[LM111347], Letter from Arthur Edwin Kennelly to Edison Electric Light Co, William J Jenks, February 20th, 1889

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Title

[LM111347], Letter from Arthur Edwin Kennelly to Edison Electric Light Co, William J Jenks, February 20th, 1889

Editor's Notes

####[page 175]####20th February 89####W.J. Jenks Esq####Director Standardizing Bureau####Dear Sir####In reply to your letter of yesterday date allow me to place before you the following considerations relating to station meters.####Since there is obviously no advantage in obtaining a higher percentage of accuracy for a station meter than can be supplied by individual meters under best conditions it is only necessary that the station meter at full load shall transfer -----al metal at the same rate as the local meters. Thus if a plant consisted of 100 no 4 meters each at a consumer's house and f cash of those meters transfer 1 ----- per amp: hr and the station meter need only transfer the same amount. If every meter were worked alike these would be say 1250 milligrammes of trnasfer monthly in both the local and the station meters with the same relative percentage of accuracy and even if as in practice, the meters did not operate equally the relative accuracy of the station meter and the aggregate of the local meter would be equal since we assume no tendency to error except through weighing.####[page 176]####(2)####Actually however by a little additional care in construction and in weighing together with the use of silver, if possible, we may expect to have all the necessary accuracy from a station meter which shall transfer 10 milligrammes hourly on full load.####Supposing that we had a station meter at work on a feeder taking 1000 amperes at full load. This would mean 100 ampere hours per milligrammes of transfer. That would probably be ample margin.####An ampere transfers hourly four (4.025) grammes of silver so that 1000 amperes would transfer 4000 grammes but our meter has to transfer only one hundreth of a gramme. Hence the [pastional?] part of the current required will be the 1/400,000 th part.####If we make the resistance of the bottle circuit 40 - and that should give us an accurate meter, then the resistance of the shunt should be the 10,000th part of an ohm or 100 microhms.####If the feeder in the station be a copper rod having a diameter of one inch its resistance would be about 10 microhms per foot and ten feet of this feeder would be sufficient for our meter shunt. As however the temperature temperature variation of our feeder might prevent our adopting it, then we must either flatten it out until without altering the weight of the 10 microhms per foot and ten feet of this feeder would be sufficient for our meter shunt. As however the temperature variation of our feeder might prevent our adopting it, then we must either flatten it out until without altering the weight of the 10 feet we make####[page 177]####its surface large enough to make the heating error negligible and the fluctuation of temperature that of the building only the fluctuation of temperature that of the building only or we must insert a shunt of platinoid. Such a shut would be 0.4 cms thick 40 cm long and 40 cm broad (16 x 16" --") the total resistance being 40 x 40/40 x40 = 100 microhms####[art]####the heating will be insignificant since the energy absorbed would be 10000000 x 100/ 1000000 or 100 Watts and the total surface 500 sq inches, or 5 sq in per Watt. As for greater amounts than 1000 amperes we need only use the same bottle and spool while we increase the number of strips. The weight of the platinoid in such a strop would be about 12 lbs, and it would cost perhaps 40 --- per lbs####It would be necessary to calibrate these shunts with great care. I could guarantee whatever degree of accuracy was commercially necessary and do not doubt but that others could do so also.####I beg to enclose a test statement of the 700 light meter which you will see agreed with our standard within1.1% reading in excess probably owing to the temperature at which the meter stood during the trial####Your very truly####A.E. Kennelly.####

Date

1889-02-20

Decade

1880-1889

Type

Folder/Volume ID

LM111-F

Microfilm ID

109:281

Document ID

LM111347

Publisher

Thomas A. Edison Papers, School of Arts and Sciences, Rutgers University
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