Motor shaft will suffer a lot of hidden troubles in course, which is mainly caused by flaws of junction with the shaft and ribs in the process of the manufacture and use, so it is particularly important to detect and analyze these flaws regularly, to assess the defects as well as overall motor shaft can provide decision-makers with the necessary basis for decision making.

In general condition,it should be allowed that eccentric error is larger than ±10% of average air-gap,but over-large eccentric value can produce very much unbalanced magnetic pull,and then increase the deflection of motor shaft,thus critical speed is influenced.