What this test proves

Evaluate a passive inductive speed/position sensor during target movement.

Tools

  • Automotive scope with an approved differential connection
  • Sensor specifications and target information

Preparation and precautions

  • Confirm the sensor is passive VR, not a two-wire active sensor.
  • Keep leads secure during cranking or rotation.

Connections

  • Measure across the two sensor conductors using a differential probe or the scope manufacturer’s approved differential method. Do not ground one conductor of a floating circuit with an unsuitable scope.

Equipment settings

  • DC coupling initially to reveal bias; set a bipolar range wide enough for speed-dependent peaks. Adjust timebase to show several teeth and any index gap.

Test sequence

  1. Capture at the specified cranking/rotation speed.
  2. Compare polarity, amplitude, spacing and target pattern.
  3. Inspect air gap and reluctor condition where accessible.
  4. Test isolated resistance only if allowed and compare to the specific sensor specification.

Expected signal / readings

Alternating positive and negative excursions correspond to target teeth. Amplitude generally rises with speed and depends strongly on air gap; an index gap can be intentional.

Interpreting results

  • Uneven amplitude may reflect target runout, damage or gap changes.
  • Adequate resistance does not prove a good dynamic signal or correct polarity.

Common mistakes

  • Applying Hall voltage limits to a passive sensor
  • Comparing captures at different speeds
  • Grounding a floating signal incorrectly