ARMATURE LAMINATIONS 25 



In the Blondel-Carpentier Hyste're'simetre the samples to be 

 tested are made up from ring-shaped stampings. These stampings 

 have external and internal diameters of 55 mm. and 38 mm. 

 respectively. These are piled up to an aggregate thickness of 

 4 mm. ; thus, if the sheets are 0'5 mm. thick, about seven rings will 

 be required to make up a sample, as this gives 3-5 mm. of iron, 

 and the remaining 0'5 mm. will be allowed for lost space. These 

 rings should be turned, and not punched. The permanent magnet 

 must be rotated at a speed of some 2 to 3 revolutions per second 

 in order to obtain a steady deflection. If this deflection is, for 

 example, 250, and if the calibration, by means of standard samples, 

 has shown the " constant " of the instrument to be 



0-0000073, 

 then for the material under test, we have 



; = 250x0-0000073, 

 = 0-00182. 



If we prefer to have the result in terms of the watts per kg. at 

 a density of 4000, and a periodicity of 50 cycles per second, we can 

 readily, by means of Table VII. , ascertain this to be 



O-60 = 0-6 7 watts per kg. 



The price of one of these instruments, inclusive of tested 

 sample, is listed at 16. 



It is said that for a given quality of iron, the results as given 

 by the Blondel-Carpentier instrument are a little higher than 

 those obtained by the Ewing instrument. This, however, is a 

 matter of calibration, and it is not apparent that there should be 

 any difference. Neither type of apparatus gives anything but 

 comparative results, which can only be reduced to absolute values 

 by comparison with specimens on which careful determinations of 

 the absolute values have been made. 



Brunswick and Aliamet 1 divide armature sheets into two 

 classes : 



Class I. Ordinary quality, for which v\ as measured by the 

 Hystere'simetre varies from 0'0016 to 0*0022, and having a specific 

 resistance of from 12 to 15 microhms per centimeter cube. 



Class II. Superior quality, for which >/ varies from 0:0011 to 

 0'0015, and with a specific resistance as high as 45 microhms per 

 centimeter cube. 



1 Construction des Induits a Courant Continu, p. 18. 



I PROPERTY OF ELECTRICAL LABOHATOKY,^ 



FACULTY OF ALLIED' SCIENCE. 



v 4 



