US2482442A

US2482442A - Control unit for discharge lamps

Info

Publication number: US2482442A
Application number: US616904A
Authority: US
Inventors: Royal F Strickland
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1945-09-17
Filing date: 1945-09-17
Publication date: 1949-09-20
Anticipated expiration: 1966-09-20

Description

P 1949- R. F. S TRICKLAND CONTROL UNIT FOR DISCHARGE LAMPS 2 Shee ts-Sheet 1 Filed Sept. 17, 1945 FigJ.

k cm M W m 2. t V W .m

Sept. 20, 1949. R. F. STRICKLAND com n L pun Foa nIsCHABGi LAMPS I 2 SheetsSheet 2 Filed Sept. 17, 1945 m m n t t B v A .mF .6 l H a Z R Patented Sept. 20, 1949 CONTROL UNIT FOR DISCHARGE LAMPS Royal F. Strickland, Cleveland Heights, Ohio, as-

signor to General Electric Company, a corporation of New York Application September 17, 1945. Serial No. 616,904

3 Claims.

My invention relates to a control unit for starting and operating gaseous discharge lamps and more particularly to a starting switch for fluorescent lamps of the type now in commercial use.

Usually. discharge lamps of this type are connected in series with a ballast across a source of electric power together with a control unit or starting switch in parallel with the lamp but in series with the lamp electrodes. When the control .unit opens the circuit between the electrodes, the ballast applies a high voltage surge to start the lamp. Such control units are known to the trade as starters and will be referred to as such in the description to follow.

Heretofore such starters have been designed to provide for an appreciable preheating time for the filamentary electrodes of the lamp to bring them up to an emissive temperature before ap plying the high voltage from the ballast to start the lamp. This was desirable because, as heretofore manufactured, the operating performance of the lamps could be materially bettered if the lamps were started after preheating of the filamentary electrodes. Howevenwith certain types of fluorescent lamps now on the market, appreciable preheating of the electrodes is unnecessary. The lamp may be started without any substantial preheat of the electrodes, for example within approximately /20 second preheat time. Or the lamp may be started instantaneously with cold cathodes.

Although present day lamps are designed for instant starting with little, if any, preheating of the electrodes, or for cold cathode starting, starters of the type now commercially available will not start a lamp fast enough to avoid a noticeable delay in lighting after the power supply switch is closed and, in any event, do not start a lamp with the speed at which the lamp is capable of being started.

One such starter now in use comprises a thermal switch in series with a glow switch, the arrangement being such that the glow switch closes the circuit through the lamp filaments, and then the thermal switch opens the circuit after a predetermined time delay. In some instances, the glow switch may be omitted and the thermal switch used alone to close and open the circuit.

Another type of starter now on the market employs a glow switch having two electrodes one of which is bi-metallic. Whenthe lamp operating circuit is closed, a glow discharge takes place between the electrodes to heat the bimetallic electrode to close the circuit through the glow switch. This extinguishes the glow discharge and causes a preheat current to flow through the lamp filaments. When the bimetallic member cools down. the circuit through the glow switch is opened causing the ballast to apply a high voltage across the filaments to start the lamp.

Although the various starters mentioned operate satisfactorily when it is desired to preheat the lamp electrodes, they fail to provide an instant starting action for lamps of the type now commercially available in which no appreciable preheating of the electrodes is required and which may, in fact, be started with cold cathodes. When thermal switches are employed, an unavoidable time delay is encountered in heating and cooling the relatively heavy bimetallic strips. When glow switches alone are employed and are relied upon to open the circuit, an appreciable delay occurs after extinguishment of the glow discharge waiting for the bimetallic element to cool down. While with present designs adapted for commer cial use, the bimetallic member of a glow switch closes practically instantaneously under the influence of the glow discharge, still some delay occurs between that time and the time that the glow switch opens with consequent delay in starting of the lamp.

A magnetic vibrator type of starter has been used in certain instances and which opens the circuit across the lamp filaments almost instantly after closure of the power switch. However, in such circuits, the actuating element of the magnetic coil of the switch is continuously in the lamp circuit during operation of the lamp to maintain the contacts in open position with consequent loss of power. This objection has been overcome to some extent by employing a voltage responsive device such as a glow lamp in series with the magnet coil, the two being in parallel with magnetically operated contacts. The glow lamp cuts oif the switch from the power supply during operation of the lamp. Such an arrangement is disclosed in Patent 2,212,427 issued on August 20, 1940, to Leo R. Peters and assigned to the same assignee as the instant application. While for certain applications, the circuit of the Peters patent operates satisfactorily, it is subject to the disadvantage that part of the voltage obtained across the vibrator contacts is absorbed in the glow lamp and hence is not available across the lamp electrodes. Moreover, a voltage drop occurs in the glow lamp which reduces the voltage obtainable across the magnet coil of the switch.

The aforementioned disadvantages are overcome by my new and improved starter. It employs a glow switch and magnetic switch in series between the lamp electrodes. It operates extremely fast to supply high voltage from the ballast to give a practically instantaneous start of the lamp after closure of the power supply switch. In certain applications, the starter may be pro vided with a lock-out mechanism which will cut the starter out of the lamp operating circuit if the lamp fails to start after a predetermined number of attempts.

Therefore, one object of my invention is to provide a new and improved control unit or starter for discharge lamps, such as fluorescent lamps, which will start the lamps almost instantaneously,

Another object of my invention is to provide an improved starter which includes means for starting the lamp instantaneously, in combination with a mechanism for locking the starter out of the lamp operating circuit if the lamp fails to start after several attempts.

Afurther object of my invention is to provide a new and improved instant starter which is interchangeable with present day starters and which may be used in existing lamp installations without modification or replacement of thelamps, lamp sockets or ballasts making up the lamp operating circuit.

In the accompanying drawing, Fig. 1 is a schematio' view showing a starter constructed in accordance with my invention and connected into a lamp operating circuit, the lamp being provided with filamentary electrodes; Fig. 2 is a view of the starter similar to Fig. 1 but with the addition of a lock-out mechanism; Fig. 3'is a schematic view of the lock-out starter of Fig. 2 connected to a lamp having cold cathodes; Fig. 4 is a detail view of part of the magnetic switch showing the structure of the switch contacts; and Fig. 5 is a schematic view of my starter provided with a modified form of lock-out mechanism.

' Referring to Fig. 1 of the drawing, I have shown my starter in schematic form connected into an operating circuit for a discharge lamp. The discharge lamp may comprise a fluorescent lamp l of the type now onthe market and which is provided at each end with electrodes 2 formed asfll'amentary cathodes. On one side the electrodes are connected across power lines 3 and 4 which/for example, may comprise a 115 volt AJ-C. power supply such as is now commercially available for residence use. Connected into the power line 3 is a ballast 5 for supplying high voltage to start the lamp. The ballast is illustrated as comprising an inductance or choke coil but it should be manifest that the ballast may equally as well comprise a transformer or resistance depending upon the voltage requirements of the lamp and the voltage available at the power supply. A switch 6 controls the application of power to the lamp operating circuit and is used to turn the lamp on and on;

While the discharge lamp 1 is illustrated as being provided with filamentary electrodes, which may be used in a circuit providing preheat, these electrodes are actually of the type which require practically no preheating before the application of the high voltage from the ballast to initiate a discharge in the lamp. In other words, the lamp is so constructed that it may be started simply by applying a high voltage across the electrodes without preheating them.

On the other side the electrodes are electrically connected in series with a control unit or starter constructed in accordance with my invention. The starter comprises a glow switch 1 electrically connected in series with a magnetically operated switch 8. A condenser 9 is connected electrically in parallel across these elements. The capacity of the condenser affects the peak output voltage obtained by the starter in a manner to be described later.

The glow switch I is of a type having two electrodes l8 and II sealed in a suitable envelope, such as a glass casing [2, the electrode ll being of bimetallic material. When power is applied to the glow switch, a glow discharge takes place between the electrodes causing the bimetallic electrode H to deflect into engagement with the electrode 10 so that a circuit is completed through the glow switch. The glow switch taken by itself formsno part of my present invention and may be similar to that disclosed in Patent 2,329,134 issued to Leo R. Peters on September 1'7, 1943, and assigned to the same assignee as the instant application. As shown in Fig. 1, one terminal of the glow switch is connected by a lead wire l3 to the left hand lamp cathode 2 while the other terminal is connected by wire i l to the magneticsWitch B.

The magnetic switch-8 comprisestwocontact members l5 sealed in a suitable evacuated envelope l6, for example, a glasscasing. Asshown-by Fig. 4, each contact member comprises a flexible wire H of tungsten 01" other suitable metal, .which is sealed to and'supported at one end on the .envelope l6. 'At its other end the wirecarries a. plate [8 of soft iron, or other material of .high magnetic permeability. The plate is provided on its inner face with a'contact surface formed of any suitable conducting material, such as tungsten wire l9. Each contact member-is manufac- 7 tured exactly the sameso that when assembled face to face, the contact wires 19 are disposed at right angles to each other to give a pointcontact. The contact surfaces arenormally biased intoengagement with each other by the action of the flexible supportingwires l1. In orderto operate the switch by opening the contact members, acoil of wire 20 is wound on a tube and placed around the outside of the glass envelope [6. One end of the coil is electrically connected to one of the contact members I5 so that the coil and contacts are electrically connected together in series.

When current passes through the coil, the magnetic flux acts on the iron plates of the contact members [5 to separate them to open the circuit through the switch. The iron plates will be polarized with like poles, such as N- N, by the magnetic flux threading through the coil core so that the contact members will repel each other.

- When alternating current is passed through the coil, the iron plates will be polarized 5-8 or N-N each half cycle and hence will be repelled once each half cycle. By mounting the iron plates at the ends of the flexible supporting wires ll, which themselves have little or no magnetic permeability, a relatively large repulsive force is attained at the ends of the wires at the iron plates. This effect, plus the extreme flexibility of the wire mounting of the contacts, makes the magnetic switch extremely fast acting. The switch operates to open the contacts when the current in the coil approaches a maximum.

The switch has been described in some detail in the instant application inasmuch as the features of construction and manner of operation make the switch particularly well adapted for use in my starting switch. In order to connect the magnetic switch into the circuit of my starter, the remaining contact member is electrically connected to the conducting wire I 4 and the free end .of the coil 20 is electrically connected to the. right hand lamp electrode 2 by a conductor 2|.

My starter operates as follows:

When switch 6 is closed to supply power to the lamp operating circuit, a voltage is applied across the electrodes of the glow switch I to initiate a glow discharge in the switch. This glow discharge causes the bimetallic electrode H to move into engagement with the fixed electrode ID. The speed of closure of the glow switch is very high, for example /5 second or less. A circuit is then completed from the power line 3 through the ballast 5, the left hand lamp electrode, the glow switch I, the coil and normally closed contacts of the magnetic switch 8, the right hand lamp electrode 2 to the other power line 4. Since the coil 20 of the magnetic switch has a relatively low impedance, a very small amount of current flows through the starter which has no appreciable preheating effect on the lamp electrodes because the flow of current is almost immediately interrupted by the switch 8. As soon as voltage is applied to the magnetic switch 8, the contact members Iii of the switch are opened by the magnetic flux of the coil 20.

As already mentioned, the speed of operation of the magnetic switch 8 is such that the contacts will .open on each half cycle of the alternating current supply. This means that the contacts It will open on the first half cycle of the A.-C. wave which is applied to the switch after closure of the glow switch I. Since the magnetic flux is greatest at the peak of the A. -C. current cycle, the contacts open at or near the peak of the current wave. Also, the magnetic flux through the ballast is a maximum at this time so that when the circuit through the starter is interrupted, a very high voltage kick is obtained from the ballast 5 and applied across the lamp electrodes. The speed of operation of the magnetic switch is such and the contacts open at or near the peak of the A.C. current wave so that the voltage applied to the lamp electrodes may be 5,000 volts or higher. This is obtained from a ballast which ordinarily would provide from 400 to 600 volts on a slower operating starter. When a starter operates at slower speeds, the time of opening of the contacts may extend over several cycles of the alternating current so that the magnetic flux in the ballast is dissipated .or averaged out to a considerable extent. Moreover, in former constructions, the contacts of the starter may not open at a maximum point of the A.-C. wave. In fact, they may open when the current is passing through zero.

However, in my starter, the contacts open .only at or near the current peaks in the A.-C. wave. This produces a corresponding high voltage kick from the ballast.

Condenser 9 functions to store part of the inductive energy obtained from the ballast. The capacity of the condenser may be varied to vary the peak output volts applied across the lamp electrodes.

Inasmuch as the magnetic switch operates on each half cycle of current, it will be apparent that a'series of voltage kicks will be applied to the lamp. Usually, the lamp will light on the first two or three half cycles of alternating current applied to the magnetic switch after the glow switch closes, but in the event that the lamp fails to light, a series of voltage kicks is obtained from the vibrating action of the magnetic switch 8 as it opens and closes. The high voltage impulses This means that several attempts I may be necessary to start the lamp.

are repeated in very rapid succession so that the ionization produced in the lamp by the first voltage impulse is continued and is built up or rein-- forced by the second voltage impulse and also the third one and so on until the lamp lights. In other words, the starter is so designed that theperiods of interruption of current, i. e., the periods during which the contacts of the magnetic switch are open to produce high voltage impulses to the:

lamp, are shorter than the deionization time of the arc discharge in the lamp.

As soon as the electrodes in the glow switch touch each other, the glow discharge is extinguished. The bimetallic electrode then cools down and again opens the circuit through the glow switch. The time taken for the bimetallic electrode to cool down may vary considerably and depends to some extent upon manufacturing tolerances in the thickness of the bimetal and also the surrounding temperature. In any event, the bimetal closes almost instantly but opens in a somewhat longer and irregular period of time. When the lamp lights, the voltage across the lamp electrodes, and which appears across the starter, is insufiicient to maintain a glow discharge in the gloW switch 1. When the bimetallic electrode ll cools down, it opens the circuit through the glow switch and the circuit continues open inasmuch as a glow discharge cannot now be maintained on the glow switch. Since the circuit is open at the glow switch, the magnetic switch 8 remains deenergized and the coil '20 is entirely out of the circuit. By my construction no power is lost in the coil to hold the magnetic switch in open circuit position.

In the event that the lamp fails to light within the first few vibrations of the magnetic switch 8, the bimetallic element ll of the glow switch will have cooled down sufiiciently to open the circuit through the glow switch and momentarily stop operation of the magnetic vibrator switch 8. This may occur, for example, within one second. However, since there is no arc discharge in the lamp, full voltage is still applied across the electrodes of the glow switch I to again initiate a glow discharge between them and cause the electrodes to reclose. The magnetic switch then again applies a series of voltage kicks to the lamp. If the lamp still fails to start, the cycle of operation may be repeated several times. In other words, the glow switch will close to operate the magnetic switch which applies a series of voltage kicks to the lamp; then the glow switch will open and immediately reclose to again energize the magnetic switch. If the lamp is defective and fails to start after several attempts have been made, I provide a lock-out mechanism for locking the starter out of the lamp operating circuit.

Fig. 2 illustrates one form of lock-out mechanism 22 which is suitable for use in my starter. It comprises an electrode 23 having a contact in engagement with a U-shaped bimetallic electrode 24, the electrodes being sealed in a suitable cas ing such as a glass envelope 25. lhe envelope is exhausted and filled with a suitable gas such as argon under low pressure. The electrodes are connected in series with the magnetic switch 8 so that as long as the electrodes are in closed circuit position, the circuit is completed from the magnetic switch 8 to the lamp operating circuit. A third electrode 26 is located in the bend of the U of the electrode 25 and is connected through a resistor 21 to the power line 53. Electrodes 2t and 26 are coated with an electron emissive material so that a glow discharge takes place between them upon application of full voltage.

During the time that the starter is making several attempts to start the lamp, full voltage appears across the

electrodes

24 and 26 causing a glow discharge to take place between them to heat up the bimetallic electrode 2 In the event that the lamp lights, the voltage appearing across the electrodes is insufiicient to maintain the glow discharge in the look-out mechanism so that the circuit through electrodes 23 and '24 remains closed. However, if the lamp fails to light after several attempts, the voltage maintains the glow discharge so that the bimetallic member 24 will become heated by the glow to an extent such that it moves away from the electrode 23. This opens the circuit through the lock-out mechanism. The resistor 21 limits the flow of current through the lock-out mechanism to a very small amount so that practically no power is consumed by the starter when in locked out position.

It will be apparent that my lock-out mechanism is one which is automatically reset when power is turned off from the lamp operating circuit or when a defective lamp is replaced. At i such times, the glow discharge in the lock-out mechanism dies out permitting the bimetallic electrode 23 to cool down and reengage the electrode 23. This recloses the circuit through the lock-out mechanism to the glow switch and magnetic switch. The starter is thus automatically reset to operative condition.

In Fig. 5 I have illustrated a modified form of lock-out mechanism. The resistor 27 serves to heat a bimetallic blade 28 which is normally in electrical contact with a second bimetallic member 29. If the lamp lights, the voltage applied to resistor 27 is reduced so that its heating efiect is insufiicient to move the blade 28 away from bimetallic member 29. However, if the lamp fails to light, full line voltage is applied to the resistor so that bimetallic blade 28 opens the circuit through the lock-out mechanism. The purpose in using the second bimetallic member 29 is to compensate for changes in ambient temperature. The two bimetallic members will deflect slightly together in the same direction under such changes. Thus the lock-out mechanism will function equally well in hot or cold locations.

In Fig. 3, a modified form of discharge lamp is shown connected into a lamp operating circuit provided with a starter constructed in accordance with my invention. The filamentary lamp cathodes having two exposed contact pins at the lamp ends are replaced with electrodes having simply a single contact pin and which operate only as cold cathodes in lamp starting. I

It will be apparent from Figs. 2 and 3 that my starter is adapted for use in lamp operating circuits which are specially designed to give either cold cathode starting or preheat startin of the lamp. In other words, the starter may be used to give instant starting in existing lamp operating circuits equipped with preheat starters without rearranging the circuit connections and without replacing the ballast or lamp sockets. It is only necessary to interchange the starters. As

already mentioned, the starter operates instantaneously to apply a very high voltage across the lamp electrodes without preheating and in this way starts the lamp with the cathodes cold in a circuit originally designed for preheating. Of course, lamps now on the market can be started with cold cathodes by very high voltages obtained from transformers without the use of a separate starter. However, such transformers are relatively expensive and require special equipment for their installation and use. One advantage of my starter mechanism is that it can be used interchangeably with preheat starters in existing installations employing relatively low voltage ballasts, when an instant start lamp is employed.

Another advantage of my starter mechanism is that by providing a glow switch in electrical series with the magnetic switch, full line Voltage is applied to the coil of the magnetic switch. N0 drop in voltage occurs across the glow switch such as would be the case if a glow valve were used. Moreover, the design of the magnetic switch is such that the starter may be mounted in any position without affecting its operation. In other words, the magnetic switch is not sensitive to position such as might be the case if a moving plunger havin some inertia were employed. This is of considerable advantage because the starter may he installed in any position as required by existing installations of fluorescent lighting fixtures.

The starter will also operate in lamp operating circuit having a D.-C. power supply, When D.-C. power is applied, a glow discharge takes the glow switch 1 to close the circuit to rrietic switch 8. The contacts of switch 8 then open quickly to apply a high voltage across the electrodes obtained by breakdown of the magn tic flux in the ballast 5. Usually the lamp will light on the first voltage kick. However, if the lamp fails to light, the magnetic switch 8 will operate repeatedly until the lamp lights. It will vibrate the natural frequency of the switch which is approximately 30 to 50 cycles per second. If the lamp is defective and fails to light after several starting attempts the lock-out mechanism will be energized to lock the starter out of the circuit.

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

1. A starter for discharge lamps comprising, in combination, a glow discharge switch having normally open contacts adapted to close quickly under the influence of a glow discharge in said switch when subjected to a predetermined voltage, and a magnetic switch having a series connected coil and normally closed contacts, said magnetic switch being electrically connected in series with said glow discharge switch and being operable upon passage of a single pulse or repeated impulses of current through the glow discharge switch to interrupt the circuit through the starter.

2. A starter for an electric discharge lamp comprising, in combination, a voltage sensitive glow discharge switch having normally open contacts adapted to close quickly under the influence of a glow disch rge in switch subjected to predetei..-nned Volta ge, and a magnetic switch having a series connected coil and normally closed contacts, said n: netic switch being electrically connected in series with said glow discharge switch and being operable upon passage of a single impulse or repeat of current through the glow discharge switch to interrupt the circuit through the starter for producing high voltage impulses for starting said lamp. the periods during which the contacts are open being shorter than the deionizaticn time of the are discharge in said lamp,

3. A starter for discharge lamps comprising, in combination, a glow discharge switch having normally open contacts adapted to close quickly REFERENCES CITED The following references are of record in the file of this patent:

10 UNITED STATES PATENTS Number Name Date 1,960,068 Rappel May 22, 1934 2,112,718 somers Mar. 29, 1938 2,212,427 Peters Aug. 20, 1940 2,200,443 Dench May 14, 1940 2,341,520 Babb Feb. 15, 1944 2,394,436 Frech Feb. 5, 1946 OTHER REFERENCES General Electric Review, July 1929, pp. 397 and 398.