A flow monitoring system for monitoring flow of a mixed-phase sample comprising at least a first phase and a second phase having different electrical conductivities, the second phase being a liquid or a gas and substantially electrically non-conductive and the first phase being a liquid and having a conductivity higher than the second phase, the system comprising: a conduit through which the mixed-phase sample can be arranged to flow tomography apparatus arranged to generate tomography data indicative of at least a first conductivity profile of at least a portion of a first cross section of the mixed phase sample when flowing through the conduit; a flow meter arranged to detect flow of the first phase though the conduit and provide a flow signal indicative of a flow velocity of the first phase; and processing means adapted to calculate, from said data, a fraction of said first cross section occupied by the first phase, and calculate, from said fraction and said flow signal, a volumetric flow rate of the first phase through the conduit, wherein the tomography apparatus comprises: a plurality of electrodes each having a respective contact surface arranged to be in electrical contact with a sample flowing through said conduit; and measurement means connected to the plurality of electrodes and adapted to perform a plurality of measurements on a sample flowing through said conduit to generate said tomography data, each measurement comprising driving a current between a pair of said electrodes and measuring a voltage across another pair of said electrodes, characterised in that at least a portion of each electrode contact surface slopes inwardly from a first axial position at which said portion is flush with an interior surface of the conduit, toward a longitudinal axis of the conduit, along the longitudinal axis, whereby accumulation of deposits on each said portion may be at least partly inhibited by sample flow past each said portion, and wherein said plurality of electrodes are equally spaced around said conduit, and the respective contact surface of each said electrode has a convex shape along the longitudinal axis, such that the plurality of contact surfaces provide a constriction in said conduit to increase axial flow velocity over the convex shaped contact surfaces. a conduit through which the mixed-phase sample can be arranged to flow tomography apparatus arranged to generate tomography data indicative of at least a first conductivity profile of at least a portion of a first cross section of the mixed phase sample when flowing through the conduit; a flow meter arranged to detect flow of the first phase though the conduit and provide a flow signal indicative of a flow velocity of the first phase; and processing means adapted to calculate, from said data, a fraction of said first cross section occupied by the first phase, and calculate, from said fraction and said flow signal, a volumetric flow rate of the first phase through the conduit, a plurality of electrodes each having a respective contact surface arranged to be in electrical contact with a sample flowing through said conduit; and measurement means connected to the plurality of electrodes and adapted to perform a plurality of measurements on a sample flowing through said conduit to generate said tomography data, each measurement comprising driving a current between a pair of said electrodes and measuring a voltage across another pair of said electrodes, characterised in that at least a portion of each electrode contact surface slopes inwardly from a first axial position at which said portion is flush with an interior surface of the conduit, toward a longitudinal axis of the conduit, along the longitudinal axis, whereby accumulation of deposits on each said portion may be at least partly inhibited by sample flow past each said portion, and wherein said plurality of electrodes are equally spaced around said conduit, and the respective contact surface of each said electrode has a convex shape along the longitudinal axis, such that the plurality of contact surfaces provide a constriction in said conduit to increase axial flow velocity over the convex shaped contact surfaces.