The Property Study Of Fiber Optic Dissolved Oxygen Sensor

On the basis of previous research, the method prepared oxygen sensing membrane of Huang Jun and Zhang Jianbiao was chose. Ttris-(4,7-diphenyl-1,10-phenanthroline)ruthenium(Ⅱ) dichloride complex was chose as fluorescent indicator. Because the sensitivity of the ruthenium complexes for oxygen increases with the rigidity of the ligand and the increase of the electron-withdrawing groups; with the growth of the carbon chain, the hydrophobic properties of the fluorescent indicator increases and the loss of the fluorescent indicator reduces, which can extend the life of the membrane. Cellulose acetate (CA) was used as matrix material in this paper. Sensing membranes of optical dissolved oxygen sensor which based on fluorescence quenching were made and their transmittance was tested. The best ratio for the production of sensing membrane has been worked out according to the status of the visual and biological microscope.The high brightness LED lamp was chosen as light source and the Y-shaped glass fiber as transmission medium of fluorescence. Photomultiplier tube was chosen as detectors because the fluorescence which was detected by the detector was weak, which is resulted from the thin fiber-optic and the few sensing membrane directly shined. In order to exclude the interference of stray light in environment, lock-in amplification technique for the determination of the lag phase shift value between fluorescence and excitation was adopted to determine the content of dissolved oxygen. In order to filter out the excitation light in the fluorescence, the tube grating spectrograph filter was used before the photomultiplier tubes. The output of photomultiplier tube need to be transformed into voltage signal and then was entered into the lock-in amplifier for phase detection. That is because the output of the photomultiplier tube was current signal. To this end, our laboratory designed the current-voltage (I-U) conversion circuit. The concentration of the fluorescent indicator, frequency of the excitation signal, duty cycle of excitation signal impact on the detection accuracy of fiber optic sensors, which was examined. The aqueous solution of the fluorescent indicator whose concentration was8mg/1, excitation signal with the frequency of60KHz,10%duty cycle rectangular signal was adopted.Finally, the properties of the optical dissolved oxygen sensor were tested. The experimental results show that the sensor’s detection limit was0.3mg/1; the detection accuracy was0.03mg/1; the response time was less than25s. And the sensor had good reproducibility, stability, strong anti-interference ability. The response curve of the sensing membrane had good linearity, which is consistent with the Stern-Volmer equation. Comparison the optical dissolved oxygen sensor with the RSS-5100oxygen analyzer was made, which show that they had no significant difference.