Chapter 5 Trigger System
47
Trigger coupling description
When the edge trigger setup menu is opened, the trigger coupling option is displayed below the menu. Trigger
coupling includes DC, AC, HFRei., LFRej., NoiseRej, see Figure 5-12:
Figure 5-12 Trigger Coupling Menu
1)
DC coupling - allows DC and AC signals to enter the trigger path.
2)
AC coupling - removes any DC offset voltage from the trigger waveform.
When the waveform has a large DC offset, stable edge triggering can be achieved using AC coupling.
3)
HFRej. (High Frequency Rejection Coupling) - removes high frequency components from the trigger
waveform, using high frequency rejection to remove high frequency noises or noises from fast system clocks,
from trigger paths such as AM or FM radio stations.
4)
LFRej. (Low Frequency Rejection Coupling) - removes any unnecessary low frequency components from
the trigger waveform, for example, power line frequencies that can interfere with correct trigger.
When there is low frequency noise in the waveform, stable edge triggering can be obtained using LF
rejection coupling.
5)
NoiseRej. (Noise Rejection Coupling) - Noise rejection can add extra hysteresis to the trigger circuit. By
increasing the trigger hysteresis band, the possibility of noise triggering can be reduced. But it also reduces
the trigger sensitivity, so triggering the oscilloscope requires a slightly larger signal.
Note: Trigger coupling is independent of channel coupling.
5.3 Pulse Width Trigger
The trigger happens when the trigger signal pulse width (8ns~10s, the trigger type indication icon at the top of
the screen is
) reaches the set condition and the signal voltage reaches the set trigger level. Pulse width
trigger menu is shown in the following table:
Trigger
Option
Setting
Description
Trigger Source
CH1
Set CH1 as trigger signal source
CH2
Set CH2 as trigger signal source
CH3
Set CH3 as trigger signal source
CH4
Set CH4 as trigger signal source
Polarity
Positive
Trigger on setting the positive pulse width of signals
