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Unformatted text preview: detect far smaller marks. © Festo Didactic GmbH & Co. KG • FP 1110 245 15. Special designs and variants of proximity sensors 15.2.6 Luminescence sensors
Markings can no longer be reliably detected by means of printing mark sensors, if
the markings are amongst other similar textures, e.g. printed labels. Also, in many
cases the printing mark is not meant to be seen. In such cases, luminescence
sensors, which respond to invisible, luminescent markings are suitable.
The emitter of a luminescence sensor emits ultraviolet light at a wavelength of
365 nm for example. The ultraviolet light excites a fluorescent marking substance,
which emits at a higher wave length range (e.g. between blue and red).
The luminescence radiation excited is detected by the receiver, which generates a
switching signal. The emitter and receiver are modulated so that the receiver only
responds to the modulated light of the emitter. In addition, optical filters are used to
prevent the influence of external light effects.
Luminescent sensors also work perfectly w...
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- Spring '12