Hysteresis

Hysteresis, also known as window size, adds a window above or below the trigger level. Hysteresis reduces false triggering caused by noise or jitter in the signal.

The Oscilloscope uses a hysteresis which is 25% of Volts/div. For example, when you set Volts/div to 0.08 V, the hysteresis is 0.02 V. The way this hysteresis works depends on the value you specify for Slope in trigger settings, as described in the following table:

Slope Description
Rising The Oscilloscope detects a trigger when the signal starts or drops below Level minus hysteresis and then rises above Level.
Falling The Oscilloscope detects a trigger when the signal starts or rises above Level plus hysteresis and then drops below Level.
Either The Oscilloscope detects a trigger when the signal starts or drops below Level minus hysteresis/2 and then rises above Level, or when the signal starts or rises above Level plus hysteresis/2 and then drops below Level.

How the Oscilloscope Uses Hysteresis to Avoid False Triggering

The following figure explains how the Oscilloscope uses hysteresis to avoid false triggering when Slope is Falling:


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  1. The Oscilloscope detects a trigger when the signal first rises above the trigger level plus hysteresis and then drops below the trigger level.
  2. The Oscilloscope does not detect any trigger, because the signal stays below the trigger level plus hysteresis since the Oscilloscope last detected a trigger.
  3. The Oscilloscope detects another trigger.

The following figure explains how the Oscilloscope uses hysteresis to avoid false triggering when Slope is Rising:


1378

  1. The Oscilloscope detects a trigger when the signal first drops below the trigger level minus hysteresis and then rises above the trigger level.
  2. The Oscilloscope does not detect any trigger, because the signal stays above the trigger level minus hysteresis since the Oscilloscope last detected a trigger.
  3. The Oscilloscope detects another trigger .

The following figure explains how the Oscilloscope uses hysteresis to avoid false triggering when Slope is Either:


1378

  1. The Oscilloscope detects a trigger when the signal first rises above the trigger level plus hysteresis/2 and then drops below the trigger level.
  2. The Oscilloscope detects another trigger when the signal first drops below the trigger level minus hysteresis/2 and then rises above the trigger level.
  3. The Oscilloscope does not detect any trigger, because the signal stays above the trigger level minus hysteresis/2 since the Oscilloscope last detected a trigger.