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Instrument Setup - Gain Slots Tab
Figure 11 - Instrument setup - Gain slots tab
An advantage of Enhanced Acquisition is that it enables the use of Wavelength Gain slots, whereby each
FBG operates within its own wavelength window that is assigned its own set of properties. Each slot can
use a different gain level so large variations in signal intensity can be accommodated on one channel
without loss of measurement resolution.
The Gain slots are set up on a channel-by-channel basis. The spectrum for the Channel in question is
displayed. The wavelength limits on the graph's x-axis have already been determined according to the laser
tuning range that was set up on the Acquisition Rate tab. The user then clicks between the spectral peaks
to add slot boundaries. Only one FBG peak should be present in each slot. The start and end points of the
wavelength tuning range are slot boundaries, so be sure not to add slot boundaries before the first FBG or
after the last FBG. Care should be taken that during operation the FBG peak will not cross a slot boundary
and that FBG peaks remain separated by at least 1.6 nm from each other and 0.8 nm from the end of the
active laser range. Do not set up more slots than the number of sensors per channel that was configured
on the Acquisition Rate tab. Slot boundaries can be adjusted by dragging them to their desired position
using the mouse. Right click on a boundary to delete it.
Once the slots are established the Gain Mode can be set. There are two modes, in auto mode the gain for
each slot adjusts automatically so that the intensity of each FBG peak is maximised but does not saturate.
The peak intensity will be maintained between 50 and 100% and will only reduce below 50% on the highest
gain level if the signal is still too small.
In Manual gain mode a fixed gain is applied to each slot. To set the gain, right click on the graph between
the slot boundaries and set the gain level between 0 and 8, repeating this process for each slot on all
channels. The optimum gain level is above 50% but without saturating; a saturated FBG peak will have a
flat top at around 100% intensity. The gain applied to each slot is displayed on the graph. Selecting a
manual gain for a slot will automatically change the gain setting from auto to manual. It is recommended
that in manual mode the gain be set as high as possible without risk of the FBG peak saturating. Peaks
below 25% relative intensity may suffer reduced measurement performance.
