Direct Pen Recording of Galvanometer Deflections

Abstract

An instrument is described which records directly the deflections of a light beam pointer without recourse to photographic development processes. The recording is easily accomplished at pen speeds of 12.7 cm per second across 25 cm of chart without ``hunting'' taking place. Essentially the basic idea of this recorder is that the pen follows the light beam from an external galvanometer by mounting a double cathode photo-tube on the pen carriage so that both move as a unit. By means of vacuum tube amplifiers operating a reversible motor, the pen carriage moves to the left when the light beam deflects to the left on to the left photo-tube cathode and to the right when the right photo-tube cathode is exposed. A movement of the light beam as small as 0.1 mm causes a corresponding movement of the pen. The instrument has been satisfactorily used, with considerable saving in time, for recording current-voltage curves in polarographic analysis, for obtaining infra-red absorption curves, and for recording ion currents in mass spectrographic work.