Liquid Concentration Of Optical Fiber Sensor Detection System

Concentration is one of important parameters to denote liquid solution, so it is widely applied of liquid concentration monitoring and controlling in many fields such as paper making, chemistry industry, refine sugar, foodstuff, and medicine. It is a main technology method to ensure and improve production quality. There are many methods to measure liquid concentration, at present mature and widely applied methods include capacitance method, photoelectricity method, ultrasonic grating method, and incidence method.Now in the aspect of liquid concentration measurement, especially in real time measurement, the technology is comparatively uncultured. This work presents a testing system which bases optical intensity modulation principle with optical fiber sensor to measure liquid concentration changes in real time.Fiber optic sense is a new technique with the development of optical fiber communication. The optical beam transmit in the fiber and is modulated by tested parameters such as liquid concentration, temperature, or refractive index, and its swing, phase, frequency or polarization state will change. We can measure the modulated optical signal, and get the tested parameters.This work presents a new method to measure liquid concentration based the study of all kinds of prevenient methods. The U-shaped sensor probe is the vital part of the experiment equipment, after it is inserted into the tested liquid, the changes of liquid concentration under test can be read straightway. The input terminal of the testing system joins a low frequency signal component with a sinusoidal signal of 1 000Hz and 5mV. A GaAs LED drived by the sinusoidal signal serves as the light source and produce amplitude modulated optical signal to the optical fiber. The optical signal travels in the optical fiber and occurs total internal reflection in the U-shaped sense probe that is inserted into the tested liquid, at last reaches the optical receiving terminal. In the optical receiving terminal a PD changes the optical signal into a magnified voltage signal. In order to get exact measurement results, an oscillograph connects the beam receiving terminal. The output voltage is sent to anA/D converter which is connected to an IBM computer. The computer can deal with the experiment data by the numbers, so test liquid concentration in real time. This experiment proves that the liquid concentration measurement system works reliably, performs stably, is effective and feasible.The method of measuring liquid concentration is: Fist, confect 12 different salt and sucrose solution as reference value. Then put the U-shaped sense probe into different salt and sucrose solution and note the measured value. We take the value of measured salt or sucrose solution as y-axis and the value of concentration as x-axis, and paint a curve. Last, sign the value of pending solution on the curve, we will get the value of concentration. In this experiment, we can distinguish at least 0.6% salt solution and 0.4% sucrose solution at normal temperature.This liquid testing system uses optical fiber optoelectronic couplers which can ignore the coupling and connection questions between the optical fiber and the optoelectronic part and simplify the design of the whole system. It only needs to design a simple terminal circuit for sending and receiving laser beam to measure liquid concentration. The sense probe is small, immune to chemistry cauterization, and can be used into auto-control measurement system in combustible and explosive surroundings.Every homogeneous matter has aptotic refractive index, and its refractive index is linear with concentration. The experiment recurs to optical apparatus, at last manufactures optical fiber refractometer. Through optical fiber refractometer, we can measure liquid concentration in real time.