A method of performing Pseudo-random-Noise quadrature covering for transmitting data via an access channel. After initiating switching, a socket associated with the current server version is left open so that the socket may continue to receive client calls. The first and second coils are coaxial and as a result induced oscillatory voltage within the stationary coil generates an eddy current within the piston that permit a measurement of the stroke of the piston by means of eddy-current signal received by the stroke sensor using the piston as a test body, and supplying the force sensor with electrical power through the second moving electrical coil. The tip end portion of the crush box is arranged so as to penetrate the reinforcement hole.