Orbit plot

The Orbit display uses two data items in the time domain. The signals from two channels are drawn on an X and Y plane to display the shaft position change against the angle of rotation. Orbit plot displays give a two dimensional visual picture of the motion of a rotating shaft.

A well-balanced shaft with no movement in any direction and would produce a dot in the middle of the plot. The shaft movement can give an indication of the vibration source, for example if there is a lot of up/down movement it may be that the machine's feet are not bolted down tightly enough.

The orbit plot is a specific display of an XY curve. To perform this kind of plot, you can switch the modulo plot that contains the X and Y displacement variables of a bearing component to an XY curve. Then you have access to the 2D orbital plot modulo plot as a graph type.

You first need to create a modulo plot that contains the variations of the bearing displacements of the shaft displacements in the directions that are perpendicular to the shaft axis. The modulo variable has to refer to the rotation angle.

Procedure

1. Click the icon in the plot toolbar, or use the Tools > XY curve(s) menu option.

2. Click the first graph.

   Figure 98: Rotary shaft displacements

   The curve is now an XY curve Figure 99: Rotary shaft displacements in XY plane

   The modulo variable is no longer used as the X axis variable. You can have access to the modulo variable value by using the replay cursor.

3. To switch to orbital rendering, right-click on the first graph and select Type > 2D orbital modulo.

   Figure 100: 2D orbital modulo graph type entry

Results

The two graphs are switch to orbital rendering:

Figure 101: Orbit plot