Aromaz 031 - Ignition coil wave forms on scope

[morpher44]

yes I agree these are digital artifacts. If you try this same thing with an old analog scope, it would be interesting to see if you get the regenerative effect you saw where the pulses build. The digital artifact theory cannot account for that phenomenon I don't think ... so that may have been real.

[Drevtoobe]

Hi Corrie, I finally figured our what is going on in this strange clip.

Start of with a basic concept: Suppose I have a 10 Hz waveform I want to measure in discrete samples over a period of one second. How many samples do I need to measure to give me a good picture of the waveform?

If you take 10 measurements, you might only measure the peaks of the sine waves and you see a straight line. You sample rate was not high enough to describe the waveform.

[Drevtoobe]

20 samples is better, but for a reasonably clear picture of the waveform you might want to take at least 50 samples. With 50 samples you can see the up and down of the sine wave.

So for a 10 Hz sine wave, you want to take samples at 50 Hz or faster to get a good "snapshot" of the wave. For a 500 Hz sine wave, you want to sample at 2500 Hz or faster.

[Drevtoobe]

You have a digital scope, and it works on this principle.

The time-base setting, the number of milliseconds or microseconds per division is controlling your sample rate.

In this clip, the sample rate is too slow because the time base is set at 100 milliseconds per division. Try speeding it up to 10 or 1 msec per division or faster and you should see the waveform get clearer.

I think that you are correct in that you are seeing ringing in the coil.

[Drevtoobe]

As you change your signal generator frequency from 80 Hz to 90 Hz, you are seeing "beat frequencies" between the too-slow sampling and the high frequency resonance in the coil. That's why you see the decay-envelope go "backwards", and other weird waveforms, it's not actually happening due to the "limitations" of the digital scope.

For more information as part of your research you may want to look up "nyquist sampling theorem." Have fun!

[Drevtoobe]

Here is the bonus round: Let's make some guesses about the ringing in the secondary of the coil. For every rising or falling edge of the input, the coil rings. We assume that the resonant circuit consists of the secondary inductance, the minuscule capacitance of the coil itself, and the input resistance of the scope.

From the equations for a series RLC circuit, the minuscule capacitance will make the resonant freq very high and the high resistance will make it decay very rapidly.

[Aromaz2012]

You almost made me happy. Yes there were some cases - originally- where the sample rate was low. But in most of these extration the sample rate was ample.  How to know? That is why I use the Frequency reading. When sample rate is too low, the frequency will also not corespond i.e SG gives 720KHz, scope read 500Hz = rate error. There is not really any strange thing, just resonance effects. Might look so because no cap or resistors, which is not normal.

[Drevtoobe]

If you see any instability in the frequency reading on the digital scope then you should ignore it. It also has limitations. It works very well for square, sine, or triangular or other fairly regular waveforms. However, if the waveform is a 100 Hz square wave with a 16 KHz ringing on each rising and falling edge then the scope frequency measurement system goes a bit crazy and gives unstable results. Like any piece of equipment or tool, you have to learn and understand its limitations.

[Drevtoobe]

Just a bit more about the basic nuts and bolts of using your scope: Your signal generator frequency is at 80 Hz, and your time base is set to 100 milliseconds per division. Therefore the total time displayed on the scope is 1200 milliseconds. For every 100 msec division for an 80 Hz input waveform, you should see 8 sinusoidal waves. In fact you don't see the 8 waves per division. Right there that is telling you something funny is going on, you are getting "beat frequencies" a.k.a. aliasing.

[Drevtoobe]

For any digital type scope as the time base gets slower and slower, you start seeing aliasing artifacts on your digital display for frequencies above a certain threshold. The threshold changes depending on the time base setting. It is very important to be aware of this. Luc thought that he was looking at a "double helix" waveform, but they were just aliasing artifacts also

For this clip, the scope display is showing invalid data. The strange waveforms on the display are not happening at all

[Drevtoobe]

Another little tip: Your digital scope is very modern. You probably have two independent movable cursors that you can move across the display. The scope can display the time period between the cursors or the corresponding frequency. You can simply move the cursors to say, two peaks that correspond to the period of a complex waveform and the scope will show you the frequency. This will give you an accurate fundamental frequency measurement, much better than the automatic frequency display.

[Aromaz2012]

The ringing does turn out to be another matter of interest. What I am in reality working on is behaviour of electrons - free from nucleus/atom. When a coil 'rings' it releases more electrons into the air around, same is also valid when there is a strong back-emf from DC motor I am trying to see what can cause the maximum release of electrons, then from that knowledge I want to start working on the opposite - to capture maximum electrons from air or environment. I think Radiant = Electrons

[Drevtoobe]

Good luck on that. You should study those Java applets. Watch carefully, when a coil rings it is an energy dance going on. The energy goes back and forth between the coil and the cap, from the magnetic field to the electric field. There are no electron's "created", if you are implying that, its more of a dance with charge moving back and forth, voltage dancing with current. "Kinetic" energy of moving current dancing with static "potential" energy of static voltage. Always 90 degrees apart.

[Drevtoobe]

For example, where can you find a huge RLC circuit? A roller coaster is like an RLC circit. When the cars are at the top of a peak, they have energy because of their height. When the cars are at the bottom of the hill, they have energy because of their motion. As you ride the roller coaster you are experiencing the energy dance in real life. Height dancing with speed, going up and down in sine and cosine waves.

In this example, height is like voltage and speed is like current.

[Drevtoobe]

And the cars are like the electrons.

[Aromaz2012]

YES, exactly. What happens if the car's wheels needs to hold onto the rail for a backward loop - and their is suddenly another set of wheels in its place?

It is getting really exciting - and so do I.

Some of the other lessor know experiments of Tesla and other does begin to make a lot more sence - and for a fact I think they understood 'electricity' better than even most 'trained' electricians today.

[Aromaz2012]

Ahh, yes; that is the normal view. However, I will now dare to differ.

1. YES, no electrons are created.

2. BUT they are 'bumped' out of the conductor into free air - gas property.

3. Because of the excitement and less positions than electrons.

4. That is why we had HV environment in my original circuits.

Now, there is a heck of a lot more about electrons than just the movement inside conductors from atom to atom - as many people tend to think.