Abstract: Apparatus for mounting on a crane or other construction equipment for detecting the presence of an electrical power line. A reference pickup coil mounted on an upper machinery works or other portion of the equipment generates a reference signal proportional to the strength of a magnetic field in a work area. Other pickup coils mounted on a crane boom or other portions of the equipment which may extend into closer proximity to power lines develop signals which are compared with the reference signal. When any of these signals exceed the reference signal by a predetermined amount a warning signal is developed. Coils having the proper ratio of core length to diameter and having coil winding which extend along approximately half the core length provide output signals which have a predictable amplitude.

Abstract: A ring supported, self-propelled truck crane and method of operation is disclosed wherein a boom is mounted on the chassis for pivotal movement only about a horizontal axis. The chassis is driven into an incomplete segmented ring set up at a working site with rollers on end portions of the chassis projecting downwardly and overlying the ring when the ring opening is closed by adding an additional segment thereto. The ring is then elevated to lift the wheels of the chassis completely off the ground and drive means interconnect the ring and the chassis to rotate the chassis about the vertical axis of the ring. Flanged rollers journaled on the chassis engage the ring to center the chassis on the ring and to rotatably interconnect and support the ring on the chassis for transportation therewith to the next site when the ring and chassis are lowered for support entirely upon the wheels of the truck crane.