| 摘要 |
The optical characteristics of a banknote are measured by using first and second sets of optical devices positioned on respective sides of the banknote path. Each device includes a transmitter and an adjacent pair of receivers, the receivers being capable of receiving light from the adjacent transmitter which has been diffusively reflected by the banknote, and each receiver also receiving light from the transmitter of the opposed device. Calibration is carried out by moving a reference body of predetermined reflectance and transmittance characteristics into the banknote path between the devices.
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