What is Real Life ODS

Real life ODS is a new way to visualize the vibration of a machine in the same way you used to do it using conventional ODS. Thanks to the technology developed by Erbessd Instruments you can collect data with your accelerometers and after that, just take a picture and you’re ready to complete a motion magnification analysis.

ODS analysis

Operating Deflection Shape (ODS) analysis is a widely used method to analyze vibrations on machinery systems and even civil engineering structures under external unknown forces. These forces may include engine speed, unbalance, misalignment, load, temperature, pressure, etc.

Traditionally, this type of analysis requires to create a 3D CAD model and obtain vibration data measured in the field with accelerometers to obtain a 3D animation that exemplifies the vibration effects on the machine or structure. However, the creation of such accurate 3D motion magnification studies is very time consuming because 3D models are not typically readily available and must be developed Furthermore typical vibration analyst’s and engineers do not necessarily have the skills required to create the aforementioned 3D model. Traditional ODS analysis has proven to be a valuable tool for troubleshooting of mechanical and hydraulic problems and a traditional 3D ODS module is already included in our DigivibeMX® Software.

Real-Life ODS Technique

Real Life ODS allows us to save precious time by removing the need of a 3D model, and achieve the visualized motion magnification with a single still image of the subject.

First, the user loads the signals, photos of the equipment and selects the measured points. Next,  DragonVision applies bandpass filters to the spectrum (FFT) to eliminate noise. Finally, the program creates 2D amplified vibration animations that contain projected 3D data from the combination of time series and frequency data by applying the Real Life ODS method to the image.

The resulting map shows small, and high frequency displacements and deflections that were not visible to the human eye.

How to do Real-Life ODS

Data collection for Real Life ODS with accelerometers is identical to the traditional vibration measurements. The advantage of this technique is that it allows you to achieve motion magnification from a wide variety of sensors and frequencies, ranging from very low frequencies in the case of civil engineering and ground vibration data, to high frequencies, e.g. High-speed turbines. The motion magnification data accuracy, amplitude, resolution and sensitivity depend solely on the selected accelerometer according to your specific needs. This ensures a fully calibrated signal and model and thus far out-performs typical video deflection analysis technology as developed by ERBESSD INSTRUMENTS and others that use similar video vibration data analysis methods.

Choosing the right accelerometer for Real-Life ODS

For any vibration analysis with accelerometers, it is important to keep in mind that the maximum amplitude and frequency range of the measured vibration determines the sensor range needs. When measuring vibration that is out of the specified range for the sensor, the signal will be distorted or saturated due to non-linear electrical response.

Another important parameter when choosing an accelerometer is its sensitivity. This parameter usually is expressed in mV/g (millivolts per gravity units or millivolts per 9.81 m/s²). For example, if an accelerometer has a sensitivity of 100 mV/g and the measured signal is 10 g, it is expected to obtain 1000 mV electrical output reading. Typically, this value is constant for a given frequency range of each sensor. As a rule of thumb, low sensitivity accelerometers have a higher amplitude range and high sensitivity accelerometers have low amplitude range.

For better motion magnification results it is recommended to use a single axis accelerometer (as the reference sensor) and one “mobile” triaxial accelerometer for measuring different points of interest.  The following is a summary of the workflow in our DragonVision Motion Magnification Software.

Once in DragonVision Real-Life ODS Software

• Take at least one still photo of the system that is being analyzed, where most of the measured points are shown. We recommend an isometric view of the whole system to visualize the 3D components of acceleration. However, if more views are required (e.g. top view, side view, etc.) you can capture more images to produce animations of multiple views. There is no minimum nor maximum requirement for the camera resolution. However, we recommend at least 2 MP image resolution (equivalent to Full HD resolution) for the best animation results. DragonVision is compatible with JPG, PNG, BMP and TIFF formats.
• In DragonVision, load one image and load the signals recorded in the field.
• The single axis accelerometer is now used as a reference to synchronize all the measurements done with the triaxial sensor, the resulting signals should all be in phase.
• In the loaded image, draw the H, V and A axes according to the accelerometer measurements orientation. This step is important to calibrate the angle of the photo with the accelerometer components and obtain the proper vibration projections within the model.
• For each measured point, select the corresponding region in the photo to generate its warp points and assign the corresponding signal/spectrum (automatic point detections or grid points). The deformed animation will contain the values from the spectrum in the points generated. For the rest of the deformed image, DragonVision will automatically interpolate amplitude values. Automatic point detection is recommended when generating a quick preview of deformation without masks. Grid points are recommended when a polygonal mask is used to draw the contours of the region to be deformed.

Machine before and after balancing process.

Why use accelerometers in Real Life ODS?

Vibration Analyzers most commonly use Accelerometers due to their excellent frequency and amplitude range as well as the low floor noise. In return, they convert acceleration into other parameters like velocity and displacements which are more frequently used in vibration analysis.

For example, with the help of our wireless  triaxial accelerometer Wiser 3X, you can get 3D vibration spectra up to 15,000 Hz with a sensitivity of 100 mV/g with remarkably high precision due to the great spatial and temporal resolution provided by field-proven accelerometers. With this, you will be able to detect bearing issues, gearbox problems and much more.

Additionally, DragonVision is compatible with 3^rd party accelerometers so you can start generating Real Life ODS visualizations right away and the accuracy and resolution is only limited by the type of accelerometer you use.

Motion Amplification/Video Vibration Vs’ Real Life ODS

In contrast, Video Vibration Software uses cameras to record the vibration in 2D and are limited by the recording resolution and framerate. For instance, using a common cellphone camera allows you to detect frequencies only up to 120 Hz (slow motion mode with iPhone). This video vibration technology becomes inherintly more expensive as motion based video vibration analysis such as those developed by others in the market is cost prohibitive and requires a dedicated PC for post processing.

In the case of  cost prohibitive, specialized high-speed cameras you could get vibration spectra only up to 6,250 Hz (Phantom V2640 12,500 fps @ Full HD resolution). While this is useful to have a big picture of the behavior for a complete area, it lacks accuracy when analyzing more in-depth problems in your machine components. Moreover, when measuring with video vibration analysis, one must be very careful about the position and calibration of the camera to obtain accurate 2D data. (It is important to mention that is nearly impossible for actual single camera motion amplification techniques to accurately measure 3D displacement or 3D acceleration and they just provide data of a 2D projection, nor is the calibration NIST traceable). 

Most real problems require 3D information or high sampling frequencies to get a proper diagnostic, and this is where video based Motion Amplification fails.