SHAPE DETECTOR FOR ROLLED MATERIAL

PURPOSE:To improve the accuracy in detection by detecting the phase difference between a displacement signal and a phase synchronizing signal, oscillating the phase synchronizing displacement signal, feeding said signal as a phase synchronizing signal to an oscillating circuit and extracting only the desired frequency component from the displacement signal. CONSTITUTION:A phase synchronizing detection circuit 1 is formed of a phase comparator 2, a low-pass filter 3 and an oscillating circuit 4. An input signal F1 and the output signal F2 from the circuit 4 are inputted to the comparator 2. The comparator 2 compares the phases of the signals F1, F2 and outputs the phase difference signal DELTAtheta thereof via the filter 3 to the circuit 4. The oscillating frequency of the circuit 4 is changed according to the voltage of the signal DELTAtheta if said signal is, for example, a voltage signal, and the output signal F2 having the specified phase relation with the signal F1 is outputted from said circuit, by which only the desired frequency component is extracted.