There are different ways to understand machinery vibration analysis that people often confuse. Is vibration the cause of the problem, the result of the problem, or both? If you confuse these, you might make some big mistakes when analyzing data! So, let’s clarify…
Vibration as the Cause
When things vibrate a lot or “too much,” it can cause a lot of problems. Excessive vibration causes fatigue failures. Shafts, couplings, bearings, seals, pipes, foundations, and any structure, can actually be damaged by excessive vibration.
Excessive vibration can also cause quality problems in our products. Imagine an HVAC fan vibrating next to a computer chip printing machine. The vibration can travel through the floor from the fan to the machine and screw up our chips. Vibration can harm humans as well and even when it doesn’t harm us, it can annoy us – just think of that unbalanced ceiling fan going “whop whop whop” while you are trying to sleep.
A metaphor I like to use is: Imagine you are driving your car really fast on a really bumpy road. If you keep driving like that, the vibration will damage your car.
When I audit people’s vibration programs and I watch how they analyze data, I often see them thinking about vibration in this way. They look at a graph, look at the highest peaks, and say to themselves “This vibration isn’t too high, the machine is OK.” Or perhaps they use ISO RMS alarm charts and compare the measured vibration to the chart. Now I will explain why this is a big mistake!
Vibration as an Effect
When we use vibration in the context of #ConditionBasedMaintenance #CBM we are frequently looking at vibration as the effect rather than the cause, going back to the car metaphor. Imagine you drive your car to work the same way every day and one day you notice a new sound. You conclude “There must be something wrong with my car!”
In this case, we are not saying that the new sound is damaging the car but rather the new noise is an EFFECT or result of the damage. It is also possible that the amplitude of that new noise might be quite low, even if the damage is serious.
In a piece of rotating equipment, consider a defect on the outer race of a rolling element bearing. The balls or rollers hit the defect as they roll over it is creating a repetitive clicking. The amplitude of the vibration caused by a ball or roller hitting this little defect on the race through a layer of grease is pretty small compared to the vibration caused by water flowing through a pump or even by the shaft rotating around – BUT – the bearing is in fact damaged – AND – if we are just looking at our vibration to see if there’s anything “High” then we might miss this important fault. This is one reason why it is NOT ok to just look at vibration in terms of absolute amplitudes.
Effect and Cause
There are some cases where the vibration is both the effect and the cause. For example, if a rotor is out of balance, the vibration amplitude will increase at the shaft rate frequency (1x). This is an indicator that the rotor is out of balance. Why do we care that the rotor is out of balance? Because the increase in vibration resulting from the unbalance can cause damage to the machine. This therefore is a case where vibration is both effect and cause.
WANT TO LEARN MORE?
Alan Friedman dba Zenco offers machinery vibration analysis courses and certification in accordance with ISO 18436-2. Click here to check out his course schedule, you can also connect with him on Linkedin. In addition to public classroom training and public virtual courses, Alan is also available for private courses virtually or on-site in addition to informal training and mentoring. Category I and II vibration are also available in Spanish.
Alan, aka the Vibe Guru, has over 30 years of vibration analysis experience, He has trained thousands of students around the world up to Category IV. One of the things that makes Alan a great teacher is his ability to teach people where they are at. Whether you are a math-challenged millwright, an engineer, or a PhD, Alan will challenge you without overwhelming you. If you are interested in condition monitoring you can also check out his book: Audit It. Improve It! Getting the Most from your Vibration Monitoring Program or hire him for an on-site program audit.
Did you know that Alan Friedman left Mobius and is now providing his own courses?
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Vibration Analysis by Diana Pereda