Efftek Diagnostic Engineers

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Condition Monitoring Services for Industry

 
     
   

Vibration Analysis

VA forms the backbone of any condition monitoring program. One reason it is so extensively used is because unlike certain other CM techniques, VA is applicable to virtually all sections of a machine train whereas some CM methods can only be carried out on the motor, the gearbox or the fan, pump etc. as you can see from the diagram below.

What CM methods can we use

  Motor Gearbox

Pump

 
  Current Analysis Lube Oil Pressure  
  Temperature Noise Flow  
  Vibration Vibration Vibration  

 

People have been doing vibration analysis long before anyone had heard of 'Condition Monitoring'

The old screwdriver trick is one of the longest standing methods of CM however, it is very subjective. What one person may consider excessive is another persons smooth!

 

 

But, using modern instruments, vibration levels can be very accurately recorded and compared to ISO and British standards for vibration levels.

 

 

However, VA is most powerful when we can also compare it to previous readings from the same point and trend how quickly a problem is developing.

 

 

Vibration analysis is also very powerful at identifying exactly what type of fault is developing on which component. How? well, all rotating and reciprocating machinery will vibrate. The different components will vibrate at their own rotational frequency. All these vibrations are mixed up together in a complex vibration waveform. Information about the condition of that machine is contained within that waveform.

As a fault develops, so the waveform will change and increase in amplitude. Vibration analysis is a non intrusive method of collecting these waveforms and using a mathematical process known as a fast fourier transform or FFT which was originally invented by some old French mathematician geezer (Joseph Fourier 17681830), this information can be broken down into its component frequencies producing a spectrum showing vibration amplitude against frequency. Analysing this spectrum can give prior warning of component failures thereby reducing the risk of unexpected breakdowns.

VA, the Efftek way

Three types of radial reading are taken at each collection point on a machine, usually in the vertical plane;

Standard Velocity Spectra detect a wide range of faults such as looseness, misalignment, mass imbalance and insecurity. These spectras can be compared against the relevant ISO and BS standards for vibration levels on rotating equipment. They can also be converted mathematically in the software into both acceleration and displacement spectras giving further insight into the machine condition.

High Frequency Band (HFB) acceleration readings indicate poor quality lubrication and early stages of bearing and gear defect.

Enveloped Signal Processing (ESP) extracts rolling element bearing defect information from bearing housing resonance to give an excellent indication of bearing condition. This is THE MOST important technique available and should always be included in any CM program as it identifies bearing defects well in advance of a problem showing up in a standard velocity spectra. Download our VA Case Study presentation to see how accurately it picked up a developing motor bearing defect.

In addition, an axial velocity reading taken from each section gives a more complete picture of machine condition.

In most cases, a monthly VA survey is carried out by a CM engineer visiting site and collecting data using a hand held vibration analyser/collector, however, in some instances assets may be deemed critical enough to warrant continuous monitoring using permanently installed equipment which sends vibration data back via the internet for analysis. This actually is not as expensive as you may imagine, Please see our Vi-Fi page for further information.

All these readings are then trended in the CM software to determine if any problems are developing and if so, how quickly, and are graded according to severity.

The VA report will explain exactly what problems are developing and suggest remedial action which should be taken to prevent the machine from failing during production.

An example VA report can be found on our downloads page.

 
 
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