Continuous Logging Using Data Buffers - Keysight N7744A User Manual

3
Power Meter Applications

Continuous Logging Using Data Buffers

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The most important parameters for the logging application are:
•
[Samples], this is the number of samples that will be performed
during the logging application, and
•
[AvgTime], the averaging time is the length of time over which a
signal is averaged. Longer averaging times increase the accuracy and
improve the noise rejection. Longer averaging times also improve
sensitivity.
The total time for a logging application is the number of samples
multiplied by the averaging time. The power range is constant during a
logging application and autoranging is disabled.
The Logging application differs from the "The Stability
Application" (see, "The Stability Application" on page
power measurements are performed consecutively without the
possibility of any pause between measurements, as shown in the
figure, above.
While performing the logging application all used ports of the
instrument will have the same averaging time and number of samples.
Setup parameters for each of the ports should be set before the logging
is started on any port. Only N7747A and N7748A allow different settings
for logging parameters on each channel.
The logging function is often used together with single-measurement
input triggering for synchronized measurement with another
instrument, especially for spectral measurements with a tunable laser.
Enhanced logging functionality is available using two data buffers for
each port.
The MPPM ensures there is no time lag between logging and data
availability by using a data buffer with a capacity of 1M samples for each
channel. You can read the most recent results out of one buffer out while
the next logging measurement is filling the other buffer.
You can use this to speed up applications with repeated logging
operations. It is especially valuable for monitoring signals over
extended periods to detect transient events.
To use the data buffers, set the logging function to perform a fixed or
indefinite number of "LOOP"s, as described in the Programming Guide.
•
When LOOP = 1, default logging behavior is selected, that is
measurements are made and the results are written to the first
buffer.
•
If LOOP = 0, logging continues, writing the results into alternate
buffers, until you stop it.
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Keysight N774x Series