Analysis And Research Of Portable Electromagnetic Log Fault Diagnosis System

Ship log indicates the ship speed and mileage; it is an integral part ofthe ship driving equipment. Electromagnetic log measures ship speed bythe principle of electromagnetic interaction, and it has been widely used inthe new built ships in the1980s and1990s. The sensors of electromagneticlog work in seawater, for the poor environment, they are vulnerable toseawater corrosion. After using for a long period, the electromagnetic logshave entered a fault-prone period. Log sensors and Speed solver operate ina serial mode, so it’s difficult to diagnose out which part of the instrumentis fault without disassembly. Thus, each part of the log should bedismantled from the ship and checked respectively in order to make faultdiagnosis. This diagnosis method is not only a waste of human andmaterial resources, but may cause huge economic losses once make amisjudgment.In order to overcome the deficiencies of traditional diagnosis method,a portable log fault diagnosis system is innovatively researched anddesigned in this paper. By connecting to aviation plug between sensors andship speed solver, fault diagnosis of sensors and speed solver can becarried out in installed place respectively. This will not only simplify thediagnostic process, but also can avoid the unnecessary loss of the shipgoing into dock. Meanwhile, diagnostic system uses virtual instrumenttechnology instead of the traditional measuring instruments, whichstreamlines the size and makes it easy to carry, and using LabVIEWsoftware programming, it has a good man-machine interface and is easy touse. The diagnostic system provides two methods on the log sensor faultdiagnosis, sensor electrode circuit conductance measurement method andsensor output speed signal detection method. And it can analog sensoroutput speed signal to make fault diagnosis of speed solver. First, sensorelectrode circuit conductance measurement method is researched anddesigned. By measuring the electrode loop conductance and judgingwhether it is in the normal range, the sensor performance can bedetermined. Through researching on the sensor electrodes loop in theseawater environment, pulse excitation method for measuring conductanceis selected. At the same time the seawater resistance between electrodes iscalculated by theoretical analysis and finite element analysis respectively.The conductivity judgment threshold value is determined according to thecalculation results. Then, sensor output speed potential detection method isresearched and designed. By detecting the speed potential and solve out theship speed and comparing with the real speed, the working performance ofsensors can be determined. For the speed potential of the sensor output isvery weak, instrumentation amplifier is selected to enlarge speed potentialto meet the requirements of high common-mode rejection ratio and lownoise. Combined with the virtual instrument, a method is designed todetect the weak signal. Finally, diagnosis method of the speed solver isdesigned. Sine wave is sent by the virtual instrument and attenuatedthrough attenuation network to simulate the weak speed signal of thesensor output. By comparing the speed from speed solver with thesimulated speed, the working performance of speed solver can bedetermined.The portable log diagnosis system designed in this thesis is easy touse, and its diagnostic speed is fast, which can greatly improve theefficiency of the ship log fault diagnosis. And diagnostic result is proved tobe accurate and reliable in practical applications. This paper not onlysolves the problems of the existing electromagnetic log fault diagnosis, butalso can be a reference for related equipment fault diagnosis.