US1614174A - Instrument shunt - Google Patents

Description

W. A. ATWOOD INSTRUMENT SHUNT Jan. 11 1927.

Filed April 9 1925 Inventor Winfield AAtUJood Page.

His Attorneg Patented Jan. 11, 1927.

UNITED STATES PATENT OFFICE.

WINFIELD A. ATWOOD, OF SCHENECTADY, NEW YORK7 ASSIGNOR TO GENERAL ELEC- TRIC COMPANY, AA CORPORATION OF NEV YORK.

INSTRUMENT SHUNT.

Application filed April 9, 1925.

My invention relates to instrument shunts ot the type adapted to be inserted in an electric circuit so :is to shunt a definite portion oft the emrent flowingtherethrough to an instrument or other device which is to be responsive to the line current.

As usually constructed. instrument shunts are nnnle ot' copper, or of a material containing a Vlarge percentage ol copper, in order to make the ten'iperature coellieient ot resistance zero, or very lou'. The temperature coefficient o' resistance ot such a shunt is .fixed and is not subject to adjustment for diil'erent instruments. .l'lig'h capacity copper shunts having; the requisite resistance drop tl'iereaeross and the heat dissil'iatiner capacity necessary toi' continuous heavy service are relatively expensive.

The object of my invention is to provide a rugged, relatively inexpensive shunt arranged so that its teuiperature Coellieient of resistance may be readily ndi usted to accommodate different instruments or other devices.

ln carrying my invention into e'lt'eet I provide a shunt made up ofi relatively inexpensive materials having different temperature coetlieients oi resistance, the tuo ninlerials being;- so arranged that the line eurrent 'lous in parallel therethrough and7 so that the relative resistance e'lii'ects of the differentmsterizilL-i may he adjusted with respect to erich other and in this Way obtain a` desired resultant temperature coeliioient ot resistance.

ln the construction olf my shunt, lY prefer to use cast iron and carbon since these maiterials are relatively iilexpensive and have opposite temperature coeliicients ol resistance. rl`he preterred construction takes the forni of corrugated cast iron Casing enclosing en adjustable stack ot' carbon discs so arranged that the current flowing through the shunt flows in parallel through thes/ inaterials. By adjusting the relative resistances ot these tu'o paths the temperature coeliiciei'it of resistance of the shunt may be changed. rl`he features ot my invention which are believed to be novel und pateutable will be pointed out in the claims appended hereto. For u better understanding` ot iny invention, reterence is made in the following description to the accompunyin;v drawing in which Fig. l represents a side view, partially in SeraL No. 22,001.

ted :1t 'l-l and contains one or more 's l preterahly ot carbon, or other niaterial hevinn similar properties, compressed between adir teble nuts 15. The adjusting nuts are preierebly made secure by loch nuts 1G. Tivo or more shunt lend terminal bolt holes, reg'nresented at 1.7, 18, 19, 20 and 21, nre provided 'to attach the leads which connect with the meinen-ing instrument or other device used with the shunt. It `vill be evident that this shunt is relatively inexpensive, both as to the cost oit' the materials used and the mechanical operations necessary ttor its construction. n

Cast iron has :L ]'i sitive teu'iperature coeli'ieient ot resistance and, consequently, would not be suitable as :i snunt it used alone. Carbon, on the othei` hand, has a. negative temperature coellicient ol resistance and likewise is not suitable for this purpose. However, by the proper combination of these materials in parallel, a desirable compromise temperature coetlicient may be obtained which, as will be more fully explained hereinafter, may readily he altered to suit ditierent instriunents. Cast iron and carbon both have positive temperature coefficients of expansion7 that of a suitable grade of carbon being somewhat higher than that ot cast iron. It Will therefore be'evident that es the shunt heats up, the castiron will estpand at n slightly less rate than the carbon discs 14, and this action will compress the carbon discs and decrezise the resistance therethrough. This has the saine effect on the characteristics ot the shunt as the negative temperature coefficient o resistance olf the carbon has. The line current in flowing through the shunt Will pass entirely through the east iron portion except that portion lying between the two sets of nuts l5 and 16.

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llet-ween these points part ot' the current will flow through the carbon discs. lt n'ill therefore be evident that to obtain a shunt ha vingi` a zero temperature coefficient ot resist` ance across the extremeJ shunt terminals 17 and lts. the resultant teniperature e( etlicient oi resistance ot that portion oi' the shunt havingl the iron and carbon connected in parallel must be negative te malte up Vt'or positive temperature coetticient ot resistance otl the remaining' portion o t the shunt which is entirely otiren. 'there are a varietyv o t" ways in which to change the resultant tenuperature cocllicient et the shunt between the shunt terminals. AFor exampleT thc mnnher` thirliness or diameter ot the carbon discs ma),v be changed and one ot' the discs has been represented as being thinner and ot a l 'i eter than the others tor this puril slight. adjustment may also be had by tight enini;l or loosening the clamping' nuts which compress the carbon discs. lt: will also be evident that tor any given iuljustnient the temperature coeliicient of resi .ance across terminals 17 and 1S will be different than that across terminals 18 and 19, since that portion ot the shunt between terminals 1T and 19 is entirely positive. Any ot these changes wil also change the voltage drop across any set ot' terminals tor a `given line current and temperature. The manner of adjustingthe shunt 't'or a given temperature coetiicient ot resistance and voltage drop will be clearer by taking;` a specitie case. Suppose it is desired to provide a shunt having a Zero ten'iperature coetiicient ot resistance and a 1 volt drop for 100() amperes line current. rl`he shunt will be constructed with the general proportions calculated to give this result. Suppose that when assembled. as illustrated in 1, the shunt gives 2.1 volts across terminals 17 and 1S and has a temperature coefficient which is slightly negative. it will appear that to correct the temperature coefficient, We must reduce the eli'ect ot the carbon path and this will increase the total drop across the shunt. Con sequently, it will be necessary7 to use shunt terminals 18 and 21 or possibly 1S and 2t). The ettectot the carbon path may be reduced by reducing' its length or increasingV its resistance. A slight loosening` ot one set ot' nuts maybe sutiicient. It not. a disc may be. removed entirely or replaced by one ot less thickness or less diameter and the nuts again screwed down to the proper tension. rl`he two conditions to be met must be considered together but by providing' a sullicient number o'l shunt terminals oi slightly ditl'erent spacing` as represented at 1S), 20, 2l. and 1i' and a suitable variety oit extra 'arbon discs these conditions may be met, The various carbon discs will preferably be marked or otherwise identiiied and the shunt terminals marked so that after the shunt is reifer-:'42

once calibrated, a calilnatiim record may lic prepared and used to facilitate obtaining the same or other desiredadjustments.

lt will be seen that ditlercnt terminals ot' this shunt may be used to simultaneousljl obtain voltage drops proportional to the line current having slightly dilt'erent resistance temperature coeticient eluuracteristic rl`hus, the same shunt may be simultaneously used to operate an instrument having` a Zero temperature coetticient ot. resistance and a rela),v having a positive ten'iperature coctiicient et resistance.

l do not Wish to limit my invention to cast iron and carbon as the materials to he used7 nor do l wish to limit. my invention to ma terials which have diti'erenttemj'veraturc cocliicients ot expansion, since it will he evident that there are various grades ot iron and steel as well as various grades ot carbon and substitutes tor carbon which may be combined in accordance with the tcachings ot this invention to obtain the beneficial result thereof. tither miuiitications will occur Vto those skilled in the art and.y consequently? I do not wish to be limited te the particular embodiment ot my invention herein described, but intend to cover in the appended claims all modifications and embodiments coming within the true spirit and scope of my invention.

llllzat l claim as new and desire to secure b v Letters `Patent ot the United States, is:-

t. .-\n electric shunt comj'nising` a conducting?Y member having` a positive temperature coetiicienti ot resistance, a conilucting` member having' a negative temperature coelicient ol resistance connected in parallel with a portion ot the first mentioned memter, and shunt lead terminals adjacent the extremities of said shunt, said conducting members having their relative resistances adjusted so as to produce a substantially zero temperature eoei'iicient ot resistance characteristic across said shunt lead terminails.

An electric shunt comprising a conductor haring a given temperature coeflicicnt ot resistance, means tor securing' line connections to the extreniities ot said conductor, shunt lead terminals adjacent the extremities ot said conductor, a second comluctor having' a temperature coetiicient ol resist.- ance opposite to that' ol the lirst mentioned coni'luctor and conncctial in parallel with said irst mentioned comluctor between the extremities thereof, and means t'or adjustingr the resistance ot said second mentioned condnctor.

il. )in electric shunt', comprising` a concluetor having a positive temperature coetiicient' resistance. means 'tor securing line connections to the extremities thereot, shunt lead terminals adjacent the extremities of said conductor and an adjustable carbon pile conllt) nccted in parallel. with a portion of said conductor.

el. An electric shunt having parallel connected conductor circuits ot" positive and negative temperature coelicients of resistance respectively, and means tor adjusting the relative resistance etllects of said parallel. connected circuit.

An electric shunt comprising a conductor having a positive teniperat-ure coefficient olE ref- .istance` line terminals therefor, shunt lead teri'uinals adjacent said line terminals, a conductor having' a negative ten'iperature coetticicntot resistance connected in parallel with a, portion oit said lirst mentioned conductor, und means tor adjustingthe length otl the parallel connected portions ot said conductors.

o. An electric shunt comprising' a castiron men'iher ha 'ing' an opening through one axis thereoli` line terminals and shunt lead terminals adjacent the extremities ot' such axis, a carbon pile in said opening electrically connected in parallel with the adjacent portion ol' said cast-iron member, and means tor adjusting the length and the compression ot' said carbon pile.

7. An electric shunt comprising a corrugated cast-iron member having a cylindrical opening' through one axis thereof, line terminals and shunt lead terminals adjacent the extremities et such axis, nuts threaded in said opening and a carbon pile compressed between said nuts.

8. An electric shunt having line terminals, diti'erent portions et said shunt between said line terminals having ditferent ten'iperature coetiicients ot resistance and means tor connecting` shunt leads across .different portions o't' said shunt so as to obtain a desired resultant temperature coetlieient ot resistance characteristic.

9. An electric shunt having line terminals, ditlerent portions ot said shunt between said line terminals havingdi t'lerent temperature coetlicients ot resistance, means for varying' the temperature eoetlicients et resistance et one portion ot said shunt, and means tor connectingshunt leads across different portions ot said shunt whereby a desired voltage drop and temperature coellicients ot resistance clnuacteristic may he obtained.

l0. An electric shunt comprising parallel comluctors having different temperature coeticients ot expansion and opposite temperature eoei'i'icieiits of resistance secured in lixed relation with each other.

AIn witness whereof, I have hereunto set my hand this 8th day of April, 1.925.

W'INFIELD A. ATVGOD.

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