Time History: Orbit and Shaft Centerline

Tacho Speed Count

The Tacho Speed Counting option is available when a time domain file is open.

The tacho speed counting tool carries out the same function used in the Aurora Tornado analysis engine to convert raw tacho signals to a speed against time plot. When the ‘Tacho Speed Counting’ option is selected the ‘Tacho Processing Options’ window is displayed. The user selects which time history channel contains the raw tacho signal and then identifies which shaft number to associate the signal with. In order to plot the speed against time the ratio between the tacho signal frequency and the shaft rotational frequency is required. The user needs to input these two values at the maximum (100%) speed of the test. The tacho frequency is input in Hz and the shaft speed is input in RPM.

When the ‘Plot’ button is selected an X-Y plot of speed against time will be produced.

Generic Cycle Count

The Generic Cycle Counting tool carries out a similar function used in the Tacho Speed Counting option and is used for analysing the frequency content of signals, such as flow meter data or a tachometer. When ‘Generic Cycle Counting’ option is selected the ‘Generic Cycle Counting Options’ window is displayed.
In the ‘Channel /Parameter Options’ the user first selects which time history channel is to be analysed. In order to plot the amplitude against time the ratio between the signal frequency and the EU is required. The user must then specify low and high cycle threshold values to ensure a suitable crossing point is used to identify each pulse.
In the ‘Period Characteristics’ section the user enters a tacho frequency value which is the shaft speed that would give the characteristic of the tacho. If EU is selected the unit entered in the ‘EU Name’ field is used. The ‘elapsed time’ value is the time taken for the number of cycles defined in the field below (number of period cycles over elapsed time).
In the ‘Analysis Options’ section the user selects whether to display % or EU. If the ‘Use smoothing’ option is selected a rolling average calculation is applied to the tacho so that the plot is smoother. The number of smoothing cycles needs to be specified which determines the number of values used to calculate the rolling average. The higher the number of smoothing cycles the smoother the plot.

When the ‘OK’ button is selected an X-Y plot of processed steady state EU against time will be produced.

Orbit

Define New Tacho

The tacho must be selected. If ‘none’ is displayed in the drop down list the user can select the ‘Define New Tacho’ button. This brings up the generic cycle counting GUI where a tacho can be defined. (Generic Cycle Counting GUI described above)

This newly defined tacho is then available for selection in the select tacho list.

Period Display

Selecting the ‘Period Display’ button brings up the ‘Period Display Settings’ form which allows the user to display the once per rev signal on the X and Y channel zoom plots and the polar plot.

The user must first select the ‘Display Period Marks’ box before being able to edit the settings. The user can select to automatically lock to peak-to-peak regions or to manually select the start point.
The automatic option is only applicable to once per rev signals and the program automatically identifies regions which correspond to one revolution. Markers are displayed on the x and y channel plots to indicate a revolution. If the user clicks outside the region indicated by the markers they reposition to highlight the next revolution.
If the manual option is selected the user can set the number of periods over which to mark the signal to a floating point value. The starting mark must then be selected. If ‘cursor’ is chosen the starting point for the highlighted signal is wherever the user clicks on the plot with the cursor and is updated each time the user selects a different point on the plot. If ‘Zoom area start point’ is selected the period mark is started from the left hand side of the zoom plot. The user can then toggle the cursors within the zoom area without the period markers being updated.
If the ‘Show only data in period range on Orbit plot’ option is selected the orbit plot only displays data over the period range defined by the user.
If ‘OK’ is then selected the ‘Orbit’ tab is then displayed with 4 plots.
An envelope plot is displayed at the top of the screen with a zoom plot below it. To zoom on the envelope plot click and drag to highlight the area of interest, the area selected on the envelope zoom plot is displayed on the other 3 plots. The two time history zoom plots display the channels x and y used in the analysis. The channel displayed can be selected from the plot’s right mouse menu.
All of the plots on the ‘Orbit’ screen can be saved to csv using the option in their right mouse menu.

Shaft Centerline

The shaft centreline plot is used to assess where the shaft is sitting within the bearing clearance. 

  1. The user must first select the 2 proximity probes for the X and Y axes to be used from the lists available. 
  2. Next the filter type must then be specified.
    1. none 
    2. rolling average 
    3. low pass filter 
  3. The tacho must be selected. If ‘none’ is displayed in the drop down list the user can select the ‘Define New Tacho’ button. This brings up the generic cycle counting GUI where a tacho can be defined. This newly defined tacho is then available for selection in the select tacho list.
  4. The user must then enter values for the delta time and delta speed triggers which will be used to select the data points in the analysis for plotting. When the speed of the selected tacho has changed by the value entered in the ‘Delta Speed Trigger’ that data point is plotted. However, if the time since the last data point is greater than the ‘Maximum Delta Time’ then that point is plotted.
  5. If ‘OK’ is then selected the ‘shaft centreline’ tab is then displayed with 4 plots.
An envelope plot is displayed at the top of the screen. The channel displayed can be selected from the envelope plot’s right mouse menu. The user can select a zoom area from the Envelope Plot. The area selected on the envelope plot is displayed on the other 3 plots. The two time history zoom plots display the channels x and y used in the analysis.
All of the plots on the ‘shaft centreline’ screen can be saved to csv using the option in their right mouse menu.

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