From Newsgroup: sci.electronics.repair

Hi again,
An Owon 2202S scope is mounted on the dash and connected to spark
plug wires 3 & 4 of my Honda now.

The picture here is from that setup. https://en.wikipedia.org/wiki/Ignition_system#Electronic_systems
Click for a bigger view.

My speculative hypotheses:
* deeper pulses are ignitions. Shallower are cross-talk,
* cylinder 4 sparks 1/4 cycle after cylinder 3.

What are your interpretations?

To improve the picture, separate the two traces more. A larger
vertical scale may fit. The glare on the nameplate of the Hantek-25
can be removed.

Thx, ... P.



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From Newsgroup: sci.electronics.repair

peter@easthope.ca wrote:

Hi again,
An Owon 2202S scope is mounted on the dash and connected to spark
plug wires 3 & 4 of my Honda now.

The picture here is from that setup. https://en.wikipedia.org/wiki/Ignition_system#Electronic_systems
Click for a bigger view.

My speculative hypotheses:
* deeper pulses are ignitions. Shallower are cross-talk,
* cylinder 4 sparks 1/4 cycle after cylinder 3.

What are your interpretations?

Very limited until more is known about the setup.
Number one, what are you trying to learn?

Meanwhile, here are some sanity checks:

Is the shape of the waveform reasonable?
Is the amplitude reasonable based on the
probe attenuation?

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?

If all the answers are yes, then your interpretation is
reasonable. It might even be correct 8-)

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.

hth,

bob prohaska

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From Newsgroup: sci.electronics.repair

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.

Is the shape of the waveform reasonable?

Was hoping someone with automotive knowledge would divulge.

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.

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.

Thanks for the questions and tips, ... P.

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From Newsgroup: sci.electronics.repair

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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