User Manual

Sampling oscill

oscope concepts

Trigger concepts

The oscilloscope uses the data in the waveform record to construct and display a waveform on the oscilloscope screen.

However, as the oscilloscope is constantly acquiring samples into the waveform record, each waveform record starts at a

random point of the input signal. This means that the waveform record s ample values are constantly changing, which results

in a displayed waveform that is unstable or jittering. An unstable waveform cannot be accurately measured, making this

display useless except for very broad measurements (type of signal, approximate peak to peak signal amplitude).

Untriggered display

What is needed is a way to set the oscilloscope to detect, or trigger on, the same signal condition or state on the input signal

for each waveform acquisition, and store the samples in the waveform record such that the same signal condition is at

the same s ample time location in the waveform record.

A trig ger sets when the oscilloscope detects a deﬁned waveform condition, such as at a speciﬁed signal voltage level on

the rising edge of the signal. The oscilloscope uses that trigger condition to store the waveform samples in the waveform

record so that the signal sample point that meets the trigger condition is at the same location in the waveform record. When

displayed, the waveform record for each acquisition shows the waveform at the same trigger point, resulting in a stable

waveform on the screen.

Triggered disp lay

Understanding and using triggers is probably the most import ant skill needed to quickly display and analyze w aveforms.

A trigger condition can be as simple as when the signal passes through a speciﬁed voltage level when going from a low

level to a high level (positive slope). A trigger condition can also be very speciﬁc, such as when the signal level is falling

and the width of a single pulse of the signal is less than a speciﬁed time period.

The trigger point in a waveform record a lso sets the zero time-reference point in a waveform record. By default, the trigg

point in a waveform record is in the center of the waveform record. This means that half of the record shows the signal

waveform before the trigger condition (pretrigger), and the other half shows the waveform after the trigger condition

(post-trigger).

26 TBS2000 Series User Manual