Improvements in Telephones and in the Application thereof to Railway Signalling.
Year: 1892

page_text: Date of Application, 25th Oct., 1892
Complete Specification Left, 24th July, 1893-Accepted, 25th Jan., 1894
PROVISIONAL SPECIFICATION.
Improvements in Telephones and in the Application thereof to
Railway Signalling.
1, CHARLES LANGDON-DAVIES, of 45 Redcliffe Square, South Kensington,
London, Electrician, do hereby declare the nature of this invention to be as
follows:-
For signalling on railways, block signalling instruments and circuits are in
common use. These block telegraph lines are very short and of low resistance,
seldom exceeding say 1,000 ohms.
Now without interfering with the block signalling instruments these block
telegraph lines may be made available also for telephonic communication by the
use of telephone instruments constructed in a novel manner namely with the coils
which are in the secondary or line circuit, of wire made of an alloy which offers
high resistance to the passage of the electric current instead of, as heretofore, of
copper, one of the best of the conductors.
In this way I make instruments having a resistance in the secondary or line
circuit amounting to 15,000 to 20,000 ohms, more or less.
Telephone instruments thus constructed will work with block signal instruments
in a derived circuit through the same line wire without injuriously interfering with
or suffering interference from the block signalling instruments.
Telephone instruments constructed as I have described are very distinct in their
articulation and are useful for other purposes besides that of working in conjunction
with block signalling instruments.
Dated this 25th day of October 1892.
Improvements in Telephones and in the Application thereof to
Railway Signalling.
I, CHARLES LANGDON-DAVIES, of 45 Redcliffe Square, South Kensington,
London, Electrician, 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 :-
For signalling on railways, block signalling instruments and circuits are in
common use. These block telegraph lines are very short and of low resistance,
seldom exceeding say 1,000 ohms.
Now without interfering with the block signalling instruments these block
telegraph lines may be made available also for telephonic communication by the
use of telephone instruments constructed in a novel manner namely with the coils
which are in the secondary or line circuit, of wire made of an alloy which offers
high resistance to the passage of the electric current instead of, as heretofore, of
copper, one of the best of the conductors.
Platinoid is an alloy which is suitable for this purpose.
The induction coil of a microphone, of an ordinary small size, is say 40 to
45 millimetres between the flanges, and its secondary coil, when wound in the
usual way of ordinary copper wire, has a resistance of say 300 ohms. I substitute
for this coil a similar secondary coil of platinoid wire of 004" diameter; this
LD

page_text: without varying to any appreciable extent the depth of the coil would give a
resistance of about 12,000 ohms. Coils of larger size such as are usually used for
longer circuits can be wound in this way to have twice or three times the resistance
named. The telephone receivers may if desired be also wound of the same wire,
and would then have a resistance of from 2000 to 4000 ohms each.
In this way I make instruments having a resistance in the secondary or line
circuit amounting to 15,000 to 20,000 ohms, more or less.
Telephone instruments thus constructed will work with block signal instruments
in a derived circuit through the same line wire without injuriously interfering with
or suffering interference from the block signalling instruments.
The mode of installation on a three wire block service is shewn by the annexed
drawing.
a is the up line block signal instrument, a' is its line wire and a² its earth
connection.
bis the corresponding down line instrument, the line wire and the earth
connection.
c is the bell, it has a separate line wire and other usual arrangements.
The terminals of my telephone are connected to the line terminals of the block
instruments at d d without disturbing any of the connections of the block
instruments.
e, e, are telephone receivers. fis the high resistance secondary of the microphone
coil. The primary microphone circuit may be arranged in any usual manner. As
a call the block bell may be used without alteration, employing a prearranged
number of shakes at the telephone call. If desired an additional push or key may
be placed near the telephone for this purpose, or other arrangements for calling
may be made.
In cases where there are not two block signal line wires available a single block
signal line wire may be used, the telephone secondary coil then having an earth
connection.
Telephone instruments constructed as I have described are very distinct in their
articulation and are useful for other purposes besides that of working in conjunction
with block signalling instruments.
They have an important advantage in reducing the noise in the telephone of the
induced currents from telegraph and other signals passing near.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
1. The combination substantially as described of block signal instruments and
telephone instruments having coils of high resistance alloy on the same line wires.
2. Telephone transmitters substantially as described having the coils in the
secondary circuit of high resistance alloy.
Dated this 24th day of Tul.. 1000
C. LANGDON-DAVIES.