Measurement of electrical conductivity of a fluid comprises directing fluid along an insulating bore 2 between first and second conductive flanges 3, 4 in contact with the fluid which are coupled by a low impedance pathway 6. A voltage is induced in the fluid via a toroidal inductor 7 at a first position between the flanges, and the current induced in a toroidal detector 8, at a second position between the flanges, by current in the fluid is measured. The inductor and detector are coaxial with the bore. The voltage within the fluid between two electrodes 9, 10 is calculated. The first electrode is located between the first flange and the inductor, the second electrode is located between the detector and the second flange, both electrodes being located sufficiently far from its respective flange to be unaffected by electrical field disturbances in the vicinity of the flanges. A temperature sensor is also disclosed to enable temperature compensation to conductivity measurements when used for calculating dissolv
