The concept of the control system. The main control strategy consists in three parts. The internal model control (marked as a blue square) is responsible to control the position of the piston pump. In order to reduce noises from measured flow signal as well to avoid drift of the piston a filter (marked F) and an additional loop which is based on a proportional-integral controller and a function Mean I were incorporated (marked as a green square). To control the mean flow rate a proportional-integral controller and a function Mean II were added (marked as a red square).