A flow controller including a unitary controller body with a chemically inert fluid conduit having an insertable constriction or orifice disposed within the conduit having a reduced cross-sectional area to thereby restrict the flow of fluid within the conduit allowing for reliable flow measurement. An integrated circuit or controller may be coupled to the control valve and also coupled to the pressure sensors by a lead structure including signal conductors surrounded by a Faraday cage, and a chemically inert housing coupled to the unitary controller body enclosing the control valve and the pressure sensors.