Vibration Analysis VS Monitoring

Implementing the proper maintenance plan will have a positive impact on the longevity of your equipment

The main approaches are:

  • Predictive Maintenance: This tends to focus on direct measurement of the item. For example, an infrared temperature gun being used to measure bearing temperatures.
  • Preventive Maintenance: This often includes the evaluation of particles in suspension in a lubricant and sound and vibration analysis machines.
  • Proactive Maintenance: These activities are designed to minimize the risk of plant or equipment failure. 

For instance…

You have bought an incandescent light bulb and the manufacturing company has told you that the life span of the bulb is three years. So, you decide to replace the bulb with a new one just before you reach the three year mark and it is scheduled for maintenance. This is called preventive maintenance. However, every day you observe the bulb in operation and, after two years, the bulb starts flickering. You predict that the bulb is going to fail very soon and decide to replace it, scheduling it for just-in-time maintenance. This is called predictive maintenance.

Companies heavily depend on maintenance to keep equipment running, but simply monitoring bearing vibrations at set intervals may not be the best way to evaluate equipment.  When monitoring and analyzing bearings on a schedule, say once per month, critical information can be overlooked.  When analyzing the trend data, the equipment may seem to be operating correctly when in fact it is not.  An example of this comes from a 2007 case study at a waste water facility in Washington, D.C.

Briefly, the wastewater treatment facility began tracking the reliability of its pumps in 2007 using vibration analysis. Working with a simple analyzer, a rotating machinery technician examined any pump with high vibrations. Due to the quantity of pumps and the multiple plant locations, it was difficult to service the pumps before they had issues.  By the time attention was given to problematic pumps, extensive repair was needed - which increased the cost as well as the downtime.

In 2009, the company shifted from taking periodic vibration analysis to a monthly monitoring schedule.  This new approach helped to reduce the cost associated with catastrophic failures.  The problem with monthly trending is that you can occasionally have higher than normal vibration peaks and they could go unseen in the overall trend data.  Even though they were having fewer failures, they were still not able to determine the problem pumps before there was an issue. After discussion with an outside consultant, it was determined that a continuous monitoring system would solve their problem.

The system consisted of a data module (DM), which was installed near the motor and pump, which had a combination of triaxial vibration/temperature sensors that were connected to the module. The DM unit transmitted a radio signal to the communication module (CM), which relayed the signal to the tower and from there to the network. Plant technicians, maintenance personnel and other operators could view the data directly on their computers, via the Internet, from any location. The results showed that vibrations spiked from a low level of approximately 0.05 inch/second (which is what the monthly single-measurement data tracked) to a high level that was close to the 0.5 inch/second alarm level.

By using the monthly monitoring schedule, the plant was made aware that there was an issue with the motor and they could now conduct an accurate analysis prior to having a failure. 

Utilization of predictive, preventive and proactive maintenance techniques allows you to pinpoint a problem, whether it is process or system related.   Determining the cause of the problem first hand not only saves time but also the cost associated with failures and downtime.