US2285450A - Electric discharge lamp and starting device - Google Patents

Description

June 9, 1942. H. J. MCCARTHY ELECTRIC DISCHARGE LAMP AND STARTING DEVICE Filed May 18, 1940 llllllllll nun-""1"."-nn-nn-u-nnumnvununnn n-unllnnnnnnnnn-.n.,

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Patented June 9, 1942 ELECTRIC DISCHARGE LAMP AND STARTING DEVICE Henry J. McCarthy, Danvers, Masa, assignor to Hygrade Sylvania Corporation, a corporation of Massachusetts Application May 18, 1940, Serial No. 335,968

Claims.

The present invention relates to electric gaseous discharge lamps and in particular to apparatus for starting and operating such lamps.

An object of the invention is to provide a starting apparatus for electric gaseous discharge lamps which will allow the cathodes of the lamp to be preheated before the discharge is started between them.

Another object is to provide a starting apparatus which will be so timed in its action that no greater interval of time will be used for the preheating of the cathodes than is absolutely necessary.

A further object is to provide a switch which will accomplish the above-mentioned objects and at the same time function under all possible conditions of starting and restarting.

'A feature of this starting apparatus is that it eliminates the unnecessary time lag present in many switches during the starting and restarting period.

Other objects, advantages and features will be apparent from the following specifications taken in conjunction with the accompanying drawing in which:

Figure 1 is a schematic diagram of the arrangement of apparatus according to the invention.

Figure 2 is a side view of the switching device according to the invention.

Figure 3 is a cross-section view of a part of the switching device according to the invention.

Figure 4 is a side view of a method in which the switching elements may be connectedwith the lead-in strips.

Figure 5 is a side view of the preferred method in. which the switching elements may be connected with the lead-in strips.

In Figure 1, an electric gaseous discharge lamp I has the glass envelope 2 with electrodes 3 and 4 sealed at each end. The glassenvelope may have a coating of fluorescent material 5 on its inner wall. The electrodes 3 and 4 may be coils of tungsten wire coated with one or more of the alkaline earth oxides to increase the electron ,emission, with the auxiliary electrode 6 and '1 to aid in starting. An atmosphere of inert gas, such as argon, and also a vapor, such as mercury, may be sealed in the glass envelope. A lead-in wire 8 from one end of one filament may be connected to one end of the power line from which the apparatus is operated. An end of the other filament may be connected through a suitable ballast impedance, such as an inductance coil I0, to the other end of the power line by the lead-in wires n. The remaining ends n and n of each filament may be connected together through the resistance It. A condenser 9 may be placed across the resistance It to cut down radio interi'erence due to the operation 01 the switch and lamp. A condenser of .006 microfarad has proven to be advantageous.

A bimetallic strip 20 is connected at one of its ends to an end of the resistor l3. The other end of the resistor I3 is connected to a contact 25 placed near the other end of the bimetallic strip. The direct circuit between the moving end of the bimetallic strip and the contact 25 is normally open. Another contact, however, is also connected to the same end of the resistor I! through the additional resistance 3| and arranged to be normally closed to the moving end of the bimetallic strip. The resistance 3| is very small compared to the resistance IS. The latter may be about 40,000 ohms while resistance 3| is only about 1 to 5-ohms. The resistance 3| is placed in a position so as to heat the bimetallic strip, and is preferably made part of the contact 20 by making the contact of carbon for example.

Figures 2 and 3 show the arrangement of the starting apparatus more in detail. A resistance rod I3 is suspended between the two lead-in wires l8 and I9. A supporting arm 2| extends inwardly from lead-in wire I! and attached to the inward end thereof is a bimetallic strip 20, which is bent around the resistance rod. The

resistance rod may have an insulating coating thereon of for example, alumina and shellac, 29. Two lead-in strips 23 and 24, one with a low resistance contact point, for example, silver 25 attached to its free end, and the other with a high resistance contact point, for example, carbon or some other material 26, attached to its free end, are fixed at a common source 21 on the lead-in wire l9, and project upwardly in the direction of the free end of the bimetallic strip 20.

The high resistance contact is normally in a closed position in relation to the strip 20 and the low resistance contact is in a normally open position in relation to the strip 20.

The whole unit may be sealed into a container 28 of metal, glass, or the like. If the unit is sealed in a metal container, the lead-in wires must, of course, be insulated therefrom.

Since the high resistance contact is normally in a closed position in relation to the bimetallic strip 20, the filaments 3 and 4 will start heating and the highreslstance contact 26 and the bimetallic strip 20, with which it is in contact will start heating when the voltage is turned on.

' The high resistance contact point and the biwith the resistor l3, which may be 40,000 ohms.,

Thus with the carbon contact closed, the resistor I3 is efiectively short-circuited and the normal heating current fiows through filaments 3 and 4;

but the carbon contact has nonetheless a resistance sufiicient to heat the bimetallic strip 20 enough to cause it to break contact at the proper time. My invention eliminates the unnecessary time lag present in other switches, namely the time which elapses between the placing of the line voltage across the lead-in wires and the starting of the preheating of the filaments. In

my invention, by reason of the normally closed position of the high resistance contact point in relation to the bimetallic strip 20, the line voltage is immediately placed across this contact and as a result, the heating of the filaments takes place immediately.

If, for any reason, the discharge does not take place across the lamp when the bimetallic strip 20' breaks from its contact with the high resistance contact point 26, my invention provides a unique auxiliary starting apparatus. If the discharge fails to take place, the resistance rod l3 will become heated as a result of receiving the full line voltage. The heat from the rod will heat the bimetallic strip 20, causing it to bend towards the low resistance contact point on the end of the lead-in strip 23. The low resistance contact 25 and the bimetallic strip 20 are so spaced that contact will be made when a voltage is placed across the rod I3. When this contact has been established the resistance rod will be short-circuited, the rod and the strip will start to cool and the filaments of the lamp will start to warm up. The contact 25 and the strip 20 are so proportioned that they will have cooled to a point where they will break contact at about low resistance contact point 25 on the end of the lead-in strip 23, thus short-circuiting the resistance rod and start the preheating of the filaments of the lamp.

Figure 4 shows a manner in which the switching elements may be connected, wherein leadin strip 24 is bent away from its extension along lead-in strip 23' from pointjl. A low, resistance contact is attached tothe free end vof the strip 20 and contacts the point 25 when the auxiliary starting feature of the apparatus is employed. t Figure 5 shows the preferred manner in which the switching elements may be connected, wherein theiree endfof lead-in strip 24 is bent back for a short distance in a U-shaped manner so as to cause the high resistance contact 26 attached thereto to become located in contact with the bimetallic strip 20 at a point opposite contact 30.

self a bimetallic strip to compensate for ambient temperature changes. The strip 24 is placed to move with ambient temperature in the same dithe same time the filaments are hot enough to start a discharge across the lamp. When this contact is broken, the bimetallic strip will move away from its contact with the low resistance contact point.

Since there is about one-half line voltage across the resistance rod during the operation of the lamp, the heat conducted to the bimetallic strip by the rod will cause the strip to take a position.

1 during the actual operation of the lamp, at a point about one-half between its normally closed position with the high resistance carbon contact, and the low resistance contact point. Thus there is no danger of the strip 20 cooling to a temperature where it would re-establish its contact with the high resistance contact point, and thus renew the starting operation.

If the current should be thrown off and immediately turned on again, without a sufiicient time elapsing to allow the strip 20 to cool sufilciently to re-establish' its contact with the high rection as the strip 20. The contacts 25 and 26 then move with ambient temperature in the same direction that the strip 20 moves, and if the length of the strip 24 is properly adjusted, they move out, not only in the same direction but also the same amount, so that the operation ofthe switch remains constant.

At the same time, the bent back portion of the strip 24 in the neighborhood of contact 26, being bimetallic, moves oppositely to strip 20 when both are heated by passage of current through the carbon 26, thus giving a quicker and cleaner break in contact. Thus this construction of element 24 has a double advantage.

The resistance rod should have a high -resistance, say 40,000 ohms. For this resistance, I have, for example, used a graphite rod, 0.45 inch long and 0.025 inch in diameter. For my high resistance contact I have used carbon, having a resistance of about 1 to 5 ohms. For my low resistance contact I have used silver, having a resistance of a fractional part of an ohm. Although I have used these particular materials, my invention does not necessitate the use of these exact same materials. It is sufllcient that a high resistance contact point, a low resistance contact point and a high resistance rod be used.

Certain specifications with regard to the lamp must be used in order to obtain the results in the switch action described above. The lamp must have a gas pressure and electrode spacing,

and a tube diameter such that when the electrodes are cold, no substantial discharge will take place between the electrodes at the line voltage used.

What I claim is: 1. In combination: an electric gaseous discharge lamp having at least two electrodes, one

at least of said electrodes being of the filamene tary type; a ballast impedance in series with said lamp; a resistor connecting one end of a filamentary electrode to the other electrode, said resistor having an impedance which is large compared with that of the ballast impedance; a high resistance contact; a low resistance contact; a bimetallic strip electrically contacting said high resistance contact when said resistor is unenergized and in a position to be distorted by the heat developed in said high resistance contact when the latter passes current, and, to open said contact when distorted sumciently; said bimetallic strip also being so positioned as to be distorted by the heat developed in said resistor when the latter passes current and to short circuit said resistor, by making contact with the low resistance contact, when distorted sufliciently.

2. The combination of claim 1 in which: The ballast impedance is such that the operating voltage of the lamp, after the electrodes have been heated, is much lower than the starting voltage when the electrodes are cold; andin which the resistor connected between the lamp electrodes is positioned so that the heat produced in it by the operating voltage of the lamp is insufficient to distort the bimetallic. strip, with which it is in contact, enough to short-circuit said resistor, but so that the voltage necessary for short-circuiting is nevertheless below the starting voltage of the lamp when the filamentary electrode is cold; v I

3. In an electric gaseous discharge lamp circuit having a ballast impedance in series with a twofilament discharge lamp: a resistor connecting one end of one filament to one end of the other filament, said resistor having an impedance large compared with the ballast impedance; a bimetallic strip in position to be distorted by heat from said resistor and having one end electrically connected to one end of said resistor; a low resistance contact connected to the other end of said resistor and near but out of contact. with the other end of the bimetallic strip when said resistor is unenergized; and a second contact closed to said other end 01 said bimetallic strip when said resistor is unenergized, said second 3 contact being connected to said other end of said resistor through a second resistor in proximity to said bimetallic strip.

4. A relay for controlling the preheating of the filaments of an electric gaseous discharge lamp, said relay comprising: a resistor; a bimetallic strip in position to be distorted by heat from said resistor and having one end electrically connected to one end of said resistor; a low' resistance contact connected to the other end of said resistor and near but out of contact with the other end of the bimetallic strip when said resistor is unenergized; and a second contact closed to said other end of said bimetallic strip when said resistor is unenergized, said second contact being connected to said other end of said resistor through a second resistor'in proximity to said bimetallic strip.

5. A relay for controlling the preheating of the filaments of an electric gaseous discharge lamp, said relay comprising: a resistor; a contact of high resistance material such as carbon: a contact of material having a resistance low relative to the resistance of carbon; 9, bimetallic strip electrically contacting said contact of high resistance material when said resistor is unenergized and in a position to be distorted by the heat developed in said contact of high resistance material when the latter passes current, and to open said contact when distorted suiiiciently; said bimetallic strip also being so positioned as to be distorted by the heat developed in said resistor when the latter is energized and. to short circuit said resistor by making contact with the contact or material having a low resistance, when distorted sufliciently.

HENRY J. McCARTHY.

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