Distributor pick-up Hall effect

The purpose of this test is to evaluate the correct operation of a Hall Effect distributor pickup based on the output voltage and frequency during cranking and engine run 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

  1. Use the vehicle wiring diagram to identify the signal circuit.
  2. Connect PicoScope to the vehicle.
  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. Crank (non-starter), start and run the engine at idle.
  6. With your live waveform on screen select STOP or press the space bar to stop your capture.
  7. Turn off the engine.
  8. Use the WAVEFORM BUFFER and ZOOM tools to examine your waveform.

Example waveform

Waveform notes

This form of trigger device is a simple digital 'on/off' switch which produces a Square wave output that is recognised and processed by the ignition control module.

The trigger has a metal disc, with openings or 'windows', that rotates between the electromagnet and the semiconductor. Any magnetic field that passes through one of the windows stops the current through the sensor. When the window is closed, the current resumes. This action produces a digital square wave that is interpreted by the Electronic Control Unit (ECM) or amplifier.

The sensor has its characteristic three connections: a live supply voltage, an earth and the output signal. The square wave signal when monitored on an oscilloscope may vary in amplitude, which is not usually considered a problem as it is the frequency that is important, not the height of the voltage. When the voltage from the Hall effect trigger drops to zero, it fires the coil. This occurs when the window on the metallic rotating vane opens.

Example Hall effect distributor pick-up

Further guidance

This form of trigger device is a simple digital 'on/off' switch which produces a digital output that is recognised and processed by the ignition control module. The trigger has a metal disc with openings that rotates between the electromagnet and the semiconductor.

A semiconductor has the ability to be a conductor or an insulator depending on whether it sees or is shielded from the magnetic field. This magnetic field is switched on and off by the rotating disc that travels between the two objects.

A magnetic field that passes through one of the windows stops the flow of current through the semiconductor. When the window is closed, the flow resumes. This action produces a digital square wave that the ECM or amplifier understands without needing any the extra circuitry to convert the analogue signal into a digital one. (Permanent magnetic pick-up amplifiers use a Schmitt trigger, while other types use an Analogue to Digital, or A to D, converter.)

The sensor, because of its convenient output, is used in many other applications including road speed sensors and speedo drives.

The sensor have its characteristic three connections: a live supply at battery voltage, an earth and the output signal.

The square wave, when monitored on an oscilloscope, varies in amplitude, but this is not considered a problem as it is the frequency that is important, not the voltage level. The output can also be measured on a multimeter that has a frequency facility.

When the signal is observed or plotted against a primary waveform, the coil can be seen to fire when the voltage from the Hall effect trigger drops to zero. This occurs when the window in the metallic rotating vane opens.

GT020-2

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

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Guided test: Hall Effect Pick-up