Proper vibration data collection and diagnostics require knowing the accurate operating (turning speed) of monitored equipment. The most common tools used for measuring equipment turning speed are a tach (tachometer) and strobe (strobe light). If a means to determine equipment speed is unavailable, then an advanced vibration analyzer like VibXpert® may have additional capabilities to help you make a precise determination.
Set your vibration analyzer to acquire a velocity spectrum via the Multimode capabilities. A lower fmax is ideal because that is where the turning speed will be identified. Also, be certain that the lines of resolution (LOR) selected are high enough to accurately measure all of the frequencies around the turning speed. For example, improper LOR selection may result in the driver (motor) and driven (fan, etc.) frequencies being combined/merged together in one peak. This can make operating speed determination inaccurate or impossible. Please note that with higher LOR settings the data will take longer to collect because additional data is being acquired by the vibration analyzer. The number of averages should be set to a minimum of four to make certain any non-periodic energy is filtered out during data collection. Once data collection is complete, a cursor can be placed on the first high peak which usually indicates the turning speed of the asset.
Also, Multimode data collection can be set to a continuous mode allowing the data to be viewed live as it is collected. Once stabilized, the cursor can be placed on the spectrum to determine the turning speed of that asset as described above.
Maintenance Tips, Vibration Analysis by Mickey Harp CRL