DC VOLT METER

The basic moving system, often called the D’ Arsonal movement, is named a basic meter. The basic meter movement becomes a dc instrument, measuring.

* Dc current, by adding a shunt resistance, forming a micro ammeter, a mill ammeter (or) an ammeter.

* Dc voltage, by adding a multiplier resistance, forming a milli voltmeter, voltmeter (or) kilo voltmeter.

* Resistance, by adding A battery and resistive network, forming an ohm meter .

The basic D’Arsonal movement are often converted into a dc voltmeter by adding a series resistor referred to as multiplier, as shown within the figure.

                      

BASIC DC VOLT METER

The function of the multiplier is to limit the present through the movement in order that the present doesn't exceed the complete scale deflection value. A dc voltmeter measures the electric potential between two points during a dc circuit (or) a circuit component. to live the electric potential between two points during a dc circuit component, a dc voltmeter is usually connected across them with the right polarity.

To future extend the voltage range of a dc voltmeter, the worth of the multiplier required is calculated as follows. Pertaining to figure in above.

I_m = Full scale deflection current of the movement

(I_fsd) R_m = Internal resistance of movement

R_s = Multiplier resistance

V = Full range voltage of the instrument.

From the circuit of figure:

V = I_m ( R_s +  R_m)­

R_s = ­V – I_m  R_m / I_m = V/ I_m  - R_m

Therefore ­R_s = V/ I_m  - R­_m

The multiplier limits the present through the movement, so on not exceed the worth of the complete scale deflection I_fsd .