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.

Abstract: A gauging apparatus for sheet materials and the like comprises a surface follower body (14,20,30) adapted to be constrained without substantial solid bodily contact and guided (e.g., by gas bearings between 32 and 36 and 38) for movement along a surface follower path that intersects the path of a traveling sheet (10) to be gauged. The body has a passage (46) adapted to carry a flow of pressurized gas to be discharged against one surface of the sheet. The discharge of the gas is effective when the body is at a predetermined distance from the surface to generate a levitating force (on 20) urging the body away from the sheet surface. Means (70,64,62) responsive to the pressure of the gas in the passage exerts on the body (at 64) a counteracting force that tends to move the body closer to the surface.