AME RICAN INSTITUTE OF ELECTRICALENGINEERtS.

SEVENTEENTH GENERAL MEETING.

PHILADELP,HIA, May 16, 17 and 18, 1900.

The opening session of the Seventeentll General Meeting wascalled to order in the Drexel Institute, on Wednesday May 16, at2 P. M. by Past-President Keiunelly.

PAST-PRESIDENT KENNELLY:-The meeting will please cometo order. The Secretaly has an announcement to miiake.THE SECRETARY:-Most of the members presenIt are aware

that the counting of the ballots for the ann-ual election tookplace last eveninig at New York. The iumber Qf ballots, castwas unusually large, amounting to over 600. 1 ha-ve this mem-orandtum from the tellers of the vote for President:

New York, M4ay 15, 1900.The result of the ballot for President of the American Institiite of Electrical

Enogineers is as follows.Carl Hering .............381M. I. Pupin.. 179

Mr. Hering received the largest number of votes and is elected.Signed, TOWNSEND WOLCOTT and SAMUEL REBERTPelle.rs,

DR. KENNEf,LLY :-Gentlemen, we have just heard that Mr.Ilering lhas been elected President of the INSTITUTE by a iuajoiityof more than 200, and I tlhink we may congratulate ourselves, aswell as conigratulate Mr. Hering upon this important announce-ment. IA can only say I am delighted to resign ini Mr. Her-ing'sfavor and it gives mne very great pleasure indeed to appoint acommittee to escort Mr. Hering to the Presidentia clhair. Thecommittee will be Mlr. Hammer and Professor Houston.

Mr. Hering, on being escorted to the chair, spoke as follows':Gentlemien, I am very grateful to you for the, honor yon lhave

conferred upoin-me and I hope that the officials which you,_ lhavejust elected will be able to conduct the af'airs of the Institute toyour satisfactionr for the next year.

283

284 SEVENTEENTH GENERAL MEETING. [May 16,

The meeting will now please come to order. The first tlhingon the programme will bean address by Dr. McAllister, Presidentof the Drexel Institute, wlhose hospitality we are now enjoying.I take pleasure in introducing to yon' Dr. McAllister of theDrexel Institute.

Dr. McAllister spoke as follows:Mr. President, and gentlemnen of the AMERICAN INSTITUrTE OF

ELECTRICAL ENGINEERS: I am very glad indeed, as President of theDrexel Institute, on behalf of the Board of Trustees to welcomeyou here to this meeting. I feel it to be a great, honor as wellas a privilege to have you with us. It is not worth my while totell you the place which is oceI pied in our time by the professionof electrical engineering. I am, in the habit of telling the stu-dents here that at the present hour there are two great leadingprofessions. Those of us who, were educated a generation ago orMore, lived in a tirmie when that profession hardly existed.There were the old-fashioned clerical, medical and legal pro-fessions, and that was about all. Nowadays the young man whohas got the stuff in him, and the ambition, usually turns in otherdirections, and to iny mind the two great professions to-day arethe engineering profession and the arehitectuiral profession.Any one in mv position knows it to be a fact-I used to talkwitlh nmy friend General Walker about this-that the best youngmen to-day are pushinig into these professions. There are mnanyreasons for this, which of course occur to us all. Of all theengineering professions the electrical profession I think is theone which Interests the mass of -the people more, because it isone that is among the newest and most interesting and nmost;marvellous applications of science to the arts of life, and has cometo play a mnost important part in the civilization of the present,and will still more in the civilization of the future. We arevery glad to have you here and I merely want to say to you thatYou are welcome to everything that we have. We would haveliked to mDake some provision for your, social enjoyment, but Iunderstand through Professor Rowland, oni beohalf of the Coni-mittee of Arrangements, that your time will be wholly ocecipiedin that regard. We have however, with the consent of the localcomlmittee arranged a complimentary organ recital for the mem-bers of the INSTITUTE and the ladies, on Friday afternoon at 3o'clock, the programme of whiclh will be distributed.

I presume most of you know very little about this institution,and entering it as you have, would be apt to get a false impres-sion of it. I want to sav to you that we think it is a fit place foran association of this kind to meet. It is ani institution devotedto artistic, scientific and technical training, and is seeking invarious new lines to work out the educational problem in theapplication of art and science to living. We have a very miiodernschool of electrical engineering, different from the larger institu-tions, in some other cities, but where with a fair amnount of sci-

1900.] SE VENTEENTL GEIVERAL MBEETING. 285

entific training and technical training there is a larger provisionfor practical work in the shop; anid if you will take the troubleto go behind the screen-this external part of the institution-you will find the libraries and workshops I think well equippedfor the purpose. For that reason we are glad to have you here.1 trust you vwill not regard the presence of the students wlhochoose to conie here as any intrusion.

This is all I can say, to again repeat the cordial welcome ofthe Board of Trustees and of the Faculty of the Drexel Insti-tute. We trust thiat you will enjoy your stay in Philadelphia,We are farnous-well, for a good mnany things, but we arefainous any way for our hospitality; we can take yleasure inthat; we are very proud of that, and I tlhink you will find your-selves as cordially welcomed here as -von ever have been in anyother city in wlhieh you have had the pleasure to meet. I begagain to give yon a cordial welcome.THE PRESIDENT:-The Secretary has an annouIneement to

rnake.THE SECRETARY:-YOU will find on the platform a bundle of

notices giving a bulletin from the Franklin Institute, which in-cludes a programme of the stated meeting of the Institute thisevenitng, May 16, at 8 o'clock, to which we have been invited.The following programine has beeni arranged: "Recent Im-

provements in the Manufacture of Liqnid Air; the separation ofair into its constituent parts, and the indnistrial use of oxygen,nitrogen, and carbon dioxide," by Professor Raoul Pictet andAloriz Burger.THE PRESIDENT:-In the absence of the fayor of Philadel-

phia, who was to address us, ye will proceed directly with thereading of the papers. The first paper out the programme is on"A New Transtmission Dynamoinieter," by Prof. W. ElwellGoldsborough of Purdue Uniiversity, who is already so wellknown to us through his work tllat lie needs no -further intro-duction.

A paer read at the 17th Genera1 Me tingof theAmerica Institute of Etech-ical Engineers,Phiiadeilhhia, May s6, 1900, President Heringin the Chair.

A NEW TRANSMISSION DYNAMOMETER.

BY W. ELWELL GOLDSBWROUGH.

The dynamometer described in this paper is the outcome of aeries of attempts to devise an instrumient for the measurement

of mechanical power comparable with electrical instrulents asregards- simplicity of design, ease of calibration, permanency ofadjustment and the accuracy of the readings obtained. The^dynamometer cannot be said to emnbody any radically new ideas.The priniciples upon which its success depends have beeni usedin several other instruments; there is presented here simply anew adaptation of these priniciples. The instrument has beenjointly developed by my assistant, Mr. E. T. Mug and minyself.The dynamometer, as shown in FigL. I and 2 is designed

especially for testing electric motors of from five to 25 horsepower capacity, and can only be used by directly connectinig itbetween the driving eleinent, the motor to be tested and thedriven element, a lynamo, adjusted to absorb the power devel-oped. It consists of a shaft, shown in Fig. 3, whlieh is made intwo parts. These are kept in line by having a portion of theleft hand section turnied down to exactly fit a concentric holebored in the right hand section of the shaft. The joint presentsa sufficient bearing surface to eniable the instrumnenit to standquite severe lateral strains, although it is not sufficient to admitof the dy-namometer being used to transmit power tlhrough themedium of belt-driven and driving pulleys attached to the outerends of the slhaft. For the dynamometer to be available forthis class of work, the two sections of the shaft should be made,in the form of quills to fit a second shaft extending completelythrough both sections.Each section of the shaft is provided with a spiral grip-

-thread, turned to fit a spiral spring of i" pitch. These threads287

288 GOLDSBOROUGH ON A [May 16,

are shown in the lower half of Fig. 3. The sections are alsofitted with jaw collars, shown in the upper half of Fig. 3, thatare turrned to the same pitch. They have their spiral jaw sur-faces cut to overhang the shaft, and make an angle of 450 withthe shaft surface. The jaw collars, when forced into positionby the lock nuts, with the aid of a spanner wrench, hold theend turns of the springs very securely, preventing them notonly from slipping around the grip-thread, but also from spring-ing out when the direction of rotation is such as to tend to un-wind the spring.

All the spirals used with the dynainometer must have a pitchof i inch, and be wound to snugly fit a shaft 2-19 inches in

FIG. 1.

diameter. The jaw will securiely lbold springs fromj .~2 inchl to6 inch .in diaieter, but nieces:siarilvthe larger spingis give amore stable adjustment and add stiffness to the int-trlnmenit, conl-sidered as a transmiittinig deviee. Withiin the capacities of tbesprings, therefore, comnparinig thiemi relativelv to onie aniothier, tileconiditions for accurate work are imore favoirable withi the largersprinigs. All thle experimiental work referred to hiere, hiowever,was carried out withi a sprinig nmade of stanidard No. 5 steel wire,whichl is slightly over .2 inceh in diameter.On the free sectionis of the sbaft, shiown betweeni tme hiexag-

onal sections and the oil grooves, ar-e mounted two instantaneouscontact wheels, insulated from the shaft by hard fibre usbin_'s.Eacheof these wheels, which are shown in Figs. 1 and 2, cariies

1900.J TRANSMISSION DYNAMOMETER. 269

at its rim a contact edge made of sheet brass and set parallel tothe shaft in a bard fibre plug, driven into an inverted V groove,and turned down flush with the surface of the wheel. The con-tact points are grounded on the shaft, and are therefore in elec-trical connection with one another, although insulated from thecontact wheels. Two brush holders mounted on the dynamo-meter bearings, and carrying 90° graduated scales, supply thebrush supports and complete the contact devices; they providefor the possibility of obtaining readings when the angular deflec-tion of one wheel rim contact point is 18O from the other.The hruslhes are carried on insulated brushl rods and are con-

FIo. 2.

nected witli oie another through several primary cells and atelephone receiver, all in series. This adjustment supplies themeans of detecting when the brushes are so placed that the con-tact points on the wheels pass under them at the same instant,since at such times a " click " is heard in the telephone at eachrevolution of the dynamometer shaft.The description thus far given indicates with sufficient clear-

ness the method of using the dynamometer and of obtaininginstantaneous readings of the torque exerted by the driving ele-ment at any time. When, in the case illustrated, the motor isstarted up, the angular deflection between the contact points is

290 GOLDSBOROUGH ON A [May 16,

increased above its initial value until the resistance to flexureoffered by the spring overcomes the frictional resistance of thegenerator, and motion is imparted to its armature. If, by,speed-ing up the motor or loading down the generator, eonditions arevaried so as to increase the resistanc,e to motion between the twomac:hines, there will be a still further deflection of the springuntil the balance is restored between the forces acting. Thevariation in the angular deflection is quickly and easily followedby shifting the cointact brushes until the click " occurs in thetelephone. In case the "click " is not sufficiently proniounced,a condenser, shown in Fig. 2, is connected i-n parallel with thetelephone receiver, and its eapacity adjusted until the " click"is sharp and clear cut. If ordinary conditions of constant loadare maintained, such as are usual in any laboratory test, the" click" in the receiver will be kept up at a constant frequency,

<;0 L~- Mhilled- 5illedHexagronal Hexagonal

Bear_n Key Bearing

Working Fir

I2Pitch ~~Sliding CollarJaw Clutch

FIG. 3.-Details of Shaft and Spiral Spring Clutch Jaws.

and the relative motion between the contact points will be zero,as shown by repeated trials, even wlhen the smallest spring isused; and when a suitable tachometer is at hand, ideal condi-tions are presented for making inrstantaneous determinationis ofthe power transmitted.

In testing a given motor, the best results have been obtainedby using a spring which will give a deflectioni of 18O' when themnotor is fully loaded. The brush setting admits of an accuracywithin .2 of one degree, aild thus the determination of thie fullload torque can be obtained within one-tenth of one per cent.This comnpares favorably with the results obtained with theusual laboratory electrical instruments.The mnethod used in calibrating the dynamometer is illus-

trated in Fig. 2. It is rapidly and easily effected with the aid

1900.] TRANSSISSION DYNAMOMETER. 291

,of the two long wrenches shown in the cut. These are adjustedon the hexagonal sectionis of the shaft, one being used as a scalearm and the other as a lever. For any given point the lever isdrawn over till the scale arm shows a tendency to raise fromits horizontal position; the brushes are then placed on the con-tact points and adjusted till a clear "'click " is obtained in thereceiver on making and breaking the battery circuit; and arecord is made of the scale arm moment and the deflectioon scalereading. The calibration curve of the dynamometer fitted with

90

80 - __ _-__ _

70

60 X _1_ _1 L

2i350

C.40

*00

LUi

010-

2 3 5 7 8FOOT POU DS

-10__

-20

FIG. 4.-Calibration Curve of Dynamonieter Spring.

the lightest spring is shown in Fig. 4, and repeated tests before-and after use fail to show any change in its calibration con-stants.As an evidence of the ease with which accurate results can be

obtained, I give here the results of a test made upon a three-,phase induction motor conjointly with Mr. Mug, and twoseniors i-n electrical engineering at Purdue University, Messrs.A. F. Chamberlain and C. R. Dooley, to determine the charac-teristics of the motor. The results may be the more interestingin view of the fact that the test embodied a very simple method

292 GOLDSBOROUGH ON A [May 16,

for obtaining the mechanical torque developed by the motor atany speed.The electrical readings were obtained by connaecting an am me-

ter and the current coil of a wattmeter in each circuit, and avoltmeter and the voltage coil of a wattmeter between eachterminal of the motor and the neutral point of the three starconnected transformers feediDg the motor. The voltage was

0~ ~ J

1---- '- C)'

12-__ __ _}

w _ L)

8 D 0 4

0CD___ -

s_

70 F _ - iv -

6 606 A 30

50 5 -EC- ,NIAL 4Ui7001X - a ,, )t

100Q 3A 0 0 0 0 00 90 10 lo 10oI 5.-pe ChAtrsiso he-paeIdcinMtr

keptconstant at 00.7 volt3 between the -otor ter-n;Ilal- 0he

spee0 4d(0~~~~~~~~~~~~

I 00

S lE D1 N PR.P,M100 200 300 000 000 600 700 800 000 1000 1100 1200

FIG. 5.--Speed Characteristics of Three-phase Induction Mqotor.kept consotanit at 53.T volts between the motor terminals. Thespeed was determined by belting a calibrated magneto-generatorto the motor shaft and readiing the voltage developed at itsbrush terminals; and the torque from the dynamometer. Everyfactor entering into the test could, therefore, be obtained simul-taneously and very accurately.The motor was started up from rest and held at a low speed

by the, generator. The generator was connected with its two

1900.1 TRANSMISSION DYNAMOMETER. 293

shunt field coils in parallel, instead of in series, across itsbrushes. With this connection it acted as a short-circuitedseries' direct-current dynamo. To add stability to the adjust-ment, the series coil of the dynamo was separately excited witha small current. The speed of the motor increased till thecounter torquie developed by the generator equalled the torqueof the induction motor. The speed then assumed a perfectly

150 _0

11X -, 2.8

130 _X_ _- 2.0

120 r + !2.4

TE TO 3PHASEMOT ORe 110 l-A-52.7V-GL - - .2r

l AF'RIL, 6 19 30\;loo t- - t-2.0

z

0

0 a-

z 6

0

0100 200 300 400 500 600 ,00 800 900 1000 1100 1200

SPEED IN R. P. M.

FIG. 6.--Torque Characteristics of Three-phase Induction Motor.

constant valne, and readings were obtainled from all theX iristrn-inents. Next, a resistance was connected in the armnature circu-itin series with the shunt windfing; the induction mzotor increasedits speedl until the counter torque of the generator again equalledthe torque of the motor; the speed again becam!e perfectly con-stant, and readings were taken. The speed stability of thisarrangement is owing to the fact that the torque of the direc:t.

294 GOLDSBORO UGH ON A [May 16,

current machine increased very nearly as the square of its,armature speed, and therefore very much faiter than the torque-of the induction motor. Using this adjjustmnent, the speed andtorque of an induction motor can be held at all com.mon valuesat will.

I hope I may be pardoned for dwelling iupon these experi--16- -_ _ ___ __ __ _ _ _ _ _ _

-1

-14

~'G.~ .L a .~ 7: 110

80 -12t -12<<09 0

CU 70 it j o-

z60fi Q^; <t°50 _ X 4IL=i.__.i<30 Xtg7- __0

O~~~~~~O

HORSE POWER OUTPUT7IG.7--Power Characteristics of Three-pha,se Induction Motor.

mental details,but I donot now recall having ever seen a descrip-tion in print of a simlple and successful method of obtaining thetorque of an induction motor for speeds below the speed ofmaxsimum torque.The curves of Figs. 5, 6 and 7 show the experimenetal values

of all the characteristics of the motor below as well as above

iOGO.] TRAASMIS/fION DYNAMOMJE7E. 295

the poinit of maximuma1 power, and bring out the relations thathold between the several factors at the very low speeds. Thecurve designiated "'electrical " torque represents the torque thatthe mnachine would develop with the given input if it had anefficiency of one hundred per cent. at all loads.The curves are chiefly valuable in showinig the acecuracy with

which torque readings can be obtained. The curve of "horsepower output" of Fig. 5 depends directly upon the product of theinstanta'ieous speed and dynamometer readings, and is veryaccurately defined by the plotted points. In tests upon motorsof larger eapacity the dynamoineter is even more satisfactoryfrom the experimenter's standpoint; not because its acecuracy isnecessarily greater, but because of the imore rigid couipling be-tween the machines. There is nothing about the dynamomneterto get out of order, the bearing friction is very small and prac-cally eliiminated in the calibrating; the springs are cheap andeasily adjusted.A spring can be taken out and another substituted for it in

about five minutes, and the dynarniometer can be calibrated infive minutes; but best of all, perhaps, it can be put in the handsof inexperienced experimenters, after having once been adjustedand be used by them with success, as there is nothing to get outof order.

Wbhen the load on the dynamiomneter is subject to rapid varia-tions, the eluteh, shiown at th1e center of the shaft in Fig. 3,should be moved over to tlle right. It will then lock with thejaw on the right hand section of the slhaft in case the deflectionexceeds 90- and prevent the possibility of the spring being over-strained.Lafa,yette, Iimd.,

April30th, 1900.

296 GOLDSBORO UGII ON A DYNAfOMVETER. [May 16,

DISCUSSION.THE PRESIDENT:-The difficulty in suich transmiissioni dynamom-

eters, has usually beeni to obtain a stationary indicator of thedeflection of a rapidly revolving spring, and this seems to havebeen overcome in the present arrangtemnent by a very ingeniousdevice. The paper is open for discussioll.

MN. C. 0. MAILLOUX:-I consider this a verv ingeinious, effec-tive and praeti(al device. Those who have had, experience withtransmiission dynamnomneters know that there is very little to besaid to cornmend the very best of theln. The most satisfactoryolnes that I know of are the so-called Emerson type, in which thelmotionl is transmitted through an epicyclical gear train where thetorsional imomlent produces a lifting mtoment, which is used as themeasuire of the power transmitted. This machine, which wasat one time very largely uised, is however open to many objec-tions, not the least of wlhieh is friction-the uncertain arrmunt of--friction which it ha-s wifthin itself. A later forty of transmissiondynamometer which is mnore satisfactory, and witlh which I per-sonally have had some practical experience, is the YVaiWinkledynamometer. It resemiibles the present dynatmiometer in thefact that it also miieasures a mnomenet of torsion, by means ofsprinlgs. It likewise gives an indication by the relative motionof two disks, which are held together by two eoiled springs, thesprin,gs being arranged sornewhat as in the so-called " Raffard"Coupling simxilar to that whiceh is used on the shaft of the Wes-ti-nghouse KKodak " dyn)amos. Again, however, there are diffi-eulties, one of them being celitrifuoal action, which tends tothrow out the springs bodily, and which canises an error in itsreading by introducing additional force, namely, that of centrifu-gal action in addition to the strain due to the motment of torsion.In the present ease the author lhas apDarently avooided this diffi-culty by placing the spring on the shaft itself where it is no lon-ger subhjected to any centrifugal action; and he has also elimina-ted, so far as one can see, all of the losses and errors due to fric-'tion. The only thling which it seemiis to me the device still lacksis a means of giving a visual indication of the torsional -mornent;that is to say, one which would read on a scale, or one for readingwhich you do not have to mriake adjustmenits. The instrument inthe present form will only give an iindication for each particularmnoment, just the same as when one measures a resistance with aWheatstone bridge set, where one has to balance for the partic-ular value. In this case the usefulness of the apparatus is some-what imipaired by that fact, because, with fluctuating loads, orwith loads which do not reilain at a constantly steady value,there must be a tendency to lose the telephone tick; that is to saythe torque either exceeds or falls below an amoutnt which corres-ponds to the position of contact which gives the click on the tele-phone. Either there mutst be somethinlg like a dash-pot, to makethe instrument lest sensitive, and thereby impair its uisefuLlness as

1900.] DISCUSSION IN PIIlLADELPHIA. 297

an instrument of precisioni, or else there must be means of quickadjustmrentt so that, when the torque varies onie can still find andfollow quickly the clicking spot, which is the thing by means ofwhich the angle of displacement in the two disks is measured. ItseemA to me that some systemn of epicyclical gearing could be de-vised anid attached to the outtit that would enable one to get adeflection indicationi. In the VanWinikle dynamyiometer a deviceof this kind is uised, whlieh is somewhat complieated, but it is pre-ferable to the present mnethod in so far as it enables one to takea large num-ber of readings in a short time, and this is particularlydesirable in the case of fluctuating loads. I should say that wherethe fluetuations are at all important a1nd large, one would haveconsiderable difficulty in getting satisfactory results with a na-chine of this kind. Y-ou inight catch it at somre points, but itseerms to me that one would not be able to get readily the mea-sure of the fluctuation, for which we miust get the extremes,whereby we may get a correct idea of the range of variatioD;which is sotnethinffl that oine ofteni wants to know in makingdynamometric tests.

I would like to kniow wlhether the author noticed any pheno-inena in the sprinigs akin to hysteresis. I have sometimes ob-served that sprintgs do not come back at once to their originalformn when the tension is released; they seem to experience akind of hysteresis effect. They eventually get back but it m-ayrequire conisiderable time. Of course the nearer the elastic limiitis reached the worse that effect would be. Still I think it is no-ticeable in certain cases even when the strains applied to thespring are muelh below the elastic limit.

I would also like information regarding the range within whicha particular outfit cani be used; that is to say, how many springswould one require in a dynamometric ouLtfit which was intendedto cover a range of from one to forty or fifty horse power. Withthe Vain Winkle dynamometer it is found niecessary to transmitthe power at different speeds in order to inerease the range. TheinstrumLiernt is not applicable to many cases for which this one isapplicable, for that very reason. In this case since we ean couplethe drivinlg and the driven niachines together it seemns to methere miglht be a very wide range of power under 'great variationof speed.

PROF. GOLDSBOuROUGI :-As Mr. Mailloux's remarks have beendirected especially to me, I think I can say, as far as the matterof the dash-pot, for instance, is concerned, that in using the in-strument we have found very little difficulty, indeed, from vibra-tion.

I have also uised a very successful dynamormeter brought out byProfessor Flathler in which the amount of torque is measured bya series of pistons. These pistons operate in little cups or cylin-ders whieh are arranged on the rim of a wheel. For instance, ifthis, represe-nts one of the spokes of the wheel (making diagram

298 GOLBSBORO UGII ON A D YNAMO2IETER. [May 16y

on the board) there would be a little eyliTnder attached, here on apin projecting ouit in this direction whicih the piston would fit,and tranismnit a pressure through suitable coni-ecting means ouit toa gauge at the end of the shaft. This is a very good form ofdynaumometer. It is one that cani be v-erv successfully used inmaking tests on all sorts of maclhinie tools, in coinnection withlathes, etc., where there are rapidly fluictuating loads, and it givesa perfect record where a proper speed counter is used, and wherea recording drum is used for recording the torque. It enlablesone also to determrline at any momenit the torque wlhieh is devel-oped. These instrumetnts are uisually of the belted type and haverelatively quite a wide range of usefuilness.As far as I know our ilnstrumtnent is most accurate for mieasuir-

ing power and determining, torque. The Van Winkleinstrument I personally do not like, for the same reason thatI object to the Flather dynamometer, in view of the fact thatthey are soimewhat comtxplicated. In getting ouLt our instrumentI wanted particularly, if I could, to devise a dynanonmeterwhieh could be used at all timles by the students witlhoutan-y danger of its getting oLt of order, anid withlout their havingto spend most of their time oni the dynamometer instead of onthe electrieal apparatus. In cases where we have used a Pronybrake, or other type of dy)namometer, we lhave usually lbad m-oretrouble with the dynamomneter thani with all the rest of the ap-paratLus put together. In using the dynamometer whiclh is dis-cussed in the paper there is no trouble at all experienced in hand-ling the instrurmient. The objection which has been raised, thatit is impossible to get a reading of the instantaneous torque devel-oped by the maehine without first setting the brushes, is, I thiuka miiore or less pertineent criticism I have made drawings for,a maclhine of the same type iii which a resistance wire will beused: by having two collector rings arrallged and a contactpoint pressing oni the resistance wire, and then having a storagecell acting on a circuit throughl the wire and a Westoni rmuilli-volt-meter the variations in the angle of torque will be determined.In othier words, whien there is no torque there will be none of theresistanee wire in the circuit, and conisequenitly a minimum read-ing of the voltage by the milli-voltmeter. As the twist takesplace in the shaft, the relative position of the two wheels ischanged, and more and moore resistance is introduced into the eir-cuit. This niecessarily cuts downi thie current andi reduces thevoltage reading on the milli-voltmeter. This arrangement, Ithink, can be successfuLlly carried out to give at all tirnes definitereadings of torquie, when the instrument has oilee beencalibrated. Onl the other hanid it introduces an additionaladjustmenit in the apparatuis itself and rnakes it just so muchmore comiplex; just so mnuch more easily put out of order.

MWre have fournd it very easy, indeed, to get settings with thetwo contact brushes. We have found that by puttin,g three Edi-

1900.J -DISCUSSION IN PHETLADELPHIA. 299

son-Lelanide cells on the circuit and using a condenser of ab-outone miciofarad, inl parallel with a teleplhone, the setting can bemade very quickly. For instance, in rLunning uip the back of theinduction mnotor torquie ciurve, before tl-he method of using the.series genierator was devised, an attemipt was made to use a separ-ately excited shunt-wound machine. A shunt-rnachine works allright until you get to a certain point on the ecurve, but after thatit is imnpossible for vou to hold the speed of the iniduction motorconstant at any onie point. For- instance, in the case of the in-ductiori mnachine discussed, the speed-torquie curve is, of course,that slhown in Fig. 5 (illustrating.) Now the torque ecurve of theseparately excited shunt generator is a straight line for any givenresistance in it-s armature circuit. This arrangemrrent holds thespeed at constant values as long as the straiglht linie speed-torquiecurves of the shtunt generator cross the speed-torque curve of theinduction motor at an abrupt angle. Wheni, however, the speed-torquie ecurve of the shunt generator becomes nearly parallel tothat of the iniduction motor, owing to the reduction of the resist-anee in the shunt generator circuit, a condition of inistability ofspeed is reached and both the speed and the torque of the inductionmllotor will continiuously rise. However, as the speed rises slowly,,we have been able to follow up the -torque reading-the man who}leads the dynamometer ealls off and the men reading the electricalinstrunments make their records at the saime time. In this way wecani work quite rapidlv and get poin ts right np the back of the speed-torque curve. If there were muLch difficulty in getting the set-ting with the dynamomyieter it wouild not be possible to followalong the curve. If you wish to hiave a great deal of stability inthe instrument it is not necessary to use a dash-pot; it is omilynecessary to put in a hleavier spring, and by using a stif springyou can mlake the adjustm-enit as stable as you wish. Of course,the finer the spring for any given power, the more difficulty youwill have in getting your settings, because the angles thirougliwhiel the torsion takes place, as the loau is changed, are veryinueh greater.

In regard to the matter of hysteresis in conInection witlh thespring, I have not inade any deterniination whatever. The onilydeterminations that we have made are these. Early in the after-noon, for instance, when an experiment is conLducted whieh in-cludes the luse of the dyniamometer,. it is calibrated. The testsare then perfori ned and immediately afterwards a second cali-bration is taken. The tAwo dvnamonmeter calibration curvegwheni plotted fall absolutely on top of one another. Whenwe calibrate a voltmlleter just before and just after an experiment, ora watttmeter or an amnmeter, we frequeintly find slight differenees.The points in the two calibrations may scatter a little, or not fallexactly on -one another. In the case of these springs we havefound that they fall exactly in line; and so, in view of the factthat the error of the dynamiometer must be inside of the error of

300 GOLDSBOROUGH ON A DYNAMOMETER. [May 16,

the electrical instruments, we have not thought it niecessary to payainy special attenition to hysteresis.

In regard to the number of sprilngs; our instrument has a rangeup to 25 H1. P. anid for that range we have five springs, the smal-lest of which is two-tenths of an inch in diameter and the largestis about seven-tenths of ani inclh in diameter. With these springswe have a range Mwhich covers all machines from two H. P. up to25 iH. P, A very good efficiency curve can be obtained with anangle of only 90 total deflection at full load. Youi can then gofrom zero to full load and get very exact readings. If you putlighter springs in, niecessarily your results are mnore accurate be-cause you get a finer adjustment in the scale. I would say, though,for an instrumenit of this size you -need at least five springs. if Iwelre going to build aniother instrutment, for larger powers, I wouldmake it for use between 25 and 100 u. P.

I have found that this dynanmometer mnethod can be used byputting two muachines in lirne and sirnply connecting a spring tothe shafts of the nmachines, thereby removinig the necessitv ofhaving an extra piece of apparatus. For instance, we have tworailway mnotors in the laboratory; thev are lined uip and a springeonnectsthe two shafts. The spring in this case acts both as aflexible connection between the imiachinies and also as a dynaroni-eter. A springr costs only about 60 cents, so that the spring isthe smallest item of expenise.

PROF. A. J. ROWLAND:-There is just one thing that occurred tomne in coninection with Prof. Goldshorough's paper, a point in de-sign which males the dynarmometer especially comrrmendable. Itis not particularly with reference to the dyniamometer either, buitin connection with the means of recording the results. I refer tothe use of a contact-maker. Anybody who has done anythinigwith contact-makers knows how elusive tney are; how smnall,trifling things, that are so suLbordinate that, thouigh they seem asif they could count for niothilig, throw one's results all out. Nowin this case we do not look for silence as usuial in such devices,hut just the reverse. It is easy enough to get a contact-maker tooperate so you can hear a tick irn the receiver; it is diflicult to geta contact-miaker to work so thlat one proeures silence. Perhapsit is obvious and so unnecessary to say, but certainly if a contact-mnaker is to be used, this means of reading, when the click of thetelephonie is made the guide for settings of the scale, is the onilymethod whieh could be applied. There is always moving ma-chinery to add to the noise in the receiver. Altogether the instru-muent as devised must be one which is easy to work with, anda dynamom)eter by which one ought to get very nice results.

PROF. GOLDSBOROUGH :- As far as the action of the telephoneis concerned: in using the machinie, my assistant first reported tome that he had no special difficulty in obtaining' readings, butthought probably the width of the contact had some effect;so 1 took somie trouble to find out just what the range of

1900.] DISCUSSION IN PHILADELPHIA. 301

accuracy -is. In our machine the brush probably has a widthof x1 of an inch and a contact poinlt width of W of an ineh.Now if you have one brush in a fixed position and movethe other, you can move it along until yo-u begin to hear aclick. Move it a trifle further and the click becomes morepronounieed until you get a imnaxinmum amount of sound.Proceedinig st-ill further the sound will diminish. By takingreadings very carefully I have fouind- thiat in ten readings wecould every time bring the pilot brush right back to the sam-lepoint. If you want to catch just a faint noise, you canX get thatadjustment. If you want to get the maximum amount of soundyou can get that adjustment. Or if you want to carry it too farahead and bring it back to a faint sounidinig position you can getthat adjustmrent. So we have found that between zero so ind onone side and zero sound on the other side, there is a limit of lessthan one-half of one degree in the scale reading where the springis adjusted to give 1800 deflection at full load. Half a degree inthis case represents a very small error. Bv careful work, ofcourse, you can make it mnuch smaller. I do not know how theinstrument would work if youi were using it on very fuctuatingloads. [1 do not know that it would be a success. It was niot de-(signed for that. It was designed to use with electrical mlachinl-ery, where we,can maintain our load with absolute constancy, youmay say, for almost ainy length of timYe; and for that pur-pose itworks nicely. What its value would be in testing lathes or ma-chine tools of variouis kinds, in which the fluctuationo are veryrapid, I do not know; but for the use of the electrician and forrapid testing in either commereial or college laboratories, it hasso far worked out very nicely, indeed.MR. MAILLOUJX:-I do not quite agree with Prof. Goldsbor-

ough as to the limlitation of this instrument. I think it is reallysuited for many miiore purposes than he thinks, provided it hasmiieans of giving an indication of the deflection. I think that isreally all it needs. It is free from the series of errors due tospeed which are incident to the Vani Winkle dynamomneter. Theolnly thinu that it lacks is a mneans of givinig an indication ofthose fluctuations, because if there are errors due to resonance,they can be measured, determined and accounted for and allowedfor. I think it is possible to apply a device that will give scaleiildications.

I think really this is a very interesting apparatus, and onewhich has a far greater range of usefulness thani Prof. Golds-borough claims for it.THE PRESIDENT:-We will proceed with the next paper on

"A Percentage Bridge," by Mr. Herschel C. Parker, of Col-umbia University.