US2890364A - Electric discharge tube - Google Patents

Description

Jun 9, 19,59

D. KQLKMAN ELECTRIC DISCHARGE TUBE Filed Feb. 17, 1956 .511% Illlnnll r/vwflaltrfltllitlllllle! tllrlltvaillst'ft. lll Illicit' INVEN-roR DIRK KOLKMAN AGE Ty United States Patent O ELECTRIC DlSCHARGE TUBE Dirk Kolkman, Eindhoven, Netherlands, assigner, by

mesne assignments, to North American Philips Colnpany, Inc., New York, NX., a corporation of Delaware Application February 17, 1956, Serial No. 566,256

Claims priority, application Netherlands February 26, 1955 2 Claims. (Cl. 313-109) My invention relates to electric Idischarge tubes.

More particularly my invention relates to the electric discharge tubes of the elongated positive column mercury discharge type having an envelope containing a phosphor layer on the inner surface and a starting strip on the phosphor layer. Such lamps are more generally referred to as fluorescent lamps.

One of the most important factors determining the life of such tubes is the number of times the tube, when energized, reaches the arc discharge condition.

Therefore a principal object of my invention is to provide electric discharge tubes of the type described which reach the arc discharge condition an increased number of times when energized.

According to my invention I surround and electrically connect one or both of the activated thermionic electrodes used in the above described tubes with separate molybdenum cylinders each having a Wall thickness of from about 10 to about 30 microns. However, if the tube contains two activated thermionic electrodes I prefer to surround only that electrode which is insulated from the starting strip with such a molybdenum cylinder.

In order that the invention may be readily carried into eiect, it will now Ibe described, by way of example, with reference to the accompanying drawing, showing one embodiment thereof.

As shown in the drawing a discharge tube comprising a glass envelope 1 is closed at its ends with conventional pinches 2 and filled with argon gas at a pressure of 3.5 mms. mercury column at room temperature and a small drop of mercury 3 which serves to maintain a low-pressure mercury vapour discharge. The inner side of the envelope is coated with a suitable phosphor 4. Extending the length of the tube over the phosphor is a graphite starting strip 5, about 3 mms. in width.

Sealed into the pinches 2 are Wires 6, 7, 8 and 9 for supporting activated thermionic electrodes 10 and 11, one of which 11, is electrically connected to the starting strip and the other 10, insulated therefrom. Surrounding electrode 10 is a molybdenum cylinder 12 which has a wall thickness of 20 microns. Cylinder 12 is electrically connected to electrode 10 by means of bent tag 13.

When the tube is connected, in series with a suitable impedance, for example, an incandescent lamp, to a source of alternating current of about 220 volts and 50 or 60 cycles, a glow discharge of about 10 to 40 ma., which is concentrated in the space between the activated thermionic electrode 10 and the cylinder 12, occurs between electrode 10 acting as the cathode and the opposite portion of the non-activated strip 5 acting as the anode. The thermionic electrode is rapidly heated to emission temperature by the glow discharge, whereupon a rectified arc discharge of about 200 ma., starting from the thermionic electrode 10 as the cathode, extends along the Patented June 9, 1959 ICC strip 5 to reach finally the activated thermionic electrode 11.

Electrode 11 is heated by the discharge moving toward it and by the current supplied to it lby way of the strip 5. After the emission temperature of the electrode 11 has been reached, the discharge changes to a symmetric arc discharge of about 500 ma. at a tube voltage of about 105 volts which is the normal operating condition.

This normal operating condition must be reached Within l0 seconds after the tube is energized, otherwise it is considered unserviceable.

The total number of times the tube reaches the arc discharge condition may be divided into the number reached within 3 seconds and the number when this period lies Within 3 to 10 seconds.

The discharge tubes of my invention reach the arc discharge condition within 3 seconds after being energized for the first 2000 times. Within 3 to l0 seconds they reach another 13,000 and hence in total 15,000 times.

If in the same tubes the activated thermionic electrode 11 connected to the strip 5 is also surrounded and electrically connected with a molybdenum cylinder having a thickness of 20 microns, the total number of times the arc discharge condition is reached decreases from 15,000 to 12,000.

With only one cylinder surrounding solely the thermionic electrode 10, but made of nickel and having a thickness of microns and otherwise with the same dimensions, the number of times the tube reaches the arc discharge condition within 3 seconds is only 1000 and the total number of times this condition is reached within 10 seconds is only 6000.

While l have shown and described the preferred embodiment of my invention, it will be understood that the latter may be embodied otherwise than as herein specilically illustrated or described and that in the illustrated embodiment certain changes in the details .of construction and in the arrangement of parts may be made without departing from the underlying idea or principle of the invention within the scope of the appended claims.

What is claimed is:

1. In an electric discharge tube of the elongated posit-ive column mercury discharge type and including an envelope containing a phosphor on the inner surface, an ionizable medium, an electrically conductive strip coated on the phosphor and extending in a direction parallel to the longitudinal axis of the tube, a first electrode located at one end of the tube and electrically connected to said conductive strip and a second electrode located to the other end of the tube and insulated from the said conductive strip, at least one of said electrodes including the second electrode being an activated thermionic electrode adapted to emit only upon heating by the discharge through said ionizable medium, at least one cylindrical member, composed of molybdenum and having a Wall thickness of from about l0 microns to 30 microns, electrically connected to one of said activated thermionic electrodes and positioned to enclose the electrode to which it is electrically attached.

2. The tube of claim l in which only the activated thermionic electrode that is insulated from the conductive strip is enclosed by a cylindrical member.

References Cited in the file of this patent UNITED STATES PATENTS 2,283,216 Lowry May 19, 1942 2,403,184 Lemmers July 2, 1946 2,549,355 Winninghotf Apr. 17, 1951 2,662,823 Elenbaas et al. Dee. 22, 1953

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