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7.9.2.1

Hysteresis

Hysteresis is a feature of the advanced trigger types in PicoScope 6 that reduces

false triggering on noisy signals. When hysteresis is enabled, a second trigger

threshold voltage is used in addition to the main trigger threshold. The trigger fires

only when the signal crosses the two thresholds in the correct order. The first

threshold arms the trigger, and the second causes it to fire. An example will help to

illustrate how this works.

Noisy signal with a single threshold

Consider the very noisy signal above. It is difficult to trigger reliably on this signal

with a normal rising edge trigger because it crosses the trigger threshold, the red line

in this picture, several times in one cycle. If we zoom in on the highlighted parts of

the signal, we will see how hysteresis can help.

Noisy signal with hysteresis threshold

In these zoomed-in views, the original threshold is the lower red line. The upper red

line is the second threshold used by the hysteresis trigger.

The signal rises across the lower threshold at (1) and (2), arming the trigger but not

firing it. At (3) the signal finally crosses the upper threshold, firing the trigger. On the

falling edge of the signal, at (4) and (5), rising edges of noise pulses cause the signal

to cross the upper and lower thresholds, but in the wrong order, so the trigger is not

armed and does not fire. Thus the trigger occurs at only one well-defined point in the

cycle (3), despite the noise on the signal.

Hysteresis is enabled by default for all the advanced trigger types. The Hysteresis

controls in the Advanced triggering dialog let you change the hysteresis voltage as

a percentage of full scale. The trigger marker shows the size of the hysteresis

window.

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