Series 8650B Universal Power Meters
3-112
Publication 31470-001, Rev C, November 2, 2017
Two simpler commands are also based on the FBUF function code:
Syntax:
FBUF [DUMP or OFF]
FBUF is the function code for Fast Buffered Mode
[DUMP] stops the data measurement and buffering, and prepares to return the data taken so far
to the host, even if fewer than the requested number of measurements have been taken. The
requested number of measurements are still returned to the host (the extra measurements
beyond those actually taken are represented by the number - 300.00)
[OFF] causes the 8650B to exit the Fast Buffered mode. All unread data is lost
Example:
FBUF DUMP
! STOP MEASUREMENT AND BUFFERING
Example 2:
FBUF OFF
! EXIT THE FAST BUFFERED MODE
3.17.3.1
Fast Buffered Mode Notes
Fast Buffered mode cannot be entered if a modulated measurement (MAP, PAP or BAP) is being performed.
Fast Buffered mode is the fastest method of collecting measurement data. Top speed in the Fast Buffered mode
is achieved by using a low averaging number (≤4), the POST trigger mode, and no time delay between
measurements.
The POST trigger mode is faster than the PRE trigger mode because in the latter mode the 8650B must check for
a trigger between each measurement. Using PRE requires some caution. The single processor in the 8650B is
constantly performing data acquisition. Sending any configuration commands while collecting the PRE trigger
data can result in interrupted timing of the data point collection. In the POST mode, the 8650B is in free-run
operation after the trigger is received.
The 8650B controls its gain ranges transparently by verifying internal range changes just before and just after
individual measurement points. If the internal range does not remain the same, the data point will be disgarded
as invalid. This can result in a successful Fast Buffered mode measurement with less measurement data than
expected according to the specified buffer parameter.
For the sake of speed, no chopped measurements are taken in the Fast Buffered mode. Be aware that this will
limit the dynamic range of the power sensor and and therefore limit the low-level accuracy of collected
measurements.
After issuing the Fast Buffered command, allow time for the 8650B to set up in Fast Buffered mode before
issuing an external TTL trigger, a BUS trigger (i.e. *TRG), or a GET (Group Executable Trigger). Typical delay time
for the 8650B to set up in Fast Buffered mode may vary from 200 msec to 500 msec based on the number of
samples to be collected.
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