Lambda SR1, Руководство по эксплуатации, Страница: 198 / 317

SR1 Operation Manual 198
© 2014 Stanford Research Systems
FFT Cursors Tab
For FFT-type traces, the FFT cursors tab offers some additional cursor measurements. Checking "Calc.
Power" displays the RMS integrated power in the spectrum between the two cursors as well as the RMS
integrated power
outside of the two cursors.
Checking "Calc. THD Ratio" calculates the ratio of power in harmonics of the fundamental to the power
in the fundamental. The fundamental is marked using the left-most cursor. The maximum harmonic
frequency included in the measurement is marked by the right-most cursor. All harmonics, odd and
even, up to the maximum frequency are used in calculating the ratio. For a more sophisticated THD
measurement that allows the choice of specific harmonics use the
THD Analyzer .
Checking "Calc SNR" calculates the Signal-to-noise ratio of the signal.Signal-to-noise is defined as the
ratio to the peak signal contained within the cursor region to the integrated power in the cursor region
excluding the peak signal.
Limits Tab
Graphs have the capability to check trace data against predefined upper and lower limits. To create an
upper or lower limit, click the appropriate radio button and click on "New...". A dialog appears allowing
selection of an existing trace on which to base the limit. The selected trace determines which of the
graph traces can by limit-tested; only traces with X and Y axes compatible with the limit trace can be
tested. For instance if the trace selected as the limit is an FFT trace then all FFT traces on the graph
may be limit tested but a time-record trace cannot be. (The X-axis of the time record is incompatible with
the frequency X-axis of the FFT).
Once the trace for the limit has been selected a list of compatible traces appears in the Limit Tab. Each
trace can be selected for limit testing by checking the box adjacent to the trace name. Once selected, a
green or red box appears indicating whether the trace data passes or fails the limit test. If both an upper
and lower limit is present the trace must pass
both limits in order to pass. The red box on the tab
indicates the "AND" of all the pass/fail results for the individual traces.
When first created a limit trace contains identical data to the trace that it was created from. Press "Edit"
to change the limit data. (Note that X-values must be in increasing order.)