US2182780A - Gaseous electric discharge device - Google Patents

Description

H. ALTERTHUM ETAL 2,182,780

GASEOUS ELECTRIC DISCHARGE DEVICE Filed Aug. 22, 1938 Fig. I.

Cuvrent INVENTQ RS Hams .Al'terthum Arved, Lomp BY ATTORNEY Pmnad Dec. 12, 1939 UNITED STATES PATENT OFFICE 1 2,182,780 Gaseous ELECTRIC- mscnanea nEvrcE Application August 22, 1938, Serial No. 226,190 In Germany September 16, 1937,

3 Claims. (01. 176-124) The present invention relates to gaseous electric discharge devices of the positive column'type and particularly to devices of this type containing mercury vapor.

5 A particular object of the invention is to provide a gaseous electric discharge device which will have a positive volt-ampere characteristic,

whereby the need for a series ballast is elimi-- nated or greatly minimized. Still other objects 10 of the invention will appear from the following detailed specification, or from an inspection of the accompanying drawing.

The invention consists in the new and novel structure hereinafter set forth and claimed. 16 It is well known that the positive column discharge in a gaseous electric discharge device has a negative volt-ampere characteristic under usual operating conditionsthat is to say, that the voltage gradient in the discharge decreases 20 with increasing current. It is for this reason that a series impedance has been used with all of these devices in order to stabilize the current.

We have now discovered that the need for such a series impedance is eliminated or greatly mini- 25 mized with a low pressure mercury vapor device of the positive column type provided certain critical conditions are established. .Thus we have discovered that by providing such a mercury vapor device with a filling of rare gas at a pressure within the range of from 48 mm. of mercury column the discharge has a distinctly positive volt-ampere characteristic at current strengths of a few up to 50 milliamperes, and a substantially constant voltage gradient for currents somewhat irrexcess of this, up to the order of 100 milliamperes, provided the rare gas consists 01 neon with an admixture of from 0.2 to 0.9% of krypton or xenon. This mixture of gases, at this particular pressure, in addition to to providing a positive volt-ampere characteristic, as thus described, whereby the discharge is uniquely sell-stabilizing, also results in an extremely low breakdown potential and re-ignition voltage which is but little in excess of the normal discharge maintaining voltage. As a result such a device will operate on a constant potential source either without a stabilizing impedance, or with at most only a small impedance to absorb the diflerence between the starting and maintaining voltages. This novel discharge device is thus not only extremely efficient, but also requires a minimum of investment for auxiliary apparatus. These novel operating characteristics are moreover retained throughout a considerable;

range of ambient temperatures, from a temperature so low that the mercury is all condensed to temperatures considerably in excess of normal room temperatures. At very low temperatures the discharge tends tobecome reddish in color, because of the reduction in the mercury vapor 5 pressure, but this is oflset, where desired, by theuse of special hollow cathodes containing mercury, with a capillary exit for the mercury vapor, the heating of the cathode by the cathode fall being suflicient to vaporize the requisite amount oi. mercury to give the characteristic mercury color to the discharge.

The reason for this unique and hitherto unknown reversal of the volt-ampere characteristic obtained with-our novel construction cannot be stated, since previous theoretical concepts of the discharge do not sumce in this particular case. Measurements, however, confirm the fact that the voltage gradient in the positive column increases in a surprising manner in this novel de.- vice with increases in current, as hereinbeiore stated, and also reveal that the voltage drop at the electrodes also increases in a surprising manner with increases in current where this novel gas mixture is used at a pressure within the critg5 lcal range, especially where cold type electrodes are used. 7

In general we prefer to use either two cold cathodes or one cold and one hot or thermionic type electrodes, although where tubes having a relatively long positive column are involved, two thermionic cathodes are employed where desired, since under these circumstances the increase in voltage gradient in the positive column is suificient to offset any possible decrease in the cathode fall at thethermionic cathode with increasing current; These devices will operate on either direct or alternating current. with op eration on direct current, however, care is preferably taken to prevent undue separation of the o gases by the electro-phoretic effect.

For the purpose of illustrating our invention we have shown a preferred embodiment thereof in the accompanying drawing, in which Fig. 1 is an elevational view, in part section, of a lamp constructed in accordance with the invention and Fig. 2 is a graph showing the operating characteristics thereof.

As shown in Fig. 1 this novel lamp comprises a tubular envelope I of suitable vitreous material having an inside diameter of 20 mm. Within said envelope there are a pair of electrodes 2 and 3 which are separated by a distance of the order of 1 meter. As shown these elecdevice.

trodes consist of sheet iron cylinders 50 mm. long and 17 mm. in diameter. One or both of these electrodes may have, where desired, an inner member 4 which forms an inner chamber within the electrode which contains a quantity of mercury 5, a capillary 6 communicating with this chamber and allowing the escape of mercury vapor therefrom. Likewise, where desired, one or both of the electrodes may be of the activated thermionic type. The envelope l is filled with neon intermixed with from 0.2 to 0.9% of krypton or xenon at a total pressure of from 4 to 8 mm., as hereinbefore described, but a preferred filling consists of neon containing 0.5% of krypton or xenon at a pressure of 6 mm. Such a device will start, with an ambient temperature of -22 C. on 800 volts, and will operate with a voltage of 650 volts at 40 milliamperes.

With currents of the order of 100 milliamperes the volt-ampere characteristic is weakly negative, and hence where a series impedance 1 is used the value of this impedance and of the applied voltage are preferably so chosen that it is impossible for the discharge to jump over onto this descending branch of the voltage-current curve. Thus as shown in Fig. 2 the curved line shows the relation between voltage and current in our novel The straight line drawn through the applied voltage Vo (equal to breakdown potential) shows the voltage available for the discharge device at any current. This line is preferably steep enough that it intersects the curved line at the desired operating current value, and then does not again intersect the curved line at higher currents. Where the applied voltage is less than the highest voltage reached on the asceding portion of the curve, as in those cases where the ignition voltage is reduced to this value, or where a starting impulse or auxiliary electrodes are employed, a series impedance is, of course, entirely unnecessary, since then there is no tendency for the discharge to run away under any condition.

In those cases where it is desired the envelope I may of course be made of fluorescent glass or coated on the inside with a fluorescent material in a well known manner in order to increase the luminous efficiency or to alter the color characteristic of the emitted light or both. It is also to be understood that various other changes,

omissions and substitutions, within the scope of the appended claims, may also be made in the structure shown and described without departing from the spirit of the invention.

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

1. In combination, a gaseous electric discharge lamp having a positive volt-ampere characteristic comprising a sealed tubular envelope, electrodes within said envelope and spaced to permit a positive column discharge therebetween, mercury within said envelope and a gas filling consisting of neon intermixed with from 0.2 to 0.9% of a gas from the group consisting of krypton and xenon, said gas being at a pressure of from 4 to 8 mm. of mercury, and means to supply a current of from a few milliamperes to 50 milliamperes to said device, whereby said device operates stably with a positive volt-ampere characteristic.

2. In combination, a gaseous electric discharge lamp having a positive volt-ampere characteristic comprising a sealed tubular envelope, electrodes within said envelope and spaced to permit a positive column discharge therebetween, mercury within said envelope and a gas filling consisting of neon intermixed with 0.5% of a gas from the group consisting of kryton and xenon. said gas being at a pressure of 6 mm. of mercury, and means to supply a current of from a few milliamperes to 50 milliamperes to said device, whereby said device operates stably with a positive volt-ampere characteristic.

3. In combination, a gaseous electric discharge lamp having a positive volt-ampere characteristic comprising a sealed tubular envelope, electrodes within said envelope and spaced to permit a positive column discharge therebetween, at least one ofsaid electrodes being of the cold type, mercury "within said envelope and a gas filling consisting of neon intermixed with from 0.2 to 0.9% of a gas from the group consisting of krypton and xenon, said gas being at a pressure of from 4 to 8 mm. of mercury, and means to supply a current of from a few milliamperes to 50 milliamperes to said device, whereby said device operates stably with a positive volt-ampere characteristic.

HANS AL'I'ERTHUM. ARVED LOMPE.

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