Instrument Functions
NRP2
80User Manual 1173.9140.02 ─ 07
In manual mode, “longer measurement” does not mean that it takes longer to display a
new result, but rather that it takes longer for the result to settle when the power
changes.
The filter settings of the "Trace & Statistics" mode and the other modes, which exclu-
sively provide average power values, differ significantly. The filter dialog box thus dis-
plays different parameters depending on the selected display mode. Filtering in the
"Trace & Statistics" mode is described in chapter 4.5.3.3, "Filtering settings",
on page
118.
All average power values are obtained from a three-stage averaging process. First, a
mean value is formed for the acquisition interval given in table 4-2
- either by weighted
or unweighted summation of samples.
A second measurement with reversed polarity of the detector output signal is then per-
formed to suppress offset voltages and 1/f noise of the amplifier. A first result is formed
by subtracting the second measured value from the first measured value. The
sequence of two consecutive measurements is repeated N times. The average value,
which is obtained from the individual measurement results, is output. The number N is
the averaging number ("AvgNo"). To obtain a high output data rate, averaging in man-
ual mode is performed continuously, i.e. a new result is fed into the averaging filter
after two acquisitions have been evaluated. The oldest result is taken out of the aver-
aging filter and a new average value is calculated.
The averaging number can be selected automatically or it can be manually set to a
fixed value. As a starting point, automatic filtering should always be used. If the auto-
matically selected filter setting proves to be not adequate, the averaging number can
be in(de)creased manually.
Two autofilter operating modes are provided:
●
"Normal"
The "Normal" mode finds a balance between measurement time and display noise.
As an additional parameter, display resolution can be used to adjust the filter set-
ting. With increasing resolution, i.e. an increasing number of digits in the measure-
ment results, the averaging number also increases.
●
"Fixed Noise"
In the "Fixed Noise" mode, the averaging number is selected so that the sensors
intrinsic noise (2 standard deviations) does not exceed the specified "Noise Con-
tent". To avoid very long settling times when the power is low, the averaging num-
ber can be limited with the "Max Settling Time" parameter. If the display noise then
exceeds the set noise content, the symbol "S/N" is displayed.
Data acquisition and parameters
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