Air flow meter is applicable for measuring flow rates of Bio-gas, LPG, Compressed air and other compressed gases in closed conduits. It is best suited for applications where affordability, reliability and ruggedness are of prime concerns. In conventional system of measurement, the differential pressure generated by orifice plate is measured by DP transmitter. The output from DP transmitter after square rooting is accepted as proportional to flow rate. This assumption is true only when the density is constant.