Abstract: A cigarette filter rod system comprises a plug combiner machine having a knife located downstream from a sensor. The knife generates a trigger signal which prompts an Inspection Unit to locate a previously stored frame of sensor data corresponding the rod which was cut by the knife. The Inspection Unit applies thresholds to the frame of sensor data to determine the location of filter segment boundaries, and then determines whether air rings are present in the data. The Inspection Unit then compares measurements made on the frame of sensor data with a pre-stored recipe indicating expected values for the frame. Statistical data is sent to a Human-Machine Interface Unit for analysis and display. The system performs filter rod rejection and cut registration based on the analysis performed by the Inspection Unit and the Human-Machine Interface.