Series 8650B Universal Power Meters
3-108
Publication 31470-001, Rev C, November 2, 2017
3.17
Measurement Collection Modes (GPIB-Fast)
3.17.1
General
The 8650B offers three special fast measurement collection modes which are available only during remote
operation over the GPIB interface. These GPIB-fast modes make it possible to take more measurements per
second, but at the cost of limited functionality compared to the standard measurement collection mode. The
GPIB-fast modes operate differently from the standard measurement collection mode in several important
ways. The three GPIB-fast modes are called Swift, Fast Buffered (also known as Burst) and Fast Modulated.
3.17.1.1
Sensor Measurements Supported
One restriction on the 8650B functionality in the GPIB-fast modes is that it cannot perform comparative
measurements (that is, measurements consisting of a comparison between the two sensors, such as A/B or A-B).
However, when the 8650B operates in the Swift and Fast Buffered modes, it does have an added capability
which is not otherwise available: measurements from both sensors can simultainiously be returned to the host.
In the Fast Modulated mode, only one sensor measurement can be performed and returned to the host.
3.17.1.2
Averaging
In standard measurement collection modes the averaging factor is taken to indicate the amount of filtering
desired. Each measurement which is returned to the host is a true running average for a period of time which is
derived from the averaging factor. This also holds true in the Fast Modulated mode.
The averaging feature has a unique implementation in the Swift and Fast Buffered modes. In the Swift and Fast
Buffered modes, the averaging factor
n
indicates the exact number of samples to be taken and averaged for
each returned measurement, with the proviso that a minimum of four samples are taken (even if a number
below four is requested). Therefore, each returned measurement is an average based on
n
independent samples
as opposed to a running average.
NOTE:
Four samples are also taken if auto averaging is selected. Each measurement returned to the host
reflects all new data. Therefore, operation will be much faster with an averaging factor of four than with
a higher number.
3.17.1.3
Disabled Features
The following features are disabled during operation in any of the three GPIB-fast modes: over-range alert, limit
checking, min/max power, relative measurements, peaking meter, analog output, and V
PROP
F correction.
3.17.1.4
Measurement Changes
Other changes to the operation of the instrument during GPIB-fast operation include the following: the
temperature of the sensors is not read and updated, so the temperature correction will become inaccurate over
time if the temperature of the sensor changes.
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