Thermal mass flow meter, also known as a thermal dispersion or immersible mass flow meters, are precision instruments used to measure the mass flow of fluid flowing in a closed channel like a pipe or a duct. Tek-Thermal 1700B is specially designed for air and N2 (nitrogen) applications and measures the gas mass flow based on the thermal diffusion method. It has a more compact design and a thin insertion tube probe. It can be used on a pipe from 1″ to 20″. It is used in high-pressure applications.