Volumetric measurement of a gas flow

In a method of measuring a flow of gas, especially air, using a volumetric direct gas meter wherein said meter is driven by a servomotor and the rotational speed of which is regulated in response to the pressure differential measured between the inlet and outlet ports of said gas meter so that said pressure differential tends to zero, the steps of providing relatively sensitive and relatively insensitive pressure differential sensors each of which is capable of providing an electrical output signal in response to the pressure differential measured by the sensor, connecting both said sensitive pressure differential sensor and said insensitive pressure differential sensor to measure the pressure differential across said gas meter, providing a slow acting integrator and a more rapidly acting integrator, integrating the electrical output signal from said sensitive pressure differential sensor through said slow acting integrator, adding said integrated output signal from said sensitive pressure differential sensor to the electrical output signal from said insensitive pressure differential sensor to provide a sum signal, integrating said sum signal through said more rapidly acting integrator to provide a set point signal, and using said set point signal to control the speed of said servomotor driving said gas meter.