Ballistic
galvanometer
A ballistic galvanometer is a type of sensitive
galvanometer, commonly a mirror galvanometer . Unlike a current-measuring
galvanometer, the moving part has a large moment of inertia , thus giving it a
long oscillation period. It is really an integrator measuring the quantity of
charge discharged through it. It can be either of the moving coil or moving
magnet type.
Grassot Fluxmeter
An interesting form of ballistic galvanometer is the Grassot
fluxmeter. In order to operate correctly, the discharge time through the
regular ballistic galvanometer must be shorter than the period of oscillation.
For some applications, especially those involving inductors, this condition
cannot be met. The Grassot fluxmeter solves this. Its construction is similar
to that of a ballistic galvanometer, but its coil is suspended without any
restoring forces in the suspension thread or in the current leads. The core
(bobbin) of the coil is of a non-conductive material. When an electric charge
is connected to the instrument, the coil starts moving in the magnetic field of
the galvanometer's magnet, generating an opposing e.m.f. and coming to a stop
regardless of the time of the current flow. The change in the coil position is
proportional only to the quantity of charge. The coil is returned to the zero
position by the reversing of the current or manually.