THE MEASUREMENT OF CURRENT 



67 



resistance terms, the variable or reactance term being almost 

 negligible for the range of frequencies used in radio-telegraphy. 

 At 1,000,000 cycles 



/r /a x = 1.0005 



instead of the value ,j 

 sistance wires are used. 



1.032 which obtains when low re- 



Copper 

 Strip 



BSC.m 



DIAGRAM FOR A SEVEN WIRE INSTRUMENT 



024 



Amperes 



FIG. 30. Plot showing distribution errors in a seven-wire high-frequency 

 ammeter. All seven wires in the same plane. 



The Utilization of the Whole Heat Production. It has been 

 stated that it is important that the whole heat production con- 

 tribute to the operation of the indicator. This may be illustrated 

 by reference to the three-wire instrument. Assume that with 

 direct currents, 10 amp. flows in each of the wires; assuming them 

 to be of equal resistance, the total heat production will be pro- 

 portional to 10 2 + 10 2 + 10 2 = 300. At 1,000,000 cycles the 

 currents will be approximately 10.3, 9.4, 10.3, and the total heat 



