Tektronix 310A, Инструкция по эксплуатации, Страница: 19 / 132

Operating ln$truction$-Type 310A
trigger signal reaches a DC voltage level selected by the
setting o f the TRIG LEVEL control. When using the inter­
nal trigger source, the setting o f the V E R TIC A L POSITION
control affects the DC triggering point.
Trigger Slope
The TRIGGER switch selects the triggering slope as well
as the source. Each source selected by the TRIGGER
switch provides both + and — slope selection. When the
TRIGGER switch is in a + (positive-going) position, the
trigger circuits respond to the positive-going portion o f the
triggering waveform; in a — (negative-going) position, the
trigger circuits respond to the negative-going portion o f the
triggering waveform (see Fig. 2-6). Since this instrument
does not have an internal delay line, the display may not
start-on the selected slope, particularly when the displayed
waveform has a high repetition rate. When several cycles of
a signal appear in the display, the triggering slope is often
unimportant. However, if only a certain portion o f a cycle
is to be displayed, correct setting of the TRIGGER switch
is im portant to provide a display of the desired portion of
the input signal.
Stability Control
The S T A B ILIT Y control determines whether the time-
base generator is free-running, triggerable, or not trigger-
able when the Trigger Coupling-Mode switch is set to AC or
DC. When the S T A B ILIT Y control is set fu lly clockwise,
the time-base generator is free-running at a repetition rate
determined by the setting o f the T IM E /D IV switch. As the
S T A B ILIT Y control is turned counterclockwise, the free-
running condition ends when the control is near midrange
(TRIG LEVEL control set fu lly clockwise). A t this setting
o f the S T A B ILIT Y control, a triggered display can be ob­
tained w ith the TRIG LEVEL control (adequate trigger sig­
nal applied). In the fu lly counterclockwise position (not in
PRESET detent), the time-base generator is inoperable and
cannot be triggered. The PRESET position automatically
sets the time-base generator fo r triggerable operation w ith
most trigger signals. In this position, only the TRIG LEVEL
control needs to be adjusted to obtain a stable display. The
S T A B ILIT Y control is inoperable in the AUTO position of
the Trigger Coupling-Mode switch.
Trigger Preset Adjustment
The PRESET ADJUST is normally adjusted during in­
strument calibration (see Calibration section) and should
not need readjustment during normal use. However, the
follow ing procedure can be used to set the PRESET A D ­
JUST if the Type 31OA cannot be triggered correctly. Be­
fore readjusting the PRESET ADJUST, be sure the trig ­
gering controls are correctly set and the applied trigger
signal is w ithin the required limits.
1. Set the T IM E /D IV switch to 1 MSEC.
2. Set the Trigger Coupling-Mode switch to AUTO.
3. Turn the PRESET ADJUST fu lly counterclockwise.
®
4. Slowly turn the PRESET ADJUST clockwise until
the trace first appears. Note the position of the PRESET
ADJUST.
5. Continue to slowly turn the PRESET ADJUST clock­
wise until the trace brightens. Again note the position of
the PRESET ADJUST.
6. Set the PRESET ADJUST halfway between the point
where the trace first appeared in part 4 and where the trace
brightened in part 5.
Trigger Level
The TRIG LEVEL control determines the voltage level
on the triggering waveform at which the sweep is triggered
(Trigger Coupling-Mode switch set to AC or DC). When the
TRIG LEVEL control is set in the + region, the trigger
circuit responds at a more positive point on the trigger
signal. In the — region, the trigger circuit responds at a
more negative point on the trigger signal. Fig. 2-6 illustrates
this effect w ith different settings of the TRIGGER switch.
The TRIG LEVEL control is inoperative in the AUTO posi­
tion o f the Trigger Coupling- Mode switch.
To set the TRIG LEVEL control, first select the trigger
source, slope and coupling. Then set the S T A B ILIT Y con­
trol to the PRESET position. Now, rotate the TRIG
LEVEL control fu lly counterclockwise and slowly turn it
back clockwise until a stable display appears. Further rota­
tion in the clockwise direction causes the sweep to trigger
at a more positive point on the triggering waveform. If a
stable display cannot be obtained in this manner w ith the
S T A B IL IT Y control set to the PRESET position, use the
follow ing procedure; (be sure an adequate trigger signal is
available):
1. Set the TRIG LEVEL control fu lly clockwise.
2. Set the S T A B ILIT Y control fu lly clockwise and then
rotate it counterclockwise until the free-running display
just disapppears.
3. Rotate the TRIG LEVEL control counterclockwise
until a stable display is obtained.
Trigger Mode
The Trigger Coupling-Mode switch (concentric w ith the
TRIGGER switch) selects the operating mode of the trig ­
gering circuits. When this switch is in the AC or DC posi­
tions, the trigger circuits operate in the normal triggering
mode. The TRIG LEVEL and S T A B ILIT Y controls must
be adjusted to obtain a stable display. When a trigger signal
is not present, there is no display. Use the normal triggering
mode to display signals w ith repetition rates below about
60 hertz, or when it is desired to select the triggering point
on the displayed waveform. This mode provides an indica­
tion of an adequate trigger signal as well as the correctness
of trigger control settings, since there is no display w itho ut
correct triggering. For information on selecting the trigger
2-11