Big scale construction machinery is absolutely necessary for the mineral resources development and various construction works. Troubles of the machinery give serious losses in the efficiency of operations and also in financial proceeds. In this meaning, machinery maintenance is very important for mining and construction works. Early diagnosis of the machinery is especially important to prevent a serious damage. Recently, diesel engine applied to excavation machinery are highly improved not to discharge exhaust gases of high concentration and to achieve high energy efficiency. However, a diesel engine involving non combustion cylinder has high probability to breakdown in a short time when the engine is used without any maintenance works.In this study, autocovariance of acceleration waves of cylinder block was calculated to obtain the period of revolution, and the combustion period of each cylinder was determined. Then rms value corresponding to each combustion period was calculated. Probability of overlapped area of two curves of normal distribution, which were obtained from rms values of normal and non combustion states respectively, was calculated. It was confirmed that non combustion cylinder of a diesel engine of V-12 type could be judged clearly using the relative intensity curve of the probability. This judgement method is considered to be superior to traditional methods where more than several numbers of accelerometers were used, especially from the viewpoint of simplicity.

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It is considered that cable sensor for vibration detection is useful, for instance, to detect the rock falling or small failures of a slope before the occurrence of a big failure. The original cable sensor is susceptible to be yielded by the tensile force, because whose tensile strength is not so enough (40 to 50 kgf). Authors have developed the steel wire cable sensor in which original cable sensor is placed instead of the string of hemp in the central portion. It was necessary to test the sensitivity of this remodeled steel wire cable sensor. As a result of the sensitivity test, following points were clarified: 1) Sensitivity of the steel wire cable sensor does not decrease when the sensor is fixed rigidly or glued continuously to the surfaces of stiff structure made of concrete or steel. 2) Sensitivity of the steel wire cable sensor decreases to 60% against the output of original cable sensor when the cable sensor is buried in the soft land. However, it was confirmed that output level was enough to use practically. In conclusion, the steel wire cable sensor could be used practically to various places to detect vibrations.

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