Vaisala RVP900

USER’S MANUAL__________________________________________________________________
120 _________________________________________________________________ M211322EN-D
completely disabled whenever 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 will be drawn cross–hatched and at a
location computed according to the current PRF. The cross–hatching
serves as a reminder that the actual location of that trigger may vary
from it's 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
whenever the RVP900 is generating multiple–PRT triggers, for
example, during DPRT mode, or during Dual–PRF processing.
Multipliers from 0.0 to +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)) would position
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.
A small but important detail is built into the algorithm for producing the
six user trigger waveforms. It applies whenever a) the trigger period is
internally determined, that is, the external pretrigger input is not being
used, and b) the overall span of the six trigger definitions combined does
not fit into that period. What happens in this case is that any waveforms
that do not fit will be zeroed (not output) so that the desired period is
preserved. This means that you can define triggers with large positive start
times, and they will pop into existence only when the PRF is low enough
to accommodate them.
For example, if Trigger #2 is defined as a 200.0µsec pulse starting at
+400.0µsec, then that trigger would be suppressed if the PRF were
2000Hz, but it would be present at a PRF of 1000Hz. Whenever a trigger
does not completely fit within the overall period it is suppressed entirely.
Thus, even though the +400.0µsec start time is still valid at 2000Hz, the
entire 200.0µsec pulse would not fit, and so the pulse is eliminated
altogether.
Start limits: -5000 µsec to 5000 µsec Width limits: 0 µsec to 5000 µsec
Maximum number of Pulses/Sec: 2000.0
Maximum instantaneous 'PRF' : 2000.0 (/Sec)
These are the PRF protection limits for this pulse width.
The wording of the "Maximum number of Pulses/Sec" question serves as
a reminder that the number shown is not only an upper bound on the PRF,
but also a duty cycle limit when DPRT mode is enabled.