US2246302A - Heating device for glow cathodes - Google Patents

Description

June 17, 1941. F. HAUFFE ETAL 2,246,302

HEATING DEVICE FOR GLOW CATHODES Filed March 50, 1939 INVENTORS FR/TZ HA UFFE HERA/l /v KROPP BY 2 ATTORNEY.

Patented June 17, 1941 HEATING DEVICE FOR GLOW CATHODES Fritz Hauife, Berlin-Friedman, and Hermann Kropp, Berlin-Treptow, Germany, assignors to General Electric Company, a corporation of N cw York Application March 30, 1939, Serial No. 264,920 In Germany March 8, 1938 6 Claims.

The present invention relates to a regulating device for the starting of glowing cathodes of electric discharge, especially of transmitting tubes with large output, by the aid of magnetically saturable choke coils.

Iron-filled saturated choke-coils are known in the prior art. Their action is based on the fact that their resistance to alternating currents is great if the iron core is only slightly saturated, and decreases resistance in proportion to the increasing saturation. Thus, for instance, battery charging devices have become known which are charged from an alternating current net Work across a rectifier of known construction. A choke coil having a magnetising winding through which the charging current traverses is provided on the primary side or input of the rectifier. If the battery counter-voltage is low, viz. at the commencement of the charging operation, a large current saturating the choke coil is flowing. With the increase of the counter-voltage of the battery the saturation of the choke coil decreases, that is to say, its resistance increases, so that the charging current decreases automatically with the progression of the charging operation, whereas simultaneously therewith the battery voltage increases.

Also compounding systems have already been suggested in which the generated voltage is kept constant in dependency of the current with the aid of a saturated choke coil. With these arrangements the choke coil has, besides the magnetising winding traversed by a continuous current, another winding subjected to the action of continuous current voltage, the action of this winding being against the action of the firstmentioned winding. With all these known connections the problem is always to maintain the generated continuous current voltage constant over the entire regulating range.

The present invention relates to a starting device for the heating implement of glow-cathode tubes. There arises in connection therewith the following problem: The ohmic resistance of the glow-cathode under normal working conditions is by a multiple larger than when the cathode is cold, in consequence whereof it is necessary, especially with tubes with a large output, to heat at first with a small current only and thereafter to increase the current in proportion to the increasing heating of the glow-cathode. If this precautionary measure is not paid attention to, considerable electro-magnetic forces may be exerted upon the individual windings of the oathode by reason of the strong initial rushes of current which are able to destroy the cathode mechanically. There exists also the risk that at those places of the glowing wire which are a little thinner than the other portion thereof a local superheating arises, in consequence whereof the heating wire will fuse.

In order to render such a regulation of the heating wire possible there is, according to this invention, a choke coil provided in the primary or input circuit of the rectifier, the magnetising winding of which is fed with the voltage of the consumer or input in contrast to the known wireconnections, in which the continuous current flows through a saturation winding.

The invention is illustrated diagrammatically and by way of example on the accompanying drawing on which Figure 1 shows the arrangement and combination of the parts concerned and Figure 2 is a representation of a diagram, all as fully described hereinafter.

In Fig. 1 it is assumed that the glow cathode is to be supplied with current from a one-phase net Work. The alternating current net work supplies the input of a rectifier G with current across a choke-coil D. On the secondary or output side of the rectifier, which may be, and preferably is, a dry rectifier the glow cathode K of the discharge gap is connected up. The magnetising winding of the choke coil D is connected to the consumer or output voltage, as already mentioned above. As long as the cathode is cold and its resistance is small the saturation of the choke coil is likewise small, that is to say, its impedance is large and only a small current flows, therefore, to the cathode. With the increase of the heating also the resistance of the cathode increases and, therefore, the voltage drop increases, too. Owing thereto, the preliminary magnetisation of the coil D by continuous current increases, the resistance of this coil decreases, and the heating current increases likewise.

Fig. 2 illustrates the conditions as regards the current and the voltage in their dependency on the time. The lines U and J drawn in full lines show the proportions pertaining to the present case. When the fall of the voltage at the consumer increases, also the current increases. The dashed line J indicates the course of the current with the known wire-connections in which the magnetisation of the choke coil is effected in dependency of the current.

Concerning the dimensions of the choke coil it has been ascertained that it is favorable to admit in the consumer an initial current amounting to from 30 to of the service current and to select the magnetic inertia so that the normal value of the current is attained after a period of time amounting to about from 0.5 to 2 minutes.

I claim:

1. A regulating starting device for an electron discharge device having a cathode comprising a choke coil having a core subject to magnetic saturation and two windings, an input source of voltage, a rectifier having a pair of input and output leads, one of the windings of said choke coil connected in series with one of the input leads of said rectifier and said input source of voltage, the other rectifier input lead connected to said input source of voltage, the other winding of said choke coil connected in parallel with the rectifier output leads and the cathode of said electron discharge device whereby the choke coil is increasingly saturated with an increase in cathode temperature and allows more current to;

flow from said source of voltage.

2. A heating device for an electron discharge device having a glow cathode comprising a source of input voltage for said cathode, a rectifier having an input and output, a choke coil having a magnetic winding and a saturation winding, said magnetic winding connected in series with one side of said source of input voltage and one side ofsaid rectifier. input, the other. side of said source of input voltage connected to the other side of said rectifier input, the output of said rectifier connected to said cathode and said saturation winding whereby an increase in resistance of the glow cathode of said electron-discharge device causes an increase insaturation of said chokecoil and permits an increase of currentto flow in said cathode from said source of input voltage. r V

,3..,,An electric regulating system comprising an electron=discharge device having a cathode the source ofvoltage, the other side of said rectifier input connected to the other side of said source of voltag,e,,and a second impedance means con-.

nected in parallel, between said cathode and said rectifier for controlling said first mentioned means whereby its resistance decreases as the cathode resistance increases. 7 l

4. A regulating device for the startingof .glow

ing an input and an output, a choke coil having a magnetic winding and a saturation winding, the dimensions of said coil being such that the initial starting currents amount to from thirty to fifty percent of the normal operating current of said electron discharge device, said magnetic winding connected in series with one side of said source of input voltage and one side of said rectifier input, the other side of said source of input voltage connected to the other side of said rectifier input, the output of said rectifier connected to said cathode and said saturation winding whereby an increase in resistance of the glow cathode of said electron discharge device causes an increase of saturation of said choke coil and permits an increase'of current to flow in said cathode circuit from said source of input voltage. 5. A regulating device for the starting of glow cathodes of an electron discharge device comprising a source of input voltage, a rectifier having an input and an output, a choke coil having a magnetic winding and a saturation winding, the magnetic inertia of said choke coil being so selected that the heating process of the cathode is completed in from one-half to two minutes, said magnetic winding connected in series with one side of said source of input voltage and one side of said rectifier input, the other side of said source of input voltage connected to the other side of said rectifier input, the output of said rectifier connected to said cathode and said sat,- uration winding whereby an increase in resistance of the glow cathode of said electron discharge device causes'an increase of saturation or said choke coil and permits an increase of current to flow in said cathode circuit from said source of input voltage. V Y

, 6. A regulating device for the starting of glow cathodes of an electron discharge device com prising a means for heating said cathode, a rectifier having an input and an output, an impedance coil having two windings, at least one of ,said windings connected in parallel with said rectifier and said cathode, the other winding connected in series with the input of,said recti-,

' resistance increases.

FRITZ HAUFFE. HERMANN KROPP.

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