Measuring displacement using accelerometers （使用加速度计测量位移）.pdfVIP

Measuring displacement using accelerometers By Renard Klubnik, Applications Engineer, Wilcoxon Research Displacement is the most easily understood vibration parameter, yet is the least commonly utilized in vibration analysis. Plant personnel have long expressed a desire to know the amount of ‘mils’ at which a machine is operating, because ‘mils’ is a readily understood parameter. One can easily feel displacement by placing a hand on a piece of machinery. Some of the earliest vibration ‘sensors’ included a pencil mounted on a machine that scribed a line on a card. The ‘peak-to- peak’ level of vibration could then be measured with a scale. Highly sophisticated vibration monitoring instrumentation exists today, but displacement remains one of the most sought after vibration parameters because it is easy to understand. There is a common misconception that measuring displacement using an accelerometer is not possible or can lead to erroneous information. In reality, accelerometers have long been used to measure displacement. However, it is important to understand that displacement measured with an accelerometer is not the same displacement measured with shaft riders or eddy current style vibration transducers. Eddy current probes are precisely thru-hole mounted into a mechanical casing and measure two very important shaft parameters. First, eddy current probes indicate the location of the shaft relative to the casing. This is very important in sleeve bearing applications because it tells the operator where the centerline of the shaft is relative to the casing. Second, eddy current displacement measurements indicate the amount of 1x rotational vibration. From this measurement, it can be determined if the shaft vibration is within acceptable limits. If an operator looks at the vibrational spectral content measured with a displacement probe, it is possible to see higher order harmonics of the shaft. However, these levels are typically very smal