Study Of A Liquid Level Sensor Based On Fiber Optic Array And Magnetic Coupling

Liquid level measurement is widely used in different areas of production and life, especially in the areas of industrial production. Besides the demand of high accuracy, liquid level measurement should be able to adapt to the special environment of industrial production field. For this reason, liquid level measurement is required to be high accurate, real-time online and stable. At present, the traditional liquid level measurement is mainly realized by ultrasound, radar or electronic sensor. These sensors have a common weakness, i.e. the introduction of electricity to the spot measurement, which limits their application in some harsh environments, such as strong EMI environment, inflammable and explosive environment. Since the optical fibre liquid level sensor inherits the characteristics of optical fibre sensor, such as intrinsic anti-explosion, electric insulating, unresponsiveness, chemical stability, time domain transform property, low loss, large capacity, high accuracy, small size and light weight, it can be suitably applied to the liquid level detection in industrial production. However, due to the technical immaturity, optical fibre liquid level sensor is currently not widely used in practice. Over the years, the research of optical fibre liquid level sensor is mainly carried out on Fibre Fabry-Perot Interferometer Sensor and Fibre Grating Liquid Level Sensor, which are not widely used due to the low accurate measurement and difficult demodulation.This thesis proposes an optical fibre liquid level sensor which is based on magnetic coupling and optical fibre array. This optical fibre liquid level sensor has the advantage of all-optical, which makes it possible for the sensor to be used in some harsh environment, such as strong EMI environment, inflammable and explosive environment. Besides, as the sensing signal is measured by light intensity’s perturbation, which is inaccurate, the light source’s instability, the loss in fibre connection and the bending loss will not have a large impact on the measurement in this sensing system. Since the measurement accuracy is decided by the density of fibre array, as long as the density is large enough, it is theoretically possible to improve the measurement accuracy up to0.1mm, which can almost meet any standard in the engineering application. This sensor uses side-polished optical fibre as linear light source, so that it makes the sensor structure simpler and the performance more stable. Moreover, due to the sensor’s special structure and the seal using special material, this sensor is not sensitive to the liquid level fluctuation caused by the non-liquid volume. Therefore, this sensor can be used in the measurement for any corrosive or opaque liquid at normal temperature. In addition, it is suitable for the liquid measurement in bus, ship, airplane and other vehicles.The innovations in this thesis are as follows:1) By using the fibre array to transmit the light signal, using the optical fibre bundle to transmission signal, using the camera imaging analysis detection signal,so it reduces the demands for light source and signal processing.2) Cylinder column and float are used in the sensor, so that its structure is more stable and it can be applied to wider areas.3) Side-polished optical fibre is used as linear light source. By analyzing the characteristics of waveguide transmission, the light intensity of the linear light source is evenly distributed.