Ignition waveform question

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Ignition waveform question

Postby rburgy » Tue Dec 02, 2014 2:58 am

I am a newer user with pico. I am doing pretty well with it.
I don't have all of the hardware I would like to have but getting there.
When it comes to ignition, is there a secret to getting a solid waveform?
First of all, all of my hardware is genuine pico. Secondly, I have enough hookups
To atleast test one cylinder of any type. My main problem is... I hookup say a
Traditional distributor type system. I check one cylinder with a wire clamp cable
And the waveform looks good but it jumps around. It gets all deformed as its running.
It's shrinks and grows, it gets skinnier and fatter ect. is there any secrets to getting
It to stabilize on the screen so that I can diagnose it?
Thanks guys
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Re: Ignition waveform question

Postby Steve Smith » Tue Dec 02, 2014 4:01 pm

Hello and thank you for your post.

Its great to see you are using the scope and sharing the symptoms you have experienced.

The scope can present more questions than answers when first used, but hang on in there it most certainly will pay dividends

From your description we have a couple of issues,

1. Voltage scale set to auto may alter the range during captures relative to the input signal peak voltage (which can fluctuate when looking at unstable ignition events)

2. The type and style of trigger used to capture the waveform may not be applicable to the ignition system under test. (Pre triggering on noise before the desired event)

Can you try the relevant pre-set for your ignition capture using the AUTOMOTIVE menu as this will configure the scope to capture a stable ignition waveform?

Could you post a PS data file with your ignition capture displaying the conditions you describe?

Here we can take a look how best to set your scope.

Thank you again for the post. Take care.......Steve
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Re: Ignition waveform question

Postby Autonerdz » Wed Dec 03, 2014 12:09 am

rburgy,

On a distributor system, the only reason you would be on a plug wire is for a sync. The ignition waveforms you seek are on the coil wire. So...Place one secondary pickup on the coil wire and another one on a plug wire. Choose secondary inverted probe for both channels. Place enough time on the screen to capture several engine cycles taking care to maintain at lest a one microsecond sample interval in properties. Then use zoom tools to examine areas of interest. The sync event will allow you to identify cylinder firing events in the parade of events by firing order. No trigger is needed but you can trigger on the sync event if desired.
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Re: Ignition waveform question

Postby rburgy » Wed Dec 03, 2014 7:45 pm

That's some good info. Thank you guys for taking the time to respond. I will take a snap shot this weekend and post what I am talking about.
Thanks again folks
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Re: Ignition waveform question

Postby Henri Malcorps » Tue Aug 25, 2015 7:34 am

When using the ignition pickup on different cars I often get rather different results. So I did some thinking about the principle of functionning, see attachment. I would appreciate very much to get comments on this.

Henri
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Getting calibrated results with secondary pick.docx
(44.3 KiB) Downloaded 120 times
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Re: Ignition waveform question

Postby Steve Smith » Thu Sep 03, 2015 9:01 am

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.

Take care…….Steve
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