Abstract: A method and apparatus for measuring the length of web in a bridge of a corrugator using an optical sensing device is disclosed. In one embodiment a variable amount of singleface web on a corrugated bridge is calibrated using a measurement of a coded moisture sequence. In another embodiment a single detector signal and an adaptive threshhold is used to detect only rapid changes of moisture content. In still another embodiment a feature of detecting the timing of a signal pattern to the pulse durations of the sprayer is used so that even as the paper speed varies the ratio of short to long remains the same.

Abstract: The system and method of the present invention determines the rate of application of liquid glue to corrugated board on a corrugator. A sensor employing the principle of infrared absorption measures the amount of water on the surface of the glue roll upstream of the point of application of the glue to the corrugated board's medium. A second sensor employing the principle of infrared absorption measurers the amount of water on the surface of the glue roll downstream of the point of application of the glue to the corrugated board's medium. Using calibration coefficients the two sensor's output signals are then converted into film thickness measurements. The downstream film thickness measurement is then subtracted from the upstream film thickness measurement to compute the reduction in film thickness caused by the intervening application of the glue to the medium.