| 摘要 |
<p>PROBLEM TO BE SOLVED: To constitute a demodulator without considering a light attenuation value and to reduce influence of individual difference of photoelectric conversion device by intervening an optical attenuator having the same light attenuation value as that of a sensor at a route of a dummy optical fiber. SOLUTION: An optical attenuator 20 having a light attenuation value equivalent to a light attenuation value of a sensor 14 is provided at a route of a dummy optical fiber 19. Thus, a light from a light emitting diode 13 is partially attenuated by the attenuator 20 while passing the fiber 19, input to a demodulator 21, demodulated, and output. And, a difference in output of both modulators 17 and 21 is calculated by a differential amplifier 22, and only a component corresponding to a voltage or current modulated by the sensor 14. Thus, since the attenuation values of the lights from both the light emitting diodes 12, 13 via the route for passing the lights become equivalent, a circuit can be constituted without considering the attenuation values in both the demodulators 17, 21.</p> |
