Handheld Test Tools Provide Predictive Help

Unplanned downtime due to equipment failure costs manufacturers up to 3% of revenue each year . For a company with a net income of $100 million, that’s a 30% reduction in profitability. No one can afford to let this kind of money slip through their hands.

The trick is figuring out what equipment needs repairing—and when. Other-wise, downtime, technician’s time and cost of parts can get out of hand. Predictive maintenance (PdM) regularly measure key indicators on critical equipment and tracks that information over time. And portable, handheld tools, such as digital multimeters (DMMs), clamp meters, digital infrared thermometers and insulation resistance testers, can make the task of getting essential measurements more efficient.

A number of key data points can be easily tracked with handheld monitoring devices, including:

Temperature. Use infrared thermometers for quick, frequent measurements of specific components while equipment is operating. Use your knowledge of your equipment to identify key hot spots to track, compare those temperature readings to operational limits, and watch for upward trends. For example, scan motor bearing housings, circuit-breaker panel switches and all equipment wiring connections.

Insulation resistance to ground. Conduct the following tests with an insulation resistance tester. However, before testing cabling and motors, disconnect any electronic controls—misapplication can destroy high-voltage test equipment:

Ground test line and load circuits at the starter to identify resistance to ground of the starter, line circuits to the disconnect and load lines to the motor and starter windings.

Ensure general thresholds are steady. AC devices can safely operate at not less than two megohms to ground and DC devices can safely operate at not less than one megohm to ground.

Measure resistance of three-phase motors between the load legs of the starter. You should see high resistance and roughly equivalent measurements between phases. Regularly measure voltage at critical equipment to verify stable supply voltage within the nameplate rating tolerances. A true-rms DMM is necessary to accurately measure AC voltage affected by harmonics, and a low-bandwidth filter is necessary for adjustable speed drive (ASD) voltage measurements.

Resistance. Resistance measurements must be made with the circuit power off to protect both the meter and the circuit. The higher the resistance, the more degraded the connection, and possible reduced voltage supply, nuisance tripping and potential equipment failure. High-resolution DMMs can measure the resistance across relay and circuit-breaker contacts. IR thermometers can identify high resistance connections.

DC and AC current. Loads will draw slightly higher current as they age. Regularly measuring current can help track equipment reliability. Use either a clamp meter or a DMM combined with a current clamp for measuring current. However, don’t forget to move test leads back to voltage before attempting your next voltage measurement after measuring current with a DMM.

Voltage balance. A DMM can help check voltage between phases for voltage drops at the protection and switchgear delivering power from the utility. A greater than 2% voltage unbalance can reduce equipment performance and cause premature failure.

Current balance. Another root cause for equipment overheating is current unbalance. Use a clampmeter or an AC current clamp with your DMM to check the current draw on each of the three legs. More than 10% current imbalance can be a problem.

Inrush current. If a motor isn’t performing correctly or if your circuit is unexpectedly tripping, check inrush current at startup with a clamp meter or a DMM designed to capture inrush current. Inrush current can reach up to twelve times the normal running current—much higher than the circuit breaker rating—without tripping the breaker, as long as the circuit isn’t overloaded. Evaluating your inrush current depends on comparisons of inrush measurements over time for that motor.

Courtesy of Fluke Corporation, Everett, Wash. Printed with permission.

PdM Measurements with Handheld Test Tools

EQUIPMENT
KEY INDICATORS
MEASUREMENT
TEST TOOL

Key : Infrared thermometer (IR), digital multimeter (DMM), insulation resistance tester (IRT), clamp meter (CM). Note : These recommendations are not a complete set of PdM measurements.

UPS/PDU
-Intermittent tripping
RMS voltage, rms current, frequency (Hz), connection resistance, data log readings over time for anomalies.
IR, DMM

-Process interrupts

TRANSFORMER
-Heat
Temperature, impedance at neutral-ground bond, voltage balance, current balance, loose connections.
IR, DMM CM

-Buzzing

PANELS/SWITCHBOARDS
-Intermittent tripping
Voltage balance, current balance, data log readings over time for anomalies, loose connections, temperature.
IR, DMM, CM

-Hot circuit breakers

CONTROLS (ASDS DISCONNECTS)
-Process anomalies
Voltage balance, current balance, inrush current, voltage sags, connection resistance, data log readings over time for anomalies.
IR, DMM, CM

-Change in system performance

LIGHTING PANELS
-Flickering lights
Voltage balance, current balance, inrush current, voltage sags, connection resistance, data log readings over time for anomalies.
IR, DMM,CM

-Buzzing

MOTORS AND OTHER EQUIPMENT (gearboxes, pumps, fans, chillers, A/C units, generators)
-Heat
Inrush current, insulation resistance to ground, temperature, nameplate rating, overloading, voltage balance, current balance, resistance, connection motor start capacitor.
IR, IRT, DMM, CM

-Intermittent tripping

There are four key steps in establishing a successful PdM program, regardless of the tools used:

Identify the potential failures and related key indicators for each equipment type.

Determine measurements that could reduce the likelihood of problems.

Determine how often equipment needs to be measured.

Collect and track the results, watch for trends and initiate repairs.

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