US919908A - Electrical-resistance device. - Google Patents

Description

- H. S. MARTIN.

ELECTRICAL RESISTANCE DEVICE.

APPLIGATION FILED JULY 13, 1908.

Patented Apr. 27, 1909.

plied,

outrun s'rATEs PATENT OFFICE f HAROLD SHEEN MARTIN, OF LIVERPOOL, ENGLAND;

ELECTRICAL-RESISTANCE DEVICE. l t

To all whom it may concern:

Be it known that I, HAROLD SHEEN MAR- TIN, subject of the King of Great Britain, residing at Liverpool, in the county of Lancaster, in the Kingdom of England, have in-.

vented certain new and useful Improvements in Electrical-Resistance Devices, of which the following is a description.

Thisinvention relates to an improved electrical resistance device adapted to be used for all purposes to which such devices are apotherwise to suit varyin requirements, for instance, when used in a amp circuit the device may be ad usted to vary the current flowing through the lamp and so permit a vanation in the amount of light given by the lamp.

The resistance body consists of a mixture of the kind hereinafter more fully described, the resistance of which varies as the pressure exerted upon it is increased or decreased, the resistance being decreased when the pressure is increased. The mixture consists "essentially of a conducting material in granular or have been forced. springs which are distorted when pressed powdered form and a non-conducting material in the form of small scales. Suitable substances are gr'a bite for the conductor and mlca' for the insu ating material. There is mixed with these two substances some other granular material, such for instance as sand. It would appear that the decrease in the resistance' is produced by bringing the grains of theconducting material into intimate contact by means of applying pressure to the mixture, the increase in the resistance being brought about by the separation of the grains of conducting material under the action of thelscales of insulating material, whichon the release of the pressure tend to move out of the constrained positions into whichthey The scales of mica act as against the granular material (sand) 'infthe mixture. On the removal of the pressurethe flakes tend to return to their original positions moving away from each other and carryin with them the powdered conducting ma= teria The proportions of the constituents of the mixture may vary widely depending 1 on the purpose for which the resistance isto be used and the range of resistance and our rent-carrying capacity required; For-gin;- stance if a low resistance of comparatiyely Specification of Letters Patent. Application filed July 13,

the device being of the kind in which the resistance can be adjusted by'hand or Patented April 27, 1909'. 190s. Seria1No.443,208.-

small range is required the relative proportion of the graphite andcontact surfaces is larger whereas, if higher resistance with greater range is required, these proportions will be reduced. As an example of propor- I tions which have been found in practice sat-7 given: I n

Powder graphite 2 grams by weight I Micafiakes 1. f Sand 7 1 I u u. u

sure plates of 12 Innis. diameter, gives a range of resistance of 73 to 220,000 oh'ms.

drawin s which show one form of which t e resistance body is used.

In these drawings, Figure 1 is a vertical sectional view of the device ,and Fig. 2" is a 'horizontal sectional view on line 22, Fig. 1.

or flakes of insulating material as forced into the constrained position, wherein the resistanceisdecreasedr The device consists ofahollow cylinder a at each end with a metal surfaces between which the 'mixtureid is compressed, the other'surface being formed by means of a disk f at the end of a plunger carriedby a rod which is screw-threaded described, for instance a pivoted lever having acam surface a used.

forrhfof device issuitable-for all ordi- 3 is an enlarged view, showing the scales by. other means than 'by the means above isfactory'for some. purposes the following is I A quantity as: this. mam-re weighing" 4 grams when placed between circular res-- now refer to the accompanying devlcein lined with insulating material I) and provided diskQ The disk '0 at the bottom of the cylinder forms one of the and ,worksthrough a screw-threaded aper o ture in abridge piece .h located over the" other end of the cylinder; The two co n1' pression'members c and f are connected-to 1 pressingupon this disk may be 7 nary purposes vvhere'currents of normal magnitude are being dealt with. In cases however where very large currents are being ance.

dealt with, the surfaces of one or both of the pressure plates in contact with the material may be varied in' addition to the adjustment of the pressure in order to adjust the resist- This may be eflected by forming one or both of these plates of a number of rings fitting one wi hin the other, the number of which rings in contact with the mixture may be varied as desired. The samelesult may be produced by formingthe plate or plates of a spring strip of metal which may e bent in such a manner that only part of it normally comes in contact with the mixture, the remaining. part however being pressed down against the material when it is desired to decrease the resistance.

'It is obvious that although specific forms ,of this device have been described in detail,

considerable modifications may be made therein without departing from the invention.

In addition to graphite I can add rare earths which become conductors whenheated. to certain temperatures, such as zirconia,

magnesia or thoria mixed with a largeor small proportion of another oxid or other substance, yttrium, cerium, orbium and didymium oxids, boric acid, calcium chlorid and tungstic acid. The eflect of heating is produced in the passage graphite.

is with the object of increasing the currentcarrying capacity in a conducting body of of the initial current through the given bulk, and preserving at the same time a high mitial resistance.

Ideclare that what I claim is:

1. An electrical resistance device comprising a resistance body in which are inti mately mixed together a material in the form of springy scales or flakes and a material in the form of grains.

2. An electrical resistance device com prising a resistance body consisting of a mixture oia non-conducting material in the form of sprm scales or flakes, a granular material, an

3. An electrical resistance device comprising a resistance body in which are intimately mixed together mica inthe form of my device by heat generated by The addition of these rare earths.-

a finely divided electrically con ,ducting material.

scales or flakes and a material in the form of grains.

4. An electrical resistance device comprising a resistance body consisting of a mixture of mica in the form of scales or flakes, a granular material and a finely divided electrically conductin material.

5. 'An electrica resistance device comprisinga resistance body consisting of a mixture of mica in the form of scales or flakes, a

-granular material, and finely divided graphite.

6. An electrical resistance device com- I prising a resistance body consisting of a mixture of a non-conducting material in the form of scales or flakes, a granular material, a finely divided conducting material, and a material which becomes a conductor when heated to a suitable temperature.

7. An electrical resistance device consisting of a resistance body in which are inti mately mixed together a material in the form of s ringy scales orflakes and a material in the orm of grains, a receptacle for said body,

and means for varving the pressure upon 9. An electrical resistance device consisting of a resistance body in which are inti.

mately mixed together a material in the form of s ringy scales or flakes and a material in the orm of grains, a receptacle for said body, two conducting plates dis osed opposite to each other in said receptac e, means for varying the distance apart of said plates, and

means for varying the conducting area in con tact with said body.

' In witness whereof, I have hereunto signed my name this 2nd day of July 1908, in the presence of two subscribing witnesses.

HAROLD SHEEN MARTIN. Witnesses:

B10111). L. CLEAVER, WM. G. TRAVIS.

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