The proposed architecture is based on the scheme of Fig. 6 where the following units are illustrated: radiation source based on LED device, a specimen block, a selector of wavelength for changing frequency according to the sample under test, a photoelectric detector and a unit of displaying based on labview interface.The preliminary overall view of the instrumentation
under construction is illustrated in Fig. 7 as ‘‘rendering
Fig. 5. Frequency response.
Fig. 6. Light transmitting and detecting process.
Fig. 7. 3D representation of proposed instrumentation.
Fig. 8. Partial view of the real system.
A. Lay-Ekuakille et al. / Measurement 47 (2014) 749–755 751 view’’ and it is also depicted in Fig. 8 as real system where we can the main parts. An interferometer is also
foreseen in space between the housing of sensors and the RGB emitters. That is the final version of the instrumentation dedicated for spectroscopic measurements [13]. The presented architecture is a part of this instrumentation. Before designing and constructing the PWM control unit, it is important to test the setting of mirrors and beam splitters of the Michelson interferometer with
respect to the signal intensity of light signal by means of a photomultiplier (Hamamatsu H7732-P11). In this case we use a laser source produced by an appropriate laser generator (VeLas 30 of Wuhan Gigaa Optronics Technology Co.). Fig. 9 describes the testing process using three different diameters of an optical fibers. The variations of fiber diameters is important for light collimation when passing through the interferometer. Resulting test data are illustrated in Fig. 10. Hence, it is now possible to start building the PWM unit [14]. The system is controlled by computer using a virtual panel shown in Fig. 11 . Thanks to it, it possible to control and change in the housing of sensors the following parameters: pressure, temperature and number of moles regarding the pollutant being monitored [15,16]. The control of the architecture of Fig. 7 is based on PWM (Pulse Wave Modulation) technique as shown in the designed (Fig. 12) and constructed board (Fig. 13). However, the used detector is shown in Fig. 14; it reveal
the LED radiation captured by the system a RGB of S7505-01 that produces noise that has been removed thanks to a dedicated conditioning circuit as included in Fig. 15. The system is very sensitive to concentration variations [17] as a touching structure.