Assembly line supervisors rely on the fast‑acting DC auxiliary contact to guarantee precise sequencing of welding robots on a vehicle body line. The contact is mounted on the pneumatic actuator that positions the chassis frame, and it supplies a clean, low‑voltage signal to the PLC the moment the cylinder reaches its travel limit. That signal locks the current welding torch, releases the interlock, and authorises the next robot to fire, preventing overlap of arc cycles and protecting the workpiece. Because the contact reacts quickly and holds its state without bounce, the line can run at the high cadence demanded by modern car factories while keeping safety interlocks trustworthy. The same device is often found in paint‑shop conveyor systems, where it confirms the clearance of a drying tunnel before the next batch of panels is admitted, thus avoiding over‑exposure. In both cases the auxiliary contact translates mechanical motion into a reliable electrical cue that triggers the hand‑over of the painted door to the next station.