| 摘要 |
In a known method of testing braking effectiveness, a sheet carrying a series of lines is attached to a moving part of a machine and these lines are sensed sequentially by a photo detector as the machine part moves. The output of the photo detector thus gives an indication of the movement of the machine part during the braking operation. In the invention the photo detector 21,22 is associated with an optical system 20 which is used to project light to the series of lines; and to focus light reflected from the lines, onto the photo detector. In this way the photo detector and associated equipment can easily be set up, e.g. on a tripod, at a position spaced from the machine whilst still enabling a reliable signal to be generated in the photo detector. An important preferred feature of the invention is the use of retroreflective material on the aforementioned sheet. This greatly enhances the strength of the signal generated by the photo detector.
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