US2105599A

US2105599A - Electric clock attachment

Info

Publication number: US2105599A
Authority: US
Publication date: 1938-01-18
Anticipated expiration: 1955-01-18

Description

Jan. 18, 1938. w HYDE 2,105,599

ELECTRIC CLOCK ATTACHMENT Filed March 19, 1956 Patented Jan. 18, 1938 UNITED r STATES PATENT OFFICE ELECTRIC CLOCK ATTACHMENT Henry W. Hyde, Dedham, Application March 19, 1936, Serial No. 69,685

2 Claims.

My invention relates to secondary electric clocks and is herein embodied in an attachment for such clocks designed to keep them running when there is a failure of the main source of current.

The widespread use of secondary clocks and particularly that type of clock which is operated by a synchronous motor supplied with current from the ordinary power mains has shown that, while such clocks are on the whole extremely satisfactory, they are subject to certain weaknesses. The chief of these is the interruption of their operation when there is a failure of the main source of current and the fact that while 5 such interruptions may be of only brief duration, the accumulated error is serious if dependence is to beput on the clocks as accurate timekeepers. Such interruptions occur sometimes at the central power stations, perhaps due to the opening of circuit breakers, at other times because of the blowing of fuses inthe house circuit, and not infrequently because of carelessness in unintentionally disconnecting the clock itself from the wall receptacle. Many of the clocks in common use are not self-starting and, hence,

even a momentary interruption is enough to necessitate the restarting of the clock. In other clocks, where a considerably more expensive type of synchronous motor is employed, the stopping due to momentary interruptions is avoided and a visible indicator is provided to show that there has been such an interruption. While this avoids the inconvenience of repeatedly restarting the clock, it takes away the users confidence in the timekeeping capacity of the clock because no way is provided of showing the length of the interruption. One quite expensive and complicated arrangement has been proposed in which there is a mechanical clock movement held in reserve and automatically thrown into operation, upon failure of current, to drive the clock. This, how ever, is not very satisfactory because of the clanger that dirt will interfere with proper operation of a mechanical clock movement which is only infrequently used. It is, moreover, too costly to be popular.

.An object of my invention is to provide a simple and inexpensive attachment for employment with electric clocks by means of which the clock is kept going in spite of interruptions of. current i from the main source with the result that clocks of even simple construction become dependable timepieces.

It is well recognized that only a small amount of power is required to operate an electric clock so that even an ordinary dry cell battery-could supply such power as is needed to operate the clock infrequently during the short intervals 'of disconnection from the main source of supply, provided the current supplied by the battery was alternating instead of direct and of suitable frequency for the operation of the clock. Accordingly, the illustrated embodiment of my invention provides an attachment suitable for interposition between a main source of current and an electric clock by means .of which'an emergency source of current, such as a battery, may be employed to operate the clock.

Also, as illustrated, the attachment comprises a transformer, the primary coil of which is 10 adapted to be connected to the direct current emergency source and the secondary coil of which provides current at a higher voltage for the operation of'the electric clock, and a vibrator associated with this transformer for interrupting the connection to the direct current source, this vibrator being tuned so that the alternating currents induced in the secondary coil by this interrupted direct current are oi a frequency to keep the synchronous clock motor in step with the alternating current generator which normally supplies power to the power mains. The result is that the clock will not only stay in operation but also may be transferred from the power mains to the attachment and back again without interruption of the operation of the cloclr.

An important feature of the invention resides in a switching apparatus of novel construction made automatically responsive to the condition or" the alternating current source and arranged to close the battery circuit thereby to permit the emergency source to become effective when needed, at the same time preventing feed back from the battery to any other load on the power mains with the consequent prompt draining oi the be. tery. This switching apparatus is also effective automatically to reconnect the clock motor to the power mains as soon as power is again available.

These and other features of the invention will behest understood from a consideration of the following description, taken in connection with the accompanying drawing, in which the single figure is a diagram of the circuits and the apparatus employed. 50

In the diagram, a secondary electric clock ill is intended normally to be supplied with power from the alternating current mains l2. This clock may be and usually will be of the synchronous motor type but it is only necessary that it shall be a clock which may be operated by means of a periodic current. When the attachment is interposed between the clock and the main source of power, the clock is attached directly to and across the terminals of a secondary coil H which, together with the primary coil I5, is associated with a magnetic core l8, usually of soft iron. Cooperating with this core '18 is a spring armature 20 indicated as supported from the bracket 22 and normally biased to rest in engagement with a fixed contact 24 which is connected through a conductor 28 to one terminal of the primary coil. This contact is carried by a screw threaded in a support. The other terminal of the primary coil is connected through a conductor 28 to an emergency source oi power, such as a battery 3!, the other side of which is joined to the spring armature 2|! through a conductor 32. with this arrangement, the flow of current through the primary coil IE will be interrupted by the vibrating armature 2U, producing an alternating current in the secondary coil H which, when supplied to the electric clock ill, will operate the synchronous motor therein. It will only be necessary to tune the vibrating armature 20, as by turning the screw carrying the contact 24, so that the periodic current produced in the secondary is alternating current of the same fre quency as that which is normally supplied from the mains l2, for example, sixty cycles per second. Since this vibrator is essentially a simplified pendulum with a definite period of oscillation, functioning similarly to electrically operated tuning forks which, as is well known, hold a definite pitch, the periodicity of the alternating current supplied to the clock may be kept within limits and the same as that of the alternating current source. This being true, it will be possible to transfer the clock from the supply provided by this attachment to that provided by the alternating current system I2 without danger that the synchronous motor will fall out of step.-

Changes in frequency resulting from expansion of the vibrator armature 20 due to changes in room temperature will be negligible because the vibrator armature is so small and short.

In order that the apparatus may be rendered automatic so that on failure of the alternating current source, the vibrator will immediately be set into action, a switching device has been included. For simplicity and lowered cost of manufacture, this has been combined with the in duction coil so that the secondary coil H has a double function and the vibrator armature 20, which may be made of conductive material, serves also as a switching device.v To accomplish this result, contact Ml is provided below the armature 20 which is connected to one terminal of the secondary coil 14, while the other terminal will, through the coil i5, magnetize the core [8 and draw down the armature 20 to close the circult through the contact 40. This will immedlately allow the coil H to be energized from the alternating current circuit directly and therefore to hold the armature in its lowered position out of engagement with the contact 24. The primary circuit will thereby be opened so that there will be no flow of current from it through the coil l8 or any feed back to the alternating current circ'uit in an attempt to supply a load connected thereto by means of the small battery. So long as alternating current is supplied through the armature, the contact 40, and the coil I, it will also be supplied to the clock l0 and the latter will operate in its normal manner. If, however. there is an interruption in this supply of current, the armature 20 will spring back into position where it will engage the contact 24. The apparatus will then act as an induction coil or transformer, the armature being kept in vibration by reason of its attraction to the core I8 and its immediate release, owing to the breaking of the circuit through the primary coil ll. As a result of this action, an alternating current will be set up in the secondary coil H which will keep the clock in operation. During such vibrations, the armature 20 will repeatedly engage the lower contact 40 and as soon as power is again supplied to the coil H, the latter will be energized, holding the armature against this lower contact and breaking the circuit of the battery.

Having described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1. In an attachment adapted to be interposed between a source of alternating current and a synchronous motor electric clock, a soft iron core, primary and secondary coils on said core, a movable armature of conductive material adapted to be attracted by said core when the latter is magnetized by current fiowing in one oi said coils, fixed contact points associated with opposite sides of said armature, circuits to said fixed contact points one oi. which is connected to one side of said primary coil and the other of which is connected to one side of said secondary coil, means for connecting said clock motor across said secondary coil, means for connecting said alternating current source to said armature and the other side oi. said secondary coil, and means for connecting a direct current source to said armature and the other side of said primary coil.

2. In an attachment adapted to be interposed between a source of alternating current and a synchronous motor electric clock, a soft iron core, a spring armature of conductive material positioned to be attracted by said core when the latter is magnetized, primary and secondary coils on the core, a contact point into engagement with which said armature is biased and connected to one side of said primary coil, means for connecting a directcurrent source between said armature and the other side of said primary coil, a fixed contact point for engagement with said armature when attracted by said core and connected to one side oi. said secondary coil, means for connecting the other side of said secondary coil and said armature across said alternatin current source, and means for connecting said clock motor across said secondary ooil.

HENRY W. HYDE.