US2144888A

US2144888A - Gas-enclosed resistance element

Info

Publication number: US2144888A
Application number: US171110A
Authority: US
Inventors: Meyer Wilfried; Neldel Hans
Original assignee: Patent Treuhand Gesellschaft fuer Elektrische Gluehlampen mbH
Current assignee: Osram GmbH
Priority date: 1936-10-31
Filing date: 1937-10-26
Publication date: 1939-01-24
Anticipated expiration: 1956-01-24
Also published as: GB484762A; DE688342C

Description

Jan. 24,-1939. w. MEYER ET AL GAS-ENCLOSED RESISTANCE ELEMENT Filed 001;. 26, 1937 2 Sheets-Sheet l Fig.2

Fig.4

Jan. 24, 1939. w. MEYER ET AL 2,

GAS -ENCLOSED RES I STANCE ELEMENT Filed Oct. 26, 1937 2 Sheets-Sheet 2 Patented Jan. 24, 1939 UNITED STATES PATENT OFFICE Patent-Treuhand-Gesellschaft fiir elektrische Glilhlampen nab. 3., Berlin, .Germany Application October so, 1937, Serial No. 111,113 In Germany October 31, 1936 7 Claims.

The present invention pertains to an improved variable resistance having low inertia. andmore specifically to an arrangement of resistance material, having a high temperature coeillcient, in a gasefllled vessel.

Resistances formed of semi-conductor materials with high temperature coemcients of resistance, as, for example, certain metal oxides or oxide mixtures, can be given diiferent resistance values at will by extraneous heating. It is easy to carry resistances formed of such materials to high temperatures in a relatively short time. There is, however, the serious defect that the temperature of such a resistance, which has been heated, drops very slowly after the heating is reduced. According to the present invention this difllculty is overcome by forming the resistance member as a hollow cylinder closely encompassing the heating element, and by placing the member in a gas-filled vessel suihciently large that the gas can freely flow around the member. By making the space between the heating and resistance elements small, flow of gas in this space, which would interfere with the heating, is prevented. The resistance element is thus rapidly heated by conduction and radiation to the desired temperature. In operation, if the encompassing vessel is sumciently large and filled with an easily mobile gas, for example, hydrogen, substantially only the outside of the resistance member is exposed to a powerful temperature influencing flow of gas. It is easily possible in this manner to maintain the outside of the resistance at approximately the temperature of the surrounding chamber. In one experiment an excess temperature of about 40 was measured. Inasmuch as the gas filling outside the resistance tube or member has a substantially lower temperature than the non-flowing gas inside the tube, the gas at the outside of the tube need not be substantially cooled, and thus has little effectv on the heat capacity of the entire arrangement. In many cases nitrogen or argon can be used instead of hydrogen. Thus by this construction a resistance which will be cooled quickly, as well as quickly heated, is provided, thatis, a resistance having low inertia is obtained.

The heating element can be made of a material having an entirely different temperature coeflicient from that of the resistance material, whereby a rapid equilibrium is attained even in cases in which use is made of a relatively low temperature of the heating element. In this case the heating element may be-made, for example, of constant or temperature-coe'mcient-free semiconductor materials. If it is desired to attain a particularly rapid adjustment of the resistance with high-heating, a heating element with higher operative temperature is selected. For this purpose heating elements of tungsten or molybdenum having an operative temperature above 800 C. are suitablef The distance between the surface of the heating element and the inner surface of the resistance element should generally be less than 3-mrn., and preferably 0.8 to 1 mm. in order to avoid a flow of the gas in this intermediate space owing 'to temperature differences. If, in order to obtain a large cross section for av semiconductor resistance element of small thickness of the wall, a large diameter tube of the semiconductor material is selected as a resistance element, it may often be undesirable or unsuitable to give the heating resistance itself such large cross section as to retain the desired small distance between the surface of'the heating element and the inner surface of the semi-conductor resistance member. In such a case it is necessary to use auxiliary means in order to suppress the flow of gas between the heating and resistance elements owing totemperature differences. For this purpose caps or discs preferably of insulating material may be provided at the ends of the resistance tube, such caps or discs extending transversely to the longitudinal direction of the tube. The distance between the vessel wall and theresistance member is preferably more than 1 cm. Hydrogen at 10-300 mm. Hg is suitable as a gas filling. A filling, at 170-200 mm. Hg, with a uniform distance of 1 mm. between resistance and heating element has produced favorable results.

Conductive spinels, such as magnesium-titanate, are particularlysuitable as resistance elements. Such resistance elements can be made of 60 parts by'weight, of'magnesium oxide and 40 parts by weight of titanium oxide, the mixture being extruded in the form of small tubes and then burned, first for an hour in air at 1100 C. and then also for an hour at 1450 C. to 1500 C. in a hydrogen atmosphere. The hydrogen, before being passed into the furnace, is passed through washing flasks filled with water, to charge it with water vapor. i

In a-preferred embodiment of the invention a-small tube of magnesium-titanate spinel, having an external diameter of 1.2 mm. and an internal diameter of 1.0 mm., as well as a length of 4 mm. between the current lead-ins, was heated by a tungsten filament taking about 4 watts. When this arrangement was placed in a gasfilled vessel, the internal friction of the gas caused by the very small inner diameter of the tube reliably prevented flow of gas in the interior of the tube. In this construction the vessel encompassed the resistance elements at about mm. distance and was filled with hydrogen at 200 mm. Hg pressure. At 4 watts heating the resistance of the tube amounted to about 10,000

ohms. After cutting off the heating current, the

i0 resistance element cooled so rapidly that already after 1.5-4 seconds it attained 90% of its cold resistance. After 4 seconds several hundred thousand .ohms were measured. This short period for cooling Was attained because, through 15 radiation, through conduction and through convection in the gas freely flowing in the glass vessel, only the heat in the inner part of the tube, in the gas enclosed in the tube and in the heating filament had to be dissipated. This -2 quantity of heat is very small and can easily be given off to the gas through the thin walls of the tube. In the accompanying drawings, we have illustrated some preferred forms and applications of .55 our invention. In these drawings:

Fig. 1 illustrates a resistance arrangement embodying our invention; ,,j I il/Figs. 1 and 1 illustrate two modifications of t e resistance element;

"Figs. 2 and 3 illustrate two applications of our invention to automatically regulate a gas-filled discharge, tube;

Fig; 4 illustrates an application of our invention-for the manual regulation of a gas-filled dis- 36 charge tube;

, Fig. 5 illustrates an application of our invention for the regulation of sound intensity of an amplifying apparatus;

Figs. 6 and '7 .illustrate two applications of our invention to the control of incandescent lamps.

Fig. 1 shows a preferred embodiment of ourinvention. The tubular resistance. element I made, for example, of uranium dioxide, encompasses the heating filament 2 at a small distance.

The heating filament 2 is rtensioned by a spring 3. The arrangement is mounted in a closed glass vessel 4 filled with hydrogen. The pinched-off portion 5 is traversed by four current leads, the

leads 6 and I passing to the resistance member I and leads 8 and 9 to the heating member 2. The

tubular resistance element has a bore 26 throughout its length; the diameter otwhich is preferably 2 mm. In the axis of this bore is arranged the heating filament 2. 3 On account of the little distance between the heating 'member and the inner surface of the resistance element the flow of gas in the bore is suppressed. If the resistance element is a tube of greater diameter, as illustrated in Fig. 1 and Fig.1", the flowing of the gas may be suppressed by discs 21 (Fig. 1 or caps (Fig.

l The discs 21 are preferably of insulating material and held in position by fingers 29 of the contact members 30. In the. construction of Fig.

1 the caps 28 are of metal and they are integral with the contact members 30.

With our invention the resistance variation in the resistance element is always produced by the differential heating through the heating resist ance and without resort to movable contacts.

The circuit can readily be such that a variation of the pre-resistance interposed in series with the heating resistance for a length unit, for example, for one or more centimeters, corresponds to a decimal power variation of.the semi-conductor 76 resistance. It is thus easily possible to cover a for the semi-conductor tube. latter function to increased extent the more ourductor tube increases.

range of three decimal powers with the semiconductor resistance.

The'resistance of the invention can be used with equal success as automatically regulating or manually regulated resistances. u

Fig. 2 shows by way of example the use of our improved resistancewith a gas-filled discharge vessel. Connected in series to the potential source I0 is a rheostat resistance I I and the semiconductor resistance element I2. In parallel with the latter is the primary coil of the transformer I3, which supplies the energy for a useful load,

for example, the gas-filled discharge vessel I4. The discharge vessel is connected to the secondary side of the transformer in series with the heating elementfor the semi-conductor resistance. It is apparent that in this connection excessive increase of the current passing through the discharge vessel will heat the heating element for the semi-conductor resistance. The temperature of the latter is thereby also increased and it takes up less potential. The result of this is that the primary coil ofthe transformer has a smaller potential. The smaller potential at the transformer automatically reduces the current through the, discharge vessel. Automatic regulation is thus obtained.

.Fig. 3 shows another arrangement. It is often desired to'use a transformer .with greater dispersion, thus having relatively great copper and iron losses, in order to limit the energy supplied to the discharge tubes. The dispersion of the transformer, that is, the reduction of potential with increasing current load, cannot be made great as desired, as thereby the transformer would be heated too much. It is, therefore, advantageous to mount a resistance member, according to the present invention, parallel with the secondary winding of the transformer. The secondary winding of the transformer I3 first feeds a rheostat resistance and the discharge tube ll in series therewith. The rheostat resistance serves at the same time as a heating resistance for the resistance element I2. Another resistance II can be interposed in series with the resistance element I 2. The heating filament has the function of serving as an interposed rheostat for the discharge vessel as well. as a heater It performs this rent is taken by'the useful load, that is, by the discharge tube. As a result of increasing current flow through the discharge tube the resistance of the semi-conductor tube drops, and at the same time the current flow th ough this semi-con- This, however, causes an additional load on the secondary coil and therewith a lowering of the transformer potential. Here also automatic regulation is obtained.

Fig. 4 shows a further preferred embodiment. The heating filament for the semi-conductor resistance I2 is in this case mounted in series with a regulating resistance It and also a tapping of thetransformer I3. The main secondary winding of transformer I3 feeds the discharge tube I4 and the semi-conductor resistance I2 in series therewith. The value of resistance I2 can be regulated, and thereby the current passing through the discharge tube adjusted to the desired value, by manually adjusting the regulating resistance I5. It is known, for example, that gasfllled discharge tubes burn .hard after long use,

that is, have ahigher potential drop across the vessel because of gas consumption. Byregulating the resistance It the potential at the disargues charge tube can easily be adjusted to obtain operative requirements. -A special advantage here is that the regulation, even with arrangements operating at high voltage, is accomplished by a desistances which form either a shunt to the inlet coil of the aerial circuit or a shunt to the grid circuit of the first low frequency tubes. The incident high frequency amplitude is more or less strongly decreased according to the magnitude of the shunt, through the potentiometer resistance. For these connections use is made preferably of the resistance arrangement according to the present invention. I p A. C. instruments the heating filament of thesemi-conductor member is placed in series with a regulating resistance at the heating coil of the transformer. With -D. C. or universal current apparatus it is mounted in parallel with a regulating resistance in the heating circuit. The potentiometers hitherto used, made for the most part of carbon resistances with sliding contacts, have great defects, as the transmission resistances between the sliding contact and the resistance material easily produce scratching noises, which are then amplified and cause disturbing noises in the loud speaker. This defect is completely eliminated by the present resistance, as scratching noises are eliminated through the absence of sliding contacts. The semi-conductor resistance when it forms a shunt to the aerial coil, is preferably selected so that-it has at room temperature a re- .sistance of 10 to 10 ohms and at the highest perative temperature a resistance of 10 ohms. If the resistance is placed between high and low frequency stages, it is selected preferably so that the cold resistance is 10 to 10 and the resistance at operative temperature is 1i) to 10'.

Fig. 5 shows an embodiment of such amplifying-apparatus. The tubular resistance element I is connected by the conductor 3| to the earth line 32 and by the conductor 33 to the grid 35 of a low frequency tube 36, a condenser 34 being arranged in said conductor 33. The resistance element l is further connected by means of a resistance 31 and an oscillatory circuit 38 to an anode 39 of a duodiode 40. has preferably a value of 0.1megohm. The oscillatory circuit 38 comprises a condenser 4i and the secondary 42 of a transformer 43. The fiow of the oscillating current in the anode-circuit of the duodiode! causes an oscillating voltage drop at the resistance element i and this oscillating of the voltage drop is transferred to the grid 35 of the low frequency tube 36. The regulation of sound intensity is effected by the regulation of the voltage amplitude at the resistance element I. For this last mentioned regulation serves the variable resistance 34 in the circuit 45 of the heating filament 2. This variable resistance 44 has preferably a maximum value of 7 ohms. The heating filament 2 and the heating filaments 48, 41 of the duodiode 40 and the low frequency tube 36 are fed by the heating transformer 43. With 49 is designated the usual resistance in the The resistance 31 grid circuit of the low'frequency tube and with 50 the loading condenser of the duodiode 40.

The resistance arrangement of the present invention can also be used for the control of incande'scent lamps. Figs. 6 and '7 show by way of example embodiments therefor. According to Fig. 6 the resistance tube It encompasses a portion of the incandescent lamp filament contained in the lamp envelope I! in the usual manner by means of a pinch base It, a supporting rod i9 and the supporting wires 20. The filament 2| is connected to the secondary winding 22 of a transformer, while the resistance element It lies parallel with the primary coil 23. The primary coil of the transformer has a resistance 24 interposed in series therewith and which resistance may be, for example, an iron-hydrogen resistance. The incandescent lamp is filled with a gas which is as fluent as possible.

In this arrangement, on increasing the load of the incandescent lamp, the resistance element I6 is heated and thereby the potential at the ends of the primary coil 23 of the transformer reduced, as the current intensity passed to the transformer from the primary side is limited by the resistance 24. parts with each other, through this arrangement either the current intensities passing through the incandescent filament 2! of the lamp can be held constant at varying net potential, which is'of advantage in such a lamp for measuring purposes, or, through back-coupling between the heating element of the resistance member l6 and the short circuiting of the primary coil of the transformer, an oscillation is produced which can be used, for example, for signalling purposes. For this purpose it is only necessary to substitute the discharge vessel ll of the arrangement according to Fig. 2 by an incandescent lamp.

In the arrangement of Fig. 7 the heating member 25of the resistance arrangement according to the invention is connected in series with the incandescent lamp filament ,2 I. incandescent lamp lies the resistance member It. This arrangement operates like that of 'Fig. 6.- Thereby the heating element 25 of the resistance arrangement of the present invention-serves as a rheostat for theincandescent lamp.

If use is made of the arrangements described in order to maintain the current load of the incan-j descent lamp invariable, the value set up can be maintained so accurately that exact exposures can be obtained in duplicating exposures'in photography. The exposure times can thus be invariably set once for all and are free from effects of fluctuations in the applied potential.

What we claim is:

1. A resistance arrangement of comprising a gas-filled vessel, a resistance member of semi-conductor material formed into a hollow body and mounted in said vessel, said hollow body being free of insulating 'material in teriorly, and a heating element within said hollow body, the spacing between said hollow body and said heating element being sufficiently small to suppress convection currents of the gas within said hollow body, whereby interference with rapid heating of the resistance member from within by interior gaseous convection currents is avoided, and the spacing between said member and the inner walls of said vessel being suillciently great to permit free-flow of gaseous convection currents about said member so that. rapid cooling of the resistance member by gaseous convection currents exterior 'to said'member is obtained.

According to the tuning of-the individual Parallel with thelow inertia,

2. A resistance arrangement of low inertia, comprising a vessel filled with hydrogen gas under a pressure of -300 mm. of mercury, a resistance member of semi-conductor material formed into a hollow body and mounted in said vessel, said hollow body being free of insulating material interiorly and a heating element within said hollow body, the spacing between said hollow body and said heating element being sufilciently small to suppress convection currents of the gas within said hollow body, whereby interference with rapid heating of the resistance member from within by interior gaseous convection currents is avoided, and the spacing between said member and the inner walls of said vessel being sufliciently great to permit free flow of convection currents about said member so that rapid cooling of the resistance member by gaseous convection currents exterior to said member is obtained.

3. A resistance arrangement of low inertia comprising a gas-filled vessel, a resistance member of metal ox des formed into a hollow body and mounted in said vessel, said hollow body being free of insulating material interiorly, and an electron conductor heating element within said hollow body, the spacing between said hollow body and said heating element being sufiiciently small to suppress convection currents of the gas within said hollow body, whereby interference with rapid heating of the resistance member from within by interior gaseous convection currents is avoided, and the spacing between said member and the inner walls of said vessel being sumciently great to permit free flow of convection currents about said member so that rapid cooling of the resistance member by gaseous convectioncurre'nts exterior to said member is obtained.

4. A resistance arrangement of low inertia, comprising a gas-filled vessel, a resistance member of semi-conductor material formed into a hollow body and mounted in said vessel, said hollow body being free of insulating material interiorly, and a heating element within said hollow' body, the spacing between said hollow body and said heating element being less than 3 mm.,

7 whereby interior convection currents are suppressed and interference with heating of said member by such currents is avoided, and the spacing between said member and the inner walls of said vessel being greater than 1 cm. so that rapid cooling of-the resistance member by gaseous convection currents exterior to said member is obtained. v

5. A resistance arrangement of low inertia,

' comprising a gas-filled vessel, a resistance member of semi-conductor material formed into a hollow body and mounted in said vessel, said hollow body being free of insulating material interiorly, and a heating element within said hollow body, the spacing between said hollow body and said heating element being 0.8 to 1 mm., whereby interior convection currents are suppressed and interference with heating of said member by such currents is*avoided, and the spacing between said member and the inner walls of said vessel being greater than 1 cm. so that rapid cooling of the resistance member by gaseous convection currents exterior to said member is obtained.

6. A resistance arrangement of low inertia,

teriorly, and a heating element within said hollow body, the spacing between said hollow body and said heating element being less than 3 mm.,

whereby interior convection currents are suppressed and interference with heating of said member by suchcurrents is avoided, and the spacing between said member and the inner walls of said vessel beingof the order of 15 mm. so that rapid cooling of the resistance member by gaseous convection currents exterior to said member is obtained.

7. A resistance arrangement of low inertia, comprising a gas-filled vessel, a resistance member of spinels formed into a hollow body and mounted in said vessel, said hollow body being free of insulating material interiorly, and a heating element within said hollow body, the spacing between .said hollow body and said heating element being sumciently small to suppress convection currents of the gas within said hollow body,

whereby interference with rapid heating ofthe resistance member from within by interior gaseous convection currents is avoided, and the spacing between said member and the inner walls of said vessel being sufficiently great, to permit free fiowof convection currents about said member so that rapid cooling of the resistance member by gaseous convection mcurrents exterior to said member is obtained. WILFRIED MEYER.

HANS NELDEL.