When Vibration Alarms are Useless

by | May 2, 2019 | Predictive Maintenance, Vibration Analysis

We all rely on alarms.

They wake us up.  They warn us when there is too much smoke or carbon monoxide in our homes.  They warn away anyone who might try to break into our house, our business or our car.

Therefore, it might seem like using alarms as part of your organization’s predictive maintenance (PdM) program is a no brainer.  After all, it would save a lot of time and effort if you could replace vibration analysis with an alarm system.  Wouldn’t it be nice to just set it and forget it?

The technology is certainly available, and the most popular is the overall alarm, which generally includes thresholds for safe, warning and danger.  Setting up overall alarm levels for each piece of equipment allows the analyst to ignore the “good” equipment, reducing the amount of equipment that needs to be analyzed, saving precious person-hours.  This way the analyst has more time to review equipment in critical condition.

That seems like a win, right?

Well, yes and no.

Think about the smoke alarms in your house.  Ever had one go off while you were cooking?  There you are, spatula in one hand and potholder in the other, standing on a chair trying to pry the alarm off the ceiling to get it to quit shrieking.  There is not a fire, but you will never convince the alarm of that!

You could encounter a similar problem with your overall alarms.  An inaccurate alarm doesn’t do you any good at all.  There are plenty of ways an overall alarm can be inaccurate:

  • Overall vibration levels are affected by many process-related conditions such as load, machine configuration, ambient temperature and accelerometer placement.  These factors can combine to make a machine that is actually in stable condition appear to be at fault
  • Many leading indicators of machinery failures are low in amplitude and can appear in a machine’s vibration signature without significantly increasing the overall vibration levels.  For example, frequency changes are indicators of machine faults that can occur without significantly raising overall alarm levels.  Low amplitude leading indicators like bearing defect frequencies can be completely overlooked on a machine that is within a “safe” overall vibration level.
  • Setting and managing the alarm levels is another issue an analyst must address.  If alarm levels are set too high, the risk of missing an indication of potential failure is higher.  If the alarm levels are set too low, most of the equipment will trigger alarms during collection.  Once set, alarm levels must be constantly maintained to ensure they are appropriate for the given machine.

All of which is to say; an analyst who relies completely on overall alarm levels must accept a higher risk of unforeseen equipment failure due to missed warning signs.  An alarm that does not alert you to warning signs is hardly an alarm at all!

Nevertheless, do not be alarmed (see what we did there?).  ATS is ready to help you set up a vibration analysis program that gets you accurate information when you need it—which is all the time.  Don’t hit snooze button.  Let us get to work for you right away.


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1 Comment

  1. Dennis Kiene

    I do not depend on overall alarms. I use band alarms and % of change alarms(% up or down). Have found these very useful and dependable over the years.


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