Improvements in Electric Clocks.
Year: 1891

page_text: COMPLETE SPECIFICATION.
Improvements in Electric Clocks.
I, HENRY SMITH PRENTISS, of 1264 Waverly Place, North Elizabeth, in the
County of Union and State of New Jersey, in the United States of America,
Mechanical 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 has reference to electric or electro mechanical clocks, and to
synchronizers for the same, and it consists essentially in combining with a series of
secondary clocks, a primary clock or a transmitter having an incorporated
synchronizing device for sending repeated impulses through the secondary clocks
at the expiration of the synchronizing period.
The primary clock, or transmitter, is provided with a main circuit closer through
which the circuit of the main line is closed at determinated intervals to actuate the
secondary clocks, and with means for switching the current through the synchronizing
line at a certain predetermined time before the expiration of the synchronizing
period. Each secondary clock embodies a switch, which dependent on the time
indicated by the clock, either iestablishes the circuit through the clock to receive
the impulses sent through the synchronizing line prior to the expiration of the
synchronizing period, to receive the same and also part or all of the impulses of the
synchronizing circuit closer, or it cuts the clock out of the circuit to lose part, or all,
of the impulses sent through the synchronizing line prior to the expiration of the
synchronizing period and also the impulses sent by the synchronizing circuit closer.
In practice the main line circuit is broken at the main switch and closed through
the synchronizing line five minutes in advance of the hour, or the expiration of the
synchronizing period, whereby all the hands of the clocks continue to be advanced
as before, with the exception of those which may be fast, which latter lose part or
all of the impulses. At the end of each hour, or the expiration of the synchronizing
period, the synchronizing circuit closer is permitted to operate, and repeated
impulses are sent through the synchronizing line. Such of the clocks as may be
slow receive these impulses and their hands are advanced until brought to the correct
time, provided the error does not exceed certain limits such as may be correct lose
all the synchronizing impulses, and those which may be, or may have been fast,
besides losing part, or all of the impulses sent through the synchronizing line before
the expiration of the synchronizing period, lose also the synchronizing impulses at the
termination of the synchronizing period.
My invention furthermore embodies certain details in construction of the clocks,
the arrangement of circuits, and the synchronizing devices and switches, all of which
is more fully pointed out in the following Specification and claims and illustrated in
the accompanying drawings in which
Figure 1 represents a face view of a transmitter provided with my improved
synchronizing circuit closer and switch.
Figure 2 is a side view thereof.
Figure 3 is a face view of the transmitter, showing the synchronizing circuit
closer in a different position from that shown in Figure 1.
Figure 4 is a face view of a secondary clock embodying my invention.
Figure 5 is a diagram illustrating the electrical connections, all the clocks being
here shown as indicating the correct time.
Figure 6 is a similar diagram, some of the clocks however being slow and others
fast.
Figure 7 is an elevation showing the connection of the transmitter with the
primary clock.

page_text: Figure 8 is an elevation illustrating the arrangement of the clocks in the relay
system.
Similar letters indicate corresponding parts.
In these drawings, I have shown my invention applied to electro-mechanical clocks,
in which the movements are normally held out of action, and released periodically
to move the hands through a space corresponding to the time elapsed, however, I do
not wish to restrict myself to the use of the synchronizing device to this particular
class of clocks, as it can be equally well applied to purely electrical clocks.
Referring at present to Figures 1 and 2, the letter A designates the frame of the
transmitter T, said frame being provided with suitable bearings for the several parts
of a train constituting a usual form of clock-movement, of which B is the main
spring and a the first or great wheel.
This latter wheel is ultimately connected through the train of wheels with a
pinion. rigidly mounted upon an arbor e, upon which latter is secured to turn there-
with a scape-wheel c, formed with a number of radial arms d. d d and d³ provided
near their outer terminals with laterally projecting teeth 1, 2, 3, and 4.
These teeth are adapted to be successively engaged in the rotation of the scape-
wheel by the pallets 5 and 6 of a pallet lever D arranged to vibrate about a pivot
the motion of said pallet lever being limited, in either direction, by contact with
suitable stops, such as e and f. The pallets 5 and 6 of the pallet lever, it will be
noticed, are arranged in different vertical and horizontal planes. Referring to
Figure 1, the pallet lever is normally held against the stope by the pressure of a
spring g', in which position of the pallet lever the upper pallet 5 thereon is in the
proper position to cross the path of the teeth on the scape-wheel and to prevent the
rotation of the latter by engagement with the upper portion of one of its teeth, say
tooth 1, consequently the train is held out of action. If now the pallet lever D is
turned about its pivot in the direction of the arrow (Figure 1) tooth 1 is released
from pallet 5 and the scape-wheel can turn in the direction of the arrow marked
thereon.
The pallet lever now being against stop the pallet 6 thereon is in the proper
plane to engage with the lower edge of tooth 1, consequently the scape-wheel at
this stage rotates only through a very small arc, when its motion is arrested by
pallet 6. The pallet lever now returning to its normal position against stop e,
pallet 6 releases tooth 1 and the scape-wheel completes a quarter of a revolution,
whereupon its motion is arrested by engagement of its tooth 2 with pallet 5 of the
pallet lever.
The proportions of the train in this example are such that for each quarter of a
revolution of the scape-wheel, the hands move over a space on the dial corre-
sponding to one minute of time.
The release of the transmitter movement can be effected by various means, for
instance by its connection with a master or primary clock P by the rod F which
depresses the pallet lever D once a minute, as shown in Figure 7. The rod D is
engaged by a cam or eccentric on the scape-wheel arbor. The lower end of the
rod rests in a socket formed in a screw on the pallet lever D, which screw is
locked after adjustment by the nut i.
C
The circuit closer of the transmitter consists preferably of a contact wheel G
and a brush H, the former being connected by gears and with the arbor c of
the scape-wheel, said gears being so proportioned that the contact is closed once
for each quarter of a revolution of the scape-wheel, that is to say, once every
minute.
On the arbor E of the minute hand m is rigidly mounted a disc I provided
with two projections or pins 7 and 8 arranged on opposite sides thereof. The. pin
is adapted, in the rotation of the disc, to engage with one end of a swinging arm
or lever pivotted at a to the frame.
This arm or lever, which shall hereafter term the synchronizing circuit closer,
can swing freely about its pivot and when not engaged by the pin 7 hangs in an
approximately perpendicular position. On the hub of the lever, to one side of the

page_text: centre line, is formed a contact o, opposite to which and extending past the same,
is arranged a spring contact arm K, secured to a suitable post p, insulated from the
frame of the transmitter.
In the rotation of the disc 1 in the direction of the arrow Figure 1, the pin once
in each rotation engages with the synchronizing circuit closer and gradually turns
it about its pivot until it reaches the position shown in Figure 3, whereupon in the
further rotation of the disc, the circuit closer is released. The impulse thereby
imparted to the circuit closer causes repeated vibrations of the same and for each
oscillation the circuit is closed once at the contact o and contact K.
The pin 8 on the opposite side of the disc I is arranged to engage with one arm
of a lever or switch L, pivotted at 7 to the frame, and provided at its lower end
with a contact or brush playing between two stationary contacts s. insulated
from the frame. A spring bearing against the switch normally holds the contact
against the contacts, when however the pin 8 engages with the switch it is turned
about its pivot to bring the contact r against contact s¹. The pin coming opposite
a notched portion of the lever permits the same to fall back to its normal
position.
It will be noticed that the contact of the switch L is brought into contact
with the contact s' at some time before the hour, or the expiration of the
synchronizing period, and in practice I make this contact preferably at least five
minutes before the hour, for a reason to be subsequently explained.
The secondary clock S, referring to Figure 4, is identical in construction to the
transmitter as far as the train and escapement devices are concerned, with the
exception that the pallet lever D is provided with an armature m', in juxtaposition
with which is arranged an electro-magnet M, which attracts said armature when-
ever one of its bobbins is vitalized.
A
On the arbor of the minute hand m, is rigidly mounted a cam I which. engages
with a switch L, pirotted at 7 to the frame and provided at its lower end with a
contact or brush playing between two contacts insulated from the frame.
spring bearing against the switch holds the same against the cam. While the
upper end of the switch is in contact with the elevated portion of the cam, the
contact is in engagement with contact, when however said switch is in engage-
ment with the depressed portion of the cam, the contact is in engagement with
contact s². It will be noticed that approximately one half of the cam l' is elevated
and one half depressed so that for one half an hour the contact is in engagement
with the contact 83 and for the same time it is in engagement with contact s³.
It now remains to describe the arrangement of the circuits and the operation of
the synchronizing device.
In Figure 5, I have shown the clocks arranged in a series, T being the primary
clock or transmitter, G H the circuit closer, S, S1 and S2 the several secondary
clocks, B✶ the battery or other source of electricity, and M, M and M² the
respective electro-magnets embodied in the secondary clocks.
These electro magnets may he double wound i.e. covered with a coil cach of the
main line and synchronizing line, or as shown in this drawing one coil of the
magnet is connected with the main line and one with the synchronizing line.
The connections of the transmitter or primary clock are as follows:
One pole of battery B is connected by wire 10 with the contact o of synchro-
nizing circuit closer J, from thence a wire 11 connects with the disc G of circuit
closer G H, from H a wire 13 leads to the contact of the main switch L and
contacts thereof is connected by wire 12 with the coil m² of the electro
magnets M M' M², 12* being the return wire to the opposite pole of the
battery.
The synchronizing circuit is as follows:
The contacts of main switch L is connected by a wire 14 with the contact
of switch lever L' of secondary clock S, wire 15 connects contact K with wire 14,
wire 16 connects contact s³ of switch L with one end of the coil m³ of electro
magnet M, wire 17 connects the opposite end of the coil with contact of switch L

page_text: on clock S¹, the contact of said switch being connected with one end of the coil m³
of electro-magnet M' by wire 18.
The opposite end of said coil is connected by wire 19 with contact of switch L³
on clock S. The contact s of clock S is similarly connected by wire 20 to coil m³
of clock S, the opposite end of said coil being connected by wire 21 with the
return wire 12*.
"
The contacts, sandy are connected respectively with wires 17, 19, and 21 by
wires 22, 23, and 24, suitable resistances R, R and R2 being interposed to balance
the line in case any one of the clocks is cut out.
During the main part of the hour the switch L is in a position to close the
circuit at contact s. The impulses now pass through the main line wire as
follows:
From one pole of the battery, over wires 10 and 11 to contact G, contact H,
wire 13, contact of the main switch, contacts through the coils m² of the electro-
magnets M, M and M², wire 12* to the battery thereby advancing the hands of
the clocks by one minute for each impulse.
When however the hands of the primary clock or transmitter are within five
minutes of the hour or expiration of the synchronizing period, the pin 8 engages
the main switch and throws it into the position shown in Figure 5, consequently the
circuit is now closed through the synchronizing line as follows :-
From one pole of battery B* over wires 10 and 11, contacts GH, wire 13,
contact, contact s', wire 14, contact r, stop s³, wire 16, coil m³, of electro-magnet M,
wire 17, contact, contact 3, wire 18, coil m³ of electro-magnet. M', wire 19, to
contact, contact 7, wire 20, coil m³ of electro-magnet M2, wire 21, and through
return wire 12 to the opposite pole of battery, thereby releasing the train of the
secondary clocks once each minute as before.
At the termination of the hour or the synchronizing period, the synchronizing
circuit closer drops, and repeated electrical impulses are sent into the synchronizing
line.
The clocks all being correct in Figure 5, the switches L', 12 and L³ at the ter-
mination of the hour or synchronizing period, will be in position to bring
contacts, and into engagement with contacts and consequently all
the impulses sent by the synchronizing circuit closer J, will be lost, .e. passed
through the resistances R, R and R².
slow and clock S² as
In Figure 6 have shown the clock S correct, clock S
having been fast by 6 minutes. The time on the primary clock is shown within
one minute of the hour, consequently the current will pass through the circuit as
follows Battery B, wires 10 and 11, contacts G, H, wire 13, contacts and s¹,
wire 14, contacts and, wire 16, coil ³ of electro-magnet M, thereby bringing
the clock S to the hour, whereupon its switch is turned to bring contact against
contacts, from the coil m³ the current passes over wire 17, contacts 23, wire 18,
coil of electro-magnet M', to advance the hands of the clock S¹ by one minute;
from coil m³ of electro magnet M' the current passes over wire 19, contacts, 50,
resistance R², wires 24 and 21 to return wire 12* and to the battery, consequently
the clock S is cut out of the circuit another minute. At the hour, or the expira-
tion of the synchronizing period, the synchronizing circuit closer is released and
the circuit is now closed as follows: Battery B*, over wire 10, contacts o, K, wires 15
and 14, resistance R¹, wire 22, wire 17, contacts 2, wire 18, coil m³ of electro-
magnet M', thereby advancing the hands of clock S' one minute and bringing it to
the correct time, whereupon the switch L² breaks contact at and closes it at st.
From the coil m³ of electro-magnet M', the current passes over wire 19, contacts
and s, resistance R2, wires 24, 21 and 12*, back to the battery. The next impulse
sent by the synchronizing device will be lost to, all the clocks. It will be
noticed that clock S has remained out of action for five minutes and is still onc
minute fast.
At the next period, it will be cut out of synchronizing circuit for one impulse
and then resume action.

page_text: It is evident that the circuit could be closed through the synchronizing line ten
or more minutes in advance of the expiration of the synchronizing period, however,
five minutes in advance is sufficient for all practical purposes.
I do not wish to restrict myself to the gravitating synchronizing device herein
described, as it is evident that a spring could be substituted to repeatedly close the
circuit.
In practice I have found that the synchronizing lever makes from three to five
vibrations at each release, so that an error of three to five minutes can be rectified
at the lapse of each synchronizing period.
In Figure 8 I have shown the secondary clocks (the synchronizing devices being
omitted) arranged in a relay system 13* and B representing the batteries. The
secondary clocks with the exception of the terminal clock are each provided with
a circuit closer G, H or GH. When the circuit is closed by the circuit
closer G, H, of the transmitter, the current passes from B* over wire 1, wheel G,
brush H, wire 3, through magnet M³ of clock S, over wire 2 back to battery B*.
The circuit closer G H of clock S, closes the circuit of battery B', over wire 4,
wheel G, brush H', wire 6, clectro-magnet M' and wire 5 back to B₁ to actuate
clock S which in turn actuates the next clock etc., to the terminal clock.
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. In an electric clock system, a switch actuated at determined intervals to break
the connection at the main line and to close it through a synchronizing line in
combination with a series of switches, one for each clock for throwing such
clocks into or out of the synchronizing line.
2. A primary clock or transmitter provided with a main circuit closer, a main
switch and a synchronizing circuit closer automatically set into operation' at deter-
minated intervals by the clock or transmitter.
3. In an electric clock system a switch actuated at determined intervals to break
the connection at the main line and to close it through a synchronizing line, and a
synchronizing circuit closer adapted to repeatedly close the circuit through the
synchronizing line at the expiration of the synchronizing period.
4. In an electric clock system a synchronizing circuit closer adapted to repeatedly
close the circuit through the synchronizing line at determinate intervals, in
combination with switches for throwing the respective clocks into or out of the
circuit.
5. In an electric clock system, a primary clock (or transmitter) provided with a
main circuit closer, a synchronizing circuit closer and a main switch, in combination
with a series of secondary clocks each provided with a switch to throw its respective
clock into or out of the synchronizing line, a battery, and electrical connections.
6: A primary clock (or transmitter) provided with a switch for closing the
circuit through the synchronizing line in advance of the synchronizing period.
7. A primary clock (or transmitter) provided with a switch for closing the circuit
through the synchronizing line in advance of the synchronizing period, in combi-
nation with a circuit closer thrown into action at the expiration of the synchronizing
period.
8. A primary clock (or transmitter) provided with means for closing the circuit
through the main line, a switch for breaking said circuit and closing it through a
synchronizing line, in combination with a circuit closer thrown into action at the
expiration of the synchronizing period to send repeated impulses through the
synchronizing line.
9. A circuit closer consisting of the pendulous lever J, combined with contacts o
and k.
10. A circuit closer consisting of the pendulous lever J, combined with the
contacts o and, and disc I engaging with said lever.
11. A clock provided with a main circuit closer, a switch and a synchronizing

page_text: circuit closer, in combination with the disc I for actuating the switch and releasing
the synchronizing circuit closer.
12. In combination with a primary clock or transmitter, a circuit closer consisting
of a vibratory arm or lever released, at determined intervals by the clock for
repeatedly making contact, and a flexible contact arranged to be engaged by said
arm or lever, in its vibrations.
13. A secondary electric clock provided with a doubly wound magnet, or two
separate magnets acting upon a common armature and respectively connected with
the main line and the synchronizing line, and a switch adapted to close the circuit
through the clock or to cut the clock out of the circuit..
14. In an electric clock system two electric circuits, a series of electric clocks
connected with the two circuits, a switch for closing the current through either
circuit and means whereby the clocks are advanced by the passage of the current
through either circuit.
15. In an electric clock system, two electric circuits, a series of electric clocks
connected with the two circuits, means whereby the clocks are advanced by the
passage of the current through either circuit, and means actuated by the clocks to
throw said clocks out of one of the circuits.
16. In an electric clock system two electric circuits, two magnets arranged to
act upon a common armature and connected independently with the two circuits,
or a doubly wound magnet similarly connected, whereby the passage of the current
through either circuit or through both circuits at the same time will produce an
equivalent effect upon the armature.
17. In combination with a transmitter, its escapement wheel and pallet lever, a
primary clock provided with a cam or eccentric, a rod connecting the pallet lever
of the transmitter with the eccentric of the primary clock and means for adjust-
ment between the rod and the pallet lever.
18. In an electric clock system, a series of secondary clocks provided with circuit
closers actuated by the respective trains, a generator of electricity, a series of relay
batteries, and electrical connections whereby one clock closes the circuit through
the next succeeding clock.
19. In an electric clock system, a transmitter provided with a circuit closer, a
primary clock having one of its moving parts in operative mechanical connection
with the pallet lever of the transmitter, a series of secondary clocks provided with
circuit closers, a generator of electricity, a series of relay batteries and electrical
connections.
20. In an electric clock, a scape wheel, a spring pressed pallet lever engaging
the same and playing between suitable stops, and means for vibrating the pallet
lever.
Dated May 20th 1891.
HENRY SMITH PRENTISS.
By Harris & Mills,
23, Southampton Buildings, London, W.C., Agents.