Whether your company is thinking about starting a machine condition monitoring program or expanding one, certain questions inevitably arise: What will this program do for us? What equipment do we need and what will it cost? How do we start?

Knowing the answers to such questions before starting a condition monitoring program can mean the difference between saving thousands of dollars or making a large investment that won’t pay off.

What is condition monitoring?

Broadly speaking, condition monitoring is the process of collecting operating information from a machine while it’s running to detect changes in the machine’s condition that may lead to failure. When such changes are detected, users analyze this data to determine the cause of the problem, pinpoint the faulty component, and predict when it will fail.

With sufficient warning of an impending problem, maintenance personnel can inspect the equipment, evaluate options, and take the best corrective action. They can schedule repairs at a convenient time long before the machine fails.

This method of combining machine condition monitoring with predictive maintenance reduces the possibility of catastrophic failure, keeps machinery running for longer periods, reduces downtime, and minimizes spare parts inventories.

The condition monitoring approach sure beats the old run-to-failure method with its unexpected downtime and costly repairs! It also avoids some of the drawbacks of preventive maintenance programs, which typically consist of periodic machine inspection, followed by overhaul and parts replacement to prevent failure. Though preventive maintenance reduces unplanned shutdowns, repairs may be premature, causing unnecessary downtime and cost.

Almost any manufacturing process can benefit from a condition monitoring program. Such programs keep production on schedule by preventing unplanned downtime and repairs that would otherwise increase costs, reduce productivity, and ultimately lose customers.

Condition monitoring is even more vital for small companies because a catastrophic failure or long-term shutdown can have a greater economic impact here than on a larger company.

In an essential facility, such as a power plant where a shutdown would cause serious consequences, you can’t afford to be without condition monitoring.

What do you measure and how?

Condition monitoring requires sensors at strategic locations to detect machine data. These sensors can be permanently fixed to a machine, or carried with portable monitoring equipment. Typical measurement parameters include:

Vibration. The most common measurement, vibration helps to identify roller bearing defects, imbalance, misalignment, loose parts, and structural problems. It is usually measured in frequency, or Hz.

Several types of vibration sensors are available, and the following will help you select those that best suit your machine’s operation.

Displacement, or eddy, probes can be used to sense the position (in mils or microns) of a rotating shaft with respect to another component, such as a bearing housing. Typically mounted in a drilled hole in the bearing housing, these probes detect shaft imbalance, misalignment, shaft bow, and bearing fluid film instability. They are best suited for measuring low-frequency vibrations, typically up to about 2 kHz, though some units can handle up to 15 kHz. Displacement probes require an external power source.

Velocity sensors measure the rate at which displacement changes (in./sec). These sensors monitor bearing or machinery housing vibration and detect conditions such as bearing fatigue, turbine or fan blade problems, gear problems, and loose parts. They’re especially effective in low to mid-frequency vibration ranges (10 to 1,500 Hz).

Velocity sensors have moving parts that can stick or fail. Therefore, they should be used only where accompanied by other sensor types, particularly on critical machinery.

Accelerometers measure the rate of change of velocity in a frequency range from near zero to 40 kHz or more.

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