MRO Magazine

Get Proactive: Condition monitoring tools a smart business investment


November 21, 2011
By PEM Magazine

Unplanned downtime caused by equipment failures costs manufacturers up to three percent of revenue every year. That’s 30 percent less profit. In an era of extreme competitiveness, no one can let that kind of money slip through their fingers.

Much of this cost can be avoided with proactive maintenance, such as measuring key indicators on critical equipment to discover impending failures and then scheduling maintenance. This practice is far more effective than waiting to perform maintenance when a failure happens, because it allows you to plan downtimes, minimize disruption and ensure spare parts are always available when needed.

Proactive maintenance programs and tools can vary from highly sophisticated processes for continuous online monitoring and automated alerts to more traditional offline programs that rely on inspection routes and manual measurements. Before looking at the tool sets needed, it is important to first establish some basic guidelines that should be support every proactive maintenance program:

  • For each type of equipment, identify the potential failures and related key indicators.
  • Determine what measurements can reduce the likelihood of problems.
  • Determine how often equipment needs to be measured.
  • Collect and track the results, watch for trends, and initiate repairs as needed.
  • Integrate all of your maintenance technologies into one computerized data tracking system so they share the same equipment lists, histories, reports, and work orders.

With these ground rules in mind, we can now look at the measurement parameters and basic test tools needed when developing a proactive maintenance program.


Insulation resistance to ground testing
This test should be conducted regularly on loads and connections to detect imminent equipment failure. Ground testing line and load circuits at the starter will identify the resistance to ground of the starter, line circuits to the disconnect, and load lines to the motor and starter windings. Note that when using an insulation resistance tester for ground testing, disconnect the components or cabling to be tested from the power system.
Tool needed: Insulation resistance tester.

Infrared thermometers are a low-cost monitoring option for quick, frequent measurements of specific components while equipment is operating. Use knowledge of the equipment to identify key hot spots to track, compare those temperature readings to operational limits and watch for upward trends. For the best measurements, get as close as is safely possible to the target, make sure the measured surface is not reflective and compensate for emissivity.

Thermal imagers are versatile tools that can play a key role as screening tools. Users can use them to quickly measure and compare heat signatures for each piece of equipment on an inspection route without disrupting operations.

Users can also quickly survey a much larger area than an infrared thermometer, and see how the temperatures of different areas relate to each other. If the temperature or thermal pattern is markedly different from previous readings, use other maintenance technologies — such as vibration, motor circuit and lubricant analysis — to assess the severity of the problem and time needed to repair it.
Tool needed: Infrared thermometer, thermal imager.

Vibration testing
Vibration is often an indication of problems with or deterioration in the condition of the equipment. If the underlying causes of excessive vibration are not corrected, the unwanted vibration alone can often cause additional damage.

Measurements are taken by placing an accelerometer near each bearing location along the drive train, using the most appropriate attachment method. It is important to ensure proper sensor placement in order to collect good data.

For consistent data over time, place the accelerometer at the exact same location each time you take a measurement. Also, be sure to take vibration measurements when the machine is running in a steady state and at normal operating temperature. (Machines tested while still cold may have significantly different vibration signatures.)

Use a vibration tester, such as the Fluke 810, to analyze the data to determine the source, location and severity of the faults, and identify potential mechanical problems weeks, if not months, prior to a failure.
Tool needed: Accelerometer, vibration tester.

A digital multimeter (DMM) can be used to check the resistance across most connections. Before beginning, remember that resistance measurements must be made with the circuit power off. In addition, high-resolution DMMs can measure the resistance across relay and circuit breaker contacts.

Infrared thermometers can also be used to identify high resistance connections, which show up as hot spots when compared to a good connection.
Tool needed: Digital multimeter, infrared thermometer.

AC and DC loads may draw slightly higher current as they age. Regularly measuring current can help you track equipment reliability. Use either a clamp meter or a DMM combined with a current clamp to measure current.

Another root cause for equipment overheating is current imbalance. A more-than-10-percent current imbalance can be a problem. Use a clamp meter or an AC current clamp with the DMM to check the current draw on each of the three legs.
If a motor isn’t performing correctly or if the circuit is tripping unexpectedly, check inrush current at startup with a clamp meter or a DMM designed to capture inrush current. Evaluating inrush current depends on comparisons of inrush measurements over time for that motor.
Tool needed: Clamp meter, CMM with current clamp.

Voltage balance
A greater-than-two-percent voltage imbalance can reduce equipment performance and cause premature failure. Use your DMM to check voltage between phases for voltage drops at the protection and switchgear delivering power from the utility and at high priority equipment. Voltage drops across the fuses and switches can also show up as imbalance at the motor and excess heat at the root trouble spot. Before a user assumes they’ve found the cause, they should double check with a thermometer.
Tool needed: Digital multimeter.

Colin Plastow is industrial product manager for Fluke Electronics Canada. He may be contacted at For more information, visit