The highest peak in Figs. 7
and 8 is the FBG reflective wavelength; and the other pattern
is the FP reflective spectrum. It is noticed that the FBG
sensor peak is much stronger than the FP sensor peak with
logarithmic scale axis. Therefore, it has a little influence
on FBG sensor peak estimation. Meanwhile, Figs. 9 and 10
illustrate the experimental and actual results (using measuring
scale and a specific gravity meter) for the specific gravity and
the liquid level, respectively. Note that the specific gravity of
the liquid (water) was increased incrementally via the addition
of carefully controlled amounts of salt. From inspection,