The reduction of noxious exhaust emissions from an internal combustion engine is achieved when the fuel supply is controlled by a feedback control signal derived from an exhaust gas sensor. In designing such feedback control system accurate measurement of fuel quantity supplied to the engine is required. Specifically, the mass flow measuring device must be capable of responding to the instantaneous variation of fluid flow. Conventional mass flow meters are not satisfactory for such purposes.
U.S. Pat. No. 3,470,741 discloses a mass flow meter which includes an ionizing means disposed in the path of fluid flow and a pair of opposed ion collecting electrodes spaced from the ionizing means transversely of the direction of fluid flow. With no fluid flow the ions would travel a median point of the collecting electrode. In the presence of fluid flow, the ions would displace from the median point and there is a difference between the charges collected by the respective electrodes, which difference is detected by a comparator.