| 摘要 |
The method is characterized in that a light beam (4) having a modulated optical frequency is emitted, two light beams or rays (i, j) are received after they have been reflected by each of the surfaces (2, 3) of a material wall (1), in that an interference is created between the two light rays (i, j) and in that the operation difference delta of the interference signal is determined. A laser diode is used as lighting source, the latter being modulated by modulating the optical frequency of the beam. Among the rays diffused by the two walls, two parallel rays are selected. With the device of the invention, it is possible to take, on each sensor, measurements spaced by 0.3 msec. It is thus possible to scan all millimetres of the periphery of a rotating bottle. Application to light or dark coloured plastic or glass bottles and to plane glass.
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