US2274399A - Starting switch - Google Patents

Description

Feb 24, 1942. L. w, COOK 2,214,399

STARTING SWITCH I Filed Sept. 20, 1941 His Attorney Patented Feb. 24, 1942 UNITED STATES PATENT OFFICE STARTING SWITCH Leonard W. Cook, Stratford, Conn., assignor to General Electric Company, a corporation of New York Application September 20, 1941, Serial No. 411,607

7 Claims.

site ends with thermionic electrodes of filamen tary form which after the lamp has been connected with the source of current supply and prior to the starting of the discharge in the lamp have their temperature raised to the point of electron emission by current passed through them in series. When the temperature of the electrodes has reached that point the circuit is interrupted between'them automatically 'by a switch whereby a surge of suflicient voltage is produced across the lamp to start the discharge therein.

In the event that the lamp employed is defective and will not start due, for example, to a loss of emission of its electrodes or to a contamination of its gaseous filling such as would result from a leak in the envelope the switch will make repeated efiorts to start the lamp. The sight of a flickering lamp such as one undergoing repeated unsuccessful attempts to get it started soon becomes annoying to most people. Moreover, if this condition is allowed to continue it may result in the overheating of the lamp ballast and in the injury or the destruction of the switch.

Under certain conditions where the starting switch employed is of the glow discharge type it sometimes happens that even though the lamp is started, the initial voltage across the lamp after it has started is sufficient to cause a repeated re-functioning oi the glow switch resulting in a flickering of the lamp.

One object of my invention is the provision of an improved starting switch which, it used with a defective lamp or if the lamp becomes defective with use, will, after making a number of unsuccessful attempts to start the lamp, thereafter cease making any further attempts. Another object of my invention is the provision of a starting switch which, should conditions be such as to cause it to make successive repetitions of its starting cycle even though the lamp has been started and is still operable, will cease such repetitions after it has made a few unsuccessful efforts to start the lamp.

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 shows one form of my invention connected with a discharge lamp of the fluorescent type, and Figs. 2 and 3 show modified forms of my invention.

As represented in Fig. 1, the switch i comprising my invention is adapted to be connected between the electrodes 2 of the discharge lamp 3 so that before it 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 cycle, 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 2 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.

The switch I comprises the evacuated envelope 9 which contains a suitable gas, such as neon or argon, in which an electric discharge will be produced between electrodes under the proper voltage and pressure conditions. Supported by the press of the envelope are the two electrodes or thermal members I0 and II both of which bend in the same direction with a rise in temperature and of which the former has a higher sensitivity to heat than the latter. This difference in sensitivity may be effected by so constructing the two members that they have different masses thereby changing the thermal characteristics of the members so as to give them different rates of temperature rise from a given source of heat. In Fig. l, for example, the member H is constructed of thicker material than the member In whereby the temperature of the member l0 rises faster from the heat of the discharge than does the member II. In addition, the amount of deflection ofthe thinner member ID will be greater than that of the thicker member II when the two members are at the same temperature. These thermal members are represented as being bimetallic strips attached at their lower ends to the terminal leads l2 and I3 which extend through and are embedded in the press. The cooperating contacts l4 and I5 are secured thereto at their upper ends. The spacing between the members and H is such that at the voltage which appears between them when the lamp is thrown on the circuit and before it starts and at the gas pressure employed in the switch a glow discharge will be produced between the members. The heat produced by this glow discharge causes the members l and H to bend in the same direction, that is, to the right as shown by the two small arrows. Preferably the members I0 and II are coated with a suitable material such as zinc to facilitate the production of the glow discharge. Movement of the member I!) and the contact carried thereby under the influence of the heat of the glow discharge is limited by the restraining member or stop 16. This member may, for example, bea rod or wire anchored in the press of the switch envelope. Its position is such that initially it has no eii'ect upon the movement of contact [4 into engagement with contact I5 but after the member H has become appreciably bent due to the heat of the glow discharge the lighter member III will be restrained in its movement and hence the contact M will no longer engage the contact I5.

The apparatus operates as follows: When the control switch 5 is closed to energize the lamp a small current initially flows through the switch 5, the ballast 6, the two lamp electrodes 2, and between the thermal members l0 and II producing a glow discharge. The effect of th heat of that discharge is to cause the free ends of those members to bend in the same direction, that is, to the right as shown. Inasmuch as the member i0 is of lighter construction and hence is more sensitive than the member II, the contact I quickly engages the contact l5. Thus a low resistance circuit is completed through the lamp electrodes which have their temperature quickly raised to the point of electron emission. By the time this has occurred, the thermal member ID will have cooled inasmuch as the glow discharge is short-circuited by the switch contacts so that the switch opens the circuit and the resulting voltage surge starts the lamp.

Should the lamp be defective for any reason or become so while in use for a reason such as that mentioned above, or should the lamp start and the arc drop voltage, namely, the voltage across the lamp when operating, be sufficiently high to cause the glow discharge between the switch members l0 and II to continue after the lamp has started, the switch would continue to go through its starting cycles until the main switch is opened or the lamp is removed provided the switch is not destroyed in the meantime. A switch such as I have shown and described above will make a few starting attempts but a continued cycling of the switch is prevented by the bending of the heavier thermal member I l away from the lighter member In to a point where the restraining member I6 no longer permits the contacts of the switch to engage each other. The

member II i maintained in this bent position with its contact out of the range of movement of the contact It by the heat of the glow discharge between the two members l0 and l l, the switch being said to be lockedopen. If in the event that the switch continues to go through its starting cycles due to the fact that the voltage across the lamp after it has started is sufllcient to produce a glow discharge between the thermal members of the switch which at the instant of starting have the minimum separation, then the bending of the member H may so increase the distance between the two members that the glow discharge is extinguished and the switch remains open.

In the modified form of my invention shown by Fig. 2 heating of the thermal members l0 and H is produced by a small high resistance heater II which is shown arranged between the two thermal members with its ends connected thereto. Inasmuch as in this form there is no need of having the thermal members enclosed in a sealed envelope, I have shown them supported on the insulating base l8 and connected with the terminals l9 thereon. A suitable cap 20 fits the base and forms therewith a dust-tight enclosure for the switch. The two thermal members may, if desired, be like those in Fig. 1 but in this form of my invention I have shown the member H as having a light construction like the member Ill and I give it greater mass so as to have greater heat storage capacity by securing to it the metallic block 2|, which block for convenience serves as the connection between the member and the corresponding terminal. Greater sensitivity may be given to one of two identical thermal members by simply locating the heater Il closer to the one member than to the other, an arrangement also illustrated in Fig. 2. Moreover, a difierence in sensitivity may be produced'by shielding the member which it is desired to be the less sensitive from the heater. This also is illustrated in Fig. 2 where the stop I6 is in the form of a strip of insulation arranged to serve the double function of stop and shield.

In Fig. 3 the thermal members In and l l are like those shown in Fig. 1 in that one is constructed of thicker material than the other. Each member has a resistance heater 23 wound about it, the two heaters and the resistor 24 being connected in series between the members. Instead of using thermal members of difierent mass I may use identical member and heat the member H with a heater of lower capacity tham that used to heat the member Ill.

The forms shown in Figs. 2 and 3 function in a somewhat similar manner to that shown by Fig. 1 in that the two thermal members are heated by current flowing through the lamp electrodes causing the switch to close and thereby provide a low resistance path for the heating current through the lamp electrodes. The switch soon after opens as a result of the cooling of the thermal members. If, as in the case of the switch shown in Fig. 1, the lamp is or becomes defective, the switch after making a number of unsuccessful attempts to start the lamp by closing and opening the circuit will cease such efforts and be automatically locked open. In the case of the form of my invention illustrated by Fig. 2, the rise in temperature of the thermal member ll due to the successive heating of the heater ll causes that member to move its contact out of the range of movement of the contact carried by the thermal member Ill whose movement is arrested by the stop [6. That form of my invention illustrated by Fig. 3 where the thermal members [0 and II are provided with separate heaters 23 functions in the same manner as that illustrated by Fig. 2.

I have chosen the particular embodiment described above as illustrative of my invention, and it will be apparent that various modifications may be made without departing from the 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 pair of normally spaced cooperating contacts, means providing'a current conducting path shunting said contacts, means responsive to heat produced by current in said path for moving one of said contacts into engagement with the other contact, means for restraining the movement of said one contact beyond a predetermined point, and means responsive to said heat to a lower degree than said heat responsive means for moving said other contact away from said one contact.

2. A thermal switch comprising a pair of normally spaced cooperating contacts, means proaway from the other contact is slower to respond I to the energization of the heater than the other strip, and a strip arranged to engage said other viding a current conducting path shunting said contacts, a thermal member for moving each of said contacts in the same direction in response to heat produced by current in said path, the thermal member which movesits contact away from the other contact being less sensitive to said heat than the other thermal member, and means for restraining the movement oi the contact moved by said other thermal member beyond a predetermined point. I

3. A starting switch for an electric discharge device comprising a pair of normally spaced cooperating contacts, means providing a current conducting path shunting said contacts, a plurality of bimetallic strips each having one of said contacts secured at one end thereof, said strips being constructed to move their contacts substantially in the same direction in response to heat produced by current in said path, the strip which moves its contact toward the other contact being the more sensitive to said heat, and a stop for limiting the movement of the more sensitive strip beyond a predetermined point.

4. A starting switch for an electric discharge device comprising a support, a plurality of bimetallic strips secured thereto at one end and having cooperating contacts carried by their free ends, a resistance heater connected between said strips, the construction and arrangement being such that the strips move their contacts in the same direction in response to heat from said heaterand the strip which moves its contact strip after the contact thereof has moved to a position to engage the other contact.

5.'A starting switch for an electric discharge device comprising a pair of normally spaced cooperating contacts, means providing a current conducting path shunting said contacts, means responsive to heat produced by currentin said path for moving one of said contacts into engagement with the other contact whereby said contacts alternately engage and disengage each other, and means responsive to the heat accumulated during a plurality of successive intervals of current flow in said path for terminating further functioning of said contact moving means.

6. A starting switch for an electric discharge device comprising a pair of normally spaced c0- operating contacts, means providing a current conducting path shunting said contacts, means responsive to heat produced by current in said path for moving one of said contacts into engagement with the other contact whereby said contacts alternately engage and disengage each other, and means responsive to the heat accumulated during a plurality of successive intervals of heat production for moving the other of said contacts out of the range of movement of said first contact.

7. A starting switch for an electric discharge device comprising a support, a plurality of bimetallic strips secured thereto at one end and having cooperating contacts carried by their free ends, a resistance heater connected between said strips and being in better thermal relation with the strip which moves its contact toward the other contact than with the other strip, said strips being constructed and arranged to move in the same direction in response to heat from said heater, ands stop for limiting the movement of the strip having the better thermal relae tion with the heater.

LEONARD W. COOK.

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