[en] An instrument has been evaluated which permits volume fraction measurement of the conductivity of the component in a two-phase flow. A unique rotating electric field technique is employed to achieve real-time response and uniform cross-sectional measurement. A spool-piece sensor replaces a short pipeline section and causes no additional pressure drop. A reference conductivity measurement is incorporated to compensate for changes in the bulk conductivity of the conductive component caused by changes in temperature and the concentration of impurities in the flow medium. Testing of the instrument was performed over the full range (0-100%) of void fractions, in both horizontal and vertical attitudes, and instrument readings during steady state flow conditions were compared with directly measured liquid-fraction values, obtained using a quick-closing valve calibration method. The resulting calibration curves proved to be nearly linear. An error analysis indicates a +-5% variation in the mid-rance test results which can be attributed to unavoidable quick-closing valve sampling error, due to the existence of a high level of slug flow during testing at high velocity. In later tests, at lower velocities, th data scatter varied less than 1%. This instrument has been demonstrated to be an effective means for measuring relative volume fraction in conductive two-phase flow