Both single axis and triaxial data are valid depending upon the application and the type of faults one is looking for. Typically, even when single axis sensors are used, more than one axis is tested per bearing, but again it depends on the application. This can take more time as the sensor has to be moved more often and more tests have to be initiated in the data collector. Data is not collected simultaneously and the possibility exists that the machine can change state (load or speed) between tests or even shut down.
A triaxial sensor can collect data on all three axis of the machine simultaneously, thereby providing more complete data in less time. Triaxial data is useful when attempting to distinguish between unbalance and misalignment and between unbalance and foundation flexibility among other things. If one is using a single axis sensor, care should be given to consider what faults one is looking for, what axis they appear in, and test accordingly.