SPATIAL MODULATION OF LIGHT TO DETERMINE OBJECT LENGTH

摘要

PROBLEM TO BE SOLVED: To determine characteristics of an object by evaluating radiation light varying with a time due to a movement of the object by using a filter device.SOLUTION: Spatially modulated light emanating from an object moving along a flow path is used to determine various object characteristics including an object length along a flow direction. Light is sensed that emanates from at least one object moving along the flow path along a flow direction of a spatial filter. Intensity of the sensed light is time-modulated according to features of the spatial filter. An electric signal varying timewise is generated that includes a plurality of pulses in response to the sensed light. A pulse width of at least one part of the pulses is measured at a fraction of a local extremum of the pulses. The object length along the flow direction is determined on the basis of the measured pulse width.