Fault diagnosis method of dissolved oxygen sensor electrolyte loss based on impedance measurement

Abstract

Dissolved oxygen affects the growth and survival of aquatic organisms and considers as an important indicator of aquaculture water quality. Moreover, the electrochemical dissolved oxygen sensor may become faulty due to flow shock or damage by organisms which destroys the dissolved oxygen permeable membrane and results in loss of electrolytes. In this paper, a method was developed for detecting electrolyte loss faults in polarographic dissolved oxygen sensors by directly measuring impedance of sensing electrodes without additional sensing elements or modifying the sensor. First, the factors interfering electrolyte concentration-impedance relationship and the requirement for temperature compensation was determined. Secondly, a fault diagnosis of internal electrolyte loss was achieved by using the difference between the theoretically calculated value and the impedance measurement value in combination with the electrode reaction law. Finally, the impedance detection method was demonstrated using artificially simulated faults. The results showed that the developed method had accurate tracking of electrolyte consumption with a Pearson coefficient of 0.987. Three different levels of breakage failures were simulated and detected as 4.48 %, 21.07 % and 73.47 %, respectively. The mean absolute error of the normal state was about 1.67, which increased to 16.3 after a period of failure. The developed method meets the requirements of embedded development because it uses a simple fault detection device and easy data processing using a simple microprocessor. Furthermore, the diagnosis result has been demonstrated as an indicator of membrane health and breakage conditions of dissolved oxygen sensors.