Trigger #1 Start: 0.00 usec
#1 Width: 1.00 usec High:YES
Trigger #2 Start: 0.00 usec + ( 0.500000 * PRT )
#2 Width: 10.00 usec High:YES
Trigger #3 Start: -3.00 usec
#3 Width: 1.00 usec High:YES
Trigger #4 Start: -2.00 usec
#4 Width: 1.00 usec High:YES
Trigger #5 Start: -1.00 usec
#5 Width: 1.00 usec High:YES
Trigger #6 Start: -5.00 usec + (-0.001000 * PRT )
#6 Width: 2.00 usec High:NO
Some subtleties of these variable start times are:
• The PRT multipliers can only be used with the RVP900 internal trigger generator. The
PRT–relative start times are completely disabled when an external trigger source is
chosen from the Mt menu.
• When PRT–relative triggers are plotted by the Pb command, the active portion of the
trigger is drawn cross–hatched at a location computed according to the current PRF.
The cross–hatching serves as a reminder that the location of that trigger may vary from
its presently plotted position.
• The PRT multiplier for a given pulse is applied to the interval of time between that
pulse and the next one.
This distinction is important when RVP900 generates multiple–PRT triggers, for
example, during DPRT mode, or during dual–PRF processing.
Multipliers from 0.0 ... +1.0 are generally safe to use because they shift the trigger into
the same pulse period that originally
defined it. For example, a start time of (0.0
μsec + (0.98 * PRT)) positions a trigger 98% of the way up to the next range
zero. But, if -0.98 were used, and if the period of the previous pulse was shorter than
the current one, then that shorter period would become incorrect (longer) as a result of
having to
fit in the very early trigger.
In some situations, waveforms that do not fit are zeroed (not output) to preserve the desired
period. This means that you can define triggers with large positive start times, and they
come into existence only when the PRF is low enough to accommodate them. It applies
when:
• The trigger period is internally determined, that is, the external pretrigger input is not
being used.
• The overall span of the six trigger
definitions combined does not fit into that period.
For example, if Trigger #2 is defined as a 200.0 μsec pulse starting at +400.0 μsec:
• The trigger is suppressed if the PRF is 2000 Hz.
• The trigger is present at a PRF of 1000 Hz.
• If a trigger does not completely
fit within the overall period it is suppressed.
This means that although the +400.0μsec start time is still valid at 2000Hz, the entire 200.0
μsec pulse would not fit, and the pulse is eliminated.
Start limits: -5000 ... 5000 μsec
Chapter 5 – TTY Non-volatile Setups
117
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