Improvements in Electrical Alarms.
Year: 1890

page_text: Date of Application, 28th Aug., 1890
Comolete Specification Left, 4th Nov., 1890-Accepted, 13th Dec., 1890
PROVISIONAL SPECIFICATION.
Improvements in Electrical Alarms.
We NORCLIFFE GEORGE THOMPSON of 13 Victoria Street S.W. and GEORGE HENRY
REW of 11 Crooked Lane E.C. Electrical Engineers do hereby declare the nature of
this invention to be as follows:-
Our invention is for the purpose of protecting safes, strong rooms &c. and
consists of an electrical apparatus which may be placed at any distance from the
protected room or object, & which causes an alarm to be raised if eitherthe protected
object or the wires leading to it be tampered with.
Our alarm consists of the electrical apparatus referred to which I shall here cal
the controlling instrument, a battery for generating the electric current, an electric bell
for producing the sound, & an electrical resistance & arrangement of contacts which
are placed inside the protected object. It is to the controlling instrument that my
invention is more particularly directed.
The working parts of the controlling instrument are 1st, a contact galvanometer
which by the action of its needle when deflected, completes a circuit through the
coils of an electro magnet. 2nd, a release apparatus consisting of the electro magnet
referred to, a rocking lover with an armature at one end & a catch at the other,
& an arm held in position by the catch of the rocking lever.
The action of this release apparatus is to release the arm when the armature is
pulled towards the electro magnet.
The arm when released completes by suitable contacts, the bell circuit & so
causes the bell to ring: it may also be made to break the circuit round by the
contact galvanometer, by the same action.
There are beside the working parts referred to four electrical resistances & the
arrangement of these resistances may be in either of the following ways.
First. Two of the resistances are constituted by two coils wound in opposite
directions round the needle of the contact galvanometer & forming part of it. A
third is placed inside the safe strong room or protected object, whilst the fourth is
fixed on the controlling instrument with the other working parts, & may consist of
a coil wound round a needle so as to form another galvanometer for indicating
the strength of current passing.
Second. Three of the resistances are placed on the controlling instrument & are
independent of the coil round the contact galvanometer which in this case is single.
One of these three resistances may also constitute part of a galvanometer as in the
first arrangement. The fourth resistanceis placed inside the protected object.
The action of our controlling instrument with resistances as stated in the first
arrangement is as follows. A current proceeding from a voltaic cell divides at the
two coil resistances constituting part of the contact galvanometer: a portion passing
by one coil through the resistances on the controlling instrument back to the cell,
& the other portion passing by the other coil returns by the resistance placed in the
protected object. Each portion passes through two consecutive resistances & if the
two paths have approximately the same measure of resistance there will be practically
the same amount of current passing round by each coil of the contact galvanometer.
The currents then will have no influence on the needle as the coils are wound so as
to give opposite deflections & thus neutralize each other's effect. If however an
infinite resistance be interposed into the part of the circuit passing round by the
protected object, which can be effected by opening the contacts or cutting the wires,
the balance will be disturbed, & more current will pass by one coil of the contact
galvanometer than by the other & the needle will be deflected. If likewise the
resistance referred to be thrown out by a short circuit such as would be the effect of

page_text: bridging the two wires leading to the protecting object the same result will be
arrived at but the deflection will be of opposite direction.
If the resistances be such as specified in the second arrangement, the working of our
controlling instrument will be as follows.
This
A current proceeding from a voltaic cell divides at two of the resistances fixed
on the controlling instrument; a portion of the current passes by one resistance
through the third resistance that constitures part of the galvanometer for indicating
strength of current, back to cell, & the other portion passes by the other resistance
through the resistance situated inside the protected object also back to cell
arrangement gives as in the first two paths each constituted by two separate
resistances, but the coil forming part of the contact galvanometer is in this case
introduced as a bridge between the four resistances & does not constitute a part of
them. It is evident that the resistances may be so balanced that no appreciable
current shall flow across by the contact galvanometer coil but on the principle of the
Wheatstone Bridge it follows that if the path leading by the resistance in the
protected object be either short circuited or cut out so as to throw the present
resistance out or put infinite resistance in, the balance will be disturbed & current
will flow across by the contact galvanometer in a direction dependent on the nature
of the disturbance & will deflect the needle either to the right or left as the case
may be.
From the above it will be seen that with either arrangement of resistances so long
as current is flowing by the circuits referred to, it is not possible to either cut or
short circuit the wires leading to the protected object or tamper with the protected
object itself in such a manner as to actuate the contact arrangements placed therein
without causing a deflection of the contact galvanometer needle. As soon as the
contact galvanometer needle is deflected it completes by contact a circuit on the
bell battery or cell which passes round by the electro magnet of the release apparatus.
The result of such action is to excite the aforesaid electro magnet attract the armature
& release the arm which on falling away establishes by contact a firm circuit
through the electric bell off the bell battery. The arm can be set back by a con-
veniert handle in the cover enclosing the controlling instrument & a suitable switch
is also placed outside for throwing the alarm in or out of action.
Dated this 28th day of August 1890.
N. G. THOMPSON.
G. HENRY REW.
COMPLETE SPECIFICATION.
Improvements in Electrical Alarms.
We NORCLIFFE GEORGE THOMPSON of 13 Victoria Street S.W. and GEORGE HENRY
REW of 11 Crooked Lane E.C. Electrical Engineers 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 :-
Our invention is for the purpose of protecting safes, strong rooms &c. and consists
of an electrical apparatus which may be placed at any distance from the protected
room or object & which causes an alarm to be raised if either the protected object
or the wires leading to it be tampered with.
Our alarm consists of the electrical apparatus referred to see A Figs. I & II
which we shall here call the controlling instrument, the two batteries B1 & B2 for
generating currents, an electric bell E for producing the sound & an electrical
resistance & arrangement of contacts S which are placed inside the protected room or
object. It is to the controlling instrument A that our invention is more particularly
directed.
The working parts of the controlling instrument are 1st a contact galvanometer C
(Figs. I & II) which by the action of its needle when deflected completes a circuit
through the coils of an electro magnet t forming part of the release apparatus to be
hereafter described. 2nd a release apparatus R consisting of the electro magnet t

page_text: referred to, a rocking lever with an armature atone end & a catch at the other,
& an arm a beld in position by the catch of the rocking lever. The action of the
release apparatus R is to release the arm a when the armature is pulled towards the
electro magnet t. The arm when released completes (by the forkeil contacts shown)
the circuit passing through the bell E and so causes it to ring. The same action
of the arm a also (by lifting the other fork) breaks the circuit round by the
galvanometer C.
There are besides the working parts referred to four electrical resistances & the
arrangement of these resistances may be in either of the following ways.
First. As in Fig. I. two of the resistances ₁ & r, are constituted by two coils
wound in opposite directions round the needle of the contact galvanometer C &
form part of the same, a third 3 is also placed on the controlling instrument with the
other working parts, & may consist of a coil wound round a needle so as to con-
stitute another galvanometer G for indicating the strength of current passing whilst
a fourth is placed inside the safe, strong room or protected object at S.
4
Second. As in Fig. 11. three of the resistances & are placed on the con-
trolling instrument & are independent of the coil round the galvanometer G which
in this case is wound so as to form one coil only. One of the three resistances 3 may
also constitute part of a galvanometer G as in the first arrangement. The fourth
resistance is also placed inside the protected object at S.
The action of our controlling instrument with resistances as stated in the first
arrangement, Fig. I is as follows.
When the alarm is switched on by a suitable switch placed on the cover of the
instrument, the current proceeds by wire, from the constant cell B1 to
terminal II & from thence to the coils of the galvanometer C, a portion pro-
ceeding by coil r₁ wire 3 round 13 of the galvanometer G & back by wire 3 &
terminal to the constant cell B1 & the other portion by the coil r₂ & wire 2 to
terminal III & thence by wire n resistance r₁ through the contact o & back by
wire m to the cell B 1. The resistance of the coils r₁ & r is equal to that of r₂ & r ₁
hence it follows that if the wires n m be joined together so as to form a circuit
outside the safe the resistance r, will be cut out, & the path which proceeds by coil 2
of the contact galvanometer, will have a less resistance than the path by r₁ & r₂ &
the current flowing by r, will be more powerful than that flowing by ₁ so that the
needle will be deflected. As soon as the needle makes contact with the U shaped
contact piece shown current will then proceed from the battery B 2 by terminal IV
& wire 5 across cups z & y, thence hy wire 4 through the electro magnet t, the
U shaped contact piece & needle to needle pivot & then to terminal III back to
battery B 2. The result of the current flowing in this circuit is to excite the magnet,
& pull down the rocking lever r, so releasing the arm a, & thereby opening the
circuit at the cups y && completing the circuit at cups w &c. The current now
flows from battery B 2 by terminal IV wire 5 cups & w terminal V by wire 7
through the bell back by wire 6 terminal VI wire 8 terminal III to battery B 2.
From this it will be seen that if either of the wires m n be cut or short circuited
or if the contact o be opened, a permanent bell circuit will be completed by the con-
secutive actions described & the bell will continue to ring till the arm a be set back.
If the resistances be such as specified in the second arrangement the working of our
controlling instrument will be as follows.
A current proceeding from battery B1 (Fig. II) proceeds by wire 1, terminal II
& wire 9, & then divides between the two resistances r₁ & r, a portion going_by
r, & 3, (resistance round galvanometer) wire 3 to terminal 1 back to battery B 1.
The other portion goes by ", wire 2 terminal III wire n, resistance r₁, contact o &
back by wire m to the battery B 1.
This gives as in the first arrangement two paths each consisting of two separate
resistances but the coil forming part of the contact galvanometer C is in this case
introduced as a bridge between the two paths.
It is evident that the resistances in the two paths may be so balanced that no
appreciable current will pass through the coil of the contact galvanometer so that

page_text: the needle will remain at rest. But on the principle of the Wheatstone Bridge, it
follows that if either of the four resistances constituting the two paths be altered
so as to disturb the balance, current will pass through the contact galvanometer C
& the needle will be deflected.
This balance will be disturbed if either of the wires m n he cut or short circuited,
or if the contact o be opened, as in the first arrangement, & the needle will be
deflected with the same result as herein before described.
Having now particularly described & ascertained the nature of our said inven-
tion & in what manner the same is to be performed we declare that what we
claim is
1st. The employment of balanced resistances for the purpose of actuating a con-
tact or circuit making galvanometer when the balance of such resistance is disturbed
by interference with the circuit leading to the safe or strong room as substantially
set forth & described.
2nd. The use of a release apparatus in conjunction with a circuit making galvano-
meter for the purpose of making a continuous & firm contact on the bell circuit
when the aforesaid galvanometer has been disturbed & thereby causing the bell to
continue to ring, whether the disturbing cause in the safe or strong room be
removed or not as substantially set forth & described.
Dated this 4th day of November 1890.
N. G. THOMPSON.
G. HENRY REW.