Electric system ammeter circuit

The electric ammeter is composed of a fixed coil and a moving coil connected in series or parallel, and a certain additional resistance is added, as
shown in Figure 5-15. The magnetizing force of the electric system instrument is greater than that of the electromagnetic system instrument, and the number of fixed coil turns is larger, causing the internal resistance of the electric system ammeter to be very large (
larger than the internal resistance of the electromagnetic system ammeter), so the meter consumes a lot of power.
    Electric system milliammeter circuit . This instrument connects the fixed coil Nl and the movable coil N2 in series, so it can be
seen that the deflection angle is related to the square of the measured current. Its
scales are distributed according to the square law. When the two coils of
    an electric milliamp meter are directly connected in series, due to
the limit of the allowable current of the moving coil and hairspring, the maximum measurement can only be
about 500mA. If the fixed coil Nl and the movable coil
NZ are connected in parallel, as shown in Figure 5-15b, then
the current of the movable coil can be limited by increasing Rz, and the range of the ammeter
is much larger than that of the series type.