Abstract: The present invention relates to the field of measurement devices, specifically to devices for measuring pressure and flow as well as derived quantities, and in particular provides a sensor device for in-line measurement of superficial gas velocity, froth depth, apparent density and holdup in flotation cells, which comprises: a first tube; a second tube; a first valve connected to said first tube; a second valve connected to said second tube; a first pressure meter connected to said first tube; a second pressure meter connected to said second tube; a first mass flow meter connected to said first valve; and a second mass flow meter connected to said second valve. The present invention also provides a system for in-line measurement of superficial gas velocity in flotation cells.