| 摘要 |
An optical encoder generates a train of digital pulses as a function of the length of web material unwound per revolution of an unwinding roll. A counter counts the encoder pulses for each revolution of the roll. The counts of the encoder pulses are accumulated over a first set of revolutions of the roll. A programmed microprocessor effects a base computation of (1) the average change in the number of pulses generated per revolution of the roll and (2) the length of web remaining on the roll after the first set of revolutions. Thereafter, the base computation of web length is updated at each revolution of the roll. The counter may comprise an addressable hardware counter chain alone or in combination with a read/write memory which counts the number of times that the counter chain overflows.
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