Data acquisition and parameters (Sensor menu)
R&S NRP
1144.1400.12 4.10
E-2
Background information
Sampling window
As the sensor amplifiers use chopping, a measurement comprises at least two sampling windows and a sensor-
specific deadtime of a few 100 µs. Samples at equal time intervals over the duration of a sampling window are
taken and a partial measurement result is formed from these samples. The partial measurement results of two
adjacent sampling windows are combined and the average is either output as the final result or is subjected to
further averaging as one of a number of intermediate results (
Filter / averaging, page 4.19).
In the remote control mode, the sampling window determines the minimum measurement time that can be
achieved (2
×
sampling deadtime). However, there is no point in selecting sampling window times very
much smaller than 1 ms if, to reduce display noise, the averaging filter has to be used. Due to the unavoidable
deadtime of the order of a few 100 µs per sampling window, the measurement time does not drop in proportion to
the reduction in sampling window time. This may even mean that, to obtain a well-defined noise component in the
result, a greater measurement time overall is required, if a sampling window that is too small is selected.
Smoothing modulated signals
With smoothing turned off, the samples within a sampling window are given equal weighting and averaged, which
turns the instrument into an integrating device. As described above, optimal reduction of fluctuations in the meas-
urement result due to modulation can be obtained, if the size of the sampling window is an exact integer multiple of
the modulation period. If this is not the case, modulation can have a considerable effect even if the sampling win-
dow is many times greater than the modulation period. This situation can be improved considerably if the samples
are weighted (raised von-Hann window) before averaging. This is like video filtering and is exactly what happens
when smoothing is activated.
