Methods and apparatus for mechanically and electronically correcting presentation of entities in a fluid flow

An apparatus for sensing characteristics of elongate entities having length and width and being carried in an airflow, at least a portion of the entities being in a looped condition in which an entity is folded back on itself along its length;

• comprising:
• a sensing volume;
• entity presentation means for receiving the entities and airflow and presenting the entities in said sensing volume, a portion of the entities being presented in said sensing volume in a looped condition and a portion of the entities being presented in said sensing volume not in a looped condition;
• sensor means for sensing the entities in said sensing volume and for producing a sensor signal corresponding to characteristics of the sensed entities, the sensor means having a source of light directed through said sensing volume and first and second photodetectors for sensing light extinguished by said entities in said sensing volume, said first and second photodetectors being positioned in a side-by-side spaced apart relationship with said second photodetector being positioned downstream of said first photodetector with reference to the airflow in said sensing volume said first and second photodetectors for producing first and second sensor signals, respectively, each including waveforms corresponding to sensed characteristics of entities in said sensing volume;
• and
• analyzing means for receiving and analyzing said sensor signal and for determining at least one characteristic of looped entities based on said sensor signals, wherein said analyzing means further comprises means for distinguishing between sensor signals corresponding to looped entities and sensor signals corresponding to not looped entities, and means;
• for identifying first and second waveforms in the first and second sensor signals, respectively, corresponding to a single entity,
• for dividing the first waveform into N equal segments,
• for cross-correlating each of said N segments to the second waveform to produce N correlations,
• based on said N correlations, for producing a compensated first waveform that compensates for varying velocities along the length of the entity as it was sensed, and
• for determining the length of the sensed entity based upon the compensated waveform.

An apparatus for sensing characteristics of elongate entities having length and width and being carried in an airflow, comprising:

• a sensing volume;
• entity presentation means for receiving the entities and airflow and presenting the entities in said sensing volume;
• sensor means for sensing the entities in said sensing volume and for producing a sensor signal corresponding to characteristics of the sensed entities;
• said sensor means comprising a source of light directed through said sensing volume and first and second photodetectors for sensing entities in said sensing volume, said first and second photodetectors being positioned to sense at first and second volumes, respectively, positioned in said sensing volume in a side-by-side spaced apart relationship with the second volume being positioned downstream of the first volume with reference to the airflow in said sensing volume, said first and second photodetectors for producing first and second sensor signals, respectively, each including waveforms corresponding to sensed characteristics of entities in said sensing volume;
• and
• said analyzer means further comprising means for identifying the beginning and the end of first and second waveforms in said first and second sensor signals, respectively, corresponding to a sensed entity, comparing at least a portion of the first waveform to the second waveform and producing a compensated waveform that compensates for varying velocities of the entity as the entity is sensed.