Improvements in Electric Thermostatic Fire Alarms.
Year: 1894

page_text: Date of Application, 9th Oct., 1894-Accepted, 10th Nov., 1894
COMPLETE SPECIFICATION.
Improvements in Electric Thermostatic Fire Alarms.
I LEWIS GARWOOD ROWAND of 112 Federal Street in the City and County of
Camden State of New Jersey one of the United States of America Electrical
Engineer 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 :-
My invention relates to certain improvements in thermostats employed for
opening or closing an electric circuit of fire alarm systems and a method of
attaching the conducting wires thereto, its main object being to construct a
thermostat of simple character which will have all its working parts protected and
not liable to derangement, and which may be readily readjusted in position after
the sounding of an alarm.
In the accompanying drawings:
Figure is a sectional view of a thermostat constructed in accordance with my
invention and shewing it situated in the wall or ceiling of a room to be protected.
Figure 2 is a substantially similar view showing the position of the parts after
the thermostat has acted :—
Figure 3 is a detached perspective view of the working portions of the device.
Figures 4 and 5 are views of details.
Figure 6 is a diagram illustrating the main and house circuits :-
Figure 7 illustrates certain features of my invention as applied to a circuit
connecting thermostat having a modified form of contact device; and
Figure 8 illustrates the same form of thermostat adapted to disconnect the
circuits.
In automatic fire signalling systems such as now commonly employed in large
buildings it is desirable to employ thermostats which may operate to close or open
an electric circuit when the temperature of tho room is raised to a dangerous
degree by fire, and many devices have heretofore been constructed for this purpose,
but in all of this class with which I am familiar, the thermostats are usually placed
upon the walls or ceiling of the room in such manner that they may be tampered
with, and, being situated entirely outside the line of the wall or ceiling, are
unsightly, and detract from the appearance of the compartment.
In that form of my improved thermostat which is shown in Figures 1 and 2,
therefore, I arrange the body of the thermostat within the wall or ceiling, in such
manner that the cap or head only will be visible, and this cap or head may be
ornamented in any desired manner, or may be sunk flush with the line of the wall
or ceiling and be coloured in the same manner as the wall or ceiling itself.
Referring to the accompanying drawing A represents a tubular casing of
non-conducting material, preferably circular in form, and adapted to be placed in
& recess, in the wall or ceiling of the room so that only the end portionia will be
exposed, and this end portion a may project from the line of the wall, as shewn in
Figure 1, or it may be placed in a counter-sunk recess so that its end is flush
with the wall or ceiling as shewn in Figure 2.
The opposite end of the casing is provided with an internal thread & to which is
adapted the threaded periphery of a plug B of rubber, vulcanized fibre or other
suitable material and through this plug extend binding posts X, Y, terminating. at
the opposite end of the plug in contact points cd which are preferably conical
in form.
which
At a short distance above the end a of the casing A is a shoulder e on
!

page_text: H
rests a disc Eaving a central opening through which passesta rod G, one end y
of the said rod being of rectangular (or equivalent) form and passing through
similarly shaped opening in the centre of the plug B, while its opposite end is
threaded to receive a nut H the outer end of which is slotted at hand is secured
by fusible solder to a disc I of a diameter somewhat greater than the opening i in
the end a of the casing, through which opening the nut H normally projects, as
shewn in Figure 1, the disc I being soldered to the nut on the outside of the cusing.
The upper portion of the rod G is of somewhat greater diameter than its lower
portion and forms a shoulder on which rests a contact plate & of German silver or
similar conducting metal, and between the plate k and the disc E is a coiled,
spring m encircling the rod G and tending at all times to force the plate k into
contact with the contact points and d, this movement, however, being normally
prevented by the engagement of the disc I with the exterior of the casing, so that
it is only on the rising of the temperature of the room and the consequent fusion
of the solder which unites the dise I to the nut H that the spring m is permitted
to move the plate into contact with the contact points and establish a
circuit.
With a construction of thermostat such as above described the parts may be
readily coupled together and after the thermostat has acted it is simply necessary
to unscrew from the end of the rod G the nut H, this operation being simplified by
the employment of the transverse slot in the end of the nut in which a screw
driver may be inserted, the opposite end of the rod G being held from rotating by
its rectangular end g engaging with the rectangular opening in the plug B. A new
nut H with its attached disc I is then screwed onto the threaded end of the rod and
to facilitate the operation I propose to drill or punch two openings n (see Figure 5)
in the disc and employ a tool such as N baving two projecting pins adapted to
engage with the openings to screw the new nut and disc in place.
A further feature of my invention consists in the method of attaching the
conducting wires to the biuding posts of the thermostat. Usually the wires are
run in pairs all through the system and' at each thermostat a single wire from each
line extends to the binding post.
In carrying out my invention a represents the energized main line and y'a
normally non-energized house line.
On reference to the diagram of circuits shewn in Figure 6 it will be seen that
the terminals of the energized main line circuit æ are connected to the opposite
poles of the battery or other generator of electricity which is represented at W;
one of the poles of the generator being also grounded.
The unenergised house line circuit y is closed and grounded and a local alarm or
signal instrument is introduced into the circuit as represented at V, a central station
test or sigual instrument W' being in the main line circuit.
The thermostats are represented at T situated between the main and house lines
so that the closing of the contact devices of either of the thermostats will result in
the energizing of the house line circuit and the sounding of the alarm instrument V.
In Figure 71 have illustrated my invention as embodied in an exposed circuit
Connecting thermostat having two spring plates c and d serving as contacts in
place of the terminals c d and spring plate of the thermostat shewn in Figure 1.
The plate c' has a loops which engages with the hooked end of a screw rod G',
the latter engaging with a nut H' which is united by fusible solder to a cap or disc I¹
occupying a recess in the face of the casing A!.
The main feature of novelty in this thermostat irrespective of the circuits, is the
shoulder w which serves as a back stop for the contact spring c¹ and prevents the
latter from being sprung back to such an extent, in setting the thermostat, as to
become permanently bent, so that it might fail to come into contact with the
plate when released.
In circuit disconnecting thermostats this shoulder or stop may be formed by one
of the contacts as shewn for instance in Figure 8, the spring plate d'in' such
case being dispensed with.

page_text: Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
1. The described system of wiring electric thermostats, said system comprising a
closed and borinally energized main line circuit connected to one of the terminals
of the thermostat, and a closed and normally unenergised house line circuit
connected to the other terminal of the thermostat, whereby the circuit closing
devices of the thermostat unite the closed main and house circuits and cause the
energizing of the latter by the former substantially as hereinbefore described.
2. The herein described concealed thermostat, comprising a casing let into the
wall or ceiling and having at the inner end a pair of contacts, a spring pressed rod
guided in the said casing so that it cannot turn therein and carrying a circuit
closing plate, a nut adapted to the threaded outer end of the said rod, and a cap or
disc united to the said nut by fusible solder, and bearing against the outer portion
of the casing, substantially as herein before described.
3. A thermostat having a screw-rod, adjusting nut, and fusibly soldered capior
disc combined with a pair of circuit connecting or disconnecting contacts, and a
stop for preventing one of the said contacts from being drawn back so far as to
impair its elasticity substantially as herein before described and shewn in Figures 7-
and 8 of the accompanying drawings.
Dated this 9th day of October 1894.
JOHNSONS & WILLCOX,
47, Lincoln's Inn Fields, Agents.