3S6 



SUBMARINE CABLE LAYING AND REPAIRING. 



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-Universal Shunt Box 



In the universal shunt all we have to deal with is the ratio 

 Tsetween one part of the high resistance shunt and the whole. 

 The multiplying powers are quite independent of the resistance 

 of the galvanometer or the shunt. With the only condition 

 that the shunt resistance must be high in comparison to the 

 galvanometer so that the sensi- 

 tiveness of the latter is very 

 little reduced, it may be of any 

 value and need not bear any 

 particular relation to the gal- 

 vanometer resistance. All that is 

 necessary is that it be accu- 

 rately sub-divided. Consequently 

 these shunts may be used with Fig. 229. 

 any galvanometer, and that is 



why they are called universal. Moreover, no temperature 

 correction is necessary. The galvanometer and shunt may be 

 wound with wires of different metals having different tempera- 

 ture coefficients or may actually during use be at different 

 temperatures without any inaccuracy in the observations. 



Another important advantage of the universal shunt is the 

 constant damping of the galvanometer, due to its being always 

 shunted by an unvarying resistance. The inductance E.M.F. 

 expends itself through this circuit for all positions of the sliding 

 contact, thus keeping the electric damping constant. With a 

 shunt of 10,000 ohms no correction is required in discharge 

 tests, even when the position of the slider (and the proportion 

 of current going through the galvanometer) is different in com- 

 parative throws. This is a most important advantage in 

 moving coil galvanometers, in fact these instruments are so 

 much more damped by inductance than suspended needle in- 

 struments that a universal shunt is a necessity for the elimi- 

 nation of the somewhat large error in momentary discharges 

 which would otherwise obtain. 



In the form of universal shunt box shown in Fig. 229 the 

 total resistance is 10,000 ohms, and the sub-divisions are 

 multiples of ten, so that the multiplying powers are easily 

 calculated. The wires to line or the rest of the circuit are con- 

 nected to Ti and Ta and the galvanometer to Gi and G2. Ti 

 and Gi are combined in one terminal. 



