Distributor pick-up Hall effect

You will require a PicoScope to perform this test. A list of suitable accessories can be found at the bottom of this page.

How to perform the test

Plug a BNC test lead into Channel A on the PicoScope, place a black clip on the test lead with the black moulding (negative) and a Back-pinning Probe onto the test lead with the coloured moulding (positive). Probe each of the three connections as illustrated in Figure 1. If you cannot reach the terminal or plug with a probe, then you may be able to use a breakout box or lead if you have one available.

The three connections being: the sensors voltage supply, an earth and the Hall effect output. The switched signal from the Hall effect is normally the centre pin. The Hall effect output has been monitored in the example waveform shown on this page.

The timebase may need to be altered if the signal is checked at varying engine speeds.

Figure 1 shows the Hall effect sensor's multiplug wiring being probed.

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.

Technical information

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.

Figure 2 shows a diagram of a Hall effect pick-up: the terminal marked 0 is the Hall voltage.
Figure 3 shows a Hall effect distributor.

AT020-2

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

  • Back-pinning Probe Set

    £48.00

  • Flexible Back-pinning Probe

    £7.00

  • Large Dolphin/Gator Clips

    £10.00

  • PicoScope Battery Clip

    £5.00

  • Premium Test Lead: BNC to 4 mm, 3 m

    £48.00

  • Premium Test Leads: Set of four leads 3 m (TA125 - TA128)

    £179.00

Share your experience

If you have any suggestions to improve this guided test please do so using the 'add comment' button.

Add comment

Your email address will not be published. Required fields are marked *

Guided test: Hall Effect Pick-up