Systems and methods for measuring shaft-relative vibration

A non-transitory computer-readable storage medium storing instructions that, when executed by a processor, cause the processor to perform steps of:

• measuring shaft displacement data with a pair of sensors, wherein the shaft-displacement data comprises shaft center X-axis displacement and shaft center Y-axis displacement, wherein the X-axis displacement and Y-axis displacement are orthogonal to each other;
• converting the shaft displacement data to shaft velocity data by calculating a difference in shaft displacement over time;
• filtering the shaft velocity data;
• sorting the shaft velocity data;
• grouping the shaft velocity data into three or more velocity groups;
• assigning a different color to each velocity group;
• and
• displaying an image of a velocity orbit plot on an electronic display, where the X-axis displacement and Y-axis displacement define coordinate pairs of a trace of shaft center displacement, and the velocity group between each coordinate pair defines a display color of the trace.

A system comprising:

• a rotatable shaft;
• a casing;
• one or more journal bearings supporting the rotatable shaft within the casing;
• two displacement sensors, comprising an X-axis displacement sensor and a Y-axis displacement sensor, attached to the casing and positioned orthogonally to each other on a plane transverse to a rotation axis of the rotatable shaft;
• a processor and memory communicatively connected to the two displacement sensors and configured to perform steps of:
• receiving shaft displacement data from a pair of sensors, wherein the shaft-displacement data comprises shaft center X-axis displacement and shaft center Y-axis displacement, wherein the X-axis displacement and Y-axis displacement are orthogonal to each other;
• converting the shaft displacement data to shaft velocity data by calculating a difference in shaft displacement over time;
• filtering the shaft velocity data;
• sorting the shaft velocity data;
• grouping the shaft velocity data into three or more velocity groups;
• assigning a different color to each velocity group;
• and
• display an image of a velocity orbit plot, where the X-axis displacement and Y-axis displacement define coordinate pairs of a trace of shaft center displacement, and the velocity group between each coordinate pair defines a display color of the trace.