http://www.home.earthlink.net/~bkwhite54/id1.html

That link up there is for my web page and I have posted a waveform in it which has me puzzled.
The waveform in question is the secondary shot, ( lower on page ).
Can anyone explain what is going on at the .4 and.5 sec areas ?
This engine had a known problem of over rich fuel mix and the plugs were fouled and miss firing with very low firing voltages so I set the trigger to 1 KV, I think that explains the noise at the base of the waveform.
On this same vehicle I had a capture of the secondary at the coil wire with at least two or three spark events contained in that downward sloping line as shown at the .4 and .5 sec area.
Is the carbon fouling in the plugs acting as a capacitor and it takes that capacitance that long to dissipate ?
I have never seen ignition waveforms as precise as are displayed by the Pico Scope.

Brad White

Hi Brad,

Sam's right.  That's way beyond the limits of your 212/3 for secondary acquisition.

Even if you had your samples dialed up to the max 32,000 in block mode, the samples would be 85 microseconds apart. 

At 10ms/div they would be 5 microseconds apart.  A secondary firing line is about 10 microseconds, so more time than that will not reliably capture them.

You can do the calculations yourself with our sample rate calculator:

http://www.autonerdz.com/java/SampleRateCalculator.html

The 212/3 is still more powerful than most of the automotive scopes in use today but everything has it's limits.

The PicoScope 3000 series has it's limits too.  These are the most powerful automotive scopes available right now.  Even if you were using one of these with one channel deployed at 200ms/div, the samples would be 6 microseconds apart.  This would reliably capture the firing KV events, but that would be the limit.  After all, that's two seconds of time on the screen