Abstract: A seam weld machine includes a voltage monitoring circuit (9) for determining weld quality. The voltage is sensed by two pick-ups. A first pick-up is in the form of a conductive rider (10), mounted to directly sense the voltage from a weld wire (4). The wire (8) from the second pick-up is short and is fed through a gap in the z-bar (6) of the machine to emerge close to the wire from the first pick-up, thus reducing electromagnetic interference and noise.

Abstract: Apparatus for welding longitudinal seams in can bodies includes upper and lower electrode wheels mounted on arms, a transducer for detecting vertical displacement of the upper wheel, a pair of pick-ups for detecting the rotational positions of the wheels, and a single processing circuit. The transducer output is divided into a set of traces, each corresponding to a single wheel rotation. The traces are averaged to produce a representation of the wheel profile. Each wheel profile is subtracted from the transducer output to produce a good indication of weld thickness. Alternatively, the transducer output is divided into a series of traces, each of which represents the vertical displacement of the upper wheel while welding a single can body. These are averaged to provide a good indication of weld thickness. The wheels have surface irregularities and each is inevitably mounted with some degree of eccentricity. Unwanted transducer output components due to these irregularities and eccentricities are removed.