How to Check the Phase on a Fluke ScopeMeter

Isolate industrial motor problems by checking Fluke ScopeMeter phases.

Fluke ScopeMeters are useful in determining the root cause of a machine problem and can reduce potential costs of repairs and downtime. Although they are used primarily for industrial machinery, they have secondary applications in avionics, medical imaging and communications. ScopeMeters are used for process controls, automation and power conversion and can help a user diagnose issues based on analog or digital signals. When used for troubleshooting, the meters can help with isolating a problem, whether it’s a motor, load or adjustable speed drive, or ASD, problem. Start with checking the phase on a Fluke ScopeMeter to diagnose a problem.

Instructions

1. Measure the current drawn by the motor. This refers to three-phase induction motors typically used in industry, which are balanced loads. Make sure each phase is about the same.

2. Check the phase balance with the following formula: “Percent imbalance = maximum deviation from average / average of three phases X 100%,” recommends Fluke. Measure phases A, B and C.

3. Calculate the average between the three amp measurements, or A + B + C / 3 = X A.

4. Determine the maximum deviation, or the lowest phase measurement subtracted from the result of the average or X A.

5. Calculate phase imbalance by dividing the maximum deviation result by the average and then multiplying by 100 percent.

6. Look for an internal cause in the motor or voltage imbalance if the phases are not the same. Phases should be less than 10 percent out of balance, but if the problem is current imbalance, phases should be less than 3 percent at the ASD output.

Tips & Warnings

• If you use the newer Fluke ScopeMeters, they come equipped with three-phase power quality analyzers that automatically make phase calculations for you.

References

• FLUKE: Is It the Motor, the Drive, or the Load?
• Optimum Energy Products: Fluke 190-202 vs Fluke 190-204 Review