Electrical Engineering ⇒ Topic : Extension of Range of PMMC Ammeter

David
 
Extension of Range of PMMC Ammeter The range of a permanentmagnet moving coil ammeter can be extended by connecting a low resistance, called *shunt in parallel with the moving coil of the instrument as shown in Fig. (a).The shunt bypasses most of the line current and allows a small current through the meter which it can handle without burning. Let R_{m}, = meter resistance S = shunt resistance I_{m} = fullscale deflection (f.s.d.) current I = full range current of the meter Voltage across shunt = Voltage across the meter
figure (a) Note that multiplying power of a shunt is the ratio of circuit current to be measured to the meter current. The multiplying power of a shunt is constant and indicates the factor by which the meter current must be multiplied to obtain the circuit current. Suppose the meter has a resistance of 5 Q and requires 15 mA for fullscale deflection. In order that the meter may read 1A, the value of shunt is given by ; Multiplying power of shunt Note that multiplying power of a shunt plays an important role in the extension of ammeter range.  
 
David
 
Extension of Range of PMMC Ammeter The range of a permanentmagnet moving coil ammeter can be extended by connecting a low resistance, called *shunt in parallel with the moving coil of the instrument as shown in Fig. (a).The shunt bypasses most of the line current and allows a small current through the meter which it can handle without burning. Let R_{m}, = meter resistance S = shunt resistance I_{m} = fullscale deflection (f.s.d.) current I = full range current of the meter Voltage across shunt = Voltage across the meter
figure (a) Note that multiplying power of a shunt is the ratio of circuit current to be measured to the meter current. The multiplying power of a shunt is constant and indicates the factor by which the meter current must be multiplied to obtain the circuit current. Suppose the meter has a resistance of 5 Q and requires 15 mA for fullscale deflection. In order that the meter may read 1A, the value of shunt is given by ; Multiplying power of shunt Note that multiplying power of a shunt plays an important role in the extension of ammeter range.  
 
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