Triggering 4
InfiniiVision Oscilloscopes User’s Guide 87
Trigger Coupling
1 Press the [Mode/Coupling] key.
2 Press the Coupling softkey, then select DC, AC, or LF Reject coupling.
• DC coupling allows DC and AC signals into the trigger path.
• AC coupling places a 10 Hz high-pass filter in the trigger path removing any DC
offset voltage from the trigger waveform. The high-pass filter in the External Trigger
input path is 3.5 Hz for all models. Use AC coupling to get a stable edge trigger
when your waveform has a large DC offset.
• LF (low frequency) Reject coupling places a 50 kHz high-pass filter in series with
the trigger waveform. Low frequency reject removes any unwanted low frequency
components from a trigger waveform, such as power line frequencies, that can
interfere with proper triggering. Use this coupling to get a stable edge trigger when
your waveform has low frequency noise.
• TV coupling is normally grayed-out, but is automatically selected when TV trigger is
enabled in the Trigger More Menu.
Note that Trigger Coupling is independent of Channel Coupling. To change Channel
Coupling see page 61.
Trigger Noise Rejection
If the signal you are probing is noisy, you can set up the oscilloscope to reduce the noise
on the displayed waveform. First, stabilize the displayed waveform by removing the noise
from the trigger path. Second, reduce the noise on the displayed waveform.
1 Connect a signal to the oscilloscope and obtain a stable display.
2 Remove the noise from the trigger path by turning on high-frequency rejection (HF
Reject), low-frequency rejection (LF Reject), or Noise Rejection.
3 Use Averaging Mode to reduce noise on the displayed waveform.
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