peter@easthope.ca wrote:
Bob & all,
In article <10oo4gp$3ujhk$1@dont-email.me>, bp@www.zefox.net wrote:
... what are you trying to learn?
My knowledge of ignition systems is minimal. My intention is to have
some diagnostic information available when the the vehicle is on the
road and the motor malfunctions.
I'd suggest digging around on the Net to find explanations of how ignition systems work. Good keywords might be CDI, Kettering, breaker points, breakerless, transistorized ignition in your choice of permutation.
The page at
https://en.wikipedia.org/wiki/Delco_ignition_system
is a not-bad start. Most likely your bike has some variant of CDI.
Is the shape of the waveform reasonable?
Was hoping someone with automotive knowledge would divulge.
As a guess, I'd suggest it'll be a fast rise to 10-40 kV, maybe
a few microseconds at peak and a rapid collapse to a few hundred
volts or less. It may ring, perhaps 500 kHz, and be over in a
millisecond or less. The pulse is likely to be negative, but
not guaranteed.
Is the amplitude reasonable based on the
probe attenuation?
Was hoping someone would divulge.
The engine was running when I caught the picture. No obvious
malfunction.
Agreed, the waveforms look reasonable to a casual glance.
Do the signals go away when disconnected from the 'scope?
Do the signals go away when the probes are shorted to ground?
Do the signals look the same when measured on a single plug?
Does measured amplitude decrease smoothly as the clamps are
opened on the wires?
Can check in the coming weekend. Thanks.
If you have the option of using a pulse transformer to
measure the spark current that might be easier to
deal with. Less noise, better calibration stability.
Voltage and current measured simultaneously are the
most persuasive measurement.
First I've heard of a pulse transformer. Will read about
it when there's an opportunity.
https://www.pearsonelectronics.com/ has application notes that
might help make clear the utility of pulse transformers to measure
high voltage pulses. It looks like your setup uses capacitive
dividers. They work, but are hard to callibrate and prone to pick
up noise. A little movement changes the attenuation and might
change what you're measuring.
If you're new to oscilloscope use I'd suggest making a practice
rig using an old coil, capacitor, switch and sparkplug. That'll
be much easier to learn with. Lots of things can go wrong with
pulse measurements, much simpler on the bench than on the engine.
hth,
bob prohaska
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