US2374315A - Starting control for electric discharge devices - Google Patents

Description

April 24, 1945. 2,374,315

STARTING CONTROL F OR ELECTRIC DISCHARGE DEVICES J. R. WHITESIDE Filed May 7, 1942 Zl-ams TA 1. Y [7 /ZZ swarm.

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B/ME TAL Patented Apr. 24, 1945 STARTING CONTROL FOR ELECTRIC DISCHARGE DEVICES Jack R. Whiteside, Cambridge, Mass., assignor to General Electric Company, a corporation of New York Application May 7, 1942, Serial No. 442,102

4 Claims.

This invention relates to the control of electricv 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 U. S. 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 starting is accomplished. A type of automatic starter heretofore proposed comprises a pair of coacting contact strips of sheet metal that are normally in contact to complete the starting circuit. These strips may both be bimetallic thermostats. With one of them may be associated an electric heater connected in a circuit of the lamp, while the other may afford temperature compensation to prevent starting troubles in very hot or very cold weather. While the heater that is thus connected in shunt across the lamp and the starting switch at starting may be of very high resistance, it nevertheless absorbs some of the energy produced by the high voltage kick that is relied on to start the discharge, thus lowering the available energy for starting. In cold weather, or in the case of lamps that are difficult to start because they are near the end of their useful life, or for other reasons, this loss of energy may be enough to prevent successful starting.

This invention aims to obviate such drawbacks by avoiding such a heater connection in shunt across the starting switch at the moment of startin and also to avoid the drawbacks of having the starting circuit normally closed. The invention has the advantage of being adaptable to locking in or locking out when the lamp with which it is associated becomes incapable of starting, so as to obviate undesirable flashing of such defective lamps, and the concomitant useless wear on the starter in futile attempts to start the lamp, as well as to temperature compensation for extremes of hot or cold weather.

Other features and advantages of the invention will become apparent from the description of species and forms of embodiment, and from the drawing.

In the drawing, Fig. 1 is a diagrammatic view of a fluorescent tube or lamp with circuit connections including the present invention, a midportion of the lamp envelope being broken out and omitted; Fig. 2 is a tilted or perspective view of one form of starting switch device such as diagrammatically represented in Fig. 1; Fig. 3 is a similar view of another form of such a starting switch device; Fig. 4 is a vertical mid-sectional view illustrating the same starting switch device together with an associated lockout switch mechanism, which is also diagrammatically represented in Fig. l; and Fig. 5 is a fragmentary sectional view taken as indicated by the line and arrows 5-5 in Fig. 4.

In the various views of the drawing, the directions of movement or deflection of thermostatic members for increase of temperature are indicated by arrows.

Fig. 1 shows an ordinary fluorescent tube lamp L of the positive column electric discharge type with a tubular envelope l0 having spaced apart activated thermionic cathodes II, II in its ends, which may be specially heated cathodes of usual coiled filament type, and areshown connected across a power-supply circuit P including the usual ballast I4, which also serves as a starting inductance, and the manual make-and-break switch 15. The envelope It) may contain a lowpressure atmosphere of starting gas, such as argon at a pressure of 2 to 5 mm. of mercury, and also a vaporizable 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 i1 inside the envelope to, and an internal coating of fluorescent material or phosphor IE 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 I l, I I, with a starting switch S included switch device S permits flow of current through the circuit H and the cathode filaments H, II in series therein for a suflicient length of time to preheat the cathodes to an adequate emissive temperature, and then suddenly opens the circuit H;

l and the resulting voltage kick between the cathodes sufllces 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 one comprising switch members 2|, 22 that are connected to opposite sides of'the starting circuit H, and coact in making and breaking this circuit with associated connective and contact means, which are here shown as a common contact member 23, functionally intermediate the members 2|, 22, and mounted on an additional member 24, which may serve for purposes of temperature compensation. The switch members 2|, 22, 24 may consist of slender, straight, approxi mately upright thermostatic bimetal strips coacting as both temperature-responsive elements and current-carrying contact members. In efiect, the parts constitute separate serially connected switches for controlling the starting circuit H, and the member 24 compensatively shifts theintermediate contact means to regulate the action of both these switches in response to ambient temperature variations. Contact pieces 25, 25 (as of coin silver wire) are shown welded to the upper free ends of the members 2| 22, and extend hereinafter, the members 2|, 22 are preferably bent in the peculiar manner. illustrated in Fig. 2, first sharply and reversely downward near their anchored lower ends,'and then upward in semicircular arcs 26, 26, th offsets represented by both these bends 26, 26 being to the right in Fig. 2. Adjacent the thermostat members 2|, 22, about concentric with their bends 26, 26, there are resistance heaters 21, 28 for heating these members The circuit connections of these heaters will be more fully described hereinafter; for the present it sufilces to say that the heater 21 for the member 2| is connected in shunt across the switch members 2|, 24, so as to respond essentially to,'the energization and voltage of the main discharge circuit P when the contacts 23, 25 of the members 24, 22am closed, as shown in Figs. 1 and 2, while the heater 28 for the member 22 is connected in the circuit H ,in series with the switch means S so as to respond to the energize.- tion of the starting circuit H and to the current flow therein. In the present instance, the member 24 serves as a resiliently yielding contact and affords temperature compensation for very hot or cold weather, so that no heater for this member 24 is shown. The thermostatic switch members 2|, 22, 24 may all be arranged to flexin the same direction (toward the right in Fig. 2) when heated, and vice versa.

The switch S may comprise as its structural frame a hollow glass stem 30 into which are sealed or fused' four wires 3|, 32, 33, 34. The

wires 3|, 32 which serve as the switchleads are connected through connectors 35, 35 on a fiber disc base 36 to opposite sides of the starting circuit H. The lead wire 3| carries the switch member 2| (which has its lower end welded t this wire), and is also extended to form one end conto the full line voltage when the circuits P, H are first energized by closing the switch l5, may preferably be of very high resistance, such as 100,000 ohms, for example. It may also be found advantageous to make this heating resistance 21 of a type having a negative temperature-resistance coeflicient, so that it may heat more rapidly and cause the member 2| to close the switch more quickly, yet not move far enough to close under the normal operating voltage of the lamp. The heater 28, through which flows the cathode preheating current in the starting circuit H when the switch S is closed, is preferably of low resistance,

such as 3 ohms, in order to minimize its energy consumption, and may consist of a coil of fine heating-resistance wire. Any suitable provision may be made to cause the heater 28 to heat the thermostat 22 and to cool ofi rather slowly, such as enclosing this heater 28 in a glass sleeve 39, so as to give it a high heat capacity. On the other hand, the heating and cooling time of the heater 21 may be minimized, as by blackening it so as to lower its heat capacity.

When the switch I5 is closed for a cold start, line voltage is applied to energize the circuits P. H and the heater 21, and the thermostat member 2| is heated and flexes to the right (Fig. 2) into contact at 25 with the member 24, closing the switch S and fully energizing the circuit H and the heater 28, and also short-circuiting the heater 21which is thus de-energized and starts to cool oif, as well as thermostat 2|. The current flow through the cathode coils H and the heater 28 in the circuit H preheats the cathodes (Fig. 1) and also heats up the thermostat member 22, which flexes to the right (Fig. 2) out of contact with the member 24 at 23, breaking the circuit H. This opening of the starting circuit H nection for the resistance heater 21. The other I lead wire 32 forms an end connection for the other resistance heater 28. The wires 33 and 34 carry the switch members 22 and 24 (which have their lower ends welded to these wires, respectively), and have connections 31 and 38 to the I other ends of the heaters 28 and 21, respectively. The heater 21, which is subject and responsive between members 22 and 24 occurs after the heating resistance 21 has been shunted out by closing of member 2| to member 24, and before heater 21 has cooled sufliciently for member 2| to reclose to member 24. It is' a quick, sharp action, giving a maximum voltage kick which is generally effective to start the discharge in the lamp L, if it is a good lamp, because it wholly breaks the circuit H and throws the whole switch S out of circuitfso that it cannot absorb any of the energy of the starting impulse. The heater 28 and the thermostat 22 are de-energized, and the de-energized thermostat 22 cools and unflexes'to the left. If the lamp L starts, the discharge in the lamp L shunts or short-circuits and de-energizes the heater 21 (in view of its high resistance) sufllcientlyto prevent it from reclosing the switch S.

If this cycle of operation of, the switch S fails to start the lamp L, then the member 2| recloses to the member 24, and the cycle is repeated one or more times. The cycle, may take the same length of time at each repetition as in the initial attempt, since all the heaters and thermostats may be allowed to cool off completely after every cycle. The action is not materially affected by variations of the ambient temperature, since the eilects of such variation are compensated for by the compensating de-' type are given:

The thermostatic members 2|, 22, 24 may be strips of the bimetal commercially known as Chace #2400 Bimetal, composed of laminae of Invar, an alloy of 64 per cent iron and 36 per cent nickel, and of chrome iron, an alloy of '75 per cent iron, 22 per cent nickel, and 3 per cent chromium, in equal thicknesses, welded together. Each of the strips 2|, 22 may be 0.005 inch thick, inch wide, and 19 mm. long before being bent. The lengths of their lower straight portions to which the wires 3|, 34 are welded may be 0.195 inch, and the diameters of their bends 24, 24 may be 0.110 inch. The horizontal distance apart of the portions of strips 2|, 22 to which the wires 3|, 33 are attached may be inch. The length of the strip 24 may be 12 mm., while its width may be inch and its thickness 0.005 inch, just like the strips 2|, 22. The contacts 23, 25 may be of 40 mil coin silver wire. The initial gap between the contacts 23, 25 of the members 2|, 24- when the switch is cold may be 0.03 inch. The heater 28 may be a helical coil of about 42 mm. of Nichrome wire of 0.0063 inch diameter wound on a 40 mil mandrel, and its surrounding sleeve 38 may consist of a mm. length of gauge Nonex glass tubing. The heater 21 may be a solid rod of high resistance (such as 100,000 ohms under a voltage of 100 volts D. C.) and characterized by a negative temperature-resistance coefficientsuch as the material commercially known as Globar BNR. The Nichrome above referred to is an alloy consisting of '15 per cent nickel, 12 per cent iron, 11 per cent chr0- mium, and 2 per cent manganese.

Though. its operation, connections, and component parts correspond essentially to those shown in Fig. 2, the switch S illustrated in Fig. 3 differs considerably as regards the arrangement and mounting of the parts. As shown, an upright insulative plate 40 replaces the glass stem as a frame for mounting the switch members, which may have their anchored ends attached to this base 40 by means of rivets 4|. The switch member 2| is shown opposite the switch members 22, 24, which are arranged side by sidesq The functionally intermediate switch member 24 carries a transverse intermediate contact bar 23a which coacts with the contacts 25, 25 of the members 2|, 22 lying at opposite sides thereof. As in Figs. 1 and 2, the contact 25 of member 2| is normally out of contact with the contact bar 23a when the switch is cold, while the contact 25 of member 22 is normally engaged with said contact bar 23a. To dispensewith and in Figs. 4 and 5 as a self-opening switch X connected in the starting circuit H in series with the automatic starter S, and. comprising as switch members a straight, upright thermostatic bimetal strip 4| and a spring 42 of resilient wire such as Phosphor bronze or steel piano-wire. The thermostat 4| is secured directly to the base disc by a rivet 44 through its laterally bent foot 45, while the lower end of the spring 42 is welded to one of the connectors 35. The free upper ends of the members 4|, 42 coact as switch contacts and otherwise as hereinafter explained, and for repetitive description, various parts and features in Fig. 3 are marked with the same arrows and reference characters as their homologues in Figs. 1 and 2, a distinctive letter being added where this appears necessary.

To obviate the undesirable flashing of defective 'lampswithout interfering with repetition of attion of the automatic control need not be an arbitrary matter of fixed adjustment, but can be made responsive to the actual attempts of starter S to start the discharge.

Such an automatic control is shown in Fig. 1

this purpose the upper end of the member 4| is bent over and cut to a bevel at 41, Fig. 5, to serve as a latch for holding the member 42 resiliently flexed and in contact, so as to complete the circuit through the switch S. The upper end of the member 42 is provided with an insulative handle 48 which extends through a guide slot 49 in the top of the casing 50, Fig. 5. A heater 5| for heating the thermostat 4| is connected in series with the switches S and X, and consists of fine wire coiled around the member 4| over its thermoinsulative covering 52, which may be of asbestos paper. When the thermostat 4| and latch 41 move to the left and release the spring member 42, this member and its handle 48 fly forward to the front end of the slot 49, opening the circuit H and making it impossible for the starter S to reclose it or for the lamp L to flash. Thereafter, the latch 41 and the switch X can be reset by pushing the handle 48 to the front in the slot 49 until the latch 41 automatically re-engages the member 42 as shown in Figs. 4 and 5.

The spring 42 is preferably so adjusted as to press resiliently against the thermostat 4|, when the switch X is closed as Fig. 4, with a certain elastic tension: in other words, the thermostat is preflexed or pretensioned. As the thermostat 4| heats up from its heater 5|, this pretension is taken up or relaxed before the thermostat actually begins to move. After this, the thermostat 4| moves to the left (Fig. 4) a short distance until the rounded spring 42 rides on the ,point of the latch 41, forcing the thermostat back and slipping pastit very quickly. This mode of operation is favorable to the desired slow action of switch X to give time for the desired number of starting attempts by starter S before switch X opens. The timing of switch X can be adjusted by adjusting the pretension of thermostat Current to heat the heater 5| and-the thermostat 4| flows through the heater when the switch .8 is closed between the members 2| and 24, and

also (as limited by the resistance 21)- when the switch is closed between the members 22 and 24. While the period of closure is only a small part of an operating cycle of switch S, yet over a series of such cycles heat gradually accumulates in the heater SI and the thermostat 4| until the latter becomes hot enough to open the switch X and the heating circuit H.

For the convenience of those'wishing to use the switch Xillustrated in Figs. 4 and 5, particulars of such a switch suitable for ordinary 30-40 watt fluorescent lamps of positive column type are ven: 1

The thermostatic switch member 4| may be made of the Chace #2400 Bimetal mentioned above. It may be a strip 0.030 inch thick, 1; inch wide, and 1 inch long from its laterally bent foot 45 to its bent-over latch portion 41. The insulative wrapping 52 may be of asbestos paper 0.007

inch thick and extending 10 mm. lengthwise oi the bimetal, whileits length that is wrapped around the bimetal may be 13 mm; The heating winding 5| may be of the above-mentioned Nichrome resistance wire, of 0.0063 inch diameter, wound 5 /2 turns around the wrapped strip 4|; giving an active length of 72 mm., while the total length may be 105 mm..including the.lead ends. The spring member 42 may be of brassplated piano wire of 0.018 inch diameter, 1% inches long.

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

1. In combination, an electric discharge device having spaced electrodes, means for connecting one end of each electrode with a source of current supply including a starting inductance, and a switch comprising two pairs of contacts connected together in series between the other ends of said electrodes, one pair of said contacts being normally open and the other pair normally closed, a thermostat connected with one contact of each pair, a resistance heater of relatively high resistance connected in shunt across the normally open contacts for heating their thermostatto close said contacts, and a resistance heater of very low resistance relative to the firstmentioned heater connected in series with the normally closed contacts for heating their thermostat to open said contacts, .the two resistance heaters being so proportioned that the normally open contacts close prior to the opening of the normally closed contacts, butthe high resistance 'heater being inefiective to hold its associated contacts closed at the potential available upon starting of the device.

2. A starting switch for an electric discharge device arranged to be connected between and'in series with the electrodes of the device, and comprising two. pairs of contacts connected together in series, one pair being normally open and theother pair normally closed, a thermostat connected with one contact of each pair, a resistanceheater bf relatively very high resistance connected in shunt across the normally open contacts for heating their thermostat to close said contacts, and a resistance heaterof very low resistance relative to the first-mentioned heater connected in series with the normally closed contacts for heating their thermostat to.

open 'said contacts, the two resistanceheaters being so proportioned that the normally open sistance heater of relatively very high resistance connected in shunt across the normally open contact and the common contact member for heating the strip carrying the normally open contact, and a resistance heater of very low resistance relative to the first-mentioned heater connected in series with the normally closed contact for heating its strip, the two resistance heaters being so proportioned and" arranged that the normally open contact engages the common contact member before the normally closed contact disengages 4. A thermal switch comprising an insulative support plate, first and second bimetallic strips arranged in spaced side-by-side relation along a surface of said plate with adjacent ends anchored to said'sup'port and carrying contacts contact on said first strip.

at their free ends,a third bimetallic strip arranged in opposed relation to the first and second strips and along a line extending between those strips, said third strip carrying a contact at its free end adjacent the free ends of the first and second strips and having its other end anchored to said plate, the contact on said first strip extending laterally of the strip and between the contacts on said second and third strips, the contact on said second strip being normally in engagement with the contact on said first strip, the contact on said third strip being normally spaced from the contact on said first strip, a resistance heater of relatively very high resistance connected in shunt across the contacts on the first and third strips for heating the third strip to close those contacts, and a resistance heater of very low resitsance relative to'the first-mentioned heater connected in series with the contact on the I second strip for heating said second strip to carry its contact out of engagement with the JACK R. wHrrEsmn.

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