Analysis and redesign of a blood level regulator for extracorporeal circulation automation

Extracorporeal circulation (ECC) is currently used in cardiac surgery. The blood volume equilibrium between oxygenator and patient must be kept within certain limits. Mathematical analysis, by the Laplace transform, of an existing blood-level regulator shows that the controller used is of the proportional type. This design yields a nonzero steady-state error due to step change of the oxygenator inflow. The redesign objectives were a zero steady-state error to such changes with smooth dynamic behavior of the pump speed. The application of a proportional/integral controller satisfied these objectives. The regulator was simulated on a personal computer with extended I/O capabilities. The design method, consisting of analysis in the continuous time domain and simulation by means of special-purpose software, proved to be quite time and cost-effective.<>