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.