US2644911A - Safety system for luminescent tubes - Google Patents

Description

July 7, 1953 n. c. HULTGREN SAFETY -sysm Fon Vrml'mzscxan'r 'rusas mea June v. 194') Patented July 7, 1953 SAFETY SYSTEM FOR LUMINESCENT TUBESl Rudolph C. Hultgren, Chicago, Ill., assignor, by mesne assignments, to Bert C.- Pretzer, Detroit, Mich., and Rudolph C. Hultgren, Chicago, Ill.,

jointly Application June 7, 1947, Serial No. 753,246

The present invention relates to systems and circuits for the operation of luminescent electric tubes, and constitutes an improvement upon the construction described and claimed in my copending application, Serial No. 587,945, led April 12, 1945, now abandoned.

Operating potentials, in the neighborhood of 600 volts, required for certain cold-cathodelighting tubes are regarded as unsafe and `my prior application discloses a safety fixture and system for protecting persons from. the high voltage conductors. It is desirable for improved economy of installation and operation to employ two tubes in series, but the higher circuit voltage required for such series operation has, understandably, been regarded as even more dangerous.

One object of the present invention is the provision of an improved system in which the haz-` ards of such a series system are no greater than those of the shunt system.

Another object is the provision of a safety control :for such a series system so that persons will be effectively protected from contact with energized high voltage conductors.

A further object is the provision ofl an improved cold-cathode, luminescent-tube system, and the provision of an improved safety control for such systems.

In the preferred embodiment of my invention, the ballast transformer has a separate, insulated secondary winding for each series pair of luminescent tubes. and the connection between the two tubes, that is the mid-point of the load, is connected to the primary circuit. Furthermore, this connection to the primary is accomplished by a circuit controlling socket that interrupts the primary to deenergize the transformer whenever a tube is removed. s

These and other objects and advantages will appear from the following description of a specilic construction which illustrates the manner in which the invention may be carried out.

In the drawings:

Fig. l is a view, partly in section of a lighting fixture and luminescent tubes therein;

Fig. 2 is a schematic diagram showing the luminescent-tube circuit of my present invention; and

Fig. 3 shows a modification of the circuit of Fig.2.

In Fig. l a housing lll contains an insulating plate l2 which supports four helical spring sockets I4. A second housing 'I6 contains an insulator I8 which supports four split-cone 3 Claims. (Cl. 315-187) 2 sockets 2l) of the type shown in my application, Serial No. 743,248, iiled April 23, 1947, now abandoned. The sockets I4 and 20 are adapted to receive and hold luminescent tubes 22. A tube is rst inserted through an yopening 24 in housing ID into a socket I4, and forced into the socket to distend it enough that the other end of the tube'22 may be inserted through a similar opening 26 in housing I6 into a socket 20, Where it is firmly seated by the force of the spring of socket i4. Metal terminal caps 28 on the tubes 22 provide the electrical connections of the tubes to the sockets I4. A similar cap 38 on the other end of each tube bridges the two halves of its socket 20. These split-cone sockets constitute switches and are connected in series by straps 32s@ that the circuit is complete only when the tube-caps 30 are seated in all four of the sockets, as is described in said application, Serial No. 743,248.

The tubes 22 areoiv the cold-cathode, instantaneously-starting type, operating with about 450 volts R. M. S. drop across the tube but requiring a somewhat higher total circuit voltage, the difference being absorbed in a reactance.

In Fig. 2, the four tubes 22 are shown schematically in my improved circuit. A transformer 40 includes a primary winding 42 and two-similar secondary windings 44 and 46 insulated ircmthe primary winding and each of which has considerable self ,inductance to provide the ballast needed for limiting the current tothe tubes 22. Any number of such secondary windings may be used. The secondary windings may have additional inductive or capacitive ballast devices connected in series with them as is well known in the art. Thus, a condenser 48 in series with Winding 44 provides ballast and improves the power factor of the current drawn by the primary winding. This winding 44 supplies a loadconsisting of two tubes 22 which at their ends remote from winding 44 (their right ends as viewed in Fig. 2) are connected to the primary circuit. Thus, although Winding 44 may 'deliver a total of about 900 volts under load, only about half of that can appear between either' left-hand tube terminal 28 and ground because one conductor of the volt input will be at or near ground potential. Furthermore,

should one tube fail to operate the other one will be thereby prevented from operating, and under such condition, winding 44 will be eiectively isolated by the extremely high resistances of the unlit tube. lNot only does the socket constructon'of Fig. 1 prevent contact with the concuit is opened and the secondary windingsde-` energized. Consequently it is impossible for a person t come into contact with highv voltage when a tube is removed unlesssocket 21V-is tampered with, as by the insertion cfa-conductor therein. But even in that case that person can receive the high voltage only throughav circuit l that includes the other tube. In this respect, the present series system is even more safe than the shunt system of my prior application, Serial No. 587,945, previouslyV referred to, which. employs a lower secondary voltage at the` trans.-` former.

In the circuit modification of Fig. 3, an impedance elcment'or condenserv ll'isconnected froml ground `52' to'a part of winding 44 inter-- mediate the terminals thereof, such as the mid-- voltage point, the core 43A of the transformer being also grounded as indicated"at"54. Alternatively, condenser Slmay be connected between said winding 44y andone of the terminals of primary winding 42: Condenser''has animpedance, atthe frequency of the supply voltage, which is high compared to that'of the tubes 22 when they are operating, but low compared to that of those. same tubes when unlit. Accordingly, when thetubes are unlit, thefpath through condenser Ell-will effectively tie the mid-voltage point of the winding to ground andso prevent the full voltage of the winding from appearing between either socket I4 and" ground when'one tube is defective or when a tube is removed vand its socket 'is tampered'with' for closing the primary circuit. When the tubes are lit, condenser 50? will be a high impedance shuntto aA part of the circuit and so have little effect.

The circuit of Fig. 2` hasy the advantage: that the winding 44 is better isolated from the other windings.

Thus the present invention provides thesafety of the shunt system but an economy; of the iseries system. Two tubes in series will strike atvless than twice the voltage required for two tubes, because the voltage will not initiallyy divide equally between the two tubes so that'they light in turn. Thustwo tubes requiring '750 volts'for shunt operation may be operated in series on 1300 volts. In addition, with the circuit of Fig. 3, the primary voltage is added to that of one of the two tubes for aiding its starting. After that one tube starts, its impedance drops to increase the voltage appliedto the other so that it starts too.

While I have shown and particularly described' a preferred embodiment of my invention, the specific features thereof, and the-detailed explanationy should not be construed as limiting except as required bythe claims.

What` I claim as new and desire-to protect by Letters Patent of the United Statesis:

1. Alsystem for energizing a pair ofluminescent electric tubes from an alternating current power supplycomprising, a transformer including a primary winding and a secondary Winding separate, andv conductively isolated, therefrom, means for connecting the primary winding to the alternating current power supply, means for connecting the pair of luminescent electric tubes in series with each other and in series with the secondary winding only of said transformer including means for connecting one end of'one tube to one endy of the secondary winding and including a condenser in series, means for connecting one end of the other tube tothe other end of the secondary winding and meansfor connecting the other ends of the tubes together, said means for connecting the primarywinding'to the alternating current supply',l includingsaid means for connecting the other endsof the tubes together so that the connection between said other ends of the tubes isat.no. time Ahigher than the potential of the alternating current power supply to the primary winding and so that when the connection between said other ends of the tubes is broken, theiconnection between the primary winding and the alternating current power supply is also broken;

2. A system for energizing a pair of luminescent electric tubes from an alternating current power supply comprising, a transformer including'a primaryy winding and a secondary winding separate and` conductively isolated therefrom, means for connecting the primary winding' to the alternating current power supply, means including a condenser for connecting the center of the secondary winding to ground, means for-connecting the pair of luminescent electric tubes in series with each other and in series with the secondary winding only of said transformer including means for connecting one end of one tube to one end of the secondary winding and including a condenser in series, means-for` connecting one end of the other tube to the other end of the secondary winding and means for connecting the other ends of the tubes together, said means for connecting the primary windingl to the alternating current supply including said means for connecting the other ends of the tubes together so that the connection between said other ends of the tubes is at no time higher than the potential 'of the alternating currentpower supply to the primary winding and so that when the connection between said other endsfof ,the tubes is broken, the connection between the primary winding and the alternating current power supply is also broken.

3. vAv system for energizing a plurality of pairs of luminescent electric tubes from an alternatingcurrent power supply comprising, a transformer including a primary winding and a plurality of secondary windings separate and conductively isolated therefrom, one secondary winding being provided for each pair of luminescent electric, tubes, means for connecting the primary Winding to the alternating current power supply, a plurality of connecting means each comprising means for connecting the luminescent electric tubes of each pair in series with each other and in series'with its associated secondary winding only of said transformer including meanszfor connectingv one end of one tube toone end of the secondary winding, means for connecting one end of the other tube to the other end of the secondary winding and means for connecting the other ends of the tubes together, said-,means for connecting the primary winding` to-the alternating current supply including. all ofY said means for connecting the other. ends ofthe tubes together so that all of said connections between said other ends of the Number Name Date tubes are at no time higher than the potential 1,950,396 Boucher Mar. 13, 1934 of the alternating current power supply to the 1,954,557 Comstock Apr. 10, 1934 primary Winding and so that when any of said 2,295,757 Russell Sept. 15, 1942 connections between said other ends of the tubes 5 2,305,096 McDermott Dec. 15, 1942 are broken, the connection between the primary 2,317,845 Boucher Apr. 2'7, 1943 winding and the alternating current power sup- 2,401,555 De Reamer June 4, 1946 ply is also broken. 2,402,207 Ranney June 18, 1946 OTHER REFERENCES Referencs Cited in the me of this patent Standard Handbook for Electrical Engineers, UNITED STATES PATENTS 7th edition, 1941 (McGraw-Hill, New York), Number Name Date page 1332 (sec. 14-68); copy in Sci. Library.

1,689,485 Hendry Oct. 30, 1928 15

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