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USING THE COMBISCOPE INSTRUMENTS 3 - 27
3.4.1.4 Pre- and post-triggering
When pre-triggering is selected, the real trace acquisition begins before the
moment that the trigger occurs. Triggering occurs when the trigger conditions are
satisfied and the instrument leaves the "Wait for TRIGger" state as shown in the
trigger diagram of figure 3.3. In a similar way, post-triggering causes the
acquisition to begin after the moment that the trigger occurs.
Pre- and post-triggering are programmed with the SENSe:SWEep:OFFSet:TIME
command. A positive parameter value specifies a post-trigger delay, whereas, a
negative value results in a pre-trigger view.
After
*
RST, the SENSe:SWEep:OFFSet:TIME is set to -0.005, which results in a
pre-trigger view of 5 ms. Because the
*
RST value of the total acquisition time
(SENSe:SWEep:TIME) is 10 ms, the trigger point is positioned in the middle of
the trace.
PROGRAM EXAMPLE:
CALL Send(0, 8, "SENSe:SWEep:OFFSet:TIME 0.001", 1) ’
1 ms post-trigger
CALL Send(0, 8, "SENSe:SWEep:OFFSet:TIME -1E-3", 1) ’
1 ms pre-trigger
Trace
begin
end
time axis
total acquisition time
pre trigger
trigger moment
SENSe:SWEep:TIME
SENSe:SWEep:OFFSet:TIME
ST7190
Trace
begin
end
time axis
total acquisition time
post trigger
trigger moment
SENSe:SWEep:TIME
SENSe:SWEep:OFFSet:TIME
ST7191
Figure 3.9 Post-triggering
Figure 3.8 Pre-triggering