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H Bearing Runout Measurements Application Note 243-7 Introduction Advanced precision machinery, from centrifuges to computer disk drives, rely on precision bearing and spindle assemblies for high performance. For example, the spacing of data tracks on a com- puter disk drive can be limited by the non-repeatable runout of the spindle bearing assembly. For reasons like these, the need to measure runout and diagnose its cause has increased in recent years. Traditionally, runout has been measured with the electronic equivalent of a dial indicator and oscilloscopes which can deter- mine the magnitude of runout. More recently, spectrum analyzers have been used because they can help identify the various causes of runout by providing the frequency distribution information, as well as the data available from other testing methods. Originally con- fined to design labs, spectrum analyzers are now finding their This note explores the advantages way into incoming inspection and of using a dynamic signal analyzer onto the manufacturing floor, to make runout measurements, where they are used to measure using both the traditional time changes in runout caused by domain measurements as well critical assembly steps. as spectrum measurements. The measurements shown were made on a disk memory spindle assembly. Test setup to Time domain measure runout measurements of repeatable and nonrepeatable runout Figure 1: In the time domain mode, the Experimental analyzer shows Total Indicated runout test Runout (TIR) as it changes with set up the revolution of the spindle. TIR has two components. Repeatable runout, the largest component (up to 2 mils in this case), is caused by the center of rotation being offset from the ph