Impulse and frequency response of a moving coil galvanometer

Abstract

The moving coil galvanometer is a linear second order system and many experiments have been described in which the galvanometer is used to illustrate the characteristics of such systems. With the advent of digital techniques and cheap computing facilities the tendency is for much simpler experiments to be performed in which the impulse response of the system is found and the transfer characteristics derived by computing the Fourier transforms of this impulse response. A special advantage of this approach is that amplitude and phase information are both available from a single measurement. The article describes an experiment for the undergraduate laboratory which demonstrates this approach. A moving coil galvanometer is the system under study and the EMF generated by the swinging coil provides the impulse response information in a form suitable for digitising and inputing to a microcomputer. The microcomputer can be used to display the digitised information and a simple discrete Fourier transform algorithm used to compute the frequency response. The results of the computation are available either in the form of the real and imaginary parts of the transfer function or as amplitude and phase data.