Here is a typical lab scope screen. Lab scopes and ignition scopes both trace patterns that we refer to as waveforms. We use the lab scope to monitor voltage changes in a circuit over a measured time period.

The Graphing multimeter (GMM) is a rather unique tester. GMMs are a digital multimeter with a screen that can display anything over time, including volts, frequency, time and amps! Graphing multimeters are useful for finding intermittent voltage changes, or glitches. They are ideally suited to this task because they take many readings from a test circuit and then display a graph that shows the minimum and maximum (MIN/MAX) values recorded during measured test intervals. The GMM’s ability to graph intermittent electrical glitches can produce some very unusual waveforms!

Lab and ignition scopes need a trigger point to properly display a waveform. The trigger point is a voltage that crosses a voltage threshold to tell the scope when to start drawing its trace across the screen. For example, an ignition scope is triggered by the # 1 cylinder inductive pick up. If the # 1 cylinder misfires, the scope doesn’t get a stable trigger, and the scope has a hard time displaying the ignition patterns in the correct firing order. The pattern is jumpy, and unstable.

Quick Tip: If this happens, move the #1 pickup to another cylinder and see if the pattern stabilizes. If it does, correct the misfire problem in # 1 cylinder and try again.

For some tests, trigger slope, type, and level need to be manually adjusted. This means turn auto setup off!