Condition monitoring of rotating equipment is a PM process where a significant change in condition is indicative of a developing failure. By definition, you are simply measuring what the condition was last week and comparing it with this week. Your first measurement is called your "baseline".
The most rudimentary form of condition monitoring is visual inspection. The experienced machine operator, or maintenance technician, notices that a particular machine is operating differently from last week: increased noise, vibration, temperature, etc... Or there could be cracking, leaking, corrosion.
The most commonly used method of monitoring equipment condition is with vibration analysis. The simplest form of vibration monitoring is to measure a value(usually amplitude), over the course of time, and trend it. If a machine is operating normally, the overall vibration levels will hold steady within a given range. If the amplitudes increase at a steady rate, it could be normal machine wear, or it could indicate bearing, gear, or seal wear. The increased value over your "baseline" gives you the relative condition of your machine.
The amplitude could spike higher(double or triple in value), which could indicate an imminent component failure, or at least a drastic change in the operation of the machine. Now is where vibration signature analysis, or spectral analysis, is used to determine machine condition. A baseline vibration signature collected during initial startup of a new, or repaired, machine can be compared with this most recent vibration spectrum.
Interpreting the information contained in the vibration signal is only as good as the experience & training of the technician. If spectrums are collected regularly(monthly or quarterly), the analyst may have been able to see a particular frequency spike steadily increasing and maybe even identify the cause, or predict it's alarm point, or impending failure. Comparing the spectrum to a baseline "picture" is important to effective condition monitoring.
Baseline vibration data is not just the lowest amplitude level at which a machine operates. Baseline amplitude for one machine could be alarm level for an identical(sister) machine. Spectrum analysis, in combination with other PM tools: infrared temp, shock pulse, oil analysis, etc..., will better provide the technician with everything he needs to make an informed decision on the condition of the machine.
Extending the working life of equipment, and preventing expensive downtime delays, is the purpose of preventative maintenance. And as any good mechanic knows, you can't do the best job without having the right tools. Invest in PM, it will save you money!
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