| 摘要 |
An element 9 which can move with the member has two different tracks which are partly reflective of the said pulses, a first 11 of the said tracks being reflective except for a narrow zone indicative of a first of the two normal positions of the member, a second 12 of the said tracks being reflective except for a narrow zone indicative of a second of the said two normal positions. A system of optical fibres 3, 7, 8 leads light pulses from emission means 1 to fixed ends permitting optical coupling with each of the said tracks respectively and the pulses resulting from a possible return reflection to the reception means 2. It imposes optical paths of different lengths for each of the said tracks respectively. The pulses, possibly reflected by one or other of the tracks, are collected in a signal which furthermore comprises an echo pulse independent of the path difference. <IMAGE>
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