SYNCHRONOUS, ASYNCHRONOUS &
SUB-SYNCHRONOUS SPECTRUM ANALYSIS
The raw
vibration data consists of a wide range of frequencies & it’s analysis in
raw form is very complex job. To analyse the data, we have to take the help of
technology. FFT Analysis is a very good tool for analysing rotating assets. Raw
vibration signal can be analysed in three ways-
·
Synchronous Vibration Analysis
·
Asynchronous Vibration Analysis
·
Sub-Synchronous Vibration Analysis
Synchronous:
The synchronous time averaging technique is used to detect the source of
vibration at the 1X frequency. 1X frequency is the running speed of the
machine. The vibration probe collects the data & the speed probe give the
speed information mounted on the reference shaft. This running speed is tracked
& the time averaged 1X data is monitored & analysed. This is very
useful in the machine trains with variable speeds or if many other machines are
running at close proximity to machine under measurement. Rotor related problems
like imbalance, misalignment; rotor related looseness & rotor rub can be
identified by using this technology. Other peaks are discarded.
Asynchronous
Vibration Analysis: Asynchronous time averaging technique is used to detect the
vibration components that are not related to rotating speed & are above 1X
speed i.e. above the running speed. These faults are bearing fault, electrical
noise, cavitation, etc. Resonance also produces asynchronous frequencies.
Sub-Synchronous
Vibration Analysis: Sub-synchronous time averaging technique is used to detect
problems like severe bearing looseness, rotor rub, vibration from nearby
machines, belt vibrations & other low frequency components. These are below
1X running frequency.
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