Abstract: Apparatus for inspecting sheet material having known characteristics is disclosed. The apparatus comprises means for providing a plurality of pixel signals each having a magnitude representing the intensity of electromagnetic radiation received from a corresponding point on the sheet material. The apparatus also comprises signal processing means for comparing the magnitude of each one of the pixel signals to a corresponding reference range defined by the known characteristics of the sheet material and generating a characteristic signal. The characteristic signal includes an event signal for each of the magnitudes falling outside of the corresponding reference range and a data signal for each of the magnitudes falling within the range, wherein the data signal represents the magnitude of the pixel signal. The signal processing means also generates an address signal representing the point on the sheet material at which the characteristic signal is generated.

Abstract: For measuring a property such as caliper of a traveling sheet, a sensor body and a target body are located on opposite sides of the sheet and constrained (e.g., by gas bearings) along a sensor path intersecting the path of the sheet. Gas bearings maintain these bodies at, substantially constant distances from the opposite surfaces of the sheet while permitting them to move in response to the position and thickness of the sheet. An active sensor element aboard the sensor body and a passive sensor element aboard the target body interact through the sheet to produce aboard the sensor body a response dependent on the sheet property. Manifestations of this response, such as light beam modulations, are produced, without solid bodily connections, at a location spaced from the sensor body where the manifestations are detected to produce a sheet property-indicative signal.