Inductive pick-up

The purpose of this test is to evaluate the correct operation of an inductive distributor pickup based on the output voltage and frequency during cranking and engine run conditions.

Connection guidance

Connection for diagnostic work will of course 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 set up. This may either have the amplifier mounted directly onto the body of the distributor or be remotely mounted in various locations.​

  1. Connect PicoScope Channel A into the distributor signal and earth cables.
  2. Start the engine and allow to idle.
  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. Select GO or press the space bar to see live data.
  5. With your live waveform on screen select STOP or press the space bar to stop your capture.
  6. Turn off the engine.
  7. Use the WAVEFORM BUFFER and ZOOM tools to examine your waveform.

NOTE,

If the engine is a non starter then select GO and crank the engine for around three seconds to capture your cranking waveform.

Example waveforms

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.

GT019-4

Disclaimer
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

    £269.00

  • Back-pinning Probe Set

    £40.00

  • Flexible Back-pinning Probe

    £3.00

  • PicoScope Battery Clip

    £2.75

Help us improve our tests

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2 comments | Add comment

Steve Smith
October 21 2016

Good catch on the text, we’ve made that adjustment. Sadly we do not have the specific details of the vehicle used within this Guided Test.

John Grady
March 28 2016

just a correction..the pickup is not “invariably mounted on the distributor shaft”..the spinning metal points are mounted there,  called a reluctor.

The pickup is mounted stationary within the distributor.

Thank you for the voltage readings ; what pickup this is,  would help the information..

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Guided test: Inductive Pick-up