An automatic field plotter

Solutions of field problems can often be approximately obtained by constructing a 2-dimensional model of the field to be studied in an electrolytic tank. A servomechanism is described which is arranged to follow the equipotential lines that exist in such a model and to plot them automatically. A rotating co-ordinate system is employed to enable the device to trace out closed curves and other multivalued functions. This co-ordinate system is automatically aligned with the equipotential lines to be followed so that the sweep velocity is constant and parallel to the desired curve and correction velocity is normal to this curve. The system is analyzed with particular emphasis on stability and accuracy. The prototype plotter was able to follow curves with a minimum radius of 1/2 inch and maintain an accuracy of 0.5 per cent of maximum travel.