Theory And Experiment Of Optically Powered Oil Tank Multi-Parameter Measurement System With

Lb ~ Theory and Experiment of Optically Powered Oil Tank Multi-Parameters Measurement System with Optical Fiber Link ABSTRACT Optically powered photo-electric hybrid optical fiber sensor is one of the hot-spot problems in the field of optical fiber sensor technology. The measurement system using this novel structure sensor can be called 揳ll optics?in measuring field. It is especially applicable in the inflammable and explosive environment. 111gb precision and good innate safe character are needed in the measurement of oil tank multi-parameters such as liquid level and oil-water boundary. At present, the usual method of liquid level measurement is mostly based on the measurement and transmission of electrical signals, so it brings inflammable and explosive problems. This paper presents a new type of optically powered multi-parameter measurement system of oil tank. The experiment model of measuring system is realized by combining theory analysis with experiment The system has the advantages of combining traditional differential capacitance measurement theory with optical fiber power and signal transmission. The optically powered multi-parameter measurement system of oil tank is presented for the first time in this paper and the unique plan that the multi-sensors are powered by a single light source is realized. The system uti]izes three differential capacitance-sensors to measure the parameters such as liquid level and oil-water boimdary and utilizes three thermistors to compensate the effect of temperature changes to measuring precision of capacitance sensor. This paper discusses the characteristics of optical fiber, light source and photo detector. The coupling efficiency of LD-optical fiber, LED-optical fiber and PD-optical fiber is analyzed in detail. It lays the theoretical foundation of the rational selection of signal optical fiber, power optical fiber and proper application of LD. The schematic diagram of optically powered system is designed. The mathematical model of the measurement of liquid level and oil-water boundary is established. The relation of pressure-capacitance is deduced and the characteristics of differential capacitance and thermistor is expounded. The theory above is the basis of the system calibration. The design of micro-power consumption probe is the key technique in the optically powered system. Larger LD power output will be need when the probe power consumption becomes larger, so there will be unsafe factor in flammable and explosive occasion. The probe uses complete CMOS circuit to realize differential capacitance-PWM-PPM, thermistor-P WM-PPM, electric-multiplex and light pulse radiation. The probe power consumption is less than 870 ii W The optically powered channel is the main part of the whole system. The stable and reliable operation voltage of the probe can be given by the following methods: (1) 20% light coupling efficiency is obtained by direct coupling of LD-optical fiber. (2) The light power is transmitted by multi-model optical fiber. (3) The largest photo-electric conversion ?II ? ABSTRACT efficiency is achieved by selecting the transformer regulation of step-up transformer. (4) The stable light intensity is achieved by using LD light feedback of driving circuit and refrigeration. In the experiment, while we adopt 20mW GsAIAs LD, 50...