Hello Henri and thank you for your post and the time taken to compile the attachment which I have found of real value and an education. Thank you again
What you have highlighted are the numerous variables that can affect the final captured data when measuring secondary ignition events. (With reference to the HT Pick-up lead)
I think it is important here to step back and look at just how we obtain the secondary ignition signal as this has always amazed me how we achieve a useable waveform with virtually no contact!
Attaching the HT pick-up lead to the insulation of an HT lead we detect the electric field about the HT lead during the ignition event. The signal obtained is then attenuated via the pick-up lead and fed through to the scope. This process alone is open to all forms of intrusion into the signal we view on screen
Simply clamping the HT pick-up lead about the insulation of a HT lead introduces a huge variable, especially as you have mentioned the diameter of the Pick-up lead clamp (8mm) in relation to the HT extension leads (7mm)
The design of the clamp and its closure about an HT lead (contact face) adds another variable that will contribute to differing values from various vehicles depending on the design of the HT leads used.
The design and properties of the materials used to construct the HT lead will introduce another variable to the signals detected about the insulation
Efficient grounding of the pick-up lead is another variable from one vehicle to another or even when using 4 x pick up leads and “stacking” the grounding croc clips.
However, the final captured results still present a valuable display of the ignition events taking place where an overview of the firing voltage, burn time, spark line and coil ringing etc. will remain evident.
The accuracy of the voltage values of all the above must be viewed with consideration to all the variables mentioned and the detailed description in Henri’s attachment.
I will discuss the HT Pick-Up lead design with our engineers at Pico as we are always looking to improve our products based upon our own research and more importantly, feedback from customers out in the field using our equipment under varying environmental conditions and multiple applications.