Automatic Torsion Pendulum for the Continuous Recording of Internal Friction at Constant Amplitude and Very Low Frequencies

A torsion pendulum of the inverted type is maintained in oscillation at constant amplitude by means of an electric device. The mechanical oscillation gives rise to a frequency modulation which is detected in an original demodulator. The signal is amplified and used to supply two driving coils acting on small permanent magnets mounted on the inertia member. The amplifier is controlled by an error signal coming from the comparison of the amplifier input signal and a reference. An example of record showing internal-friction peaks in neutron irradiated iron is shown.