Abstract: A structure to be coupled to a machine for treating surfaces, comprising a centre web (1) joined to a machine (2) in which are movably and tightly fined with the aid of bearings a pair of telescoping superposed arms (6-6′) whose segments can be locked at any relative position, the segments ending in clips (19) for attaching the vertical tubes (24) that in turn incorporate on their lower corresponding sensors, with another clip (25) provided in the centre web (1) for attaching another sensor at this intermediate position. The sensors are thus capable of adopting any relative separation with adjustment operations that are extremely quick and simple, by simply releasing and again locking, while the height of said sensors can also be adjusted by loosening and tightening the clips (19).