| 摘要 |
PROBLEM TO BE SOLVED: To obtain a highly accurate inexpensive stroke measuring device which is not affected by electromagnetic dielectric noise associated with a heavy current and a high voltage. SOLUTION: A stroke measuring device is provided with a body 21 to be measured formed of an ND filter of which optical density is continuously increased along the direction of the movement of the body 21 and a light emitting diode 22 to be a light source to project light orthogonally to the body 21. In addition, on the opposite side of the body 21, an interference filter 23 to transmit only the waveform of light emitted from the light emitting diode 22, a photodiode 24 to receive light transmitted through the interference filter 23 and to convert it into an electric signal, and a signal processing device 25 to convert an output signal from the photodiode 24 into the stroke of the body 21 are arranged at locations opposite to the light emitting diode 22.
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