Boonton 4540 Peak Power Meter User Manual - Manual (Page 192)

Boonton 4540 Series RF Power Meter
Remote Operation 5-58
5.6.13 SENSe:MBUF Data Array Commands
The MBUF commands (which are grouped under the SENSe subsystem) are used to control buffered data capture and output
of a long array of sequential readings (the ―Measurement BUFfer‖). This capability is useful for capturing readings at a rate
higher than the host system can read back in real time. These commands are used in all but Statistical modes, and allow
control of buffer size, reading rate, status reporting, and buffer array output. Up to 1M readings may be captured at
programmable rates up to 1000 readings per second in Modulated mode, and up to 1000 triggered readings per second
(timebase dependent) in Pulse mode.
The measurement buffer may be operated in either fixed length mode or circular/FIFO mode, as controlled by
SENSe:MBUF:SIZe. In fixed length mode, the buffer fills from the beginning with a programmed number of readings, and
then stops buffering and asserts the ―measurement complete‖ status. Measurement action may or may not continue,
depending upon settings, but the buffer contents will be preserved.
In circular/FIFO mode, the SIZE parameter is not used, and the buffer ―wraps‖ at the end, with data buffering continuing
indefinitely. In this case, when the entire buffer has been filled, fresh data begins to fill again from the beginning, and
overwrites the old data. As the buffer can store 1M readings before wrapping, there is usually plenty of time (many minutes)
to retrieve all of the buffered values before overwrite occurs.
Partial buffer results are available to the user as soon as they have been acquired, with no need to wait until buffering is
complete. The user may query the current acquisition position and may define a read position and count, or simply request
all unread buffer points. When operating in circular/FIFO mode, the buffer operates like a 1M long FIFO, in which each read
begins with the oldest unread point and ends with the most recent.
In Modulated mode, each stored reading in the measurement buffer is the value that would be returned as the current average,
minimum or maximum power measurement over the GPIB, including all filtering. To ensure no overlap between
measurements, it may be preferable to set filtering off, or to a value shorter than the buffer period, which is the inverse of the
SENSe:MBUF:RATe setting.
In Pulse mode, each stored reading in the measurement buffer is the average, minimum or maximum power within the
defined marker interval for that sweep, including all averaging. To ensure no overlap between measurements, the trace
averaging (SENSe:AVERage) should usually be set to 1, and the timebase (DISPlay:PULSe:TIMEBASE) should be set to
1 μs/division or slower. If it is important that the average power over every pulse be recorded, with no pulses missing, then
sufficient time after each trigger must be allowed for the power meter to complete the sweep, process the sampled data, and
rearm for the next sweep. The acquisition, processing and rearm time varies with timebase, trigger delay and holdoff, marker
interval, and
Maximum buffer rate in pulse mode is highly timebase dependent, and is somewhat affected by other settings such as the
number of channels enabled, trigger position on screen, and marker interval duration. Rearm time will also be directly
extended by trigger holdoff, and pre- or post-trigger delay if these features are used. The following table shows the
maximum buffered sweep rate achieved versus timebase.
These values are typical 4542 pulse-mode trigger rates with two channels
enabled, trigger position set to "1.0 division", zero holdoff and trigger
delay, and marker interval set to two display divisions. Trigger rate will be
faster for single-channel operation, and slower for longer marker intervals.
Timebase Typical Trigger Rate
1us/div 625Hz
2us 500Hz
5us 400Hz
10us 333Hz
20us 200Hz
50us 100Hz
100us 50Hz
200us 30Hz
500us 20Hz
1ms/div 20Hz