DIS primary ignition (voltage) (using the 10:1 attenuator)

The purpose of this test is to check the primary ignition event for burn time, the dwell period and the induced voltage.

Connection guidance

Note: This helpfile refers to a 10:1 attenuator. If you are using a 20:1 attenuator please adjust the Probe settings for the relevant channel. These settings can be found under the Channel Options button, then: Probe > 20:1 Attenuator.

How to perform the test

  1. Attach a 10:1 attenuator to PicoScope channel A.
  2. Connect Channel A to the DIS coil pack primary negative terminal.
  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 engine and allow it to idle.
  5. Start the scope.
  6. With your live waveform on screen stop the scope.
  7. Turn off the engine.
  8. Use the Waveform Buffer and Zoom tools to examine your waveform.

Example waveform

Waveform notes

This known good example shows a typical primary waveform.

Waveform Library

Go to the drop-down menu bar at the lower left corner of the Waveform Library window and select, DIS / wasted spark ignition primary voltage

Example DIS coil pack

Further guidance

The ignition primary waveform is measuring the negative side of the ignition coil. The earth path of the coil can produce over 350 volts.

Within the primary picture there are several sections that need closer examination. In the waveform shown, the horizontal voltage line at the centre of the oscilloscope begins fairly constant at about 40 volts, but then drops sharply into what is referred to as the coil oscillation. 

There is no current in the coil's primary circuit until the dwell period which is when the coil is earthed and the measured voltage drops to zero. The dwell period is controlled by the ignition amplifier, and the length of the dwell is determined by the time it takes to build up the requisite 5-10 amps (depending on system). When this predetermined current has been reached, the amplifier stops increasing the primary current and maintains it until the earth is removed from the coil, at the precise moment of ignition.

The vertical line at the centre of the trace, called the 'induced voltage', is above 200 volts. The induced voltage is produced by a process called magnetic induction. At the point of ignition, the coil's earth circuit is removed and the magnetic field or flux collapses across the coil's windings. This in turn induces an average voltage between 150 to 350 volts. The coil's High Tension (HT) output is proportional to the induced voltage. The height of the induced voltage is sometimes referred to as the primary peak volts.

GT396-2

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

  • Large Dolphin/Gator Clips

    £10.00

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Guided test: Primary Voltage