User manual

28
Trigger System
t
1
<t
i
<t
2
: The pulse width ti which will generate the trigger
is less than the adjustable referance time t
2
and greater
than the adjustable reference time t
1
.
not(t
1
<t
i
<t
2
): The pulse width which will generate the
trigger is greater than the adjustable reference time t
2
and
less than the adjustable reference time t
1
.
As with the pulse trigger, for t
i
≠tort
i
= t you can set a refe-
rence time with the soft menu key TIME and the universal
knob. Selecting the soft menu item DEVIATION allows you
to use the universal knob and KEYPAD key in the CUR-
SOR/MENUcontrolpaneltosetthedeviation∆twhichde-
nesthetolerancebetweensetreference time t and valid
and real pulse width t
i
(permissible tolerance range)..
To change the threshold values for the logic states “one”
and “zero”, it is necessary to use settings in the channel
menu (MENU key in the VERTICAL section). Select the
POD
24
). If logic mode is already activated, the digital chan-
nels will be displayed in the channel display section of the
display (framed and marked with “POD:xxxV“). Pressing
the MENU key
21
in the VERTICAL section allows you to
activateoneofvepredenedlogiclevels.Threeofthese
arexedforTTL,CMOSandECL.Afterpressingtheres-
pective menu item, two customized logic levels may be set
from –2 V to 8 V (USER1 / USER2) with the universal knob
or the KEYPAD key in the CURSOR/MENU section. The soft
menu key SET TO DEFAULT POS. & SIZE activates the dis-
play for all digital channels of the selected group by using
default values for the vertical position and size. You may
alsodenethenameforthecurrentsignalbyusingthesoft
menuLABEL.Alibraryprovidesalistofpredenednames.
The name can be activated, deactivated or edited.
6.3.4 Video Trigger
The video trigger allows you to trigger on PAL, NTSC
SECAM standard video signals or on HDTV signals. After
selecting the VIDEO trigger press the SOURCE
32
key. The
FILTER
36
menuallowsyoutodeneadditionalsettings.
The oscilloscope triggers if the CVBS signal (Color Video
Baseband Signal) selected in the SOURCE menu features
the attributes set in the FILTER menu. Select the desired
standard by pressing the respective soft menu key STAN-
DARD. Use the universal knob in the CURSOR/MENU sec-
Fig. 6.5: Logic channels’ settings display
tion or press the soft menu key again to select the desired
standard. The following modes are available:
PAL
NTSC
SECAM
PAL- M
SDTV 576i Interlaced
HDTV 720p Progressive
HDTV 1080p Progressive
HDTV 1080i Interlaced
The second setting will apply to the polarity of the sync
pulse (may be positive or negative). With positive video
modulation (the highest brightness is represented in the
image by the maximum signal voltage), the synchroniza-
tion pulses are negative, with negative modulation they
are positive. The slopes of the synchronization pulses are
used for triggering which explains why a faulty polarity
setting causes irregular triggering by image information.
Next you can select between frame triggering (FRAME)
and line triggering (LINE). Selecting LINE allows you to
denetheexactlinebetween1and625viauniversalknob
or the KEYPAD button in the CURSOR/MENU section. The
soft menu item ALL LINES enables the oscilloscope to
trigger on the start of the lines in the video signal. This key
selects all lines i.e. even when other trigger conditions are
met, the oscilloscope will trigger on each line. If FRAME
is selected for frame triggering, the lower menu items will
allow to trigger on ODD or only EVEN half frames. In this
case, the oscilloscope will trigger on the start of the half
frames in the video signal. The respective key will select
the odd (even) half frames, i.e. even if the other trigger
conditions are met, the oscilloscope will trigger on each
odd (even) half frame.
6.3.5 Trigger Hold Off Time
The trigger hold off time indicates how long after a trigger
the R&S®HMO3000 series waits until the trigger system
is ready again. The trigger system is active again only
after the trigger hold off time has expired. This allows the
function to guarantee stable triggering in case unwanted
events are triggered. Ideally, the hold off time is used to
trigger on periodic signals with several slopes.
HOLD OFF is a dual soft menu key. If the top section of the
Fig. 6.5: Video trigger menu