Proceedings PaperSingle Fiber Shutter Type Sensor Using A Self Detecting LED
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A reflective encoder disc is illuminated by the light from a continuously forward biased light emitting diode (LED). As the disk rotates so the level of light coupled back into the LED itself is modulated. By monitoring the LED terminal voltage, the modulation, and hence the motion of the disc itself may be detected. Measurements of optical detection sensitivity in forward biased LEDs and also in silicon photodiodes are presented to illustrate the competing photo-and thermal-detection effects. At low bias currents incident light and voltage change are in phase. at high currents in antiphase. A fiber-connected self-detecting opto-coupler and tachometer based on these effects is described with a signal to noise ratio of 56dB in 10kHz bandwidth.