continuously while its width allows for the accumulation of a quantity of debris sufficient for obtaining weight measurements that can be interpreted the tray is preferably made with aisi 304 stainless steel which does not deteriorate as a result of chemical attack produced by substances dissolved in residual drilling fluid and by the abrasive action of the debris itself the tray has rear discharge ports intermittent millings which allows liquid to seep out of the slurry retaining the solid said tray 7 is provided moreover with two lateral fins 13 a and 13 b which serve in fact to retain the debris laterally preventing leakage thereof the position of the tray when collecting slurry is slightly slanted in such a way as to drain the liquid part not involved in the measurement the slant of said tray can be regulated referring in particular to fig3 the actuation assembly which generates the movement of the tray 7 comprises a connecting rod 16 connected to the spherical joint integral by means of a through pin with a rotation shaft 17 the movement of the tray 7 is essentially generated by the compressed air piston 14 which pushes or pulls the connecting rod 16 via the spherical joint 15 according to whether it is loaded or unloaded this piston 14 is actuated by a solenoid valve eex i coupled to a distribution manifold which by releasing pressurised air at the two inlets.