The noise caused by the coupling capacitance between the adjacent electrodes of an electrical impedance tomography sensor was measured to help solve the problem that traditional sensors need to be rebuilt and installed according to the change in the outer diameter of the detected pipeline. A portable differential electrode sensor with an adjustable electrode to the distance between the axes of the pipeline (electrode spacing) was designed for these measurements. The control module adjusts the electrode spacing so that a single sensor can be used for pipe measurements with an outer diameter ranging from 60 mm to 100 mm in the dynamic range. The differential electrode structure allowed the sensor to fix the radial electrode of appropriate length and eliminated the measurement noise caused by some parasitic devices in the sensor. The experimental results show that the new sensor can detect pipes with different diameters, and the differential electrode improves the imaging quality of multiphase flow.