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.

Connection guidance

Connection for diagnostic work will vary dependent on application.

Technicians should whenever possible gain access to the test circuit without damage to seals and insulation. If this is not possible then make sure appropriate repairs are completed.

General connection advice

PicoScope offers a range of options within the test kits.

Dependent on difficulty of access, choose from:

  1. Breakout leads.
  2. Back-pinning probes.

Testing sensors and actuators (to include relevant circuit/connectors):

  • When testing a sensor, it is desirable to gain access at the control module.
  • When testing an actuator, it is desirable to gain access at the actuator.

How to perform the test

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 data to identify the ignition circuit functions and component location.
  2. Connect PicoScope Channel A to the distributor signal circuit.
  3. Minimise the help page and with the example waveform on your screen PicoScope has already selected suitable scales for you to capture a waveform.
  4. Start the scope to see live data.
  5. Crank and start the engine, run at idle.
  6. With your live waveform on screen stop the scope.
  7. Turn off the engine.
  8. Use the Waveform Buffer, Zoom and Measuring 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.

Waveform notes

As the metal rotor spins, a magnetic field is altered which induces an AC voltage from the pick-up. The output voltage rises as the metal rotor approaches the winding, sharply dropping through 0 V as the two components are aligned and producing a voltage in the opposite phase as the rotor passes.

The voltage produced will rise from as low as 2 to 4 V when cranking to over 50 V at high engine speeds.

Example Inductive distributor pick-up

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