US1749780A - Incandescent-cathode device - Google Patents

Description

March 11, 1930. H. c. RENTSCHLER INCANDESQENT CATHODE DEVICE Filed Jan, 51, 1922 INVENTOR HARV EY C. RENTSCHLER.

Patented Mar. 11, 1930 UNITED STATES PATENT OFFICE HARVEY CLAYTON RENTSCHLER, OF EAST ORANGE, NEW JERSEY, ASSIGNOIR TO WEST- INGHOUSE LAMP COMPANY, A CORPORATION OF PENNSYLVANIA INCANDESCENT-CATHODE DEVICE Application filed January 81, 1922. Serial No. 583,105.

The present invention relates to electricaldischarge devices of the gas-filled incandescent-cathode type, particularly such devices as are employed for rectifying alternating currents.

' An object of my invention is to provide a rugged and simple device of the above designated character that shall have a commercially'long life and one which may be operated with a minimum expenditure of energy.

Other objects will be apparent from a reading of the following description.

t has been suggested to start an arc and, consequently, the flow of the current, between electrodes of refractory metals in an atmosphere of an inert gas by providing an auxiliary independently heatable electrode, and, while this auxiliary electrode is at incandescence, operating an arc between the auxiliary electrode and one of the main electrodes to heat this main electrode to incandescence and then to start the main arc, with the incandescent main electrode acting as cathode. In these devices,'separate presses, as well as separate leading-in wires, are required for the incandescent electrodes, which add considerably to the costof production and retard quantity output.

Another form of rectifier of the hot-cathode type is that in which there are only two electrodes, one of which is a coil of tungsten wire which is maintained at incandescence durin the operation of the rectifier. The life of this type of rectifier is shortened because of localized electrical erosion occurring at the heated electrode and also because of unequal strain being set up in the press of the hot-cathode leading-in wires whichresults from unequal current conditions in such wires. These rectifiers require more power to continually operate them than the type employing an auxiliary electrode, because, in the latter, the heating current may be discontinued after the arc has been started between the main electrodes, whereas, in the former the heating current must be maintained while the device is operating, which, obviously, is an additive current to that for maintaining the are between the electrodes.

In accordance with my present invention,

I provide an even simpler apparatus than that of the auxiliary-electrode type without losing any of the advantages that type ossesses over the two electrode :rectifier, and in addition, I provide a more rugged construction than the two-electrode rectifier and one which may be operated at no greater expenditure of energy than the auxiliary-electrode device and without danger of breakage at the press;

The accompanying drawing illustrates a device embodying my invention.

The device shown in the drawing comprises a transparent envelope 1 formed of glass or the like and containing two main electrodes 2 and 3 which are connectedby leading-in wires 4 and 5 extending through presses 6 and 7 to a suitable source of alternating current (not shown).

The main electrode 3 may be formed of any suitable material, such as graphite, tungsten, iron or the like, and is made considerably larger than the electrode 2 to prevent it from becoming heated to electron-emitting temperature and thus prevent it from functioning other than as an anode during the operation of the rectifier.

For the purposes of my invention, I prefer to construct the electrode 2, which, in the normal operation of the device, becomes the cathode, of a material having a higher electron emissivity than tungsten, A material suitable for my purposes is thorium or zirconium. The reasons for utilizinga material having a high electron emissivity will be more fully appreciated hereinafter. It may be found preferable to form electrode 2 of a base substance such as tungsten and apply a coating of a metal having a high electron emissivity. The electrode 2 may be pointed to facilitate its being heated.

Although the device thus far described may be operated Without the employment of any additional apparatus, I prefer to utilize such auxiliary devices because lower starting potentials may be used. To this end, I may connect, in series with the main electrode 2, a heating coil 8 connected to a current source by a leading-in wire 9 extending through thepress 6. The heating coil may be formed of any suitable refractory material, such as tungsten or the like, but,

for the purposes of my invention, the metal of which the coil, is formed should have a lower electron emissivity when at a definite temperature than that ofthe metal of which the main electrode 2 is composed. Preferably, the heating coil 8 is arranged at an angle with respect to the longitudinal axis of the container and at a lower level than the electrode 2, in order that the heat arisingv from the, heated coil 8 may cause the electrode 2 to become heated by convection, as

well as by conduction, to a temperature sulfiabout 2000 C., the temperature of the main electrode 2 becomes about 1500 C. to 1700 C. at which temperature its electron emissivity is greater than that of the more highly heated body 8. With such an arrangement,

the are which forms betweeif the main electrode 3 and the heating coil 8 finally leaves or deserts the heating coil and seeks the main electrode 2 between which and the electrode 3 the discharge then occurs. The heating coil may then be disconnected by a suitable switch 10 placed in the circuit.

The simplicity of the structure is apparent, as but one press is necessary to accommodate the leading-in Wires-for the heating coil and the cathode. Furthermore, this construction permits the current required to bring the heating coil to incandescence to be disrupted after the arc is formed between the main electrodes, thus effecting an economy in the current consumption.

In the preparation of the device, the spac within the envelope should be carefully evacuated of all gases and vapors. Preferably, a filling of an inert gas, such as argon, neon or the like, is thenintroduced within the en- .velope. The pressure of the gaseous atmos phere will vary in accordance with the voltages and other electrical operating conditions. Ordinarily, the pressure should not be below several millimeters to avoid destructive electrical erosion of the heated cathode. For low-voltage rectifiers, a pressure of about .5 to 12 centimeters of mercury is desirable.

Modifications falling within the scope of the appended claims are considered as pertaining to my invention.

What is claimed'is:

therebetween mental cathode, said supplemental cathode comprising a heating coil for heating said main cathode to electron-emitting temperature, and being positioned with respect to said anode to permit a discharge to pass said main cathode being formedof a material having a higher electron emissivity than the material of said coil.

2. A rectifier comprising a sealed envelope, a main anode, a main cathode, asuppplemental cathode comprising a heating coil in series with said main cathode, said supplemenv tal cathode being positioned with respect to formed of a material of higher electron emissivity than the material of saidheating coil.

4. An electrical device comprising a sealed envelope, an anode of any suitable material, a thorium cathode, and a heating coil of tungsten in series with said cathode and so disposed with respect thereto as to heat the same by convection and conduction.

'5. An electrical-discharge device comprising a sealed envelope, an anode of any suitable material, a cathode of a refractory ma terial, and a heating coil of a refractory material of lower electron emissivity than said,

cathode material, said heating coil being disposed adjacent said cathode to heatthe same. 6. A rectifier comprising a large iron anode, a small thorium cathode and a tungsten heating coil in series with said cathode.

In testimony whereof, I have hereunto subsgiibed my name this 30th day of January, 1 2.

HARVEY CLAYTON RENTSCHLER.

said anode to permit a discharge to pass

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