5120A/5115A Operations and Maintenance Manual 45
5.3 Configuring the Phase Difference Plot
The phase difference plot shows real-time measurements each second. After approximately nine
minutes, data pans to the right as new data becomes visible. All measurements are referenced to
the Input signal.
The phase difference plot shows the following:
Value of the center line, or its origin and slope when linear trend is removed. See “5.3.2
Removing the Linear Trend” on page 45 for details.
Value per division on the y axis in seconds.
Value per division of the x axis in seconds. This cannot be changed.
5.3.1 Scaling the Phase Difference Plot
The phase difference plot can do the following:
Automatically scale the y axis to fit all data.
Display the y axis in fixed-scale mode.
The x axis displays 60 seconds of data per division.
To scale the plot:
1. Press Phase Diff Plot (see “3.1.1 Navigation” on page 12).
2. Press Config Phase Diff.
To automatically scale the y axis, press Auto Scale Y Axis.
To use a fixed scale, press Fixed Scale Y Axis, then press one of the following:
• Use Shift Up 1 Div and Shift Down 1 Div to shift (scroll) the data up or down
one division on the screen.
• Use Increase Time/Div or Decrease Time/Div to increase or decrease the values
for each division on the plot.
• Use Center Median to center the data’s median vertical value.
5.3.2 Removing the Linear Trend
Phase difference measurements often exhibit a linear trend. This results in plots which appear as
diagonal "lines" when they are scaled in a way that fits all data. This is the result of a large units
per division selection on the y axis, which in turn results from accommodation of the oldest and
the most recent measurement which continually grow further apart. The large units per division
setting decreases resolution and makes it difficult to observe measurement details.
Consider the phase difference measurements plotted in Figure 13 Linear Trend in Phase
Difference Measurements. Over time they exhibit the trend discussed thus far. The white line
segment shows this trend, as it is measured by the Measure Linear softkey. The slope of this line
segment (from the first to the last available measurement) is taken into consideration when the
trend is measured.
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