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Why won't scope work well on car's injectors?

Discussion in 'Electronic Basics' started by Ricky Spartacus, Oct 15, 2003.

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  1. I'm new to an EZ oscilloscope 5020G. And disappointed to see that when
    hooked to a car`s fuel injector, I can`t seem to hold the square wave
    still so to measure size of the square wave. The car idles rough and
    probably made the square wave drift away from the oscilloscope`s
    screen slowly. Is there a way I can hold it still so I can measure the
    duration of a fuel injector? Measuring the duration is important
    becasue it may tell if it`s a rich or lean mixture. I`ve tried what I
    can on the oscilloscope.
  2. Kevin Carney

    Kevin Carney Guest

    or the scope was in "auto" trigger mode. try "normal trigger" mode.

    change .combo to .com for correct email

    "We ought always to know precisely why a given job
    is done in a particular way, and why it is done at
    all, and why it can't be done more efficiently,
    if it must be done at all."-- T.J.Watson

  3. Baphomet

    Baphomet Guest

    You should be able to trigger the scope on the positive (or negative) slope
    of the waveform so that measuring pulse width (duration) shouldn't be a
    problem. If you can't get a good internal trigger, try triggering
    externally. I think you may have had the sweep in the "free running" mode.
  4. I tried positive, negative, norm and auto mode but maybe it requires
    skill since I'm new. On the back of the scope it says, "external
    trigger input." I assume I need an external trigger device? I never
    seen an external trigger device. What is it?

    I assume a $500 scope should be able to see a pulse width of a fuel
    injector, shouldn't it? The scope is a 20MHz 2 Ch, Dual Trace &
    Function Generator Model OS-5020G Manufacturer by EZ Digital (Formerly
    Goldstar / LG Precision)

    I will take both advice and begin twisting and turning knobs veeeryyy

    Thanks very much.
  5. It helps a bit if you understand what the knobs do.

    Normal mode waits indefinitely for a trigger signal (that starts the
    horizontal sweep of the trace) while auto times out and generates a
    trace, even if there has been no trigger signal for a while. If you
    are not sure if your scope is actually seeing a trigger event, Start
    with auto mode, to get the trace on the screen, then switch to no
    normal mode to adjust the trigger conditions. That way, even if you
    don't see anything useful in the trace, you will know when the trigger
    condition has been met by the flash of a trace going by.

    Then you can experiment with the conditions that must be met to
    produce a valid trigger event. This is where the positive/negative
    going selection comes in. And also the source of the signal that is
    being looked at for slope and magnitude by the trigger generator
    circuit. The source choices are usually, A or B channel, the line
    signal coming through the power cord, or an external signal you are
    connecting to a separate connector (usually on the right side of the
    front panel). If you had access to some other clean pulse signal that
    had a precise timing relationship to the one you want to see, (say,
    the primary of the ignition coil) you might start the trace when that
    popped (via the external trigger input), and then see how long after
    that channel A and/or B showed some activity.

    If you want to watch channel A and trigger on the waveform you are
    watching, make sure the trigger source is not set to channel B.

    The filter options on the trigger signal (AC, DC, horizontal sync,
    vertical sync, noise filter, etc.) just optimize the chance that you
    will create a trigger event only when you want one, and not on some
    other accidental part of the trigger waveform that barely happens ot
    meet the trigger conditions. The DC position is usually the
    unfiltered position, so start with that. If you get overlapping
    traces indicating that you are triggering two different places in the
    waveform, even when you sweep the trigger threshold (voltage level)
    knob back and forth, then you may want ot try the noise filter
    position to see if it eliminates the extra triggers.

    Then, once you achieve a clean sweep that puts many copies of
    essentially the same waveform on top of each other (a stable trigger),
    you will need to adjust the sweep speed (seconds per CM knob) to
    compress or expand the waveform to see the details in the best time
    scale. Then adjust the vertical gain (volts per cm). If you are
    triggering on the vertical input signal, expect ot have ot go back and
    adjust the trigger threshold to compensate for the change in vertical
    gain. If you are using an external trigger, adjusting the vertical
    gain has no effect on the sweep trigger process.
  6. Do you have the trigger set to the same channel you are looking at?
    They have to match before you will get a proper trigger. You also need
    enough signal to make it trigger. If the signal is 0 to 12 volts, set
    the scope for 2 volts per division.
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