US2394436A - Starting control for electric discharge device - Google Patents

Description

Feb. 5, 1.946. T. w. FRECH 2,394,436

STARTING CONTROL FOR ELECTRIC DISCHARGE DEVICE Filed. Dec. 1'7, 1943 lnvenfov: Theodor'e W. Frech,

Patented Feb. 5, 1946 STARTING CONTROL FOR'ELECTRIC DISCHARGE DEVICE Theodore W. Frech, Cleveland, Ohio, assignor to General Electric Company, a corporation of New York Application December 17, 1943, Serial No. 514,611

, 2 Claims.

This invention relates to the control of electric discharge devices, and is especially concerned with the starting of devices having an operating atmosphere of gas or vapor, or both, and employing cathodes which are electron-emissive. Very commonly. thermionic cathodes of such devices are specially heated to produce ample emission, and particularly as a preliminary to starting the dischargefor after starting, many types of cathodes are so efiectively heated by the discharge itself that special heating becomes unnecessary, The invention is particularly useful for fluorescent tubes or lamps of the usual positive column discharge type, as well as for other discharge devices operating at relatively low internal pressure.

The ordinary type of low pressure discharge lamp has a thermionic type of cathode that is rendered freely emissive at relatively low temperatures by being coated with activating oxides such as a mixture including barium and strontium oxides-and is heated for starting by passing electric current through heating means or resistance incorporated or embodied in the oathode(s). To permit of fully effective operation on alternating current, as well as to make the device operable on direct current circuits without regard to which end of the device is connected to which side of the circuit, such thermionic cathodes are provided at both ends of the discharge device, and are connected to opposite sides of the main current supply or discharge circuit of the device. In fluorescent lamps. the cathodes commonly consist of coiled or coiled coil tungsten filaments which carry the activating material and also embody and constitute the cathodeheating resistance means. A current-limiting choke or ballast having inductance is commonly included in the discharge circuit. For starting purposes, a circuit including a switch is connected across the supply circuit through the cathodeheating means, so that while this starting switch is closed, current flows through the several cathode heating means in series. When the cathodes have thus been heated to adequate emissive temperature, the starting switch is suddenly opened, and the resulting voltage kick between the cathodes (due to the inductance in the supply circuit) suiilces to initiate discharge.

The usual switch for the starting circuit is an automatic thermal or glow switch that heats and opens in a length of time which is determ ned and fixed, by designand adjustment, to assure that the cathode(s) of any lamps of the type for which the switch is designed shall have a chance to heat to adequate electron-emissive temperature. But it is diflicult to make a simple switch of either type which need not be energized to keep it open during operation of the main discharge, and which also gives adequate time of cathode preheat-especially for a discharge lamp having relatively massive, slow-heating electrodes.

I have devised a novel starting system which overcomes these drawbacks, giving as long a preheat time as desired without the complication of heating current connections from the starter to the main discharge circuit, and without donsumption of energy by the starter during normal operation of the main discharge device. This I am able to accomplish by a novel combination of control means. Various other features and advantages of the invention will appear from the description of a species or form of embodiment, and from the drawing.

In the drawing, Fig. 1 is a diagrammatic view of a discharge tube or lamp with circuit connections and starting arrangements according to my invention; and Fig. 2 is a similar view illustratin a modification.

In Fig. 1 there is represented an ordinary iiuorescent lamp L, of the positive column electric discharge type, consisting of a tubular envelope is having spaced apart thermionic cathodes II, II in its ends, such as the specially heated activated cathodes of usual coiled filament type above described. These cathodes H, II are shown connected across a power-suppl circuit P (A, C. or D. C.) includingthe usual inductive ballast H, which also serves as a starting inductance, and the make-and-break power supply switch i5. With each cathode Ii ma be associated the us ual unemissive electrode(s) Hi, to function as anode(s) when the cathode II in question is positive. The envelope in may contain a, low-pressure atmosphere of starting gas, such as argon at a pressure of 2 to 4 mm. of mercury, and also a vaporizable and ionizable working substance such as mercury. A supply 01' mercury, which may exceed the amount that will vaporize during operation of the lamp L, is indicated by a drop I! inside the envelope I0, and an internal coating of fluorescent material or phosphor l8 on the envelope walls is also indicated. A starting and electrode-heating circuit H is shown connected across the circuit P through the filamentary cathodes Ii, Ii with the circuit-control combination S according to my invention included therein: e. g., as shown, the terminals or connectors 49, II of the control S (comprising the parts in the dot-and-dash rectangle, which represents a common casing or base for this control system or unit) are connected to opposite sides or the circuit H. I

By means of the control system S, when opens the circuit H, a high starting voltage (exceeding that of the main discharge circuit P) is impressed across the electrodes H, I to initiate the main discharge between them.

As shown in Fig. 1, the starting control system S includes a time switch T and an electromagnetic relay switch M connected in series with one another between the terminals l9, l9 and thus in the circuit H. The switch T shown is a normally closed thermal switch comprising coacting thermostatic bimetal switch and contact members or strips 2|, 22 with a resistance heater 23 in series with them for heating the member 2|, which is arranged to flex away from the member 22 when heated, and thus open the circuit H. The member 22 may be unheated and serve as a more compensator for ambient temperature variations; or it may be arranged to be also heated by the heater 23 and to flex away from the member 2|. .A capacitor or condenser 24 of suitable capacity may be connected across the switch members 2|, 22, to prevent sparking when the open and break the circuit H. The relay switch M shown is a magnetic switch comprising coacting switch and contact members 25, 26 which are normally open, with an electromagnet 21 in series with them for closing them when it is energized by current of sufficient strength flowing in the circuit H. Besides these switches T, M, the starting control S includes a current control device G of electric discharge type connected between the terminals |8, l9 and in the circuit H in parallel with the contacts 25, 25 of switch M, but in series with electromagnet 21 and with switch T.

In Fig. 1, the device G is shown as a glowlamp. This glow-lamp G has a breakdown voltage less than the supply voltage across the main discharge device L, and when in operation passes suflicient current to close the relay switch M; but whenit is shunted by discharge in the main device L, it goes out and ceases to pass currentthe voltage then applied to it being kept down by the ballast l4 and the resistance 23. A capacitor or condenser 29 of suitable capacity may be connected across the terminals I9, I! and the whole control system S, to prevent radio interference.

A mode oi operation of the system is as follows:

When the switch I is closed to start the discharge device L, the normally closed switch T allows full supply voltage across the device G, which passes current to energize and close the switch M. thus shunting out the discharge and current flow in the device G. Current continues to flow through the circuit H and the main lamp cathode(s) heating the latter and also heating the resistance 23 and one or both oi! the thermostatic members 2|, 22, until the accumulation of heat in the switch T raises the thermostat(s) to a suflicient temperatureto open the circuit H and thus start the discharge in the lamp L. When the switch T opens, the switch M also opens.

By design and adjustments, the switch I can be made to remain closed just long enough to heat the cathode(s) H, H to a proper temperature of electron emission, thus assuring prompt starting while obviating damage to the cathodes by positive ion bombardment without the full protection of adequate emission. When the switch T opens, it ceases to heat, cools oil, and recloses; so that the cycle above described will be automatically repeated if the main discharge in device L has not started on the flrst attemptand so on indefinitely until the circuit H is locked open or locked closed, or the device L is removed.

The modification illustrated in Fig. 2 consists in the substitution of a thermal glow-switch G0 for the glow-lamp G of Fig. l-such, for example, as the glow switch shown in U. S. Patent No. 2,329,134, of September 7, 1943, to L. R. Peters. The effect of this substitution is to delay the closing of the switch M and the fully effective heating of the cathode(s) II, II until the glowswitch Gg heats up and closes; whereupon the switch M closes and shunts out the glow switch, which promptly reopens. The opening of switches T and M follow as before.

If the magnet winding at 21 has a suflicient number of turns, the glow-switch G9 will pass current to close switch M by mere glow-discharge, without needing to close in order to operate switch M: in other words, the glow-switch Ga will operate as a glow-lamp, as described in connection with Fig. 1.

With either form of starting arrangement shown, it is impossible for the discharge in device L to be started prematurely, before the cathode s II have heated adequately, because the cathode heating current necessarily fiows in circuit H and holds switch M closed as long as switch T remains closed, quite regardless of when passage 0! current through device G (or Go) ceases. When switch T opens, however, switch M also opens, and-device G (or G9) has become incapable of passing current; so that during normal operation of device L, no current flows in any part of the control system S, and no energy is used to keep circuit H open.

In Fig. 2, various parts and features are marked with the same reference characters as those corresponding in Fig. 1, in order to dispense with repetitive description.

What I claim as new and desire to secure by Letters Patent 01 the United States is:

1. The combination with a gaseous electric discharge lamp device having cathode means embodying heating resistance, a main discharge circuit connected to said cathode means, and means for preheating said cathode means comprising a starting circuit connected across said main discharge circuit through said heating resistance, of means for interrupting said starting circuit and imposing a starting voltage across said discharge device comprising a normally closed thermal switch in said starting circuit, a switch connected in said starting circuit in series with said thermal switch having normally open contacts and electromagnetic closing means in series with them, and electric discharge means shunting said switch contacts but in series with said electromagnetic means and with said thermal switch, said thermal switch being designed,

to open to start the discharge in the lamp only after shunting of said electric discharge means by closure of the electromagnetic switch, said electric discharge means being operable at the voltage applied across the lamp for starting but inoperable at the lower voltage existing thereacross after said lamp has started.

2. In a start-timing system for a gaseous electric discharge lamp device having cathode means embodying heating resistance, the combination with a main discharge circuit connected to said cathode means, and means for preheating said assure 3 tacts but in series with said electromagnetic means and with said thermal switch, said thermal switch being designed to open to start the discharge in the lamp only after shunting of said electric glow-discharge means by closure of the electromagnetic switch, said electric glow-discharge means being operable at the voltage applied across the lamp for starting but inoperable at the lower voltage existing thereacross after 10 said lamp has started.

THEODORE W. FRECH.

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