US2298785A - Starting switch - Google Patents

Description

Oct.13, 1942. w OOK 2,298,785

STARTING SWITCH Filed Sept. 27, 1941 Inventor: Leonard W. Cook,

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Patented Oct. 13, 1942 s'mn'rmc. swl'rcn Leonard W. Cook, -Fairfield, Conn, asslgnor to General Electric Company, a corporation of New York Application September 21, 1941, Serial No. 412,531

5 Claims.

My invention relates to switches for starting electric discharge devices.

A well known form of starting switch for discharge devices, such as fluorescent lamps, which require a preheating of their electrodes has its contacts connected in a shunt circuit across the lamp and in series with the electrodes, the contact actuating means being also in the same series circuit. If the lamp fails to start the first time the contacts open the circuit they automatically close again and reopen, the switch continuing to go through successive starting cycles in its effort to start the lamp. In the event that the lamp is defective or may become so in use due, for example, to a leak in the envelope thereof, the successive efforts of the switch to start the lamp may produce a flickering thereof which is very annoying to a person using the lamp. Moreover if the condition is allowed to continue indefinitely the switch and lamp ballast may be damaged.

It is the object of my invention to provide an improved starting switch which if used with a defective lamp will reduce the annoyance of the flickering of the lamp and also the liability of damage to the switch and to the lamp ballast.

In accordance with my invention I have constructed .a starting switch which after a few unsuccessful efforts to start the lamp have been made will materially reduce the frequency of subsequent starting efforts.

My invention will be better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

Referring to the drawing, Fig. 1 is a cross sectional view of one embodiment of my invention; Fig. 2 is a circuit diagram thereof and Fig. 3 is a view similar to Fig. 1 showing a modification.

As shown in Fig. 2, the switch I comprising my invention is adapted to be connected between the electrodes 2 of the discharge lamp 3 such as a fluorescent lamp so that before the switch starts the discharge in the lamp it controls the heating of the electrodes in a well known manner. The lamp is shown connected with a source of supply 4 of alternating current which for example may be a 60 cycle, 115 volt lighting circuit, the connections including the control switch 5 and the ballast reactor 6. The lamp may be of the usual tubular form comprising the glass envelope 1 containing mercury vapor at low pressure and having the inner walls coated with a suitable phosphor which under the influence of an electric discharge through the mercury vapor produces fluorescence. The lamp electrodes are shown of filamentary form and may comprise a. suitable refractory metal such as tungsten wire wound in a helix and coated with a suitable electron emitting material such as barium oxide or strontium oxide.

As shown by Fig. l, the switch I comprises the insulating base 9 secured to which is the metal cap Ill having the heat insulating lining I l which cap forms with the base a dust-tight heat confining enclosure for the operating elements of the switch. The thermal member l2 having relatively high heat storage capacity, shown as a bimetallic strip, has one end secured to the base by the terminal l3 and at the other end carries the contact l4. This member is constructed and arranged to bend in a direction away from the cooperating contact to be described later, that is, in the direction of the small arrow in response to an increase in its temperature. The resilient member 16 such, for example, as a phosphor bronze spring has one end secured to the base by the terminal I! and at the other end carries the contact III which is adapted to cooperate with the contact ll. The tension in the member 16 is such that it tends to hold its contact I8 out of engagement with the contact ll. Secured to the member ii at a point intermediate its length is the insulating block I! which, for example, may be porcelain having a notch in its upper face. Looped through this notch is the resistance conductor 20 which, for example, may be Nichrome wire, the ends of which are connected with the base terminals 2|. At ordinary room temperatures the tension of the loop 20 is sufficient to overcome the tension of the member l6 and to hold the contact l8 in engagement with the contact ll. When a current is passed through the loop 20 sufficient to raise its temperature'materially the elongation of the loop due to-the expansion of the material thereof permits the member ii to separate its contact l8 from the contact ll. It is to. be noted that the loop 20 constitutes both a heater and a member responsive to heat produced therein and being of filamentary form has a relatively low heat storage capacity. The action is therefore rapid requiring, for example, only 2 or 3 seconds. Connected across the contacts of the switch is the usual capacitor 22.

Referring now to the operation of the thermal starting switch I, when the control switch 5 is closed to energize the apparatus current flows in a series circuit through the ballast reactor 6, the loop 20, the lamp electrodes 2 and the switch I. This current quickly raises the temperature of the electrodes to the point of electron emission.

By the time their temperature has reached that point or soon thereafter, the loop in has been heated by the same heating current to such a degree that the resulting elongation of the loop has permitted the member 56 to withdraw its contact 3 from the contact M. Presumably the lamp then starts and thereafter the current taken by the lamp in passing through the loop 20 is enclosure l and hence the temperature of the member l2 thereby causing it to move its contact it in a direction away from the cooperating contact l8. Since the heating of the thermal member 52 lags behind the heating of the air within the enclosure the contact It on the member i2 is carried somewhat beyond the limit of movement of the cooperating contact 58 as the loop cools in which position of the contacts the switch is open. The contacts remain separated until by the gradual cooling of the interior of the enclosure the contact id is moved into engagement with the contact it. The switch will again endeavor to start its lamp but after a few more unsuccessful attempts have been made the member l2 will again withdraw its contact so as to hold the switch temporarily in open circuit position thus repeating the cycle. From the above it will be seen that in the event of a defective lamp the switch does not continue to make rapid successive attempts to start the lamp but rather after making a few unsuccessful attempts will cease further efforts for a time, then after making a few more efiorts will cease again. Thus, there are intervals of starting activity followed by intervals of inactivity, the relative lengths of the active and inactive intervals depending upon the particular design.

While I have shown and described the various elements of the switch arranged within a dust excluding, heat confining enclosure, I may in some cases dispense with the means for heat insulating the enclosure and may even dispense ,with the use of any enclosure. In that case the heating of the thermal member l2 will be limited substantially to the heat radiated to it from the loop 20 during its successive periods of energization.

In the modified form of my invention shown in Fig. 3 the contact I 8 is'supported and moved by the thermal member 24, shown as a bimetallic strip, which member has a high heat sensitivity and at normal room temperatures holds its con= tact l8 in firm engagement with the contact M. The strip at one end is secured to the base by the terminal I! and at the other end supports the contact l8. Heat is supplied to this member by the resistance heater 25 which preferably is arranged in a loop formed in the member as shown by the drawing, the heater being connected between the two terminals 2|. In this form of my invention I have shown the switch mechanism mounted in a modified form of enclosure which comprises the insulating dust exs eaves tary bottom in which is secured the terminals it and ii] and having the spring disk iii; closing the top. The apparatus comprising this modification operates in substantially the same manher as that shown in Fig. l. The therma member 24: at ordinary room temperatures h ds its contact it in firm engagement with the contact id. During the electrode preheating interval the current traversing the heater 25 heats the mem= ber 24 causing it to withdraw its contact 88 from the contact .86 thereby opening the switch which remains open due to the lamp current in the heater 25. If the lamp cannot be started after a few operations of the switch the thermal member 62 having a low heat sensitivity becomes surficiently heated indirectly by heat originating in the heater 2% to withdraw its contact 66% away from the contact it as already described abovein connection with the form shown by Fig. 1.

I have shown the particular embodiment described above "as illustrative of my invention and it will be apparent that various modifications may be made without departing fromthe spirit and scope of my invention which modifications I aim to cover by the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. A thermal switch comprising 'a plurality of normally closed cooperating contacts, a resistance heater comected in a series circuit therewith, means responsive to said heater for separating said contacts whereby the switch undergoes cycles of alternately opening and closing said circuit, and means comprising a member constructed to have high heat storage capacity and arranged to receive heat from said heater for interrupting said cycles in response to heat received by it from the heater and accumulated in it after a plurality of successive energizations of the heater.

2. A thermal switch comprising a plurality of normally closed cooperating contacts, a resisteluding, heat retaining housing In having a unirating said contacts whereby they alternately open and close said circuit and a, thermal device including a member having high heat storage capacity responsive to heat accumulated therein from a plurality of operations of saidheater to lock said switch temporarily in open circuit position.

3. A thermal switch comprising a plurality of normally closed cooperating contacts, a resistance heater connected in a series circuit therewith, means responsive to said heater for moving one of said contacts away from the other contact whereby said circuit is alternately opened and closed, a thermal device, and heat confining means enclosing said thermal device and said heater, said thermal device being responsive to heat accumulated within said heat confining means from a plurality of successive operations of said heater for moving said other contact in a direction away from said one contact.

4. A starting switch for an electric discharge device comprising a plurality of cooperating contacts, a resilient member tending to move one of said contacts away from the other contact, a resistance conductor connected in series with said contacts and arranged to restrain said movement of said one contact, a thermal member and a dust excluding, heat confining enclosure for all of said parts, said thermal memberbeing responsive to heat produced by said resistance conductor and confined by said enclosure for moving said other contact in a direction away from said one contact.

5. A thermal switch including a heat confining enclosure, switch elements therein comprising a plurality of normally closed cooperating contacts, a resistance heater connected in a series circuit therewith, means having a high heat sensitivity responsive to said heater for moving one of said contacts away from the other contact to open said circuit, and means having a low heat sensitivity responsive to heat accumulated in said enclosure for moving said other contact in a direction away from said one contact.

LEONARD W. COOK.

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