Special designs and variants of proximity sensors

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Unformatted text preview: the receiver with an adjustable critical value. The threshold corresponds to a specific grey-scale value on the object. If the threshold of the grey-scale value is fallen below of or exceeded, the printing mark sensor changes its switching status. Depending on the different types of application (varying reflection with different colour contrasts), printing mark sensors are often equipped with optical sensors whose wavelengths can be changed by using different light emitting diodes. Even bulbs in conjunction with selectable colour filters are used. Printing mark sensors can be used with fibre optic adaptors. However, in such cases, luminous radiation is as a rule unfocussed and the sensing width may vary; however contrast sensitivity quickly diminishes as the distance increases. Printing mark sensors are also able to detect very small marks. Designs incorporating an LED light source are for instance able to detect printing marks of a dimension of 0.5 mm at switching distances of 20 mm, whereas designs using laser radiation source are able to...
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