Resistance Measurement

Precise verification of the ohmic winding resistances is one of the most important prerequisites for ensuring consistently high manufacturing quality of armatures and stators. Resistance measurement monitors both compliance with wire parameters (such as diameter and number of turns) and the correct wiring within the DUT—both essential for a flawless and long-lasting end product.

Measurement method and contacting

The test object is contacted using the four-wire method (Kelvin measurement), which effectively eliminates measurement errors caused by lead and contact resistances. To compensate for the temperature dependence of the measurement values, the results are automatically recalculated to a defined target temperature (more information).

Typical resistance measurements for armature and stator

Exemplarischer Anker mit schmatischer Darstellung der Widerstandsmessung eines Querwiderstandes

Armature:

  • Diametrical resistance: Total resistance of all coils in the armature.
  • Bridge resistance: Resistance of the short-circuit bridges at the commutator.
  • Bar resistance: Total resistance across specific commutator bars.
  • Coil resistance: Resistance of individual coils (using compensation of the parallel coil chain).
Exemplarischer Stator mit schmatischer Darstellung der Widerstandsmessung eines Querwiderstandes

Stator:

  • Coil resistance: Resistance of individual coils or coil chains.
  • Phase resistance: Resistance of interconnected coils within a phase.
  • Trace resistance: Resistance of conductor traces on connection plates.

Evaluation and monitoring

The evaluation of the resistance measurement can be flexibly adapted to the respective quality requirements:

  • Absolute or relative deviation: Monitoring compliance with defined tolerances.
  • Range monitoring: Defining permissible measurement ranges.
  • Maximum value and spread control: Monitoring the maximum deviation and the difference between minimum and maximum values.
  • Mean deviation: Comparing individual measurement values with the mean value.

Special case: 2-flyer method

For armatures wound using the 2-flyer method, the resistance measurement of the individual coils enables a direct comparison of symmetry between both winders. Differences in the wire or winding tension can thus be detected at an early stage and specifically corrected.

Advantages of modern resistance measurement

  • Highest measurement accuracy thanks to four-wire technique and temperature compensation
  • Early detection of manufacturing errors and deviations in the winding process
  • Automated evaluation and flexible monitoring criteria
  • Optimal process control for series production and development

Conclusion

The resistance measurement is an indispensable tool for quality assurance in the manufacturing of electrical machines. It enables fast, precise, and automated monitoring of all relevant winding parameters and makes a significant contribution to reducing scrap and rework.

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