engleski

CHOPPING FREQUENCY OPTIMIZING IN THE NIR MOISTURE METER

The near infrared (NIR) moisture meter is designed and realised by the authors. Its optoelectronic part is theoretically and practically analysed in this paper by means of the measuring results. The measurement system is based on the cooled PbS photoconductive detector and a mechanical chopper. The moisture measuring is realized via reflected radiation at narrow band range around 1940nm in the NIR region. The signal obtained from the detector can be very small and mixes with the noises from various sources. The optimal chopping frequency is estimated regarding the resumption of the maximal output detector signal and maximal signal versus noise ratio with other given parameters. The power line generated noise as well as its influence on the optoelectronic system and on the measuring results are partly removed with the embedded frequency filter and partly with the choice of the matching chopping frequency.

moisture meter; NIR; near infrared; chopping frequency

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