Abstract: Faults can be detected in sheet material, particularly in tufted fabric during manufacture of same, by scanning a surface of the material with an electrical scanning device which produces an electrical output representative of characteristics of the scanned surface. The electrical output is monitored to detect deviations from a norm representative of a fault condition. The scanning may be effected with a scanning device, comprising for example a light receiver which picks up reflected or transmitted light from the material, which is moved across the sheet transversely to the direction of advancement of the sheet.

Abstract: A yarn tension detector having a cage-like form pivotably moveable between predetermined limits about the pivot point and under the control of the tension of a moving yarn. The detector includes a pair of spaced abutment members in an electrical circuit with a lamp. The cage-like member makes a circuit whenever it engages one or the other of the abutments to thereby cause the bulb to light. The member also includes oppositely directed guide formations about which a yarn is trained and as the yarn is fed from a creel to, for example, a tufting machine the tension in the yarn as it moves through the guide formations pivots the member. One of the guide formations progressively opens when the yarn tension is in excess of a predetermined high tension to release the yarn from the detector after it has indicated the yarn tension fault.