| 摘要 |
One or more dimensions of a workpiece, such as sheet material, are determined by passing the material between opposing linear arrays of ultrasonic transmitting and receiving transducers. The dimension of the sheet material is a function of the number of receiving transducers which receive a transmitted signal as compared to the number of receiving transducers which no longer receive a transmitted signal due to blockage of the signal by the sheet material. The strength of the signal is a function of the amount the receiving transducer is blocked by the workpiece, which in turn is a function of the position of an edge of the workpiece relative to the receiving transducer. A more accurate determination of the workpiece dimensions is obtained by establishing various threshold levels of signal strength and by comparing the receiver signal to these threshold levels. In order to compensate for differences in receiver output due to differences between individual transducers, a correction offset for each receiver signal output is measured when the workpiece is not present, and the correction offsets are later added to the corresponding receiver outputs which are generated when the workpiece is present.
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