A device for measuring a flowrate of a fluid that flows within a duct, said device comprising: - a first portion and a second portion that are adapted to be connected to said duct by a fluid-tight fastening means, wherein said first portion protrudes within said duct and said second portion is left outside of said duct; - a sensor means comprising: - a probe constrained to said first portion, such that said probe in use is arranged within said duct, said probe equipped with a fluid engagement member that is configured to receive from said fluid a fluid dynamic thrust responsive to said flowrate and to perform a measurable displacement (s,δ) due to said fluid dynamic thrust from a rest position, when said flowrate is zero, to a measuring position responsive to said flowrate; - a load cell (30,30') constrained to said second portion, said load cell (30,30') configured to receive from said probe a force responsive to said measuring position and to produce an electric measurement signal responsive to said measuring position; - a data output means for exporting flowrate data that are obtained from said electric measurement signal, said data output means including an electric connection means arranged to convey said electric measurement signal to a local and/or remote control and/or display unit of said electric measurement signal; characterised in that said first portion and said second portion are fluid-tightly separated by a fluid-tight wall having at least one portion that is permeable to a magnetic field, and in that said probe and said load cell (30,30') comprise a magnetic interaction means arranged for transferring said force through said fluid-tight wall between said probe and said load cell (30,30') when said probe performs said measurable displacement (s,δ) and as long as said measuring position is maintained, wherein said magnetic interaction means comprises respective magnetic elements (47,37) that are associated with said probe and/or with said load cell (30,30') and/or it comprises magnetic portions (47,37) of said probe and/or of said load cell (30,30'). - a first portion and a second portion that are adapted to be connected to said duct by a fluid-tight fastening means, wherein said first portion protrudes within said duct and said second portion is left outside of said duct; - a sensor means comprising: - a probe constrained to said first portion, such that said probe in use is arranged within said duct, said probe equipped with a fluid engagement member that is configured to receive from said fluid a fluid dynamic thrust responsive to said flowrate and to perform a measurable displacement (s,δ) due to said fluid dynamic thrust from a rest position, when said flowrate is zero, to a measuring position responsive to said flowrate; - a load cell (30,30') constrained to said second portion, said load cell (30,30') configured to receive from said probe a force responsive to said measuring position and to produce an electric measurement signal responsive to said measuring position; - a data output means for exporting flowrate data that are obtained from said electric measurement signal, said data output means including an electric connection means arranged to convey said electric measurement signal to a local and/or remote control and/or display unit of said electric measurement signal; - a probe constrained to said first portion, such that said probe in use is arranged within said duct, said probe equipped with a fluid engagement member that is configured to receive from said fluid a fluid dynamic thrust responsive to said flowrate and to perform a measurable displacement (s,δ) due to said fluid dynamic thrust from a rest position, when said flowrate is zero, to a measuring position responsive to said flowrate; - a load cell (30,30') constrained to said second portion, said load cell (30,30') configured to receive from said probe a force responsive to said measuring position and to produce an electric measurement signal responsive to said measuring position; - a data output means for exporting flowrate data that are obtained from said electric measurement signal, said data output means including an electric connection means arranged to convey said electric measurement signal to a local and/or remote control and/or display unit of said electric measurement signal; characterised in that said first portion and said second portion are fluid-tightly separated by a fluid-tight wall having at least one portion that is permeable to a magnetic field, and in that said probe and said load cell (30,30') comprise a magnetic interaction means arranged for transferring said force through said fluid-tight wall between said probe and said load cell (30,30') when said probe performs said measurable displacement (s,δ) and as long as said measuring position is maintained, wherein said magnetic interaction means comprises respective magnetic elements (47,37) that are associated with said probe and/or with said load cell (30,30') and/or it comprises magnetic portions (47,37) of said probe and/or of said load cell (30,30').