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BELL SYSTEM TECHNICAL JOURNAL 



ment is high. However, the usual case we have to consider is the 

 measurement of the effective resistance of coils of high Q. It is in 

 such measurements that the greatest corrections are necessary, and 

 it is also in such measurements that the greatest errors in effective 

 resistance are produced by incomplete shielding in the bridge. Con- 

 sequently it is in the measurement of effective resistance that shielding 

 is most essential, and although this shielding may introduce a necessity 

 for larger corrections due to the capacitance it introduces, these 

 corrections may be made with a certain degree of precision and having 

 made them the value obtained will be more reliable than in the case 

 of a complete absence of shielding. 



Table IV gives the figures for the measurement of effective resistance 

 of three coils having a high Q. Referring to equation 5 we see that 

 q\ and q^ are positive when the reactance is inductive and that Qa is 



TABLE IV 



always negative. The column headed Re is obtained from equation 5. 

 The column headed R/ is obtained from a resonant method of measure- 

 ment which has the same order of accuracy as the present method. 

 Consequently the last column of differences gives the combined error 

 in the two methods. In these measurements covering the most used 

 range of inductance and a frequency range of 1,000 to 3,000 cycles, 

 the largest difference between the two methods is 3 per cent. The 

 total corrections to be made are in some cases extremely large, especially 

 for the higher inductances and frequencies. This correction may 

 amount to 30, or 40 per cent in some cases, and this means that an 

 effective resistance obtained by the Owen bridge when not corrected 

 may be in error by this amount. However, after allowing for the 

 necessary corrections we can say that the bridge is capable of an 

 accuracy for the measurement of effective resistance of about 2 per 

 cent over the greater range of inductance and frequency. 



