Reactive, avoidable equipment repairs are a leading contributor to lost productivity in industrial manufacturing operations. Parts with an average selling price of just a few dollars can cost manufacturers many times that in repairs and unrealized revenue once they fail. In a worst-case scenario, undetected faults can cascade through the system, causing widespread damage and triggering major and expensive production outages.

Vibration in rotating machinery typically occurs at frequencies from 6 to 10 KHz.
Historically, manufacturers have relied on preventative measures to keep their production floors up and running. While an improvement over after-the-fact repairs, preventative maintenance typically requires costly service contracts and ultimately is limited in its ability to ensure continuous equipment up-time. Consider the rotor bearings that turn the blades of a 200-foot wind turbine. Emergency repairs and spot maintenance are expensive—and in this case may even be dangerous as technicians are required to work at high elevation. Moreover, if the turbine is tied into the power grid of a local municipality, unscheduled downtime could result in lost energy production and possibly disrupt electrical service.

A new industrial sensing technology is helping manufacturers optimize their equipment by using a form of predictive maintenance that anticipates part failures. While many forms of industrial sensing exist, vibration sensing is perhaps the most effective and efficient. According to a study by Lindsay Engineering, a provider of predictive maintenance products and services based in Camarillo, Calif., vibration sensing delivers three times the return on investment of steps such as regularly changing gear or motor oil.

Benefits of Vibration Analysis

Vibration analysis is commonly used in rotating machinery to detect loose or worn bearings, equipment misalignment, or low fluid levels that might cause a change in vibration. Typically this vibration will occur at frequencies between 6KHz and 10KHz.

Other data is also available at higher frequencies, but is typically very difficult to measure due to magnitude of the response and requires expensive technologies such as ultrasound. By measuring that frequency range and monitoring changes in the response, manufacturers can schedule maintenance or bring down equipment when it is most convenient and before the part is damaged to the point where it can cause even more costly secondary system failures.

Additionally, various statistical formulas, such as mean time to failure (MTTF) and mean-time- between-failures (MTBF), can be used to forecast the life of the system. Utilizing those formulas, along with raw data from the system will allow customers to focus directly on the potential problem. For example, using MTTF you find out that a certain bearing has a high degree of failure, you can use a vibration sensor to carefully monitor that particular machine and bearing to make sure that the failure does not happen.

The two most common means of implementing industrial vibration sensing are to retrofit existing equipment with sensor systems or contract with a third-party service that conducts regularly scheduled equipment tests. The latter option can be expensive, and periodic checks are less effective than mounting sensors directly to the equipment. The system-mount approach affords manufacturers continuous monitoring but this option has also had historical limitations.

The majority of today’s vibration sensors typically operate below 5 kHz of bandwidth, which is significantly lower than the frequency at which most equipment failures can be detected. Additionally, conventional sensors are most often based on high-voltage piezoelectric technology that requires a bulky metal-can package, and the devices demand frequent calibration and are not easily manufactured in large volumes.

MEMS Approach

MEMS sensors such as Analog Devices’ ADXL001 sensor can sense component failures at frequencies up to 22 kHz, thus providing early warning of equipment malfunctions.
An alternative to piezoelectric vibration sensors is the more recent development of micro-electro-mechanical-system (MEMS) sensors. Able to operate in harsh industrial applications, MEMS devices such as Analog Devices’ ADXL001 sensor are able to sense component failures at frequencies up to 22 kHz, which enables the early detection of potential equipment malfunctions.

In contrast to large metal-can sensors, MEMS-based devices are available in packages as small as 5mm x5mm and operate on industry common supply voltages, allowing for easy integration into the majority of applications. This not only allows system designers to retrofit their equipment with smaller, more accurate MEMS devices, they are able to begin integrating vibration sensors directly into the programmable logic controller or motor control at the point of original system design.

MEMS vibration sensors are robust, using ceramic package technology that originally was developed for automotive operating environments, and they require no calibration, which simplifies implementation and subsequent vibration monitoring.

The upshot is that today’s industrial equipment manufacturers are finally gaining access to an accurate, reliable, designer-friendly and affordable sensing technology that addresses one of the industry’s most costly—and preventable—productivity issues. Already in use in the automotive industry for more than 15 years, MEMS sensing is a proven technology that promises to significantly improve equipment up-time and usher in the era of predictive maintenance.

This article was written by Max Liberman, Product Marketing Engineer at Analog Devices, Norwood, MA. For more information, please contact Mr. Liberman at This email address is being protected from spambots. You need JavaScript enabled to view it., or visit http://info.hotims.com/15140-329.


Motion Control Technology Magazine

This article first appeared in the October, 2008 issue of Motion Control Technology Magazine.

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