Vibration measurement and analysis

Broadband vibration measurement is the most widely used and cost-efficient method for the diagnosis of overall machine condition. There are two ISO recommendations concerning machine condition monitoring using this type of measurement; the much-used ISO 2372 and the more recent ISO 10816, which is a replacement of the older standard.

Features

  • Reliable diagnosis of overall machine condition

  • Condition monitoring based on ISO recommendations

  • Vibration severity measurement to detect common machine faults such as imbalance, structural weakness, loose parts, etc.

  • Evaluated vibration analysis with three sets of machine condition data in our diagnosis and analysis software

 

Technical description

ISO 10816

Measurements are made in three directions (horizontal, vertical, and axial). Machine condition is generally diagnosed based on broadband vibration measurements returning an RMS value. ISO 10816 keeps the lower frequency range flexible between 2 and 10 Hz, depending on the machine type. The upper frequency is 1000 Hz.

ISO 10816 operates with the term vibration magnitude, which, depending on the machine type, can be an RMS value of vibration velocity, acceleration or displacement. If two or more of these parameters are measured, vibration severity is the one returning the relative highest RMS value. For certain machines, ISO 10816 also recognizes peak-to-peak values as condition criteria.

The ISO 10816 standard consists of several parts, each involving a certain type of machine, with tables of limit values differentiating between acceptable vibration (green range), unsatisfactory vibration (yellow range), and vibration that will cause damage unless reduced (red range).

Vibration analysis (EVAM)

EVAM stands for Evaluated Vibration Analysis Method. The method generates three sets of machine condition data:

  • Condition parameters, which are measured and calculated values describing various aspects of machine vibration;
  • Vibration spectra, where significant line patterns are found, highlighted, and evaluated with the help of preset fault symptoms;
  • Machine specific condition codes (green, yellow, red) and condition values, based on a statistical evaluation of the condition parameters and fault symptom values.


For each measuring point, the user can make an individual selection and define the type of data best suited for the surveillance of a particular machine. Alternatives include:

  • enveloping
  • time synchronous averaging
  • band alarms and averaging of measurement results for improved alarm reliability
  • time signal analysis for a detailed evaluation of all kind of symptoms direct from the raw signal

Random high readings caused by resonance or other sources of disturbance are filtered out, minimizing the number of false alarms.

Time signal analysis

The time signal is the source for all evaluation and calculation of frequencies from the machine. The time signal is the electrical signal coming from the transducer. It gives a reflection of all events happening in the machine. It shows the time between events and how much energy is generated from the event. It is possible to distinguish between various faults that occur with the same pattern in an FFT spectrum.

Condition parameters

Condition parameters are measured for a selected frequency range. They can be individually activated and are shown in measuring result tables and as diagrams. Available condition parameters are:

 VEL  RMS value of vibration velocity
 ACC  RMS value of vibration acceleration
 DISP  RMS value of vibration displacement
 CREST  Crest value; the difference between peak and RMS
 KURT  Kurtosis; the amount of transients in the vibration signal
 SKEW  Skewness; the asymmetry of the vibration signal
 NL1-4  The noise level in the four quarters of the frequency range


Peak and peak-to-peak values are shown in the unit selected for the time signal.

Spectrum analysis with 'symptoms'

For easy pattern recognition in spectra, EVAM supplies a range of ready-made 'fault symptoms'. These are instructions to highlight a spectrum line pattern and display the sum of the lines' RMS values as a symptom parameter (which can be evaluated and trended). Most fault symptoms are automatically configured by using the rpm as a variable. Some require an input, e. g., the number of vanes on a rotor. Suitable symptoms and symptom groups are selected from a menu in the Condmaster analysis and diagnostic software when the measuring point is set up.

Machine specific condition codes

In Condmaster, alarm limits can be set on all active parameters. Once measuring results are collected, an EVAM 'criterion' can be created that compares new parameter values with the statistical mean value and displays a dimensionless condition value against a green-yellow-red scale.

Phase measurement

The phase is a time delay expressed in degrees of rotation. We calculate the time delay between the passage of the tachometer pulse and the peak of the frequency component of interest from the vibration transducer at the speed of rotation. The value presented is a relative angle, not an absolute, because there is no compensation for phase lag in the transducer or the electronic circuits.

Learn more

Learn more about our High Definition technologies providing extremely long pre-warning times, thus maximizing the horizon for maintenance and repairs.

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High Definition Shock pulse monitoring in a very broad RPM range, even on ultra low speed applications (0.1 - 20 000 RPM range). Instant evaluation of bearing condition is given in an easily understood green-yellow-red color scheme.