US2332392A - Current regulator tube - Google Patents

Description

Oct. 19, 1943. c, c, MlNTER 2,332,392

CURRENT REGULATOR TUBE Filed Nov. 19, 1941 INVENTOR C C". M/A rf')? Aim/um ATTORNEY meme a. 19, 1943 UNITED STATES PATENT OFFICE" 2,332,392 CURRENT REGULATOR TUBE Clarke 0. Minter, Em Orange, N. .1. Application November 19, 1941, Serial No. 419,669 9 Claims. (01. 201-64) This invention relates to the control oi. electrical current flowin in a circuit which includes a metallic electrical conductor of the first class, that is to say, a conductor formed of a metal or alloy characterized by relatively high electrical conductivity, and which has, according to the accepted classification, a positive temperature coeilicient, so that an increase in the temperature of the conductor always reduces its currentcarrying capacity under normal conditions.

The invention relates especially to a circuit in which a length of such a conductor of the first class, in wire or filament form, is confined in an envelope with the space between the conductor and envelope occupied by a confined gaseous atmosphere; and, more particularly, the invention relates to means for varying the current through a conductor so confined, by control oi. variations in the thermal conductivity of the aforesaid gasare induced eous atmosphere, which variations by changes in the ambient atmosphere and propagated through the envelope to the confined gaseous atmosphere.

An object of the invention is to provide a controllable means for amplifying the normal efiect of ambient temperature on the current-carrying capacity of such a conductor, so that it the nor-, mal effect of an increase in ambient temperature is to reduce the current-carrying capacity of the conductor, one object is to produce in the conductor, upon a given increase in ambient temperature, whether natural or stimulated, a reduction in current-carrying capacity which is several times greater than has been predictable prior to the present invention.

An important advantage of such an increase in resistance and consequent decrease in currentcarrying capacity will be readily apparent to those skilled in the art when it is realized that the aforesaid increase in resistance increases greatly the sensitivity to changes in ambient temperature of any circuit in which the improved device of the present invention may be included;

- for example, a circuit provided with instruments for measuring or indicating changes in ambient temperature, one such application being to circuits with instruments for supplying visible indications of changes in ambient temperature atfecting the conditions under which aeroplane engines operate, especially during changes in altitude.

Furthermore, it is well known that the currentcarrying capacity 01' a few alloys is, for all practical purposes, independent or the ambient temperature. Another class of substances, compris- Those skilled in the art will recognize without further elucidation that in all sorts of electrical circuits in which it is desirable to compensate, or neutralize, the positive coeificient of resistance of some essential part of the circuit, it would be of great advantage if a conductor of the first class could be endowed reliably with the ability to behave like a conductor of the second class in the important respect that it will exhibit a negative temperature coefiicient of resistance.

Accordingly, it is another object of the present invention to provide for so constructing and arranging a device of the class described, embodying a conductor of the first class, having normally a positive temperature coeflicient of resistance, that an increase in ambient temperature will produce in the conductor a predictable and measurable decrease in resistance.

Ancillary to the last-named object, the following objects are among those realized by the present invention, viz.,

(1) To provide a novel means of reversing the normal effect of an increase in ambient temperature on the current-carrying capacity of such a conductor, so that, if the normal efiect of an increase in ambient temperature is to reduce the current-carrying capacity of the conductor, per contra, the efiect will be to produce a desirable increase in current-carrying capacity.

(2) To provide for accomplishing the desired changes in current-carrying capacity of such a conductor of the first class confined in an envelope containing a gaseous atmosphere surrounding the conductor, by means adapted to eifect controlled changes in the thermal conductivity of the gaseous atmosphere, by changing the concentration of molecules in the space surrounding the conductor, and thus to condition the conductor suitably for the above recited purposes:

(a) By imparting to the conductor an exceptionally large positive temperature coeflicient of resistance, much greaterthan normal; and, alternatively,

(b) By decreasing the resistance of the wire, and thereby to increase the current-capacity thereof.

Other objects and features of the invention will become apparent to those skilled in the art, as the description of the illustrated embodiment progresses.

In the accompanying drawing,

Fig. 1 is a view in longitudinal sectional elevation 01 an electrical resistance device in the construction of which the instant invention has been embodied;

Fig. 2 is a similar view or" a modification of the device shown in Fig. 1;

Fig. 3 is a similar view showing another modification; and

Fig. 4 is a similar view showing still another modification.

Referring now to the drawing in detail, the reference character 5 designates in general a device which may be of the well known form exemplified by so-called ballast tubes, incandescent lamps, or other suitable appliances, embodying an envelope or tube 5, preferably made oi! glass or metal and confining a conductor 5 of the first class as hereinbefore defined, taking the form preferably of a wire or filament supported at each end by heavy metal leads 8 which are sealed suitably into the end walls of the envelope 6, the space 9 within the latter and surrounding the conductor 1 being occupied by a gaseous atmosphere ID, the molecules H of which are conventionally indicated by stippling, without special regard to accuracy in proportions, the size of the molecules being exaggerated, while their number is, or course, of a much reduced order for the sake of convenience in drafting.

If now the conductor I be energized by the imposition on its terminals of a potential of suitable voltage, such as the usual commercial potential, the conductor will be heated and its temperature will rise above that of the surroundings. It will thereupon lose heat, principally by conduction, through the gaseous atmosphere Ill to the walls of the envelope 6, and thence to the surroundings.

If the temperature of the envelope 6 be regarded as the same as that of the ambient temperature, or only slightly above it, and always proportional thereto, it has been shown theoretically that the difference between the temperature of the wire 1 and the temperature of the wall of the envelope or tube 6 may be expressed accurately by the subjoined known equation A,

in which Tw is the temperature of the wire (conductor), T: is the temperature of the tub (envelope), I is the current through the conductor, R the resistance of the conductor, J is the mechanical equivalent of heat, and K is a constant, while S is the thermal conductivity of the gaseous atmosphere l0 surrounding the conductor I.

Analysis of equation A shows that, if the power (1 R) dissipated in the conductor I remains constant, th difference between the temperature of the conductor I and that or the envelope i will vary with the thermal conductivity S of the gaseous atmosphere In, and by keeping the temperature T: of the envelope 6 constant, if the thermal conductivity S of the gaseous atmosphere I0 is decreased, the temperature Tw' of the conductor I will increase; while an increase in the thermal conductivity S of the gaseous atmosphere ID, on the other hand, will lower the temperature Tw of the conductor I. Since the conductor I is of the first class and has a positive temperature coefficient of resistance, its resistance will increase when the thermal conductivity S of the gaseous atmosphere I0 is decreased; and, for the same reason, he resistance or the conductor I will decrease when the thermal conductivity S of the atmosphere I0 is increased.

The temperature Tr of the envelope 6 will, of course, vary in direct proportion to changes in the ambient temperature, and the effect of an increase in ambient temperature will be to decrease slightly, or not affect at all, the temperatur Tw of the conductor I, and the resistance of the conductor I.

This decrease in resistance of the conductor 1, accompanying an increase in ambient temperature, is not what would be expected normally from the positive temperature coeilicient of resistance of the conductor, and the greater decrease is due to the increase in thermal conductivity S of the gaseous atmosphere ID as the ambient temperature is increased, thereby acting to keep th temperature Tw of the conductor I practically constant as the temperature Tr of the envelope increases. It is to be noted that, according to the equation A, the product of is practically constant.

The properties and behavior toward changes in ambient temperature of a conductor enclosed in a gaseous atmosphere are well known, but have been discussed above in order to clarify the manner by which the procedure of the instant invention has been evolved in the novel development of principles known in the art.

From equation A it can be seen that the thermal conductivity S of the gaseous atmosphere In plays a very important role in governing the temperature Tw of the conductor, as th temperature of the envelope 6 varies with the ambient temperature; and it will be realired by those skilled in the art that by the provision, according to the instant invention, for causing the thermal conductivity S of the gaseous atmosphere to increase rapidly, and alternatively to decrease, in a reliable and predictable manner, a useful and notable advance in the art has been achieved. The manner in which provision has been made for such control will now be disclosed fully.

Taking first the problem of producing by an increase in ambient temperature a decrease in the thermal conductivity S of the gaseous atmosphere III, instead of the normal increase in S produced by the positive temperature coeflicient of thermal conductivity of the said atmosphere 10, this result can be obtained byemploying the device shown in Fig. 2, which is preferably exactly the same in general structure as that shown in Fig. 1, and like parts in each are accordingly identified by identical reference characters; but the envelope 6 in Fig. 2 contains also a. volatile liquid H, the vapor molecules l3 of which will mix with the molecules ll of the gas already present in the atmosphere I0.

It is clear that, owing to the increase in vapor pressure of the liquid as the ambient temperature increases, the concentration of vapor molecules l3 in the atmosphere ill will increase, and the thermal conductivity S of the atmosphere II) can be made to increase or decreasawith an increase in ambient temperature merely by changing the nature and density of the atmosphere l0.

It the thermal conductivity S of the gas-vapor mixture l0|3 decreases as the concentration by an" increase in ambient temperature, it will be seen of the vapor in the mixtureis increased from equation A that the difierence between the temperature Tw of the conductor 1 and that temperature T1; of the envelope 6 (or the ambient temperature) increases.v This means that the temperature Tw of the conductor 1 increases faster than the ambient temperature, and the conductor exhibits an exceptionally large positive temperature coeificient of resistance, much greater than normal.

A suitable mixture for the above purpose comprises hydrogen at a pressure of approximately 10 mm. of mercury, the liquid [2 being any volatile liquid, such as water, alcohol, acetone, etc. As an example of the results obtained with such an envelope, I containing hydrogen and using water as the liquid, I found by actual measurement that when the conductor I was made of nickel wire having a diameter'of .001, and carried a current of 175 milliameters, the ambient temperature being C., the resistance of the wire was 20.6 ohms.

At an ambient temperature of 295 C. the resistance of the wire when carrying only 152 milliamperes was 30.5 ohms.

This increase in resistance is exceptionally large for'an increase in ambient temperature of only 29.5 C. In fact, for nickel, with a temperature coefi'icient of .005 ohm C.- the increase should have been only 3 ohms.

If to the fully evacuated envelope a volatile liquid l2 such as water is added, the following figures are cited from actual measurements to show that under these conditions the wire 1, again nickel of .001" diameter, exhibits a negative temperature coefficient, in accordance with the present invention, and contrary to previous experience of other workers in this field.

For example, when conducting a current of 128 milliamperes, the wire had a resistance of 44.6 ohms when the ambient temperature was 0 C., but when the ambient temperature was increased to 28.5 C. and the wire was carrying 134 milliamperes, its resistance was only 40.7 ohms.

Combinations of diiferent gases under varying pressures with a volatile liquid have been tried, the results obtained varying with the gas and liquid employed. Using gases varying in atomic weight from argon to mercury, it is possible to obtain a gaseous combination having positive or negative temperature coefiicients of thermal conductivity of almost any desired degree, giving to a current-carrying conductor of the first class mounted in such an atmosphere an increasing or decreasing current-carrying capacity as the ambient temperature is increased.

For purposes of obtaining a negative coefficient, a preferred embodiment of the present invention is that illustrated in Fig. 3, the general structural design of the device being the same as that shown in Fig. 1. There is also a small amount of volatile liquid [2 as shown in Fig. 2, but the atmosphere l4 surrounding the conductor 1 consists in this instance entirely of the vapor molecules [3 of the liquid l2. No fixed gas is used, the envelope 6 being pumped as free of air as possible. i

The effect of an increase in ambient temperature on the current-carrying capacity of the conductor 1 in the Fig, 3 device is to enable the conductor 1 to carry more current at the higher temperature. This is readily understood when 3 it is realized that as the ambient temperature increases, the vapor pressure of the volatile liquid l2 increases, and a greater number of vapor molecules l3 pass from the liquid I2 to the atmosphere I4 surrounding the conductor 1.

II the density of the vapor molecules l3 in the atmosphere I4 is kept below the point at which the thermal conductivity of the vapor molecules becomes independent of density, an increase in ambient temperature will produce an increase in thermal conductivity of the atmosphere I4 by increasing the concentration of vapor molecules l3, and thereby enable the wire I to carry more current at the higher temperature. Any volatile liquid can be used and liquids varying in volatility from alcohols to mercury have given satisfactory results when so used.

A further modification of the invention, having as its purpose to provide an increase in the thermal conductivity of the atmosphere l5 urrounding the conductor 1, is illustrated in Fig. 4, the general structural disposition of the envelope 6 and contained conductor 1 being preferably as in Figs. 1 to 3.

In this modification the increase in the number of molecules in the gaseous atmosphere l5 as the ambient temperature increases is not produced by a volatile liquid, as in the devices of Fig. 2 and Fig. 3, but is caused by the effect of an increasing ambient temperature on the adsorption or occulsion of a gas or vapor.

In the Fig. 4 device when the confined gas is hydrogen at a suitable pressure, a small quantity of activated material such as activated platinum, activated palladium, or a mixture of the two, or under favorable circumstances of nickel or copper or other metal in production, is provided in the envelope as indicated at I6, and an increase in ambient temperature will cause the activated material to liberate occluded hydrogen into the atmosphere I5, thereby increasing its thermal conductivity and the current-carrying capacity of the conductor 7.

In the Fig. 4 type of device the activated porous material I 6, whether metallic or non-metallic,

may have adsorbed a gas or vapor, and as the ambient temperature increases, the porous material 5 will liberate gas or vapor into the atmosphere I 5, thereby increasing its thermal activity and the current-carrying capacity of the conductor 1.

What is claimed:

1. An electrical resistance device comprising a sealed envelope having a unitary chamber, an electrical conductor of the first class confined within, said unitary chamber, the space between said conductor and the wall of said unitary chamber containing a gaseous atmosphere having substantially a given concentration, and a material within said unitary chamber for varying to a prescribed extent the concentration of said gaseous atmosphere between the wall of said 3. An electrical resistance device comprising an electrical conductor of the first class suitably mounted in a sealed envelope having a unitary chamber, the space between said conductor and the wall of said chamber containing vapor molecules 01' a volatile liquid, and a small quantity of the said liquid adhering to the walls of the envelope.

4. An electrical resistance device comprising an electrical conductor of the first class in the form of a. wire suitably mounted in a sealed enveloped forming a unitary chamber, the space between the wire and the wall of the unitary chamber containing molecules of a fixed gas, and vapor molecules of a volatile liquid, and a small quantity of said liquid adhering to the wall of said chamber.

' 5. An electrical resistance device comprising an electrical conductor of the first class suitably mounted in a sealed envelope forming a. unitary chamber, the space between the conductor and the chamber of the tube containing molecules of hydrogen, and a quantity of activated palladium or platinum or a mixture of the two suitably positioned on the wall of the envelope.

6. An electrical resistance device comprising an electrical conductor of the first class suitably 7. An electrical resistance device comprising a sealed envelope forming a unitary chamber, an electrical conductor confined within said unitary chamber having a positive temperature coefllcient acting normally to decrease the currentcarrying capacity of the conductor in response to increase in the ambient temperature, the spac between said conductor and the wall of sai unitary chamber containing a gaseous atmosphere, and a material within said unitary chamber to reverse said normal decrease in currentcarrying capacity of said conductor in response to increase in the ambient temperature and thereby to increase the current-carrying capacity of said conductor by increasing the thermal conductivity of said gaseous atmosphere in response to said increase in ambient temperature.

8. An electrical resistance device comprising a sealed envelope forming a unitary chamber, an electrical conductor confined within said unitary chamber having a positive temperature coefllcient, the space between said conductor and the wall of said unitary chamber containing a gaseous atmosphere, and a material within said unitary chamber to change the thermal conductivity of said atmosphere to cause the current-carrying capacity of said conductor to be increased or decreased selectively in response to an increase in the ambient temperature.

9. An electrical resistance device comprising a sealed envelope having a unitary chamber, an electrical conductor of the first class confined within said unitary chamber, and a heat conducting medium of a given volume in said unitary chamber and having a fixed concentration of molecules at a given temperature and operable to vary the concentration of its molecules within said unitary chamber in response to changes in ambient temperature to cause a variation in the current-carrying capacity of said conductor.

CLARKE C. MINTER.

Images