my invention into effect; Fig. 1 being a vertical section, Fig. 2 an elevation, and
Fig. 3 a corresponding plan.
Fig. 4 is a similar view to Fig. 3, but with the arm or steelyard removed.
Figs. 5 and 6 are details showing the mode of arranging the knife-edge centres
whereon the arm is balanced.
Apparatus constructed in accordance with this invention comprises an outer
tube A and an inner tube B; the transverse section of the metal whereof the
former is composed being considerably less than that of the latter. The outer
tube is perforated and is supported on a pedestal C attached to the base board D ;
the inner tube B being mounted on a central stud E arranged within the pedestal.
The outer tube is furnished at its upper extremity with an internal ring a provided
with radial arms a' which are arranged so that they barely touch the circumference
of the tube B; the said arms a¹ serving to preserve the concentricity of the tubes
when expansion takes place under the influence of a sudden rise in temperature.
From a ring a, surrounding the outer extremity of the tube A, project the arms a³
provided with bearings for receiving the knife-edge centres f of the balance arm or
steelyard F; the inner tube B being furnished with a pointed extremity 6 which
normally bears against the arm F. At the lower extremity of the pendent
portion F1 of the balance arm or steelyard is a contact piece c, which may be of
platinum, and so arranged that, on the arm being put in equilibrium, the said
contact piece c will be brought against another platinum contact piece d, carried
by the flexible metal strip e. This strip is supported on a bracket g attached to
the base board D, and its relation to the extremity of the pendent arm F' may be
regulated by means of the adjusting screw h. The arm F of the steelyard should
be of such a weight as to establish an equilibrium.
To the terminal i is connected one wire of an electric battery or other source
of supply, while the other wire is attached to the terminal 3; an alarm bell or
other means of warning being placed in the circuit.
The action of the apparatus is as follows:- -Upon a sudden rise in temperature
occurring, the tube A, by reason of the metal of which it is composed being thinner
than that of the tube B, expands more quickly than the tube B, and raises the
arm F to a slight degree, in which position it becomes less supported by the
point b; with the result that the arm or steelyard F F' is put in equilibrium.
The swinging of the arm F causes electrical contact to be made at c, d, whereupon
the circuit is closed and the alarm bell sounded.

page_text: When the increase in the temperature is slow, the tubes expand almost simul-
taneously. Under such circumstances, the closing of the circuit is not effected.
It will therefore be seen that the apparatus only becomes operative on exposure to
a sudden increase of temperature.
The perforations in the outer tube are for the purpose of admitting air to the
space between the two concentric tubes.
When two tubes are employed, the one enclosed within the other, as illustrated
in the present design, it will be apparent that the desired effect results to a great
extent from the fact that the outer tube, being exposed, is more quickly affected
by a sudden change of temperature in the surrounding atmosphere; the inner tube
being, for the moment, protected from such influence. I would, therefore, have it
known that, although I have described my invention as dependent for its operation
on the differential expansion which takes place between two strips of different
sectional area, or tubes of different thickness, I do not regard the action of my
apparatus as necessarily dependent solely on differential expansion due to such
conditions. When one tube or body is exposed and the other shielded, equivalent
results may be brought about with bodies of equal or unequal sectional area.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, I claim :-
1
1. The method of operating electric fire-alarms, substantially as herein described,
and consisting in utilizing the differential expansion resulting from the exposure of
two strips or tubes of metal of different susceptibility to a sudden increase of
temperature, the equilibrium of a steelyard or balance arm being affected, an
electric circuit completed and an alarm sounded.
2. The improved means for operating electric fire-alarms, arranged substantially
as described with reference to the accompanying drawings; the same comprising
two tubes and a balance arm connected with the said tubes in such a manner that,
upon their being subjected to differential expansion, the arm vibrates, closes an
electric circuit and gives an alarm.
3. In fire-alarm apparatus of the type herein referred to, the combination with
two tubes A, B, of unequal transverse section, or unequally exposed to change of
temperature, of a balance arm or steelyard F F', the pendent portion F' of the
said arm or steelyard carrying a contact maker c for making electrical contact
with an adjustable strip or spring e, substantially as and for the purpose set
forth.
Dated the oath th FT 1 1005