this invention is a method to determine the condition of rotating equipment , namely drive spindles , to enable the timely maintenance or replacement of same . the method uses an electrical signal from a vibration sensor mounted on part of the drive train to measure the level of vibration energy when the equipment is rotating under loaded and unloaded conditions . the relative vibration under the loaded and unloaded conditions is used as an indicator of equipment condition . typically there is more vibration under load when the equipment is in good condition . when the level of vibration under the no - load condition matches or exceeds that seen under load , the equipment needs to be serviced or replaced .