US2144509A - Circuit arrangement for a variable electric resistance - Google Patents

Description

Jan. 17, 1939; G, N s 2,144,509

CIRCUIT ARRANGEMENT FOR A VARIABLE ELECTRIC RESISTANCE Filed March 11, 1935 Z 6 i o o 4 3 2 9 f?! 1 5555? I0 g JI v 4 A i i I 5 5 5- E I v i n iflqnnwi L Q 14# 0' 5 1'0 15 0 5 7' 70 2 7' INVENTOR GUSTAV 2ATUS BY Ai'ToRNEY Patented Jan. 17, 1939 UNITED STATES PATENT OFFICE CIRCUIT ARRANGEMENT FOR A VARIABLE ELECTRIC RESISTANCE Application March 11, 1935, Serial No. 10,386 In Germany March 10, 1934 2 Claims.

(Granted under the provisions of sec. 14, act of March 2, 1927; 357 0. G.

The present invention relates to a circuit arrangement which includes a regulable or selfregulating resistance made of materials possessing a high temperature coefiicient. A feature of 5 the invention is that the resistance value of the device is governed predominantly by a separate source of heating dependent upon the value or size of the current or the voltage to be regulated rather than upon the self-heating produced by the current flowing therethrough. The resistance circuit connection according to the invention may serve both for the abbreviation of the heating period of indirectly heatable cathodes as well as for the regulation of current and potential fluctuations in load or consumer circuits, it being understood, however, that the applications hereinbefore mentioned by way of example by no means limit the use or scope of the circuit scheme.

In the accompanying drawing, Figure l illustrates an embodiment of the invention wherein the controlling resistance is in series with the heaters of the tubes; Figure 2 illustrates an embodiment of the invention wherein the controlling resistance or resistor is in parallel with the heaters; and, Figures 3a and 3b are curve sheets which are used to compare the present invention with other known systems.

With a view to shortening the heating period of indirectly heated cathodes, the suggestion has 30 been made to arrange in series with the heating means for the cathodes, resistances possessing a high positive temperature coeificient which are to be endowed with such high thermal inertia that the entire resistance structure will attain the steady-state temperature and thus the working resistance value only after a relatively prolonged period of time. It is to be made thus possible to feed the heater wires of discharge tubes during the initial heating period an amount of current 40 which is higher than the steady-state or normal current.

Resistances of the sort mentioned above involve the drawback that they must be calculated very exactly for a definite resistance value, a definite e5 current strength, and for a definite amount of heat to be carried off or dissipated. Inasmuch as these values are interdependent, a resistance of this kind would be useful only in a very definite arrangement or in a very definite apparatus. 50 The said resistances, moreover, have the drawback that, immediately after connection in circuit, the resistance value experiences a relatively marked growth in proportion to the initial heating time so that the initial excess heating current at the very incipiency of the heating period, is

again decreased in a steady manner, with the result that the intended reduction of the initial heating period will, in part at least, be offset again. (see Fig. 3a.)

Applicant is aware of the existence of precision resistances possessing an extremely low temperature coeilicient which are used as calibration standards, and that these, by the aid of a heater device of an exactly fixed temperature, may be stabilized at an extremely constant value in such a way that the calibration temperature is chosen so high that, no matter what the season, it will never be attained by extraneous natural agencies.

Applicant is also familiar with German Patent No. 404,261 disclosing pastils or buttons consisting of oxides and other chemical compounds which in a convenient manner may be used as variable high-ohm resistances.

For the purpose of stabilizing current or voltage in consumer circuits it has been previously suggested to use carbon pressure resistances or iron resistances confined within a hydrogen atmosphere. The former kind of resistance requires a complicated regulating device, and they are therefore costly and of large size. The socalled iron-hydrogen resistances (Nernst variators) are appreciably limited in so far as their range of regulation is concerned. Both kinds of regulating resistances, moreover, are adapted to be used for the regulation only of a definite current or a definite potential so that special types have to be calculated for each individual case arising in practice. The range of regulation of these kinds of resistance lies around 80-100 percent of the value to be regulated, in other words, the resistance variations are approximately as 2:1.

These disadvantages, according to the invention, may be obviated by the use of a resistance consisting of a resistance element (resistor) having a numerically high temperature coeificient and a thermal source associated therewith which governs the temperature of the resistance element and thereby the value of its resistance. For the heating thereof may be used either an existing thermal source or else a distinct heat source, the same being so chosen according to the invention that it will be a function of a certain current or voltage value of the apparatus. An advantageous application thereof resides in electrical apparatus, more particularly circuits incorporating indirectly heated tubes, wherein the new resistance arrangement herein disclosed insures an appreciable reduction in the initial heating period and, during normal or steady-state operation, a substantial automatic regulation in the presence of supplyline fluctuations with a view to. stabilizing current and voltage throughout the entire apparatus or V in parts thereof.

The present, invention which is of particular importance in broadcast apparatus shall therefore by way of example be described in more de-, tail in connection with a tube arrangement.

In Figs. 1 and 2 identical reference numerals efer to and denote similar or equivalent elements.

A plurality of discharge tubes I, 2, 3, and optionally 4, the cathodes of which are to be incandesced by distinct heater or resistor elements (indirectly heated tubes) are connected either in series (as in Fig. 1) or else in parallel (as shown in Fig. 2), according to the nature of the source of current or the mode of application;

In the joint or common filament or heating supply lead Hi there is connected a resistance device 5 provided with resistor element'ii the resistance value of which is fixed so low in an unheated state, that it has a value only about /5 or the value it would have in the steadystate of operation in order to diminish the heating current of the tubes to the normal working value. The resistance 6 is so dimensioned and disposed that the current flowing .therethrough Will not heat it so intensely that, say, by selfheating,it will be able to attain the value of steady working state. By such under-dimensioning,conditions are made so that the cathodes of the discharge tubes will draw a relatively large current for a relatively long time, that is to say, nearly throughout the entire incipient or initial heating period. In order that the cathodes after attaining their state of normal electron emission will not become overheated, a heater device I, preferably in the form of a heater wire inside an insulating bush or tube 8 is associated with the resistance element in such a way that, when the cathodes are heated to their full value, the resistance element 6 will also be caused to assume its steady-state value.

This variable electric resistance, for instance, is

, constructed in a manner similar to an indirectly heated cathode but in such a way that in place of the electron-emission layer the resistance element 6 is mounted on an insulation bush or tube 8. If this resistance heating device is heated by the same current as the cathode heaters (in series with cathode heaters) or by the same voltage (in parallel with cathode heaters) there is insured an automatic regulation of the current I or the potential E owing as the case may be to the fact that, with decreasing values of I or E, the heating a of the heater wire I diminishes so that thereis brought about a corresponding reduction of the temperature of the resistance element and thus of In this way the heater shown in Figs. 1 and 2, in addition to low cost and simplicity, ofier the following three special advantages: (a) The main increase in the value of the series resistance 5 occurs only a short while prior to the end of the initial heating period T (see Fig. 3b). At about the same instant when v the full electron emission sets in in the discharge tubes, the outside of the resistance support (8) attains the requisite high temperature. As a result the initial heating period or the starting time of indirectly heated cathodes is substantially shortened compared with the methods known in the prior art (see Fig. 3a) for the reason that the relatively high initial excess heating current .is fully active nearly throughout the whole initial heating period (see Fig. 3b) in other words, it is not diminished again almost at the very beginning of the initial heating period (as in Fig. 3a). This is of material value particularly for the reason that the heat evolution is directly proportional to the second power of the current.

(12) The working value of the regulating resistance depends markedly upon the temperature governed and determined by the heating device 7. Thus, if the heating device is connected in parallel relation or in series relation with the consuming circuits, each and every fluctuation in the current or in the potential will be brought to act upon the heating means of the resistance element in such a fashion that the same is caused'to change its value such that the fluctuation will be compensated, and the result is that the desired current or voltage value of the consumer will be stabilized and preserved. (c) If, in addition, the heating device of the resistance element is provided with a regulating resistance 9, it is possible to use the same resistance whenever there is a change or substitution, or an increase or decrease in the number of the tubes, in other words, in the presence of a variation of the current or of the voltage to be regulated; in fact, once the set has reached a steady-state of operation, all that is necessary is to so adjust the additional heating so that the resistance will have the desired value.

This condition is ascertainable in a simple way by measuring the value of the emission current. Such a wide range of regulation or regulable range (which ranges. up to 1000%) is not even closely, attainable by any other resistance oir cuit arrangement known in the prior art and yet retain all of the advantages hereinbefore cited. An approximate calculation shall be made by the following numerical example for the practically obtainable resistance rise with the use'o-f tungsten: .Let' Ro=th8 resistance value of the resistance element at 0 degree 0.

t=the highest practically admissible tempera.-

ture of the resistance element. t=2000 degrees C. for tungsten. a.=4.6 per degree is the temperature coefficient for tungsten. In the approximate calculation only the abbreviated (simplified) formula shallbe employed:

Rt=Ro(1+at) Rt=Ro(1+4.6X10 X200O) Rt=Ro(l'+9.2)

For tungsten and 13 2000 degrees C. the change in resistance takes place at this ratio It will'be understood that resistance materials could also be used having some other, and preferably a higher, temperature coefficient;

What may also be mentioned is that for'heating the resistance in a circuit arrangement as hereinbefore disclosed there may be used a source 'ofheat comprised either in the same set or in a set or apparatusassociated therewith. For example, the heat dissipated in another resistance element, voltage divider, etc., could thus be profittageous to confine the resistance, for the sake of protecting it from harmful or undesired air currents and heat conduction, within an exhaust vessel or, for the sake of safeguarding it against oxidation, in a vessel filled with a suitable gaseous atmosphere.

In a case where a resistance change is desired only within narrow limits, part of the requisite total resistance may be provided in the form of a constant resistance, while the balance or remainder may be provided in the form of a resistance connected in a circuit and manner as hereinbefore disclosed, and it may then be found desirable in marry instances to constructionally combine the two resistances.

I claim:

1. In an arrangement adapted for use in electrical circuits incorporating at least one tube having an indirectly heated cathode and a heater for the cathode adapted to be energized by connection thereof to a source of current and wherein said connection is made through a resistance 1 element which possesses a relatively high positive temperature coefficient of resistance, the combination of an electric heater for heating the resistance element and an energizing circuit adapted to be connected to the source of current, said energizing circuit including in series, the resistance element, the heater for the indirectly heated cathode and the electric heater for the resistance element whereby variations in the resistance value of the resistance element due to the heating thereof by its electric heater, controls the flow of current through said energizing circuit.

2. In an arrangement as described in the next preceding claim, a variable impedance means shunted across the electric heater for the resistance element for controlling the flow of current through said electric heater only.

GUSTAV RENA'I'US.

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