US2023748A - Electrical resistance apparatus - Google Patents

Description

Dec. 10, 1935. s c, SHIPLEY 2,023,748

ELECTRICAL RESISTANCE APPARATUS Filed May 16, 1954 42 48 l0 /6 x 40 1e 22 ,6 3a 24 4:" 'IIIIIIII. 8 I I I I all! v/ll 68 r INVENTQR SYLVAN sQSI-IIPLEY B I I A'I'TORNKYS I Patented Dec. 10, 1935 UNITED STATES PATENT OFFICE ELECTRICAL RESISTANCE APPARATUS Application May 16, 1934, Serial No. 725,971

3 Claims.

This invention relates in general to electrical resistance apparatus adapted to vary the resistance in an electrical circuit. Common forms of such apparatus are potentiometers and rheostats.

Electrical apparatus of this type usually have an electrical resistance element over which a movable contact mechanically frictionally slides to vary the resistance between one or both ends of the resistance element and the movable contact. In such devices, there is considerable electrical resistance between the movable contact and the resistance element which is known as contact resistance. This contact resistance is different for different positions of the movable contact. It also changes from time to time for the same position because dust and other foreign particles get under the contact and also because the contact and resistance element tend to corrode with age. There is also a tendency for the movable contact and resistance element to burn and pit because of a poor contact and thus further increase the contact resistance. This contact resistance is very detrimental to the life and accuracy of such apparatus.

When such devices are operated manually or where a large amount of power is available for operating them, a heavy contact pressure may be used and, as a result, the contact resistance does not seriously affect their accuracy or usefulness. However, when they are operated automatically by thermostats and other such devices which produce a very small amount of power, they are not satisfactory. If a heavy contact pressure is used to overcome the detrimental contact resistance then they do not readily respond to the automatic means and are therefore unsatisfactory. If a light contact pressure is used to make them readily respond to the automatic means the contact resistance becomes quite large and seriously interferes with the accuracy and usefulness of the device. This light contact pressure makes it easy for dust and other foreign par ticles to get under the contact and cause burning and pitting of both the contact and element which additionally increases the contact resistance.

One of the objects of this invention is to provide an improved variable electrical resistance apparatus which can be successfully operated automatically with a minimum of power.

Another object of this invention is to provide a potentiometer or rheostat type of device which has a low contact resistance that does not change with use or age.

Another object of this invention is to produce a potentiometer or rheostat type of device which has the movable mechanical contact replaced with a body of conducting fluid.

Another object of this invention is to provide a potentiometer or rheostat type of device which is not affected by dust and other foreign matter 5 in the air and which will not corrode or oxidize.

Another object of this invention is to provide a potentiometer 0r rheostat type of device which has the resistance element and movable contact hermetically sealed.

Another object of this invention is to provide a potentiometer or rheostat of the fluid contact type wherein the liquid can be made to assume any desired position with respect to the resistance element with a minimum of effort.

Other objects and advantages reside in certain novel features of the construction, arrangement, and combination of the parts which will be hereinafter more fully described and particularly pointed out in the appended claims, reference 20 being had to the accompanying drawing forming a part of this specification, and in which:

Fig. 1 is a side elevation of a form of fluid contact type of device having circuit-connections adapting it for use as a potentiometer or rheostat. 25

Fig. 2 is an enlarged vertical section of the device shown in Fig. 1, but having the flexible leads and insulating compound omitted.

Fig. 3 shows a thermostatic actuating mechanism operating the device shown in Fig. 1.

In the drawing there has been disclosed a preferred form of the invention for the purpose of explanation and description. In the specific form shown, the container or envelope I0 is made of soft glass but may be made of various other 35 materials well-known in the mercury switch art. The envelope III has an elongated member projecting therein. This projection is here shown as a tube I! which is preferably of soft glass and integral with the envelope. The envelope l0 and 40 the tube l2 are made up separately and may then be fused together at ll but it is not essential that they be fused together for other means of supporting the tube l2 inside the envelope l0 may be employed.

An elongated resistance element I6 is supported on the inwardly projecting member such as the tube l2. The resistance element It is shown in the drawing as a coil of wire wound on the outer face of the tube l2 and therefore within the envelope ID. This wire may be commercial Chromel C" resistance wire which is an alloy resistance wire composed of iron, chromium and nickel. However, any resistance material which will not deteriorate in the presence 55 of mercury will be satisfactory. The resistance element l6 has Dumet" leading-in wires l8 and 20 attached to its ends at 22 and 24. The Dumet leading-in wires 18 and 20 are sealed through the glass tube l2 at 28 and 28 in accordance with the well-known practice in the mercury switch art. Dumet is known in the art to be copper clad invar electro-welded to-.

gether. It is not necessary that the resistance element It be wound on the tube l2 since it is only necessary that it be properly supported within the envelope l preferably parallel with the lower wall thereof. When the device is used as a rheostat it is obviously not necessary to have both leading-in wires l8 and 20. In such case either one may be omitted or not connected in any circuit. But, when used as a potentiometer both leading-in wires are essential.

A movable body of conducting fluid 30 herein shown as mercury is in the envelope l0 and in engagement with the resistance element I 6.

This fluid makes a good electrical contact with the resistance element and therefore gives a very low contact resistance. The mercury 30 is .arranged to move from one end of the envelope in to the other end and in doing so to engage various points on or portions of the resistance element IS.

The external circuit for the mercury may be provided by the lower wall of the envelope when it is made of conducting material but, where as here shown, the envelope is of glass means must be provided to cause the mercury to complete an electrical circuit between the resistance element l6 and an external circuit connection. Therefore, in this preferred form, an electrode 32 is provided which is in engagement with the mercury 30 and which may be made of the various electrode materials used in the mercury switch art but is herein shown as being made of commercial Chromel C resistance wire. The electrode 32 is of suillcient cross sectional area to prevent the resistance per unit length from materially affecting the operation of the device. A Dumet" leading-in wire 34 is welded to the electrode 32 at. and

'is also sealed through the wall of the envelope in at 38. This method of assembling electrodes and leading-in wires and sealing them through an envelope wall is well-known in the mercury switch art.

After the above elements are assembled, the

envelope I0 may be exhausted of air and then sealed off at 40, or the envelope may be refilled with hydrogen or some other arc-suppressing gas before it is sealed off. This prevents dust and other foreign matter from interfering with the contact and also prevent corrosion and oxidation of the contact elements. The Dumet leading-in wires I8, 20, and 34 are equipped with insulated flexible circuit connecting wires 42, 44, and 46 respectively. The connections between the leading-in wires l3 and 20 and the flexible wires 42 and 44 are covered with an insulating cement 48 which closely adheres to the envelope l 0 as disclosed in Phelan et al. Patent No. 1,826,570 granted October 6th, 1931. The connection between the leading-in wire 34 and the flexible wire 46 is also covered with a similar cement or compound 50.

The envelope Ill, tube l2, and electrode 32 are all slightly curved for the purpose of providing aj-curved passageway or runway for the body of mercury 30 over the floor of the envelope l0 thereby causing the body of mercury 30 to assume a definite position for each position of the envelope Hi. If the envelope III were straight, then the mercury 33 would only have two stable positions and these would be at the ends of the envelope III, for if the envelope III were tilted sufllciently to cause the mercury 30 to move at all, it would move the full length of the envelope Hi. The curvature of the envelope I0 is just suilicient to cause the mercury 33 to have a stable or definite position for each position of the envelope I0. By slightly tilting the envelope ID, the body of mercury 30 will move accordingly and thus change the point at which the electrode 32 is connected to the resistance element Hi. The resistance between wires I 8 and 20 is fixed by the amount of resistance in the resistance element l6 and remains constant, but the resistance between either of the wires l8 or and the wire 34 is determined by the position of the body of mercury 30. With the mercury 30 in the posi- 20 tion shown in Figs. 1 and 2, the resistance between thewires l8 and 34 is about equal to the resistance between the wires 20 and 34. But with the mercury 30 in the position shown in Fig. 3, the resistance between the wires [8 and 34 is relatively large and the resistance between the wires 20 and 34 is relatively small which is a phenomenon characteristic of a potentiometer.

In Fig. 3 there is shown an automatically operating mechanism for tilting the envelope Hi. In the form here shown this mechanism automatically responds to a physical condition, such as temperature. The envelope I0 is secured in a clip 52 which is pivoted to .a base 54 by a stud 56. The clip 52 is equipped with a pin 58 which cooperates with a slot 60 in the upper end of an operating lever 62. The lower end of the lever 62 is formed to cooperate with a pivot 64 which is secured to the base 54. A volatile fluid temperature-sensitive bellows 66 is secured at one end to a bracket 68 which is fixed to the base 54. The other end of the bellows 66 is equipped with a pin 10 which cooperates with a socket 12 on the operating lever 62. The lever 62 is also acted upon by a tension spring 14 one end of which is attached to the base 54 through an adjustable or temperature setting stud l6 and the other end is attached to the bracket 62 by a stud 18.

On the base 54 there are two stops 80 and 82 to limit the travel of the upper end of the bracket The spring 14 tends to hold the lever 62 against the stop 82 but the bellows 68 which expands on a temperature rise tends to force the lever 62 against the stop 80. The tension of the spring 14 which may be varied by the adjusting stud 16 determines the temperature at which the pressure in the bellows 66 will just balance the tension of the spring 14 and cause the lever 62 to assume a position half-way between the stops 88 and 82. When the lever 62 is in this mid-po- 6o sition, the envelope III will be in the horizontal position as shown in Figs. 1 and 2. If the temperature should increase the bellows 56 will move the lever 62 towards the stop 80 which will in turn move the left end of the envelope l0 up 65 .and cause the mercury 30 to move towards the right end of the envelope ID as shown in Fig. 3. If the temperature should decrease, the pressure in the bellows 65 will decrease and the spring 14 will move the lever 62 towards the stop 82 which will in turn move the right end of the envelope I 0 up and cause the mercury 30 to move toward the left end of the envelope [0. The adjusting stud 16 which varies the tension of the spring 14 also moves the pointer 84 over the graduated aoaams dial '8 which permits the mechanism to be set for any desired temperature.

The curvature of the envelope ll causes the mercury 30 to assume a definite position for each position of the operating lever 62 and thus make contact with a particular part or section of the resistance element ii to place a definite amount of resistance in the circuit. This curvature of the envelope it! being such that when the envelope is tilted to a new position, the mercury 30 will not move beyond the position corresponding to the new position of the envelope ii.

A potentiometer or rheostat of this construction only requires a very small amount of power to change the position of the body of conducting fluid and thus change the resistance in the circuit. The electrical resistance between the fluid and the resistance element which is known as contact resistance is very low because the fluid makes a good contact with the element. Also, this contact resistance remains constant for the elements are hermetically sealed and prevent dust and other foreign matter from interfering with the contact. Since the elements are hermetically sealed they do not corrode or oxidize with use or age.

Although the device here shown and described is in the form of a potentiometer, it will be apparent that it can be used as a rheostat by only using wires 42 and 46 or wires 44 and 46. In this case one or the other of the leading-in wires l8 and 20 may be omitted. The envelope I0 may be made of metal and the resistance element l6 insulated therefrom, in which case the electrode 32 can be dispensed with and the wire 46 attached to the envelope in.

While but a single embodiment of the invention is herein shown and described, it is to be understood that various modifications thereof will be apparent to those skilled in the art without departing from the spirit and scope of the invention set forth in the following claims.

Having thus described my invention, what I l. A device of the class described comprising in combination, a sealed envelope having a pro- Jection on the inside thereof extending longitudinally from one end toward the other in parallel relation to the lower wall of the envelope, 5 a resistance element mounted on the projection, an electrode extending along the lower wall of the envelope, electrical connections for said resistance element and said electrode and a body of conducting fluid in the envelope arranged to 10 make contact between the electrode and various portions of the resistance element as the envelope is tilted.

2. A device of the class described comprising in combination, a hermetically sealed elongated l5 curved envelope having a reentrant integral curved tube extending from one end of the envelope longitudinally toward the other end thereof,

a resistance wire wound on the tube and having external connections one of which is sealed 20 through the tube near the closed end thereof, an electrode entering the envelope and extending along the floor thereof, a body of conducting fluid in the envelope arranged to make contact between the electrode and variousparts of the re- 25 sistance wire, and means for varying the relative position of the fluid and the wire whereby the resistance between the electrode and the external connections is varied.

3. A device of the class described comprising in combination, a hermetically sealed elongated envelope having a reentrant integral tube extending from one end of the envelope longitudinally toward the other end thereof, a resistance wire wound on the 'tube and having external 35 connections, an electrode entering the envelope and extending along the floor thereof, a body of conducting fluid in the envelope arranged to make contact between the electrode and various parts of the resistance wire, and means for vary- 0 ing the relative position of the fluid and the wire whereby the resistance between the electrode and the external connections is varied.

SYLVANUS c. smrmr.

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