Abstract: The speed of a DC motor is stabilized to correspond to a reference speed by a motor driving control that is instantaneously responsive to the interval between reference pulses corresponding to the reference speed and actual observed pulses corresponding to the actual motor speed.

Abstract: Subtle streaklike defects in running webs and sheets are identified by transversely scanning adjacent lateral sections of the webs or sheets by means of radiant energy means. Transmitted or reflected radiation is received on corresponding photocells that produce measurement signals that are representative of a defect in the webs or sheets. The signal-to-noise ratio of the measurement signals is increased by multiplicative correlation, on the condition that the ratio of the signal component V.sub.d to the effective noise component V.sub.n of the measurement signal V.sub.m is greater than one.

Abstract: Subtle streaklike defects are detected in running webs and sheets by transversely scanning distinct lateral sections of the webs or sheets by means of lines of radiant energy extending parallel with the direction of movement of the webs or sheets. Transmitted or reflected radiation is received on corresponding photocells that move synchronously with the lines of radiant energy. During each scan of each section of the webs or sheets, a large number of comparisons occur between the output signals of each photocell at a given first lateral position and at a second lateral position that is separated from the first one by a distance that is of the order of magnitude of the width and preferably half the width, of a streaklike defect to be identified.