HBK FS22SI, User Manual

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31
FS22SI
MEASURING
Power
in dBm
Threshold
Wavelength in nm
detected peaks
undetected peak
Fig. 4.4 Conventional detection method
4.3.2 Smart Peak Detection (SPD)
SPD allows the effective use of the high dynamic range offered by the interrogator
through the introduction of individual and adaptive thresholds, referenced to the peak on
each sensor's configurable range (
refer to Fig. 4.5 ).
As in the conventional measuring method, the threshold value corresponds to the consid­
ered power level for the FBG peak computation and it is defined in dB for each optical
channel individually. The difference on the SPD is that the threshold value is referenced
to the highest peak of each range, operating individually in every range.
Within each sensor range, even though it happens, either permanently or occasionally,
that multiple peaks overcome the threshold, only one FBG sensor will be computed, thus
eliminating problems indexed to the measurements. Additionally, any influence these
spurious peaks could exert on the measurements is canceled.
Summarily, the increased robustness provided is especially suited to overcome the limi­
tations found in the conventional methods where low and high reflectivity FBGs coexist
and signal losses are often a problem. SPD therefore improves the stability and accuracy
of the measurements, contributing to the system's efficiency.
Information
When SPD is active, the total number of sensors that can be measured by the interrogator
should not exceed 400.