Mintel Study Of Temperature FBG-based Ice Thickness Detection And Ice Water

The realization of the continuous and automatic detection of the thickness of the ice layer and the changing process of the ice layer of the rivers, lakes, oceans, glaciers and reservoirs is the real-time and on-line monitoring of the distribution of the ice water temperature. And the problem of ice condition detection has been the issue that needs urgent solution for many areas both domestically and aboard. While the detection is often carried under the hard and tough environments as in the wilderness, with inconvenient transportation, with weak or without power supply, under harsh climate environment and etc. At present, the methods for detecting the ice thickness and the water level under ice are testing by artificial holes or instrument detection after drilling ice and the traditional way for data recording and submitting is adopted. The detection method is not only with low accuracy and efficiency, with low speed of data transmission, but also is exposed to bad environment and risk.Methods to monitor ice conditions domestically and abroad can be grouped into three types:manual measurement method, instrument measurement, radar measurements. Manual measurement method is totally relying on the eyes and experience of the observers or relying on simple devices, and is applicable to any waters. But the shortcomings are low accuracy and that the results vary among the testing personnel. Applying to the high-latitude waters, instrument measurement method is relying on the instruments and tools, manual operation and data reading, without ensuring automatic and continuous monitoring at a monitoring point and the receiving of monitoring data of the ice changing process. The radar measurement method is based on the adoption of aircraft, ships and satellites as platforms to place monitoring device for detecting ice conditions, and is applicable to large range waters instead of small area with big investment.In this article, the detection of the ice thickness can be realized though the temperature testing on the basis of the temperature difference of ice-water. The Bragg grating in the testing apparatus is used as the sensing element and spiral optical fiber Bragg grating is designed as temperature sensor, then U-tube with external thread and straight pipe with internal thread is connected to finish the apparatus. The spiral distance (the distance between the straight pipes) can be adjusted according to changing the angle between the U-tube and the straight pipe. Or AIO by material with good plasticity can be used. And based on the characteristic of good plasticity of the material, the spiral structure and the distance between the measuring points can be adjusted according to the requirements on the accuracy of the measurements. By placing the apparatus in the waters tested, the real-time and on-line monitoring on longitudinal temperature distribution and ice water temperature of the waters can be realized, as well as the automatical and continuous receiving of temperature change data in the process of complete ice changing. Moreover, ice thickness range can be known according to the turning point between ice layer and water. The optical fiber Bragg grating temperature sensor can be applied to any waters. The main contents are as follows:(1) An optical fiber Bragg grating sensor unit is designed and tubular packaging optical fiber Bragg grating temperature sensor linear array can be used for the detection of the temperature of the ice conditions.(2) According to the object of the sensor detecting and the characteristics of the fiber Bragg grating, connective spiral structure is designed and in turn the distance between the measuring points can be conveniently adjusted accordingly. Besides, copper with good thermal conductivity is selected as the material for the spiral structure.(3) Size of the line array of the sensor:length of straight tube is120mm; length of internal thread between ends is12mm; radius of U-tube is30mm; length of external thread between ends is120mm. External diameter of the selected pipe is3mm; the internal diameter is1.8mm and the wall thickness is0.6mm. According to the actual situation and the experimental conditions of the actual test, seven optical fiber Bragg gratings are sealed together to comprise the sensing line array as limited by the experimental conditions.(4) The sensitivity of the sensor line array of every monitoring point is proved to be more than10pm/℃by calculating after comparative test. Linearity error and repeatability error is small, and the hysteresis is not large.(5) Analysis of test results:this detection more accurate ice thickness, ice thickness and the thickness of the steel ruler detected detected are basically the same, to measure the magnitude of the error size of the distance between the measuring point decision error range is [0, d/2], where d is the spacing between the respective measuring point, the distribution of the temperature of the aqueous layer is substantially linearly decreased with increasing depth, but in an ice-water layer with the increase in depth The temperature increases, the single maximum is not greater than4℃.(6) Analysis of test results:a relatively accurate ice thickness is obtained, which is consistent with that tested by steel ruler, and the change in temperature is0.1℃for every10mm increasing or decreasing of ice thickness.