METROLOGICAL EVALUATION OF OPTICAL EMITTERS AND DETECTORS APPLIED TO THE CHARACTERIZATION OF ATMOSPHERIC PARTICULATES POLLUTANTS / AVALIAÇÃO METROLÓGICA DE EMISSORES E DETECTORES ÓPTICOS APLICADOS À CARACTERIZAÇÃO DE POLUENTES PARTICULADOS ATMOSFÉRICOS

AUTOR(ES)
DATA DE PUBLICAÇÃO

2003

RESUMO

The atmospheric pollution is a latent world-wide problem, and it is harmful to the health, visibility and climate. For these factors, several studies and researches have been developed to characterize the chemical composition of the pollutants, concentration, size of particles, etc, with the objective of constructing adjusted instruments for the control of the air quality, but these instruments are sophisticated, complicated and very expensive. This dissertation is a study about the feasibility to use simple optoelectronic components, such as light emitting diodes (LED) and optical photo detectors, as sensors for measuring the variation of the concentration of atmospheric particulate pollutants in relation to time. The measurement principle is based on the optic properties of the light: reflection, refraction and absorption that occur when a light beam arrives on particles of any pollutant, taking place the attenuation of the intensity of the incident beam, which is proportional to the pollutant concentration. LED and photo detectors were selected according to information given in the specifications supplied for the manufacturer. Four different types of Pairs formed Emitters-Detectors, (Pairs E-D), where each LED worked with a specific photo detector. The evaluations were made in function of the Pairs E-D according to the recommendation of the manufacturer and two types different of Pairs E-D were selected, which presented better physical characteristics, time of response (11 and 16µs), level of the signal generated by the photo detector, (between 2,50V and 3,50V), and stability in a range of temperatures between 20oC to 30oC. To test the functioning of the Pairs E-D as sensors for measuring of the variation of the concentration of the atmospheric particulate pollutants. It was built an instrumented reduced model with eight Pairs E-D was built, four of each type of the Pairs E-D selected previously. It was taken care of the physical disposition of the Pairs E-D to prevent light interferences. To reduce the noise of the circuit, the Protoboard was substituted by a circuit board printed. The relation signal/noise was 3,242V/0,020V, (162:1). A specific program was developed in the software LabVIEW. The goal was to register the signals generated by photo detectors at each 10µs, and to store the data for posterior analysis. The instrumented reduced model and the software to the data acquisition represent a system for measurement and the characterization of the dispersion of the atmospheric particulate pollutants. To verify the performance of the instrumented reduced model and the software for acquisition, simulations of ambient contamination were made. A FOG machine was used to generate smoke on the reduced model, The results were satisfactory. Working with the eight active E-D Pairs, it was possible to get 12500 data per second for each Pair E-D. This amount of registered data by the acquisition program in LabVIEW was enough for the construction of the preliminary curves of characterization for the E-D Pairs.

ASSUNTO(S)

poluentes concentration of pollutants concentracao de poluentes emissores opticos metrologia metrology detectores opticos optical emitters pollutants optical detectors

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