Primary vs secondary ignition (10:1 attenuator, secondary pickup)

The purpose of this test is to examine primary and secondary ignition voltage on a distributor type ignition system.

 

WARNING

This test involves measuring a potentially hazardous voltage.

Please ensure you follow manufacturers' safety instructions and working practices and ensure the rated voltage for all accessories you are using meets or exceeds the expected voltage.

 

 

WARNING

Uninsulated HT pickups are designed to clip around double-insulated HT leads only – they are not designed for direct connection to a hazardous live voltage.

To prevent injury or death, when connecting or disconnecting an HT pickup:

  1. switch off the ignition
  2. clean the HT leads
  3. inspect them for damage
  4. clip the HT pickup over the desired undamaged HT lead
  5. ensure all test leads are kept clear of hot or rotating parts before starting the engine

 

How to perform the test

View connection guidance notes.

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. 

  1. Connect a 10:1 attenuator to PicoScope channel A.
  2. Connect channel A to the negative terminal on the ignition coil and to earth.
  3. Connect a secondary HT pick-up lead to PicoScope channel B and onto the ignition coil king lead. Ensure the HT pick-up lead has a good earth.
  4. Start the engine and allow it to idle.
  5. Minimize the help page. You will see that PicoScope has displayed an example waveform and is preset to capture your waveform.
  6. Start the scope to see live data.
  7. With your waveforms on screen stop the scope.
  8. Stop the engine and turn off the ignition.
  9. Use the Waveform Buffer, Zoom and Measurements tools to examine your waveform.

Example waveform

Waveform notes

The example waveform shows the exact relationship between the ignition's primary circuit and the secondary output. The primary circuit transfers its characteristics into the secondary through 'mutual inductance' and mirrors the primary exactly.

The blue trace shown in the example is the Low Tension (LT) signal, measured from the coil's negative terminal (marked number 1). The red trace is the High Tension (HT) output voltage measured at the king lead.

A permanent or intermittent loss of the secondary picture is usually due to a failing coil or HT (High Tension) voltage tracking to earth. Losing the primary picture will result in a total loss of HT voltage.

Waveform Library

Go to the drop-down menu bar at the lower left corner of the Waveform Library window and select, Distributor ignition primary voltage or Distributor ignition secondary voltage 

Further guidance

GT389

Disclaimer

Suitable accessories

  • Secondary ignition pickup (capacitive with BNC)

    £58.00

  • 10:1 Attenuator

    £64.00

  • Multimeter Probes

    £6.00

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Guided test: Primary vs Secondary