Abstract: A connection device (1) for the measurement of at least one physical quantity of a fluid comprises:-a tubular connection element (2; 2?) having a front connection portion (2b) and a rear portion (2a), the tubular connection element (2; 2?) defining a through-cavity (C1-C3) having a proximal opening (O1) and a distal opening (O2) opposite to each other, which are in the rear portion (2a) and in the front connection portion (2b) of the tubular connection element (2; 2?), respectively-a detection unit (5) capable of detecting at least one physical quantity characteristic of the fluid. The front connection portion (2b) of the tubular connection element (2; 2?) is connectable, at least at or near the distal opening (O2) of the through-cavity (C1-C3), to a fluidic system (PD), in particular a device for treatment of the fluid.