Models ST51 and ST51A are a compact, low cost solution for accurate, repeatable flow measurement of biogas, digester gas, landfill gas, methane and natural gas as well as air, compressed air or nitrogen. This insertion-style flow meter has no moving parts and is available in probe lengths for installation into pipe diameters from 2.5 inches to 24 inches [63 mm to 610 mm]. It is easily connected into the pipe via a 1/2 inch or 3/4 inch NPT compression fitting. ST51 uses constant power thermal dispersion drive technology, with a slightly heated sensor, which uniquely provides a subtle drying effect on the sensors that results in effective measurement in moist gas applications.