Light Barrier - Bosch WAT28400 Repair Instructions

Design and function
3.5

Light barrier

A light barrier is an electronic-optical system which detects the interruption of a
light beam.
3.5.1 Structure
Fig. 6: Components of the light barrier
1 Light-emitting diode
2 Light beam
In the case of a light barrier the light-emitting diode (1) and the phototransistor (3)
are arranged opposite each other. The light beam (2) from the light-emitting diode
hits the phototransistor.
3.5.2 Function
The infrared light-emitting diode transmits light to the light-sensitive base of the
phototransistor. The phototransistor becomes conductive as a result. The voltage
on the phototransistor drops.
If the light beam is weakened or interrupted, e.g. by a turbid liquid, the light is no
longer adequate to activate the phototransistor.
The voltage on the phototransistor is evaluated by the electronics.
2017-05-22 / DIS 113_58300000186503_ara_en_c
3 Phototransistor
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