THE LOCALISATION OP BREAKS AND FAULTS, 535 



For example, take a galvanometer which when unshunted 

 indicates 0061 microampere per division at standard focus, 

 and measures 819 ohms at the temperature at which the shunt 

 is correct at 1 ohm. 



With the whole shunt on, the multiplying power is 



^ + 1 = ^ + 1=^820 

 S 1 



And any total current passing through the combination will be 

 indicated on the instrument at the rate of 



820x0-061 , .„, ,. , . / f.^^. 

 = Jq miUiampere per division, (or 005). 



The equivalent in millivolts on the instrument may be found 

 by multiplying the resistance of the shunt by the current pass- 

 ing through it. There is so very little difference between the 

 current through the shunt and the total current that they may 

 be taken as equal. Consequently when the full shunt of 1 ohm 

 is on, tbe instrument indicates at the rate of 



0-05 X 1 = 0'05 millivolts per division. 



When the galvanometer wire is connected to the half-shunt 

 currents are indicated at the rate of 



0*05 millivolt , ,„. j- • • 



. :=TTr milliampere per division 



0-5 ohm ' "^ ^ ^ 



Similarly with the quarter and tenth shunts 



0-05 , .„. ,, . , 



— — =5" milliampere per division 



and 77?;— = 2 milliampere per division. 



So that for deflections up to 300 divisions, that is with zero in 

 the centre of scale, the ranges would be : — 

 Full shunt 0/1 5 milli amps. Each division reading to o^omilliamp. 

 Half shunt 0/30 „ „ n » ro" » 



Quarter-shunt 0/60 „ „ >■ » 5 >> 



Tenth-shunt 0/1 50 „ >> » >» 2 " 



The ranges of course would be doubled if reading from zero 

 at one end of the scale, the maximum current with the tenth- 

 shunt then being 300 milliamperes. 



