The present invention relates to a method of and apparatus for protecting a rotating machine such as a centrifuge including a rotating body or rotor rotating at high speed.
High-speed rotating machines such as centrifuges tend to produce a self-excited vibration when an excess clearance exists between rotating parts. Furthermore, a rotor of such machines is apt to be in an imbalanced state when a sample is inaccurately set by a user. Under such condition, the rotor of the machine oscillates at a large vibration amplitude and bearings for supporting the rotor are subjected to increased radial loads exerted thereon. To prevent damage or breakage of the bearings, it has been customary to detect the imbalance of the rotor, in terms of the amplitude of vibration of the rotor or a drive shaft connected to the rotor, so that rotation of the rotor is stopped when the detected amplitude of vibration exceeds a predetermined allowable value A.sub.0 as at a point e shown in FIG. 3 of the accompanying drawings. The conventional practice is not satisfactory if the allowable value is set to a relatively low level because the detection of the amplitude of vibration of the rotor is greatly affected by external disturbances. This means that the detected vibration amplitude readily exceeds the low allowable value under the influence of the external disturbance, which causes frequent stopping of the rotor. On the other hand, an allowable value A.sub.0 set at a high level permits the rotor to continue rotating while oscillating at an amplitude of vibration f which is slightly smaller than the allowable range A.sub.0. Under such mode of operation, the bearing life is substantially reduced.