This mode is best used when viewing a signal drop-out or glitch detection. The normal scope mode will only display a waveform when the signal crosses a specific preset trigger level. When viewing a signal the trigger level must be set at a proper voltage level in order to view a stable signal horizontally. This is where you would want to vertically align the trace to the ground tick mark. When selecting the automatic mode, a trace will be on the scope’s screen. THE TRIGGER MODE: Typically, there are two modes: automatic and normal. When we use the invert function of the scope in this example we also invert the trigger slope function.ģ. Most secondary firing events are negative firing events. We will look at the secondary in detail later. Another example would be when looking at a secondary firing event we would set the trigger slope to the positive side. THE TRIGGER SLOPE: The cardinal rule here is that if the output device, for example, an injector, which in most cases is ground side controlled by the PCM, we would then set the trigger slope to the negative side. Another example might be when scoping out a DREF or RPM signal for integrity we would set the trigger level at about the 2.5-volt level considering that the signal is a 5V/0V toggle.Ģ. For example, if you are scoping out the secondary ignition system and looking at a 10 KV event, it would be necessary to set the trigger level at about the 4 KV point. THE TRIGGER LEVEL: This is where many technicians get discouraged because the waveform is not stable or walking across the screen.
In this example, we want to bring some awareness to the credible use of the DSO (digital storage oscilloscope).įirst and foremost there are 4 cardinal fundamental rules in order to master the use of the DSO.ġ. There are times when we need to go into the front door of diagnostics and look at the raw waveform. Someone once said that using scan data alone is basically back door diagnostics, meaning that the data we see, although mostly reliable, is basically homogenized has-been information. 1 diagnostic weapons of choice, we sometimes realize that there are some severe limitations on the data.
Although our scan tools are still our No. You have certainly heard the phrase that “a picture is worth a thousand words of information.” That especially is true on lab scope waveforms from both sides of the ignition system as well as input sensors and output devices.
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