The purpose of this test is to monitor the relationship between the primary ignition circuit and the secondary ignition event of a DIS unit.
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.
Uninsulated HT pickups are designed to clip around double-insulated HT cables only – they are not designed for direct connection to a hazardous live voltage. To prevent injury or death, switch off the engine and secure against restart. Clean and inspect the HT lead for damage to insulation and fit only to undamaged fully insulated leads. Ensure that leads are safely clear of hot and / or rotating parts. The engine can now be restarted for the test duration.
If the expected voltage is greater than the overvoltage protection level of the scope (200 V), the 10:1 attenuator must be used. The PicoScope software can compensate for the attenuator so that the correct voltage is displayed on the screen. Our example waveform shows a peak of nearly 350 V.
Warning: When attaching or removing secondary ignition pickups from damaged HT leads there is a danger of electric shock. To avoid this risk, attach and remove the secondary ignition pickup with the ignition turned off.
Figure 1 shows the universal breakout lead connected to the primary ignition circuit and the secondary ignition pickup lead connected to the plug lead.
The example waveform shows the close relationship between the ignition's primary circuit and the secondary output. The primary circuit transfers its characteristics into the secondary through mutual inductance, causing the secondary to mirror the primary exactly.
The blue trace 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 plug lead.
Both waveforms show exactly the same burn time of 2 milliseconds (ms). 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.
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.
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