Analysis of constant-current characteristics for current sources

A current source is one of the most important circuits in Electrical Impedance Tomography (EIT) hardware systems for measuring conductive multiphase flows. One of its important and challenging features is to deliver a relatively large and constant current for a wide range of resistive loads, high signal to noise ratio, and a large bandwidth. To resolve this problem, three different current sources are discussed and compared. They are the Howland current source, an enhanced Howland current source and a dual op-amp current source. The constant-current characteristics is analyzed and compared in circuit principle. Simulation and experimental results show that the enhanced Howland is most stable among the three current sources when the frequency or load changes. Initial tests have proven the feasibility of EIT system with the enhanced Howland current source.