Trig'd; Level; Trig Pos; Atrig Pos - Tektronix 7D20 Operator's Manual

Operating Instructions-7D20
TRIG'D
This indicator light illuminates when signal acquisition is triggered . In the ROLL
digitizing mode triggers are not required so the TRIG'D light doesn't illuminate
except when the HOLD NEXT function is active (refer to the discussion of the HOLD
NEXT mode . In the absence of a trigger event the digitizer ceases to update and the
last triggered acquisition is displayed . If the trigger light is on but the display is
unstable, this usually indicates an aliasing condition . Turn the TIME/DIV control
clockwise until a stable display is obtained . Refer to the Operational Theory, Section
3 for a discussion of aliasing .
LEVEL
The LEVEL control adjusts the voltage level on the trigger signal at which triggering
occurs. When the LEVEL control is set in the clockwise direction, the trigger circuit
responds at a more positive point on the trigger signal . When the LEVEL control is
set in the counterclockwise direction, the trigger circuit responds at a more negative
point on the trigger signal .
The LEVEL control range is approximately ±fi .4 divisions in the AUTO and NORM
TRIGGERING MODES . Refer to TRIGGERING MODE in this section for level range
information in the P-P MODE .
To set the LEVEL control, first select the triggering MODE, COUPLING, SOURCE,
and +SLOPE . Turn the LEVEL control fully counterclockwise then, rotate it clockwise
until the display of the acquired signal begins at the desired point .
aTRIG POS ~
The TRIG POS (trigger position) stewing keys allow you to increment ~ or
decrements the trigger position by whole divisions from its zero position on the left
vertical graticule line . The trigger position appears in the upper right corner of the
display as shown in Figure 2-52 . A full 10-divisions of pre-trigger can be displayed
by moving the trigger position fully to the right of its zero position . In the opposite
direction, the trigger position can be moved to the left of zero to achieve up to 1500
divisions of post trigger . When a TRIG POS key is pressed and held, the trigger
position automatically stops incrementing or decrementing when its limit is
reached . Likewise, when moving it back toward zero by pressing and holding the
appropriate key, the trigger position automatically stops at zero . Trigger position 0
on the graticule includes several points of pretrigger data prior to the graticule line .
In the extended real-time mode 10 pretrigger points are shown, and in the digitizing
modes, 12 points of pretrigger are displayed .
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