Apparatus for Continuous Recording of Internal Friction

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Abstract
An internal friction apparatus based upon the principle of the torsion pendulum is described. Attached to the inertia member of the pendulum are two coaxial coils which are located in the field of a permanent magnet. Oscillations of the pendulum induce an emf in one coil (the pick‐up coil). The signal is amplified and converted into a square wave of constant amplitude which is used to energize the other coil (the driver coil). Interaction between the driver coil and the magnetic field maintains the system in oscillation, the amplitude being proportional to Q. The output of the pickup coil is measured on a strip chart recorder. After a straightforward calibration procedure, the Q of the system is quantitatively related to the output. The device has been used from 4°K to 150°C.