Fig. 3 shows the experimental setup schematics and
the photography of the interrogation unit. The interrogation
unit has 4 independent red LEDs (peaking at 660 nm,
model IF-E96 from Industrial Fiber Optics Inc), and 4 photodiode
(model FB120-ND from Industrial Fiber Optics Inc)
followed by an electrical transimpedance amplification
stage with controlled gain. The control module uses a
16-bit microcontroller (model PIC24FJ256DA206 from
Microchip Technologies) with a 16-bit ADC, which operates
in a range from 0 to 2.5 V, resulting in a resolution of
38.15 lV. The amplifier gain and the ADC input voltage
range were optimized in order to maximize the overall
resolution.
The acquisition module can be controlled remotely via a
wireless system (module MiWi™ – P2P from Microchip
Technologies), paired with a computer or through a USB
cable connection, where the data acquisition and analysis
is performed in real time using a Labview application.
The system also comprises a battery for field monitoring
and the capability of record data to an SD card.