Learn to Love Vibration with our Glossary of Useful Vibration Analysis Terms

February 14, 2013

Average – In vibration analysis, an average usually refers to the process whereby the vibration software will, after converting waveforms into spectrums via FFT, add the resultant spectrums together and then divide by the number of spectrums added together. The result is an “averaged spectrum”.

Band – A band is simply a range of frequencies e.g. A band from 0 Hz, to and including 5 Hz, is a band that is 5 Hz wide.

Band Pass Filter – A filter that blocks all data above and below its defined band.

Condition Monitoring – The use of specialized equipment to deduce the actual condition of equipment as pertains to its fitness for continued use. Condition monitoring is the foundation of Predictive Maintenance and the two terms are sometimes used interchangeably.

Cycles per minute (CPM) – In vibration analysis, cycles per minute refers to the number of vibratory cycles that occur in one minute of time. Cycles per minute is a quantity of frequency.

Cycles per second (CPS) – In vibration analysis, cycles per second refers to the number of vibratory cycles that occur in one second of time. Cycles per second is a quantity of frequency.

Enveloping – Enveloping, also known as envelope de-modulation, is a data processing technique whereby a spectrum is created from a demodulated or filtered waveform.

FFT – Fast Fourier Transform (FFT) is a mathematical process that transforms a waveform into the components of its frequency spectrum.

Fmax – Fmax stands for “maximum frequency”. It is the high frequency boundary for a set of data.

Fmin – Fmin stands for “minimum frequency”. It is the low frequency boundary for a set of data.

Frequency Markers – These are visible marks that can be overlaid on a spectrum at specific frequencies to help identify likely machinery problems.

Hertz (Hz) – The same as “cycles per second”.

High Pass Filter (HP) – This filter blocks all data below it and only allows the data that is higher to “pass” and be recorded. It determines the “low frequency cutoff” or Fmin.

LOR – LOR stands for “Lines of Resolution”. It is the number of digital bins of amplitude information a spectrum will be constructed from.

Low Pass Filter (LP) – This filter blocks all data above it and only allows the data that is lower to “pass” and be recorded. It determines the “high frequency cutoff” or Fmax.

Negative Averaging – A procedure whereby, having previously taken a reading, a second reading is taken and all data in the first reading that matches data in the second reading is subtracted.

% Overlap – % overlap is the amount several otherwise sequential waveforms, being sampled and averaged into a spectrum, will “overlap one upon the other” as they are being sampled.

Peak-to-Peak – The measure of vibration amplitude in a waveform, from the negative peak to the positive peak.

Unbalance – A measure that quantifies how much the rotor mass centerline is displaced from the centerline of rotation.

Waveform – In vibration analysis, a waveform is a display of vibratory energy over time.

 

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