The Analysis of Orbit and Shaft Center line Plot
As you are aware, measuring vibration data from a shaft is feasible in multiple ways:
1- Measuring shaft relative vibration
2- Measuring shaft absolute vibration
3- Measuring bearing absolute vibration
In ordinary vibration measurements from machinery, absolute data is collected from bearing housing. This is acceptable when the distance from casing to bearing is short but in big machinery same as turbo machinery in which the above mentioned distance is too much, rotating machinery is equipped with proximity sensors to measure relative shaft to casing vibration.
Acquired data from sensors must be analyzed and monitoring the machinery must be done. In many vibration cases in turbo machinery, the acquired data from seismic sensors are different from relative shaft vibration. Those diagrams that resulted from proximity sensors included in two main categories AC and DC. AC data provides plots such as orbit, spectrum, time signal, waterfall and cascade diagram and etc. From the other side, DC provides other information such as temperature, overall vibration, shaft center line and… data.
As checking and analyzing mentioned plots is very vital in diagnostics of big machinery (those which are equipped with journal bearings), a training course titled analysis of orbit and shaft center line plot is organized. The course outlines is provided in a download section.