DC AMMETER

 

The basic movement of a dc ammeter may be a PMMC galvanometer. Since the coil winding of a basic movement is tiny and lightweight. It will carry solely terribly tiny currents once massive currents square measure, it’s necessary to by pass major parts of the present through a resistance referred to as a shunt.

The resistance of shunt can are often calculated victimization typical circuit analysis.

The basic dc ammeter as shown in figure 3.1

                               

R_m = Internal resistance of the movement

I_sh = Shunt current

I_m = Full scale deflection current of the movement

I= Full scale current of the meter + shunt  ( total current)

Since the shunt resistance is in parallel with the meter movement, the fall across the shunt and also the movement must be same.

Therefore  V_sh = V_m

       I_sh  R_sh  = I_m  R_m ,  R_sh  = I_m R_m/I_sh

 However                I_sh  = I-I_m

 Therefore             R_sh = I_mR_m// I-I_m

For each needed value of full scale meter current, we are able to confirm the worth of shunt resistance.