US2372148A - Starting control for electric discharge devices - Google Patents

Description

March 20, 1945 J. R. WHITESIDE 2,372,148

STARTING CONTROL FOR ELECTRIC DISCHARGE DEVICES Filed Dec. 10, 1941 Z3 5 L J 23 H InvenTor: Jack R.Whi+eside, by .M

' His At'torneg.

Patented Mar. 20, 1945 STARTING CONTR DISCHARG L FOR ELECTRIC E DEVICES Jack R. Whiteside, East Cleveland, Ohio, asslg'nor to General Electric Company, a corporation of New York Application December 10, 1941, Serial No. 422,416 7 Claims. (Cl. 315100) This invention relates to the control of electric discharge devices, and is especially concerned with the starting of such devices. The invention is very useful in connection with fluorescent tubes or lamps of the positive column discharge type, and

is hereinafter explained with particular reference to lamps of this character and their usual starting arrangements-as exemplified in U. S. Patent 1,951,112, March 13, 1934, to Wels, or Patent 2,212,427, August 20, 1940, to Peters, for instance. Ordinary tubular fluorescent lamps have electrical starting circuits which are energized and broken to start the discharge. Sometimes this has to be done several times before the discharge actually starts. For this purpose, automatic means are commonly provided which will make and break the starting circuit indefinitely until a starting is accomplished.

Through deterioration in service or as the result of accident, fluorescent lamps and other discharge devices often or eventually become incapable of starting and normal running, so that the only effect of the automatic eflorts to start such a lamp is a continual flashing in it that is very annoying to those in the area that receives. the light of the flashing lamp, besides uselessly wearmay result from dissipation or other loss of activating material on which the emission depends. The objectionable flashing of such a lamp goes on indefinitely, until the power supply is shut off, or the lamp is removed from the circuit.

, The purpose of my invention is to obviate the tion of the starting circuit as to continuity either in the negative sense or in the positive sense. I have chosen this latter method for purposes of illustrative description herein, and have shown and explained the invention as applied to a double thermal switch type of starter.

Various features and advantages of the invention will become apparent from the description of one species and form of embodiment, and from the drawing.

In the drawing, Fig. 1 is a diagrammatic view or a fluorescent tube or lamp with circuit connec tions including myinvention, a mid-portion of velope walls is also electrode-heating circuit H is shown connected the lamp envelope being broken out and omitted; and Fig. 2 is a tilted or perspective view of one form of starting switch device.

I will first describe the portion of the circuits and apparatus shown which have heretofore been in use, and which permit the objectionable flash ing of a defective lamp as described above.

Fig. 1 shows an ordinary fluorescent tube lamp L of the positive column electric discharge type with a tubular envelope if! having spaced apart activated thermionic cathodes H, il in its ends, which may be specially heated cathodes of usual coiled filament type, and are shown connected across a power-supply circuit; P including the usual ballast H, which also serves as a starting inductance, and the manual make-and-break switch The envelope l0 may contain a low-pressure atmosphere of starting gas, such as argon at a pressure of 2 to 5 mm. of mercury, and also a vaporizabie and ionizable working substance such as mercury. A supply of mercury, which may exceed the amount that will vaporize during operation of the lamp L, is indicated by a drop I! inside the enveldpe i0, and an internal coating of fluorescent material or phosphor 58 on the enindicated. A starting and across the circuit P through the filamentary cathodes H, il, with a starting switch S included therein, which may be of thermal type. A caidoi suitable capacity (e. g.,

13.05 microfarad) may be connected across the switch S, to minimize radio interference as well as arcing vwhen the switch S opens and breaks the circuit H. a

The general mode of operation in starting the lamp L with this circuit arrangement is that when the switch i5 is closed to turn on the lamp L, the switch device S permits flow of current through the circuit H and the cathode filaments H, H in series therein for a sufiicient length of time to preheat the cathodes to an adequate emissive temperature, and then suddenly opens the circuit H; and the resulting voltage kick between the cathodes I I, H suflices to initiate discharge between them-or, in other words, starts the lamp.

As shown in Figs. 1 and 2, the switch device S is a thermal switch of so-called four-terminal or four-lead type, and may comprise as its base" a hollow glass stem 20 through which are sealed the four current leads-2|, 22, 23, 24. The switch leads 2|, 22 are connected to opposite sides of the starting circuit H and to the switch members 25, 26 that coact in making and breaking the circuit H. For convenience, these switch members 2i, H (as of coin silver wire) are shown welded to the upper free ends of the members 25, 26. For reasons that will appear hereinafter, the

members 25, 26 are preferably bent in the peculiar A Fig. 2, first sharply and retheir points of anchorage then upward in a semi- Adjacent the manner illustrated in versely downward near on the leads 22, 23, and circular are of greater radius. thermostat members adjacent the member 25, and about concentric with its bend 28) is a resistance heater 29 that is connected between the leads 23, 2d of the current supply and discharge circuit P leading to the discharge electrodes Ii, ll, so as to respond to the energization and current flow in this circuit. Thus this heater 29 is heated by the cathode-pre heating current before the lamp L starts, and by the discharge current after the lamp starts. In other words, heater 29 and its associated thermostat 25 are always heated by and responsive to current flow in the discharge circuit P. In Fig. 1, the parts of switch S are shown in their normal positions for a cold start of the lamp L. I

The general cold start operation of such a switch S (as thus far described and as heretofore constructed) would be that when the circuits P and H are energized as a result of closing the hand switch l5, current flows in both circuits, heating not only the cathodes ll, i l, but also the thermostat member 25, until these members bend and separate, opening the circuit H and starting the discharge between the electrodes ii, If. Thereafter, the circuit H is kept open by the influence of the heater the discharge current flows through this heater. However, if the discharge fails to start on the voltage kick due to this opening of the circuit H by the switch S,- there is no longer any current flow in the open-circuited heater 29, so that the members 25, 26 coollofi, and the switch S closes and 25, 26 (but more immediately 29 on the member 25, since terior surface of this heater then repeats the same starting cycle or effort,

just as before; and if this effort is not successful in starting the main discharge, it is again repeated-and so on. If the main discharge cannot be started at all, the lamp L would (with the circuit arrangement and parts so far described) go on to flash in the objectionable manner referred to above.

In accordance with my invention, means of control are provided for determining the condition of the circuit H as to continuity in such a way that after reasonable efforts of the starter S to start the main discharge, a condition of circuit H that prevents flashing of the lamp L is established and maintained, independent and regardless of any further action or operation of starter S-indeed, the ordinary operation of starter S For this purpose, automatic control means may be employed whose period of operation (as fixed by design and adjustment) is long enough to include whatever number of attempts by starter S may be considered reasonably worth-whlle-a g., a period of about a minute under favorable voltage conditions, embracact/area ing some five to ten attempts, say. The action of this automatic control need not be an arbitrary matter of fixed adjustment, however, but can be made responsive to the actual attempts of starter S to start the main discharge. As already mentioned, the particular control here illustrated determines the continuity of the circuit H in the positive sense-by closing it-in order to prevent continued flashing or blinking of the lamp.

A simple control for this purpose is shown in Figs. 1 and 2 as effected by cumulative or progressive heating and movement of the thermostat members 25, 2t. These members 25, 25 are arranged to flex in the same direction (to the left in Fig. 1, but to the right in Fig. 2) when heated,

instead of oppositely, as in some starters of double bimetal strip type; an additional heater 3c is provided more immediately adjacent the thermostat member 26 (as shown, about concentric with its bend28) and a contact 3! is arranged in the path of heat-responsive movement of one of the members 25, 26, and is connected by a conductor wire 32 to the same side of the circuit H as the other of the members 25, 26. In the present instance, this contact 3i is arranged in the path of the first thermostat member 25, and its lead 32 is connected to the lead 22. The heater 3!! is shown connected to be responsive to energization of the starting circuit H, between the leads 2|, 22, and thus in shunt with the members 25, 2B of switch S. The heater 29, through which the discharge current flows, is preferably of low resistance, such as 3 ohms, in order to minimize its energy consumption; the heater 30, which is subject to thehigh ballast-output voltage when the switch S opens, is preferably of very high resistance, such as 100,000 ohms, for example, in order to prevent it from materially lowering the voltage available for starting the discharge when the switch S opens. When closed, the switch S effectually shorts out the heater 30; so that the latter only heats while the switch is open, either on'the attempts of the switch S to start the discharge in the lamp L, or while the latter is in operation. Any suitable provisions may be made to-cause the heater 30 to heat the second thermostat 25 rather slowly, such as blackening the ex- I and brightly polishing that of the member 25. The heater 30 may also be lagged or otherwise constructed to conserve its heat, so as to cool ofi but rather slowly.

In starting a good inbefore described functions essentially in the usual manner-very much as if the heater 30 were absent, and the member 26 were a mere fixed contact. Even though several operating cycles of the starter S should occur beforethe lamp I.- actually starts, the heater 30 and the thermostatic properties of the member 26 do not radically aflectthe action of the starter. There is, nevertheless, this difference: as the heater 29 and the member 25 gradually heat up more and more with successive efforts to start the discharge, so, likewise, do the heater 30 and the member 26; so that the ranges of movement of these members 25, 26 in the attempts to start gradually shift over toward the contact 3|. The actual amplitude of motion of the member 25 in successive starting efforts gradually diminishes, and the recycling time of the switch therefore decreases.

In the case of a defective lamp, likewise, the

I cumulation of heat incident to the continual and oft-repeated interruption of the circuit H causes the member lamp L, the starter S here- 25 to flex and move progressively toand of chrome iron, an alloy of 75 aware-a self performing in a similar manner, flexing and moving progressively in the same direction, away from the member 26, as heat accumulates in it. Hence each futile starting effort takes place with the members 25, 26 further and further over toward the contact 3|. When the member 25 (or the projecting upper end or its contact 21) touches this contact 3|, the switch S and the heater 30 are short-circuited or shunted out, so that this heater and the member 26 cool off, and the starting efforts of switch S are suspended; but current continues to flow through the start ing circuit H and the heater 29, thus keeping the member 25 against the contact 3i and maintaining the closed condition of the circuit H, so that s the lamp cathodes I I, H glow continuously and steadily. Thus the switch S locks in, so to speak.

However, if the circuit H is de-energized (by opening the hand switch IE, or by removing the defective lamp L and replacing it with a good one), and is allowed to remain de-energized long enough for the heater 29 and the members 25, 26 to cool oh. fully, the shunt at the contact 3! will be opened, the members 25, 26 will come together in their normal cold-starting position shown in Fig. 1, and the starter S will again be ready to start the lamp in the usual manner.

The switch device S offers a number of possibilities for design and adjustment to secure just 3 the action desired. For example, the temperature-resistance coeflicient of the heater 3E influences the period available for efforts to start the discharge before the member 25 engages the contact 3i and thus locks in, as above described; and it may be found desirable to employ a heater 3i! of negative temperature-resistance coefiicient in order to reduce this period to a desirable brevity. The device operates satisfactorily in the air; but its recycling time may be reduced (with some concomitant reduction of the voltage kick for starting) by providing a proper atmosphere in a suitable envelope, such as hydrogen or helium; or the recycling time may be increased by enclosing the switch in a total or partial vacuum.

For the convenience of those wishin to use my invention, illustrative particulars of a device such as shown in Fig. 2 are given:

The thermostatic members 25, 28 may be strips of the bimetal known commercially as Chace #2400 Bimetal, composed of laminae of invar, an alloy of 64 per cent iron and-36 per cent nickel, per cent iron,

22 per cent nickel, and 3 per cent chromium, in equal thicknesses, welded together. Each of the strips may be 0.006 inch thick, /8 inch wide, and 22 mm. long before being bent. The lengths of their lower straight portions to which the leads 2!, 22 are welded maybe 4 and the radii of their semi-circular bends 28 may be 1 /4 mm. on The horizontal distance apart of the portions to which the leads 24 '22 are attached may be 9 mm. The contacts 21, 2'! may be of 40 mil coin silver wire. The initial contact pressure between these parts 27, 2? when the switch is cold is adjusted to give just a quite adequate time for preheating of the lamp cathode ll, H, without danger of closing of the switch S on low service voltages and currents after starting has been effected. The gap between the contact 3| and the contact 7 27 of the member 25 when the switch is'cold may be 7 mm. The heater 29 may be a helical coil of' about 11 turns or 6.3 mil nichrome wire wound on a. 40. mil mandrel. The heater 3!! may be a solid rod of'high resistance material 1; inch in diam- 3 eter and inch long, showing a resistance of 100,000 ohms under a voltage of volts-=-sucl1 as the material commercially known as Glo ar BNR.

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

l. The combination with a discharge device having a discharge circuit and a starting circuit shunting the latter, and an automaticstarting switch interposed in said starting circuit comprising coacting first and second switch members and means always responsive to current flow in said discharge circuit for producing progressive movement of the first switch member in a direction away from the second switch member, and thus interrupting said starting circuit to start the discharge in said device, of means responsive to repeated interruptions of said starting circuit as aforesaid for producing follow-up movement of the second switch member after the first switch member, and means in the path of movement of one of said switch members for engaging the same and coacting therewith to close the starting circuit and maintain it uninterrupted, regardless of contact or separation of said first and second switch members.

2. The combination with a discharge device having a discharge circuit and a starting circuit shunting the latter, an automatic starting switch interposed in said starting circuit comprising coacting first and second switch members respectively connected to opposite sides of said starting circuit, with an actuating thermostat for moving said first switch member to open the starting circuit to start the discharge in said device when said thermostat is heated, and a heater for said thermostat that is always heated by current flow in said discharge circuit, of a shunting contact connected to the side of said starting circuit to which said second switch member is connected and located in the path of the heat-responsive circuit-opening movement of said first switch memher, for engaging said first switch member and thus closing the starting circuit regardless of contact or separation of said first and second switch members.

3. The combination with a discharge device having a discharge circuit and a starting circuit shunting the latter, an automatic starting switch interposed in said starting circuit comprising thermostats and coacting first andsecond switch members actuated thereby and respectively connected to opposite sides of said starting circuit, said first and second switch members being closed when the thermostats are unheated and being moved in the same direction by said thermostats when the latter are heated, and a heater conheated in said discharge circuit for heating the actuating thermostat of said first switch member and thus moving said first switch member away from the second switch member to open said starting circuit to start the discharge in said device, of a heater connected across said automatic starting switch for heating the actuating thermostat of said second switch member when the starting circuit is open, and a shunting contact connected to one side of said starting circuit and located in the path of heat-responsive movement of the switch member that is connected to the other side of said starting circuit, for engaging the last-mentioned switch member and thus closing the starting circuit regardless of contact or separation of said first and second switch members.

4. The combination with a discharge device having a discharge circuit and a starting circuit shunting the latter, an automatic starting switch interposed in said starting circuit comprising thermostats and coacting first and second switch members actuated thereby which are respectively connected to opposite sides of said starting cirstart the discharge in said device, of a heater of relatively high resistance connected across said automatic starting switch for heating the actuat= ing thermostat of said second switch member when the starting circuit is open, and a shunting contact connected to the side of said starting circult to which the second switch member is connected and located in the path of heat-responslve movement of the first switch member for engaging said first switch member and thus closing the starting circuit regardless of contact or separation of said first and second switch members, besides shorting the aforesaid heater for the actuating thermostat or" said second switch member.

5. A starting switch for electric discharge devices comprising first and second contacts carried by first and second heat responsive members respectively, said members being closed when unheated and movable in the same direction when heated, a low resistance heater having means to connect it in the current supply circuit to said device and being mounted in more effective thermal relation to the first heat responsive member than to the second member to effect separation of the contacts whereby said contacts are alter-= nately opened and closed, a high resistance heater connected in shunt to the switch contacts and arranged to heat the second heat responsive mem ber upon separation of the said contacts to progressively move the second contact toward the first contact, and a third contact located in the path of movement of the first heat iesponsive member and electrically connected to the second switch contact so as to shunt the said first and second contacts when heat accumulated in the said first heat responsive member after a number of operations of the switch causes the said first member to engage said third contact.

6. In combination, an electric discharge dev'ce comprising a pair of electrodes adapted to be preheated, a source of current supply connected to said electrodes including inductive ballast means, and a starting switch comprising first and second contacts carried by first and second bimetallic strips respectively, said contacts being closed and connecting said electrodes in series when said bimetallic strips are unheated, and said strips being arranged to move their contacts in the same direction'when heated, a low resistance heater mounted adjacent the first bimetallic strip and connected in the current supply circuit-to the device, a high resistance heater mounted adjacent the second bimetallic strip and electrically con nected in shunt to said first and second contacts, and a third contact mounted in the path of movement of the first bimetallic strip and electrically connected to the second contact, the low resist ance heater being proportioned and arranged to cause the first bimetallic strip to move the first contact away from the second contact to breals the series connection between the electrodes and permit a discharge to be started therebetween,

the ballast means thereafter limiting the operating current flow to a value insufficient to cause said low resistance heater to effect movement or said first strip suflicient to carry it into engagement with the said third contact, but said ballast means permitting sufficient preheating current to flow when said first and second contacts are closed so that heat accumulated in said first bimetallic strip during a predetermined number of operations of the switch causes said first strip to engage said third contact and thereafter retain such engagement, said high resistance heater being heated by the voltage available thereacross when the device fails to start upon opening of the first and second contacts so that the second bimetallic strip moves the second contact toward the first contact to maintain a definite relative spacial relationship between said first and second contacts, but said high resistance heater being proportioned and arranged so that the voltage available thereacross when the device is operating is lnsuiilcient to cause it to movesaid second strip sufficiently to carry the second contact into engagement with the first contact.

7. In combination, an electric discharge de vice comprising a pair of electrodes adapted to be preheated, a source or current supply connected to said electrodes, and a starting switch comprising first and second contacts carried by first and second bimetallic strips respectively, said contacts being closed and connecting said electrodes in series when said bimetallic strips are unheated, and said strips being arranged to move their contacts the same direction when heated, and a third contact mounted in the path or movement of said first strip and electrically connected to the second contact, means for heating said first strip to v at noint intermediate the second and third contacts to start a discharge between the said electrodes in an operative device, but said means being proportioned and arranged to cause accumulation of heat in said first strip during successive periods of closure of the first and second contacts when the device tails to start, so that said first strip is moved suficiezitly to cause it to engage the sa d third contact, and means for heating the second bimetallic strip only upon opening or said first and second contacts suificiently to maintain a definite spacial relationship between said first and second contacts.

JACK R. WHITESIDE.

move the first, contact and maintain it

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