Abstract: An imaging apparatus includes a collection of optical elements arranged in a predetermined sequence and cooperable to define a dark-field optical arrangement and a bright-field optical arrangement. The dark-field optical arrangement and a bright-field optical arrangement may be defined along the same or different optical path(s). At least one of the optical elements is operative to enable at least one of the dark field or the bright-field optical arrangements. In a first embodiment said one optical element is movable from a first to a second position to enable either the dark-field or the bright-field optical arrangement. In a second embodiment said one optical element is operable to enable simultaneously both the dark-field and the bright-field optical arrangements. Both opaque objects and phase objects in a fluid stream are able to be detected and quantified.

Abstract: An electro-optical scanner for detecting variations in a web and generating output signals representative of the variations is provided with discriminator logic and alarm circuitry that indicates when the output signals shift from a value exceeding a predetermined positive (negative) threshold value to a value beyond a predetermined negative (positive) threshold value within a prescribed minimum period of time as an occurrence of an abrupt change in web density and processing circuitry for determining and indicating when the number of such occurrences per unit time exceeds a threshold or predetermined number.