A novel tomographic sensing system for high electrically conductive multiphase flow measurement

Electrical resistance tomography (ERT) has been widely applied in order to extract flow information from various multiphase flows, e.g. the concentration and velocity distributions of the gas phase in gas-water two phase flows. However, the quality of measurement may become very poor from a multiphase flow whose continuous phase has a considerably high electrical conductivity, e.g. seawater (5.0 S/m), using a conventional current-injected ERT system. It is known that a large current excitation is necessary in order to enhance the measurement sensitivity. In practice, it will be very challenging to build a current source with a large amplitude (more than 75 mA) and a high output impedance at a high excitation frequency. This paper presents an implementation of an ERT system with a voltage source and current sensing to overcome the limits of the current source. The amplitude of the current output can reach more than 300 mA. A logarithmic amplifier is used to compress the signal's dynamic ranges from 18.32 dB to 1.66 dB. The structure and features of this system are presented in this paper and the performances of key circuits are reported. Finally the experimental results from a highly conductive flow (1.06 S/m) are analysed and compared with the measurements obtained from a low conductive flow.