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Unformatted text preview: objects. Red or infrared light is used for this purpose. Semiconductor light emitting
diodes (LEDs) are a particularly reliable source of red and infrared light. They are
small and robust, have a long service life and can be easily modulated. Photodiodes
or phototransistors are used as receiver elements. When adjusting optical proximity
sensors, red light has the advantage that it is visible in contrast to infrared light.
Besides, polymer optic cables can easily be used in the red wavelength range
because of their reduced light attenuation.
Infrared (non visible) light is used in instances, where increased light performance is
required in order to span greater distances for example. Furthermore, infrared light
is less susceptible to interference (ambient light).
With both types of optical proximity sensor, additional suppression of external light
influences is achieved by means of modulating the optical signal. The receiver (with
the exception of through-beam sensors) is tuned to the pulse of the emitter. With
through-beam sensors an electrical band-pass is used in the receiver. Particularly in
the case of infrared light, the use of daylight filters further improves insensitivity to
ambient light. 9 Oscillator (1) Switching...
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This note was uploaded on 11/01/2012 for the course CHEMICAL 102 taught by Professor Jamesrodriguez during the Spring '12 term at Universidad Politécnica de Cartagena.
- Spring '12