ORBIT ANALYSIS

Orbit analysis is a necessary tool for vibration analysis of rotating machinery. The process is essentially an extension of time waveform analysis plotting time-domain data from a pair of orthogonal probes on an orbit graph with consideration for the physical location of the proximity probes.

This F1 manual is dedicated to setup and settings explanation, additional info about the Orbit Analysis module itself can be found in the PDF manual available on our download webpage —>
Orbit analysis manual

Setup

In the channel setup section of the orbit analysis plugin applicable measurement parameters are set through a designated user interface. The settings are grouped into six major sections for easiness of use:

* Frequency channel setup * RPM Setup * Calculation Setup * Runout compensation * Reference orbit * Machine configuration

Frequency channel setup

Under frequency channel section of setup, the type of frequency source is selected and the correct sensor is configured. The module supports different sources both analog and digital as well as direct input of the frequency channel

Frequency source: Counters, Analog pulses, RPM channel

Sensor: Tacho, Encoder, CDM, Geartooth, X-n sensors

Frequency channel: input channel with connected tacho/counter sensor

For tipical Orbit Analysis application a third proximity probe, often called ”Keyphasor” is used. When Analog pulses frequency source is used, there will be an additional setup section that can be accessed via the three dotted icon as shown below:

By clicking on the icon, a setup for Angle Sensor Math will open as this math is used in order to detect the rotation frequency:

Further explanation of the above settings can be found in F1 manual section dedicated to Angle Sensor Math.

RPM setup

Under RPM setup section, lower and upper limits are defined as well as Delta RPM and the direction of the test.

Direction: Both, Runup, Coastdown

Delta RPM: user inputs the desired value, the lower the value the higher the resolution and the more CPU power needed.

Upper & Lower RPM limit: user inputs desired values, they should corresond to the values of the measured rotor.

Calculation setup

Calculation parameters are set up under the following section, such as: list of desired harmonics, type of FFT window, resolution and update settings.

Harmonic list: input desired harmonics for calculation (e.g. 0, 1, 2).

Order resolution: 1, 1/2 , 1/4 , 1/8 , 1/16, 1/32, 1/64.

Max order to analyse user selects the highest order to be included in the analysis. If set to lower than 32, this needs to be configured also in Options\Settings\Extensions\Order tracking.

Time FFT lines: supports Auto, predefined values selection from dropdown or arbitrary definition of number of lines. Affects the FFT cascade output, higher number of lines results in better resolution and higher CPU load.

FFT window: Blackman, Rectangular, Hanning, Hamming, Flat top, Triangle.

Amplitude: toggle amplitute to be displayed on bode & polar plot.

Frequency axis unit: user selects the desired units for frequency axis - Hz or CPM.

Update interval: user inputs desired values. Buffer duration is calculated according to the input value and is displayed as an output message in orange on top of the ch. setup screen.

Order waterfall: select the desired checkbox to output either order vs. RPM, FFT vs. RPM or both as waterfall.

Machine configuration

Machine configuration setup can be further broken down into three subsections:

1 - Quick settings: selection between Pair/Mono configuration of proximity probes, clockwise or counterclockwise(CW/CWW) shaft rotation direction, assignment of the input channel to which proximity probes are connected as well as their Angle and Position.

2 - Measure: by pressing this button, DC gap is measured and compensated for

3 - Setup: opens additional settings for the bearing, further explained in the following section

By clicking on the + button, additional bearings are added to the machine train.

All bearings in the same machine train use the same frequency source so this configuration is suitable for measuring bearings on the same shaft or shafts with the same gearing.

If you measure on multiple bearings that are located on different shafts where each has its own rotating frequency this can be configured by adding another instance of Orbit Analysis module and assigning the corresponding frequency source.

In such cases, each shaft needs its own sensor as a frequency source or alternatively, if the gearing is known, the tacho for the subsequent shafts can be derived from mathematical multiplication or reduction of the tacho signal from the first shaft.

Bearing setup

When selecting Setup subsection, a pop up dialogue appears with advanced bearing setup options.

1 - Component properties: input field for user defined name, typically corresponding to the measured bearing

2 - Sensors: expansion of Quick Settings with visual representation of set parameters. This section is dedicated to configuring the proximity probes and tacho - position, angle and assignement of input channels to which the sensors are connected.

3 - Runout compensation and reference orbit: : dedicated dropdown for selection and definition of runout compensation or reference orbit. input data into the designated table or simply paste/import it from elsewhere.

4 - Shaft: set shaft rotation direction(CW-clockwise, CWW-counterclockwise) and starting position

5 - Clearance: select clearance circle shape(circle or ellipse) and input its size

6 - Average orbit: define number of periods shown and averages taken into the average orbit calculation

7 - DC Gap manually input DC Gap if the value is known and does not need to be measured

Measurement

Orbit analysis comes with a set of designated widgets needed for precise analysis and representation of results. These widgets can easily be configured to show standard parameter combinations used in orbit analysis. Different standard displays are further elaborated in the following section.

As with any other Dewesoft module, additional inputs can be easily added and shown on the same or different display. Below is an example of Orbit Analysis measurement display.

Orbit analysis widgets

Below is a list of typical displays used in orbit analysis that can easily be created using predefined display widgets within Dewesoft Orbit Analysis.

Raw orbit with clearance circle

In the predefined measurment display there are two Orbit Plots by default and on any of the two, Raw Orbit can be displayed. To switch on also the clearance circle, please select the Clearance checkbox under Drawing Options on the left side of the screen:

Raw orbit is seen in turquoise on the graph with clearance circle in orange.

X and Y mark the position of proximity probes, whereas T marks the tacho’s position.

Rotation direction is also shown on the graph with an arrow.

Shaft centerline with clearance circle

Displayed on Orbit Plot, by assigning Shaft Center to it and switching on Clearance in the left side settings tab for Orbit Plot.

Shows shaft centerline movement in white vs. RPM inside the clearance circle.

Full motion graph

Full motion graph consists shows Shaft centerline, Clearance circle and Raw orbit on the same display widget.

Average orbit with clearance circle

This representation is created by assigning Average Orbit channel to the Orbit Plot and switching on Clearance in the left side settings tab for Orbit Plot.

Average orbit is seen in white on the graph with clearance circle in orange.

X and Y mark the position of proximity probes, whereas T marks the tacho’s position.

Rotation direction is also shown on the graph with an arrow.

Nx/Filtered orbit

Depending on the list of harmonics to be extracted, there will be a harmonic orbit available for each order. They can be shown directly on Orbit Plot.

Above display widget shows example of filtered orbits in red, white and orange. The particular orbits shown are: 1X(Red), 2X(White) and 3X(Orange).

In addition, the software supports extraction of Subsynchronous/subharmonic orbit, that can be displayed in the same way as the harmonic ones.

Polar plot

For each probe per bearing, a dedicated Polar channel is created by the Orbit Analysis module. To represent the data, a dedicated widget is available - Polar Plot.

A single display in polar plane displaying phase and amplitude(displacement) at certain RPMs.

If your test consists of different states of the machine e.g. runup, coastdown the polar plot will take into account the state of the user input control dropdown on top of the screen. Depending on the state selected there, data will be written in dedicated channel for runup and a different one for coastdown - this way it is easy to disctinct the two and both sections can be shown on the same Polar Plot, using different color for each.

Bode plot

Display widget for complex channels with different available data to display: Phase, Magnitude, Real and Imaginary components.

Waterfall

Both order vs. RPM and FFT vs. time waterfalls are supported. Above image shows and example display of order waterfall vs. RPM with added digital display for speed.