COMPUTER AUTOMATION OF DATA ACQUISITION FROM A KNUDSEN, TORSION-EFFUSION PENDULUM

A computer-automated data acquistion system has been developed for a dynamic torsion pendulum applied to measurement of vapor pressures at high temperatures by the torsion-effusion method. Laser beams reflected from mirrors on the pendulum are detected by a bank of photodetectors which, in turn, transmit signals representing pendulum positions through an encoder and interface to a laboratory computer with an internal clock. The computer uses pendulum position and time data with stored information to solve the equation of motion of the pendulum and to calculate vapor pressures. The physical parts, electronic circuits, and software are described and discussed. The rest point of a dynamic torsion pendulum has been reproduced within 1 min of arc.