A shield for a resistance welding tool is disclosed that is formed in a generally tubular bellows-like configuration. A received signal distorted in a transmission path is phase-rotated by the phase rotator and is then estimated by the maximum likelihood sequence estimator. Either or both the male component and female component may have a notched appearance to provide additional flexibility and comfort to the closure. A greater working distance can thereby be obtained . The control unit determines a state variable of the current operating state of the vehicle.