Deflection Recorders

Abstract

The most straightforward type of recorder depends upon deflection of the pen by a conventional meter movement. The signal to be measured appears as a current flowing through a coil of wire pivoted or suspended between the poles of a magnet. The interaction of the magnetic field produced by the current with the static field tends to produce circular motion. This motion must be counteracted by some restoring force which is usually supplied by a pair of hairsprings, one above and one below the coil, that also serve to make electrical contacts. If the coil is suspended rather than pivoted, the restoring force must be supplied through torsion of the suspension. Rigidly attached to the coil is a pen or stylus which leaves a trace on a moving strip of paper. Figure 2-1 suggests how this may be done.