Magnetic Hysteresis loss in Straight Iron Strips. 275 



Standardizing our wattmeter in this way with a continuous 

 current, we then made another set of hysteresis measure- 

 ments, with 12 strips of perfectly new annealed transformer 

 strips (Sankey's), with the results shown in Table VI. Two 

 other sets of observations for hammered and hardened iron 

 are given in Tables VII. and VIII. 



As a matter of fact, in the above experiments in the obser- 

 vations given in Tables 111., IV., V., VII., and VIII., the 

 wattmeter was standardized by sending known and measured 

 currents through the copper coil and obtaining a wattmeter 

 constant by finding the deflexions corresponding to known 

 copper losses in the copper coil. Thus are found the following 

 figures, when using the wattmeter to measure power taken 

 up in the magnetizing coil alone : — 



Known copper loss 

 (C 2 K.) calculated from 



observed current and 

 coil resistance in watts. 



Scale-deflexions of 

 wattmeter in 

 millimetres. 



Watts per millimetre 



of scale-deflexion of 



wattmeter, 



•398 

 •292 

 •197 



39-1 



28-9 

 19-0 



•0102 

 •0101 

 •0103 



In the case of the observations given in Table VI., we 

 employed the method of determining the wattmeter constant 

 by passing known currents through its coils joined up in 

 series and used as a dynamometer, and from the curve 

 showing relation of (current) 2 to deflexions we could at any 

 moment find the wattmeter constant. 



The method described above has this great advantage that 

 the test can be made on fairly large samples of iron, and it 

 can be made with an alternating current having any desired 

 and practical form factor. The iron is tested under conditions 

 which are exactly similar to those under which it will be used 

 in transformer manufacture, and, in fact, the straight mag- 

 netizing coil and iron sample constitute an open circuit 

 transformer of very small power factor. 



The above described method effects a great saving of time 

 in comparison with the ballistic method, whilst at the same 

 time it is an absolute method and does not depend upon com- 

 parisons with other iron samples of supposed known hysteretic 

 value. 



