HBK FS22DI, User Manual

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FS22DI
BRAGGMONITOR DI USER INTERFACE
58
around 3000 and no FBG side lobes are detected as peaks. These settings can be config­
ured independently for each optical channel.
Gain is directly related to the optical power used on the mea­
surement of the optical channel. The gain value should be raised
to overcome losses on the network. Gain is an integer value
between 0 and 255. The current gain value can be found using
the get gain button (number
3 in Fig. 7.15 ). The gain value is
updated every time the Spectral View tab is selected or a new
channel is defined. To define a new gain value, write it on the
gain box (number
4 in Fig. 7.15 ) and press “set gain” button
(number 5 in Fig. 7.15 ).
Important
Upon setting the gain attention must be payed to the fact that the optimum gain value will
depend on the selected sampling rate for the acquisition. For the same gain value signal
power will decrease with the increase of the sampling rate. Because the spectrum is repre­
sented with the interrogator operating at 50 S/s, consider a slight saturation of the signals
when defining the gain for an acquisition at higher speeds than 50 S/s.
Threshold defines the line between usable signals and noise. It
is an integer value between 200 and 3200. Operations for getting
and defining threshold values can be performed on a similar way
to the gain, but using the threshold buttons (number
6 , 7 and 8 in
Fig. 7.15 ). The threshold value is updated every time the Spectral
View tab or a new channel are selected. This value is also repre­
sented graphically as a horizontal line on the power bar graph.
7.2.4 FFT View
FFT View tab shows the Fast Fourier Transform (FFT) graph of the acquired measure­
ments. This computation is based on a predefined FFT function, considering the mea­
sured values exponential weighted (with no averaging), being the latest signals more sig­
nificant for the calculations.
Once the “start” button is pressed, all previous measurements are erased from the FFT
temporary memory. FFT is shown for the active sensors on the sensors list (number
1 in
Fig. 7.16) as defined on the Graphical View tab. This list of sensors cannot be edited on
the FFT View tab. To enable/disable any sensor, tick the sensor tick box.
Information
To choose sensors that are not present in the sensors list, edit the list on the Graphical
View tab.
Gain
Threshold