US2748231A

US2748231A - Electrical indicator

Info

Publication number: US2748231A
Application number: US459315A
Authority: US
Inventors: Hudson Kenneth Clifford
Original assignee: Honeywell Inc
Current assignee: Honeywell Inc
Priority date: 1954-09-30
Filing date: 1954-09-30
Publication date: 1956-05-29
Anticipated expiration: 1973-05-29

Description

May 29, 195.6 K. c. HUDSON ELECTRICAL INDICATOR Filed sept.. so, 1954 F I G. 4

F I G.

FIG. 3

INVENTOR. KENNETH C. HUDSON ATTORNEY.

I 5 l/ l n United States 2,748,231 Patented VMay 29, 195.6

ELECTRICAL INDICATOR Kenneth Clifford Hudson, Philadelphia, Pa., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application September 30, 1954, Serial No. 459,315

15 Claims. (Cl. 201--55) A general object of the present invention is to provide a new and improved form of electrical resistance element. More specifically, the invention is concerned with an improved variable resistance element of the type utilizing an electrically conductive fluid to variably shunt a resistance coating on the wall of a hollow tube wherein the hysteresis error due to meniscus variations of the fluid in the element is minimized.

When a variable resistor is formed by coating the inner surface of a hollow tube with resistance material and the coating is shunted by a short circuiting fluid, it has been found that a dead spot will appear in the apparatus due to the shape of the meniscus of the iluid changing. The meniscus shape change is accompanied by volume change of the fluid, in the vicinity of the coating which is shorted by the Huid, without any change in the point at which the tluid contacts the resistance material. The present invention is directed to the elimination of this dead spot in resistance units of the present type by maintaining the meniscus of the iluid in a substantially constant shape even though the tluid level may change within the resistance unit.

It is therefore a more specific object of the present invention to provide means for regulating the meniscus shape of a fluid used in a variable resistance unit of the present type.

Another object of the present invention is to provide a uid meniscus control for use in a variable resistance wherein the control element is in the form of a nonwettable rod which extends into the fluid.

In some forms of the present invention, it is desired not only to regulate or control the meniscus of the fluid used, but also to vary the level of the uid in the tube. Adjustment of the tluid level may be accomplished by varying the depth to which the meniscus control element extends into the fluid.

Another object of the invention is then to provide an improved form of adjustable element for the uid level in the resistance unit used in the present apparatus.

A further object of the invention is to provide an improved resistance element including a movable meniscus control element which may be variably extended into the uid of the resistance unit to regulate the iluid level of the unit.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its advantages, and specific objects attained with its use, reference should be had to the accompanying drawings and descriptive matter in which there is illustrated and described preferred embodiments of the invention.

Of the drawings:

Fig. l is a representative showing of the variable resistance unit connected to a recording instrument;

Fig. 2 shows an enlarged cross section of a resistance unit of the type used in the present invention wherein no meniscus control is utilized;

Fig. 3 shows an enlarged cross sectional detail of a portion of Fig. 1 wherein a meniscus control element is used;

Fig. 4 shows a modified form of the present invention wherein the meniscus control rod is adjustable in the amount that it extends into the iluid of the unit; and

Fig. 5 shows one manner in which the meniscus control rod of the present invention may be characterized to provide a non-linear response of the resistance unit to uid level changes as effected either by the movement of the rod or other movement.

Referring rst to Fig. l, the numeral 10 represents a thermometer bulb which may be filled with mercury or some other suitable thermally expansible material having electrical short circuiting properties. The bulb 10 has formed on the upper portion thereof a glass or ceramic type of capillary tubing 1l. The tubing il has a resistance coating 12 formed on the inner portion thereof. Contacting the coating at either end thereof are a pair of

contacts

13 and 14. As explained thus far, the unit is substantially the same as that disclosed in the copending application of Edward F. Zoltanski, Serial No. 290,601, tiled May 28, 1952.

Centered within the hollow portion of the tube -11 is a meniscus control element 15. This element is fastened at the upper end of the tube il at lo and at the lower end of the tube lll at 18. The meniscus control element 15 is preferably formed of a non-wettable material such as quartz or tungsten. The type of material selected depends upon the fluid or liquid used in the device. it has been found that quartz and tungsten are very effective when used with mercury.

Connected to the output terminals of the resistance unit is a suitable indicating and recording instrument 20. This instrument may well take the form of the instrument disclosed in the patent to Walter P. Wills, No. 2,423,540, issued July 8, 1947.

In considering the operation of Fig. l, temperature changes of the bulb 10 are accompanied by a resultant expansion or contraction of the mercury which fills the bulb. The level of the mercury will accordingly rise and fall over the resistance coating 12 so that the coating will be variably short circuited or shunted by the mercury and the resistance between the output contacts i3 and 14 will change. This change may be reilected into the instrument 20 which will give an appropriate indication of the magnitude of the resistance. While a thermal bulb l0 has been shown, it will be readily apparent that any suitable means for inducing the flow of the fluid in the tube 11 may be employed within the teachings of the present invention.

Fig. 2 shows the mercury meniscus change resulting from some force acting upon the column of mercury to cause a movement thereof. The solid line 25 over the mercury column 9 represents the normal meniscus shape to be expected inside of the tube 11. The edges of the mercury contacts the resistance coating 12 at 26. lf the mercury column 9 is subjected to a force tending to move it in an upward direction, the meniscus level will change in an upward direction and take the shape of a dotted line curve 27 before the edge of mercury in Contact with the surface l2 will leave the contact point 2o. if there is a decrease in the force acting on the column 9, the column will be lowered and will assume the shape identified by the dotted line curve 28 before the edge of the mercury column 9 will depart from the contact point 26.

It will be readily apparent from a consideration of Fig. 2 that there may be a considerable change in'the volume of the mercury column 9 in the vicinity of the resistance coating l2 without any accompanying chang:k in the contact point of the mercury with the resistance coating. This volume change appears as an apparent dead 'spot in the operation of the sensing unit. For precision measurement purposes, such a dead spot is intolerable.

As is shown in enlarged detail on Fig. 3, the appa ratus of Fig. l overcomes the shortcomings present in the apparatus of the type represented in Fig. 2. Added to the apparatus shown in Fig. 2 is the meniscus control rod 15 which may be formed of quartz, tungsten, or some other suitable non-wetting material. With a meniscus control rod l present within the tube li, the shape of the meniscus Will remain substantially that as shown regardless of whether the uid level is increasing or decreasing in its position within the tube l1. Consequently, the dead spot area present within the apparatus is substantially eliminated. It has been found that the most eective diameter for the meniscus control rod should be at least one tenth the inside diameter of the tubing 11.

An additional advantage has been observed in the addition of the meniscus control rod to the apparatus in respect to eliminating gas bubbles which may be formed below the normal level of the mercury by separation of the mercury in the tube 11. With the arrangement disclosed and including the control rod l5, gentle tapping upon the tube has been found sufficient to cause the bubbles or separations to be eliminated so that the mercury column is solid all the way down into the bulb 10.

In the modication of Fig. 4, the meniscus control rod is made adjustable so as to facilitate ready adjustment of the level of the mercury within the resistance element. There is provided in this modication a hollow tube 3i) having a resistance coating 31 on the inner surface. Filling the lower portion of the tube 30 is a suitable shunting liquid 32 such as mercury which is adapted to move over the resistance coating 31 and variably short the same. A pair of

contacts

33 and 34 are displaced on opposite ends of the resistance coating 31 and provide output terminals for the apparatus. Fastened to the upper end of the tube 30 is a chamber 35 of enlarged cross section. Separating the chamber 35 from the tube 30 is a threaded portion 36 which is adapted to threadedly receive a meniscns control rod 37, the latter having a projection 38 which extends down into the mercury 32. The upper end of the rod 37 has fastened thereto a permanent magnet 39 which is adapted to cooperate with a permanent magnet assembly 40 disposed outside of the chamber 35. The magnetic assembly 4t) may be rotatably adjustable by the gearing dsl- 42.

In operation, the tube 30 and the coperating elements may form a variable resistance which is varied solely by the movement of the rod 37 with extension 38 varying the level of the mercury 32 upon the resistance coating 31. The extension 38 of the rod 37 serves the meniscus control function of the rod of Fig. l. When the gearing 41-42 is rotated, the magnets 40 follow the gear 41 and the permanent magnet 39 will follow the magnet 40 so as to rotate the rod 37 and vary the depth to which the extension 38 extends into the mercury 32. This form of the apparatus may well be used for establishing a predetermined resistance change for a certain input angular motion.

In the event that it is desired to provide a zero adjustment for apparatus of the type shown in Fig. l, the principles incorporated in Fig. 4 may well be substituted in the apparatus of Fig. l.

In some instances, it is desired to provide a non-linear response between liquid motion and the resistance change of the coating. For this purpose, the non-linear element or rod 45, shown in Fig. 5 may Well be substituted for the rod 37 and its extension 38. The rod 4S will function as a meniscus control element as well as a means for introducing a non-linear response in the apparatus.

While, in accordance with the provisions of the statutes, there has been illustrated and described the best forms of embodiment of the invention known, it will be apparent .to those skilled in the art that changes may be `made in the forms of the apparatus disclosed without departing from the spirit of the invention as set forth in the appended claims, and that in some cases certain features of the invention may be used to advantage without a corresponding use of other features.

Having now described the invention, what is claimed as new and for which it is desired to secure Letters Patent is:

l. A variable electrical resistance device comprising a ceramic capillary tube having an electrically conducting but resistive coating positioned on the inner surface of the capillary, electrical contacting means positioned at spaced points along said capillary and engaging said coating, an electrically conducting iluid having a negligible electrical resistance disposed in cooperative relation with said coating to variably shunt the electrical resistance of said coating between said points, and an elongated element supported within and extending coaxially along the length of said capillary tube, said element having a cross sectional diameter less than that of the inner portion of said tube.

2. Apparatus as dened in claim l wherein said elongated element is not wettable by said fluid so that said element acts to control the meniscus level of said fluid in said tube.

3. Apparatus as defined in claim 2 wherein said elongated element is formed of tungsten.

4. Apparatus as defined in claim 2 gated element is formed of quartz.

5. An electrical resistor comprising a hollow tube having an electrically conducting but resistive coating formed on the inner portion of said tube, an electrically conducting liuid having negligible electrical resistance disposed relative to said coating to variably shunt the electrical resistance of said coating7 and a fluid meniscus control element extending into said iluid to maintain the meniscus thereof of substantially constant shape when said fluid variably shunts said coating.

6. A variable resistance element comprising a hollow tube having an electrically conducting but resistive coating formed on the inner portion of said tube, an electrically conductive uid having negligible electrical resistance disposed in variable shunting relation with respect to said resistive coating, an elongated rod extending along the length of said tube and into said liuid, and means for adjusting the length of said rod extending into said liuid to vary the level of the Huid acting on said coating.

7. Apparatus as defined in claim 6 wherein said rod has a non linear characterization so that movement thereof will produce a non linear change in level of the uid acting on said coating.

8. Apparatus as defined in claim 6 wherein said elongated rod is formed of a substance which is not wettable by said fluid.

9. Apparatus as dened in claim 8 wherein said rod is formed of quartz.

l0. Apparatus as delined in claim 8 wherein said rod is formed of tungsten.

ll. A variable resistance element comprising a hollow tube having an electrically conducting but resistive coating formed on the inner portion of said tube, an electrically conductive uid having negligible electrical resistance disposed in variable shunting relation with respect to said resistive coating, an elongated rod extending along the length of said tube and into said fluid, means threadedly supporting said rod in said tube, and means for rotating said rod in said support to variably position said rod in said fluid.

l2. Apparatus as defined in claim l1 wherein said means for rotating said rod comprises a magnetic coupling including a magnetic member inside of said tube on said rod and a second magnetic member outside of said tube mounted for rotational movement.

wherein said elon- 13. Apparatus as dened in claim 7 wherein said elongated rod is formed of a substance which is not Wettable by said uid.

14. Apparatus as defined in claim 7 wherein said rod is formed of quartz.

15. Apparatus as defined in claim 7 wherein said rod is formed of tungsten.

References Cited in the le of this patent UNITED STATES PATENTS