Meters and troubleshootingQuestion 742 of 1506

How can a permanent-magnet tachogenerator show the direction of rotation?

  1. The output voltage polarity reverses when the rotation reverses
  2. The output voltage doubles each time the shaft speed is doubled again
  3. The output current becomes zero
  4. The output frequency changes with the rotation speed
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Correct answer: The output voltage polarity reverses when the rotation reverses

The sign of the voltage tells which way the shaft turns.

Source: Lessons in Electric Circuits I: DC (Kuphaldt), 9.4: Tachogenerators

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Questions last reviewed: 18 October 2026