Image Number 5 for United States Patent #5583828.
A series of pulses of ultrasonic wave emitted from the transmitter with a specified period are received by the receiver. The received signals are rectified to a smooth wave with a single peak. The occurrence time of the peak is determined to gain and store the peak value, which corresponds to the edge position, thickness or splice position of the web. Alternatively, the transmitter emits a series of pulses of ultrasonic wave with a specified period and the peak value in the signals received by the receiver is once held in the peak-holding circuit. The peak voltage held is discharged and reduced with the discharge device and smoothing of the charged voltage yields its mean value, which corresponds to the edge position, thickness or splice position of the web.