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10.7
Configuring the measurement modes
The following chapter describes the settings needed for configuring a measure-
ment mode.
10.7.1
Configuring a continuous average measurement
The "Continuous Average" mode measures the signal average power asynchro-
nously within definable time intervals (sampling windows). The aperture time
(width of the sampling windows) can be defined.
Reducing noise and zero offset
The continuous average measurement can be performed with chopper stabiliza-
tion to obtain more accurate results with reduced noise and zero offset. When
chopper stabilization is used, a single measurement is performed over two sam-
pling windows, the polarity of the detector output signal being reversed for the
second window. By taking the difference of the output signals, the effect of the
video path on noise and zero drift is minimized.
The smoothing filter can further reduce result fluctuations caused by modulation.
But when activated it increases the inherent noise of the sensor module by
approx. 20%, so it should remain deactivated if it is not required.
Configuring continuous average measurements of modulated signals
When measuring modulated signals in continuous average mode, the measure-
ment can show fluctuation due to the modulation. If that is the case, adapt the
size of the sampling window exactly to the modulation period to get an optimally
stable display. If the modulation period varies or is not precisely known, you can
also activate the smoothing function.
With smoothing activated, the selected sampling window has to be 5 to 9 times
larger than the modulation period for the fluctuations caused by modulation to be
sufficiently reduced. The sampling values are subjected to weighting (raised-von-
Hann window), which corresponds to video filtering.
If you deactivate the smoothing filter, 300 to 3000 periods are required to obtain
the same effect. The sampling values are considered equivalent and averaged in
a sampling window, which yields an integrating behavior of the measuring instru-
ment. To obtain optimum suppression of variations in the result, exactly adapt the
modulation period to the size of the sampling window. Otherwise, the modulation
Configuring the measurement modes
