	Laborelec/ULB research
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ULB: click on icon ULB for home page The engineering school of ULB covers a wide range of disciplines. Among these are Mechanical Engineering, where most of the experimental test rigs are concentrated in the Department of Applied Mechanics (SMA)

Headed by Prof. Leduc.

Laborelec is the Research Center of the Belgian Utilities located in StGenesius Rode B-1630 LINKEBEEK BELGIUM.

Outline

This page summarizes some of the results from a joint research programs between Laborelec and SMA-ULB on a few selected topics about predictive maintenance for rotating machinery.
It supplies some software developed during this program. They are all wriiten in LABVIEW to produce virtual instruments (vi 's).

In order to escape the ghetto of the laboratory, many of these vi's are being migrated to powerful portable PCs to extend the lab experience to field use.

The increasing execution speed of such portable PCs

with PII 400 100MHz bus (already 2 years ago! ),
plenty of SDRAM
AGP graphics adapters (better now with games)
PCI-based versatile multi-purpose data acquisition cards like the PCI E series of National Instruments

allows to combine in a single portable PCs an array of advanced diagnosis virtual instruments. This is a shortcut to avoid moving cargoes of dedicated and expensive devices to perform advanced field diagnosis. It si also the door open to escape proprietary solutions from vendors confining themselves to pure S&V products.

Also possible: an industrial interface for field application in front of the NI series card featuring isolation amplifier to remove all ground loops between the MIO and the field sensors (e.g. 4-20 mA based) plus floating gains and offset and AC/DC couplings in front of the isolation amplifiers plus antialiasing filters. All these features are fully programmable from the PC via the MIO card. Armed with such an interface, one can then perform field measurements without endangering the industrial process by sampling the signals of sensors used in such critical applications as control loops. Without proper ground-loop isolation, you may trip important processes. Always keep this in mind when moving from the lab to the field.

Topics of research

Topics of predictive maintenance focused on defect signatures in rolling-element bearings, due to shaft and bearing misalignments, in gear boxes due to tooth profile wear and mounting inaccuracies, shaft vibrations as caused by unbalances, misalignments, rubs, thermal growth alignment problems, etc.. with some topics off the beaten track...

An odd topic is pdm of generators. It focuses on HV insulation problems, although vibrations of bars in slots and endwindinsg are ofen the root cause of insulation problems.

Use of test rigs

Using industrial-scale test rigs shown in the various sections below to simulate generic defects, one gathered sound, vibration and stress-strain signatures.

Data processing techniques

The signatures were then data processed with advanced methods such as cepstra, joint-time-frequency methods, double-sided Fourier transforms, time-frequency spectrograms, integration and various filtering schemes( FIR and IIR). Rather easy with Labview and its toolkits and fool-proof for field engineers.

Special data acquisition schemes

Signatures in rotating machinery require different and sometimes sophisticated data acquisition schemes ranging from

asynchronous fixed time-base data acquisition for roller bearings in the vibroacoustic frequency range. Rather straightforward. Then one must sample signatures over a longer time span depending on the geometry of the bearing and its rotating speed. Then based on energy criteria, one must zoom the fianl buffer for data processing to correspond to
phase-locked and variable frequency data acquisition for shaft vibrations allowing phase retrieval without leakage and periodic averaging
data acquisition phase-locked with the revolution of both pinions and gear in a parallel gear box in the vibroacoustic range for period averaging phase-locked with precise pairs of meshing gear profiles. This phase-lock scheme requires two singletop/rev references one on each pinion.

A good acquisition scheme for problems related to rotating machinery is very useful prior to data processing. Vibrations (and structure-borne sound for that matter) are often indexed with the shaft revolutions (cam shaft in internal combustion engines)

Phase-locked data acquisitions at frequencies multiple of the shaft rotational frequencies can either be implemented via

incremental encoders mounted on the shafts whose outputs are used as external clocks dor data acquisition
from a single top/rev triggering the start of the data acquisition at an fixed oversampling rate. The data buffer is then decimated to produce a power of 2 samples per shaft revs. The decimation scheme is driven by the successive occurrences of the tops per rev. In the past, this last approach turned out to strain the capacity of older PCs. No longer. Besides it is convenient since it does not require the retrofit of encoders on existing machines. It is implemented in real-time on the PCI MIO E-1 card from National for all the applications below.

Try the executable version of vi's (some with complete Windows installers)

For fun , we are adding vi's to see how they perform the different diagnosis tasks. In this way you can get some advanced training in:

Diagnosing rolling-element bearing surface faults (6 Mbytes with data files and vi): a departure from spike energy, PeakVue,

acceleration enveloping focused on detection instead of severity.

Performing time-frequency analyses on gear train vibroacoustic signatures (9 Mbytes with data files and vi)
Getting acquainted with full spectra for shaft vibrations with positive and negative frequencies (watch for future facelift for this simulation vi which is next)
Newest is a full package for vibration monitoring of large power trains with a Windows installer (last entry in the Table below). With very multiple input/output E series cards from National Instruments (e.g. PCI 6204)

Main research topics can be selected by clicking on the pictures below. For more information download pdf files where available.

pdf document	A Labview mini expert to identify defects in anti friction bearings. How to make a smart use of the kinematics and dynamics of anti friction bearings.
pdf document	Static and dynamic reactions of flexible couplings in presence of misalignments and torques. Never quite believe that some flexible couplings are that flexible!
pdf document 1 (general) pdf document 2 (JTFA for gears)) pdf document 3 (fine analysis) pdf document 4 (timefreq notions)	Gear diagnosis using time frequency analyses in LABVIEW. A primer. For more information download pdfs. Click on the left-hand side picture to move to
pdf document primer for full spectra try this requires some facelift...	A Labview shaft vibration analyzer with synchronous sampling and vibration vectors. No link yet. Read the pdf file instead. Full spectra in Labview as defined by Bently Nevada.
Vi Panel for Thermal Growth	Bearing alignment with Labview and permalign. A vi front panel for thermal growth with real data from a large turbosets during shutdown.
	Recasting the problem of shaft and bearing alignment in large turbomachinery as a problem of material strength. Your comments are welcome!
	High-voltage generator and predictive maintenance (some pdf and doc are pass word protected) How to monitor HV insulation integrity plus related topics.
Acrobat document: some application of virtual instrumentation	Summary of bearing, coupling, shaft vibration and NDT applications
	Virtual instrumentation in the field during railways tests. Click on the left-hand side phot to know more about this in a pdf file (in French).
How to find us	A detailed map of the freeways around Brussels, completed by a street map and a map of the old campus of the free University of Brussels where the SMA is located.
Hardware/Software.	This site may be interesting for people wishing to move their Labview lab applications to the field. an NI E series card + Labview drivers with examples + programmable antialiasing filters + ground-loop isolation +floating programmable offsets and gains
Click on the above picture to get a full demo executable package for vibration monitoring if you have a NI E series card.. 14 Mbytes Windows Installer. Worth trying....	If you have a standard E series card from National Instruments, you can monitor vibrations of rotating machinery in real-time, complete with vibration vectors (nyquist), waterfalls, digital single and double integrations of velocity pick-ups and accelerometers, trends, etc.! Thanks to the rise of PC computing power and Labview 6.