A special measuring head ensures that the true-running of the commutator is precisely determined. Smooth running,
large scale concentricity deviations or the far more dangerous small area concentricity deviations are documented and displayed graphically.

If any defects are detected on the commutator surface during this test, the commutator can be reworked where necessary. During maintenance, the commutator can be overturned or ground, the mica insulation milled. The commutator can be made as good as new in this manner if there is sufficient commutator coating available for processing. This minimizes brush wear and brush sparking.

Any standstill that may be required for maintenance and repair can therefore be optimally planned and will not occur at an inappropriate time.

In addition, system or control faults can also be detected in this test. It is, for instance, possible that a current flows through the commutator and the rotor winding without the rotor rotating. This causes burnouts on the surface of the commutator. These are more or less ground smooth by the brushes in operation, but after a while the brushes will start sparking due to the unevenness. It is therefore sensible, over the long term, to find out what is causing these changes so that the system does not require constant overhauls or risk failure.