Contents - Index

Order Analysis

Order Analysis is a technique used for spectral analysis of rotating machinery.  Order is defined as the normalized rotational speed.  The first order is the basic rotational speed and order M is N times the rotational speed.  Order components are harmonically related to the rotational speed.  

Order Analysis:
  • Converts Frequency into Orders
  • Reveals which spectral components are related to the rotational speed of the machine because all the shaft related peaks line up 
  • Allows you to separate structural resonances (fixed frequencies) from rotational ones (variable frequencies)
  • Requires a tachometer (Data Translation DT9826, DT9837, DT9839 or DT9857)

    With rotating machinery, many vibrational properties change with speed. You only can observe some mechanical faults, such as resonance, as the rotational speed approaches or passes the critical speed.  For this reason, machinery tests often require run up or coast down tests.
     
    Order Analysis is supported by the analyzer and can be used in any of the modes (Realtime, Recorder or Post Processing).  

    Connect a tachometer to the Data Translation module and enable the tachometer channel and one or more input channels under the Options - Processing Settings - Device Input menu.  Also connect the accelerometers or microphones to their respective input channels.

    Order Analysis is performed primarily using the Spectrogram plot.  This plot normally displays Frequency vs Time with the Amplitude in color.  If tachometer data is available the spectrogram can be configured to display RPM instead of Time and Order instead of Frequency.  These options are selected in the Spectrogram Plot Options dialog box.

    If you double click on the spectrogram, the Order Spectrum plot will be displayed at the RPM corresponding to the mouse position.