User Manual

46
After the oscilloscope begins to capture data, the oscilloscope operates by first filling the pre-
trigger buffer. The oscilloscope starts searching for a trigger after the pre-trigger buffer is filled
and data continues to flow through this buffer while it searches for the trigger. While searching
for the trigger, the oscilloscope overflows the pre-trigger buffer and the first data put into the
buffer is pushed out.
When a trigger is found, the pre-trigger buffer retains the events that occurred just before the
trigger. Then, the oscilloscope fills the post-trigger buffer and displays both buffers on the screen.
Press the Auto, Normal or the Single button on the front panel to select the desired trigger mode.
The lighted button indicates the current trigger mode.
Auto: The oscilloscope waits for the trigger logical conditions to be satisfied, but if the trigger
conditions are not satisfied after a period of time, the oscilloscope generates an internal trigger
event, causing the trace to be displayed. Auto mode is useful for measuring DC voltages and
unknown signals. Once a signal is displayed, you may want to change to Normal mode.
Normal: The oscilloscope waits for the trigger logical conditions to be satisfied; when they are, a
trigger event is generated and the trace is displayed. The triggering circuitry re-arms itself and
again waits for the trigger logical conditions to be satisfied. Use normal triggering when you do
not want to see the horizontal line when the input is DC or there's no signal.
Single: This mode is the same as the normal mode, except the oscilloscope is put into the Stopped
state after the trigger event has occurred. The single trigger mode is commonly used to capture
infrequent transient events that do not repeat in time. One example of use is to capture the
contact bounce of a mechanical switch.
5.6 Trigger Level
The level and slope define the trigger point for an edge trigger. The trigger level can be adjusted
for an analog channel or external signal by turning the Trigger Level knob.
Push the Trigger Level knob to set the level to the middle of the waveform. If AC coupling is used,
pushing the Trigger Level knob sets the trigger level to approximately 0 V. The position of the
trigger level for the analog channel is indicated by the trigger level icon (if the channel is on)
on the right side of the display. The value of the analog channel trigger level is displayed in the
upper-right corner of the display. The color of the icon tells you which channel is providing the
trigger signal (more detailed information is in the trigger box in the right column of the screen.
Figure 44 - Trigger level for an edge trigger
Trigger Level
Negative Slope
Positive Slope
Trigger Point
Input Signal