Distributor pick-up (inductive) - voltage

The purpose of this test is to investigate the operation of an inductive distributor pick-up based on voltage and frequency output during engine cranking and running conditions.

How to perform the test

View connection guidance notes.

The connection will vary depending on the distributor type. There may either an amplifier mounted directly onto the distributor body or remotely mounted in various locations.

  1. Use manufacturer's data to identify the ignition circuit functions and component location.
  2. Connect PicoScope Channel A. to the distributor signal circuit.
  3. Minimize the help page. You will see that PicoScope has displayed an example waveform and is preset to capture your waveform.
  4. Start the scope to see live data.
  5. Crank and start the engine, run at idle.
  6. With your waveform on screen stop the scope.
  7. Turn off the engine.
  8. Use the Waveform Buffer, Zoom and Measurements tools to examine your waveform.


If the engine is a non-starter start the scope and crank the engine for around three seconds to capture your cranking waveform.

Example waveforms

Cranking conditions

Running conditions

Waveform notes

These known good waveforms have the following characteristics:

  • A cyclic pattern with a smooth upward concave curve to around 4 V, followed by a steep drop to around -3.5 V and a smooth convex curve back towards 0 V.
  • A peak to peak voltage around 8 V, whilst the engine is cranking.
  • When the engine is running, the waveform amplitude and frequency increase.
  • There are no drop-outs or anomalies within the waveform.

Further guidance

This particular type of pick-up generates its own signal and therefore does not require a voltage supply to power it. Recognisable by its two electrical connections, the pick-up is used as a signal to trigger the ignition amplifier.

The voltage produced by the pick-up will be determined by several factors, these being:

  • Engine speed.
  • The proximity of the metal rotor to the pick-up winding, a larger air gap will reduce the strength of the magnetic field seen by the winding and the output voltage will be subsequently reduced.
  • The strength of the magnetic field offered by the magnet. The strength of this magnetic field determines the effect it has as it cuts through the windings and the output voltage will be reduced accordingly.

There are two types of permanent magnet pick-ups these are called Annular and Limb. The distinguishing factor between the two types is that the limb pickup has only one reluctor point where as the annular will have a reluctor point per cylinder.


This help topic is subject to changes without notification. The information within is carefully checked and considered to be correct. This information is an example of our investigations and findings and is not a definitive procedure. Pico Technology accepts no responsibility for inaccuracies. Each vehicle may be different and require unique test settings.

Suitable accessories

  • Premium 6-way breakout lead set


  • Back-pinning Probe Set


  • Flexible Back-pinning Probe


  • PicoScope Battery Clip


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Guided test: Distributor pick-up (inductive) - voltage