Triggering on Waveforms
TDS 684A, TDS 744A, & TDS 784A User Manual 3–59
LF Rej removes the low frequency portion of the triggering signal. Low
frequency rejection attenuates signals below 80 kHz.
Noise Rej provides lower sensitivity. Noise Rej requires additional signal
amplitude for stable triggering, reducing the chance of falsely triggering on
noise.
NOTE. When you select Line as the trigger source, the oscilloscope uses AC
coupling to couple a sample of the AC line voltage to the trigger circuits.
Although trigger coupling can be set to other than AC when in Line, the
oscilloscope ignores the setting until another source (one of Ch1 through Ch4) is
selected.
In similar fashion, when you select DC Aux (Rear Panel) as the trigger source,
the oscilloscope uses DC coupling to couple an auxiliary signal to the trigger
circuits. Although trigger coupling can be set to other than DC when in DC Aux,
the oscilloscope ignores the setting until one of Ch1 through Ch4 is selected.
You can change the holdoff time and select the trigger mode using this menu
item. See Trigger Modes and Trigger Holdoff beginning on page 3–51 for a
description of these features. To set mode and holdoff, do the following steps:
1. Press the TRIGGER MENU ➞ Mode & Holdoff (main) ➞ Auto or
Normal (side). The modes operate as follows:
In Auto mode the oscilloscope acquires a waveform after a specific time has
elapsed even if a trigger does not occur. The amount of time the oscilloscope
waits depends on the time base setting. (Auto mode triggering is not
available in InstaVu mode; see Incompatible Modes on page 3–45.)
In Normal mode the oscilloscope acquires a waveform only if there is a valid
trigger.
2. To change the holdoff time, press Holdoff (side). Enter the value in time
using the general purpose knob or the keypad.
If you want to enter a large number using the general purpose knob, press the
SHIFT button before turning the knob. When the light above the SHIFT button
is on and the display says Coarse Knobs in the upper right corner, the general
purpose knob speeds up significantly.
You can set holdoff from 250 ns (minimum holdoff available) to 12 seconds
(maximum available). See Holdoff, Variable, Main Trigger in the TDS 684A,
TDS 744A, and TDS 784A Performance Verification and Specifications manual
for typical minimum and maximum values.
To Set Mode & Holdoff