| 摘要 |
A banknote validator takes both reflection and transmission optical measurements at different wavelengths. An emitter and sensor on one side of the banknote path are used to make a calibration measurement using light reflected from a window on the other side of the path, overlying another optical device. Each measurement is normalised on the basis of multiple measurements of different wavelengths, distributed over a substantial area, such as along the relevant scan line, preferably using a value representing the dispersion of the measurements.
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