Built on a design developed from an advanced mathematical model, a practical fiber optic sensor, which is an analog of the familiar ‘hot-wire’ wind velocity monitor is developed, as an intrinsically-safe sensor device for coal mining monitoring applications. The underpinning optical fiber-based principle used is the shift in the center wavelength of a Fiber Bragg Grating which is cooled by the gas flowing over it and the device sensitivity found was determined to be ~1370pm per unit m/s wind velocity (in the range of 0-0.57 m/s), ~109pm per unit m/s in the range 0.57-2.26 m/s and ~33pm per unit m/s in the range of 2.26-5.66 m/s. In this paper, the factors that influence the device response time, such as the sensor probe surface heat transfer coefficient, wind (gas) velocity and pump power have been investigated in the laboratory. It was found that the greater the surface dissipation factor of the sensor, the shorter the response time, furthermore, the response time was observed to decrease as the wind velocity increased. A method of further shortening sensor response time using wind speed variation slope is proposed.
Optical humidity measurement is essential in current industry, especially in environment with adverse electromagnetic field and strong corrosion. This paper focus on the fabrication and test of a novel fiber bragg grating based humidity sensor. The sensor is fabricated by uniformly coating humidity sensitive material on fiber bragg grating. The sensing characteristic test of the sensor shows: the wavelength shift following humidity is linear; the minimum response time of the 2-layer coated sensor is 10 s with sensitive coefficient can be controlled by changing coating time; hygroscopic hysteresis of 3-layer coated sensor is 2.7`%RH. Therefore, the sensor is promising to be used to meet the quick response and in vivo measurement demand in industry.