390 



SUBMARINE CABLE LAYING AND REPAIRING. 



As the slider is moved further in the same direction the 

 joint resistance falls and the shunt resistance increases untili 

 when the shunt is equal to E ohms at the end of the range, 



the joint resistance becomes— — -. 



tr + K 



The curve in Fig. 232 has been plotted to show this varia- 

 tion for a galvanometer of 1,200 ohms and universal shunt of 

 10,000 ohms. The joint resistance for any shunt can be seen 

 at once by this curve, and it is useful to plot a curve of this 

 kind for the particular instrument and shunt in use, and hang 

 it on a card in the test room so that at any time the joint 

 resistance can be obtained by inspection without calculation. 





1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 10,000 

 Slide Headings on Universal Shunt. 



Fig. 232. — Joint Resistance of Galvanometer and Universal Shunt. 



Where a considerable amount of deflection work is done it is 

 desirable to dispense with calculations or the carve altogether, 

 and apply the compensation principle. For compensating a 

 universal shunt the author has suggested an arrangement as in 

 Fig. 233, in which the arm or slider travels over two sets of 

 resistance contacts, one being the shunt and the other the 

 compensating resistance. 



The arm is shown in the position in which the joint resis- 

 tance is a maximum — that is, when the shunt (on the top set of 



r* -4- T? 



contacts) is equal to — - — . As the arm is moved away from 



this position in either direction, the joint resistance falls, and 

 the compensating resistance is added by the lower set of 



