Transactions: An electronic arc-length monitor

IN THE March 1935 issue of Electronics, a voltmeter for d-c arc welding was described. In this instrument the arc voltage was applied over a high resistance to the grid of a vacuum tube and a condenser was shunted across grid and cathode. The rapid fluctuations of the arc voltage are filtered out by this combination, and a meter placed in the plate circuit of the tube can therefore be calibrated in terms of average arc voltage. It was also possible to spread the scale of the meter so that it covered the range of welding voltage only, which leads to an increase of accuracy in determining the average arc voltage.