Photoelectric Tachometer
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A photoelectric tachometer's sensing system is composed of a source of light directing a light beam toward the rotating object, reflecting marks affixed to the object, and a photosensor focused on the area with the marks. When the object rotates, it modulates light by reflecting marks, producing a tray of pulses whose frequency is proportional to the speed. Instead of marks, some inherently reflective spots on the object can be used to change the intensity of light reflected toward the photosensor.
Photoelectric tachometer, w = angular speed, 1 = rotating object, 2 = reflecting mark, 3 = light source, 4 = photosensor.
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