Electrical Engineering ⇒ Topic : Multirange ammeter

Multirange ammeter. The single movement may be usec with several shunts to make a multirange ammeter as showr in Fig. (a). The switch selects which shunt (R₁, R₂ or R₃) to be used across the meter. With the switch at position 1, only resistance R₁ acts as the shunt. Likewise with switch at position  2, only resistance R₂ acts as the shunt. Note that the shape of the moving contact of the switch is short-circuiting type. This is to ensure that when this moving contact is shifted from one position to another, it makes contact with the new fixed contact before it breaks contact with its previous fixed contact. This will ensure that, at all times, there is a shunt across the meter. Otherwise, when the switch is changed from one position to another, there might be an instant when there would be no shunt across the meter. Under such circumstances, the full circuit current flowing through the meter coil may burn it.

                                                          figure (a)