Abstract: A seam tracker in which a shaft containing a position-indicator-member, e.g., a ferromagnetic portion, is attached to a probe, and is mounted on a ball joint and the ball joint is mounted on a pin the ends of which extend through slots in a housing. Spring means urge the pin ends against one end of the respective slots. A mechanical-null-position spring urges the shaft to a mechanical null position off of the longitudinal axis of the housing and thus away from the mechanical null position. Means responsive to changes in position of the shaft from the electrical null position give an output to drive a control apparatus to correspond to changes in position of the probe as it tracks the seam, represented by changes in position of the shaft.

Abstract: An improved control circuit is disclosed for controlling the arc voltage of welding apparatus. The circuit includes an automatic servo control circuit operative to gradually start the electrode positioning motor in the presence of an error signal indicating that the arc voltage is not at the desired level, to accelerate the motion of the positioning motor until the error signal is nulled and then quickly decelerate the motor to minimize electrode overshoots. The improved circuit is operative to prevent electrode servo "hunting" and results in improved welding operation. Other features and improvements are disclosed.