Use the AC coupling feature to eliminate unwanted DC signal components or keep DC offset by using DC coupling.

Hint: Always use AC coupling when the AC signal is superimposed on a DC voltage that is higher than the trigger level setting range. However, we recommend AC coupling in many other measurement situations as well. When you measure symmetrical signals, such as sine and square/triangle waves, AC coupling filters out all DC components. This means that a 0 V trigger level is always centered around the middle of the signal where triggering is most stable.

Figure 8. AC coupling a symmetrical signal.

Hint: Signals with changing duty cycle or with a very low or high duty cycle do require DC coupling. Figure 8 shows how pulses can be missed, while Figure 9 shows that triggering does not occur at all because the signal amplitude and the hysteresis band (please see for explanation of what is Hysteresis Band) are not centered.

Figure 9. Missing trigger events due to AC coupling of signal with varying duty cycle.
Figure 10. No triggering due to AC coupling of signal with low duty cycle.

Hint: always use DC coupling for signals below 10 Hz.