Study On The Failure Diagnosis System For Ship Log Sensor Off Shore Abstract

Ship log is an important instrument of naval equipment, it can provide speed and range signal to calculate the ship's position. On account of working on the sea,electromagnetic sensor which is a major outbreak of the fault,is susceptible to corrosion,resulting to the error in the transmission of speed signal . The conventional testing method for sensor is measuring electrode resistance by multimeter or other tools after being up to slipway. The electrode resistance is very small, but in the event of failure, there will be very large change. Although this method is simple, large projects and a lot of time are needed. What's more, misjudgment will cause huge losses.To achieve field measuring the failure of the sensor, if take the traditional method of measuring resistance, the sea water must be an essential part of measurement circuit, which will lead to a series of complex electrochemical reaction, and interfere the measurement. To solve this problem, this thesis presents a kind of field measuring scheme and design a sea fault diagnosis system according to the scheme. The working principle of the fault diagnosis system is making use of intermediate frequency bipolar pulse excitation to measure electrodes of the integrated system constituted of sensor, electrodes and water. The purposes are to minimize polarization effects reaction and capacitance effects, so the result can be gained by comparing with the standard library established, with this method the sensor's working condition can be judged quantitatively. This thesis establishes a mathematical model of the sensor system's conduction mechanism based on electrochemical principle which provides support to approve of the feasibility of the design from theories. In addition, the mathematical model can provide the basis to create standard library. Because of working on the sea, testing system can monitor the working condition of sensors real-time, overcome the shortcoming of traditional methods and avoid a great amount of work, such as docking and being up to slipway, as a result a lot of manpower, resource and time can be saved. Judged from experiments, here are significant differences in conductance between the fault sensor and the sensor working in good condition. The results show that the diagnostic system can identify abnormal sensor very well.