Yung-Li L., Mao-Hsiung C., Wuu-Wen L.

This paper studies a low frequency design of a low cost vibration detecting sensor. The design principle is based on the reaction of a spring-mass system to the vibration source. The spring-mass system then induced a strain on the FBG (Fiber Bragg Grating) which is mounted on it. An ASE (Amplified Spontaneous Emission) is used as a light source. Only these specific light beams of the broad band light source which satisfy Bragg condition can induce interference. The spectrum of the interference is modified by the spring mass mechanism which acts as a mechanical filter. The interference light beam which contains the information of measurand is transformed into electrical signal by a photodector and then demodulated further by a signal processor. Finally, the characteristics of vibration can solve. In this paper, we design a low frequency optical fiber vibration sensor. Some important characteristics are narrated as follows: (1)The dynamic range of the optical fiber Bragg grating sensing head is 45 ¡Ó 1dB with frequency band between 100 ~ 400 Hz. (2)The minimum detectable of vibration level is around 7.5 ¡Ó 1 ¡Ñ 10-3 rad. Keyword: Fiber Grating, Vibration Sensor.