of any type any particles larger than those allowed by the sieve could pass since those possible particles of larger size are detected and then collected in a secondary compartment or tank which sends them back to the flow of the product to again pass through the milling process in order to complement the description which will be made below and with the aim of helping towards a better understanding of the characteristics of the invention in accordance with a preferred practical embodiment thereof a set of drawings have been included as an integral part of said description wherein the following in an illustrative and non limitative character has been represented fig1 u2014 shows a schematic representation according to a side elevational view of the device of the invention applied to a milling process of products such as grains fig2 u2014 shows a view such as that of the previous figure with the device detecting particles of larger size than that pre established fig3 u2014 shows finally a view such as that of the previous figure discharging the particles of larger size detected by the device of the invention towards a channel which reincorporates the product back into the flow intended to be milled again as can be observed in the referred to figures the device of the invention applicable to a milling machine or process with a hopper chute 1 a sieve 2 for the passage of particles and a transport conduit 3 such as an auger conveyor or suchlike starting with these characteristics the device of the invention is constituted from a special tray 4 situated at the outlet of a sampler 5 disposed in.