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How do I properly look at secondary ignition waveform with my RIGOL scope?

Discussion in 'General Electronics Discussion' started by apples, Jan 7, 2020.

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  1. apples

    apples

    97
    2
    Jul 1, 2012
    I just tried, again, to get a better trace of my cars secondary ignition waveform with my RIGOL DS1052E oscilloscope. I did get a picture with the basic idea of what is going on, but I need more detail from it.

    I see you can get inductive probes or capacitive probes for this kind of job. I was simply just grounding to the engine block then touching the tip of my probe onto a spark plug wire. Probe on 10x and same in the scope settings.

    Attached is a photo of what I managed to get. How can I get a better trace, notice how there is a lot of "ringing" after the initial voltage drop down. This must be noise or something because I am not using a proper probe, yes?

    Maybe someone has made a capacitive probe and has some easy plans to make one? Also the rest of the traces that were running were quite messy too, this was one of the cleaner traces I could manage. I guess a better probe would fix that hey?

    And for reference I have included a picture of what a trace should look like. Webp.net-resizeimage.jpg index_clip_image002_0008.jpg
     
    Y2KEDDIE likes this.
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    10,079
    2,153
    Nov 17, 2011
    What makes you think the ringing is du eto the probe?
    The reference image shows the identical ringing (only labeled "presence of turbulence").
    The iginition signal itself is messy. I think you can be happy with an image like the one you managed to capture.
     
  3. Alec_t

    Alec_t

    2,844
    760
    Jul 7, 2015
    I agree with Harald. Your trace looks to be in good agreement with the reference.
    What is the maximum voltage rating of your scope probe? I'm surprised it can cope with spark plug voltages.
     
  4. apples

    apples

    97
    2
    Jul 1, 2012
    What makes you think the ringing is du eto the probe?
    That's just my uneducated assumption haha.

    The reference image shows the identical ringing (only labeled "presence of turbulence").
    I think they mean turbulence as in from the cylinder head valves. I mean the first ringing on the left of the picture, not the right side.

    What is the maximum voltage rating of your scope probe? I'm surprised it can cope with spark plug voltages.
    How do I find out that the max voltage rating of my scope probe is? Here is a mark on the probe, 10x 300v CATII

    If I am reading the trace correct, when the voltage is up at 12-14volts as it comes in from the left of the picture. The coil opens starts to charge up, that is the trace dropping down. Then as it charges up the trace returns back up to the 12-14v height. In that section there it happens so quick. It's like 7-800.us before the line is back at its original voltage. Which means that the coil primary would be charged with power and ready to fire.
    That seems odd to me because looking at other secondary traces they all take longer than that.

    And the other part is the spark burn line. Mine is a big whoopie, and generally they are more of a horizontal line profile. I mean that might be accurate, but I don't know if the scope is accurately representing what the ignition coil is doing because I am not using a proper secondary ignition capture probe.

    Yes I too think that I have captured a pretty good trace, but just not sure how accurate it really is.

    1InkedWebp.net-resizeimage_LI.jpg .jpg
     
  5. Harald Kapp

    Harald Kapp Moderator Moderator

    10,079
    2,153
    Nov 17, 2011
    Thi
    This is also shown in the reference image.
    300V at the probe tip will result in 30 V at the scope input. The max. input voltage of the scope you'll find in the manual of the scope, sometimes also printed next to the input of the scope.
    The scope will not see the full ignition voltage as the capacitive coupling from ignition wire to probe and the input capacitance of the scope will capacitively divide the signal. To be on the safe side a 100x probe could be used.
     
  6. DJL33B

    DJL33B

    9
    3
    Aug 22, 2019
    From my days of auto tinkering many years ago, as I recall, the scope pattern of an individual cylinder is less important than the comparison of all cylinders. This would be the center connection of the distributor, or if the car has individual coils, it would require comparing cylinder to cylinder. The effect of input capacitance would be equal for all cylinders as long as the probe is consistently held against each spark plug wire.
     
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