An optical monitoring system is provided for use with a blood processing system. The system includes a light source configured to illuminate a disposable flow circuit received in a centrifuge and a light detector configured to receive an image of the disposable flow circuit. A controller combines two or more of the images received by the light detector to generate a two-dimensional output. The output is used to control the separation of blood within the disposable flow circuit. The monitoring system may also be used to verify that the disposable flow circuit is suitable for use with the centrifuge or that the disposable flow circuit is properly aligned within the centrifuge. The monitoring system may be positioned outside of the centrifuge bucket which receives the centrifuge.
